IPCS INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 17
MANGANESE
This report contains the collective views of an
international group of experts and does not
necessarily represent the decisions or the stated
policy of the United Nations Environment Programme,
the International Labour Organisation, or the World
Health Organization
Published under the joint sponsorship of
the United Nations Environment Programme, the
International Labour Organisation, and the
World Health Organization
World Health Organization
Geneva, 1981
ISBN 92 4 154077 X
(c) World Health Organization 1981
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR MANGANESE
1. SUMMARY AND RECOMMENDATIONS FOR FURTHER STUDIES
1.1. Summary
1.1.1. Analytical methods
1.1.2. Sources and pathways of exposure
1.1.3. Essentiality of manganese
1.1.4. Magnitude of environmental exposure
1.1.5. Metabolism
1.1.6. Effects on experimental animals
1.1.7. Effects on man
1.1.7.1 Occupational exposure
1.1.7.2 Community exposure
1.1.8. Organomanganese compounds
1.2. Recommendations for further studies
1.2.1. Analytical methods
1.2.2. Environmental exposure
1.2.3. Metabolism
1.2.4. Experimental animal studies
1.2.5. Epidemiological and clinical studies
in man
2. PROPERTIES AND ANALYTICAL METHODS
2.1. Chemical and physical properties of manganese
and its compounds
2.2. Sampling and analysis
2.2.1. Collection and preparation of samples
2.2.2. Separation and concentration
2.2.3. Methods for quantitative determination
2.2.3.1 Optical spectroscopy
2.2.3.2 Atomic absorption spectroscopy
2.2.3.3 Neutron-activation analysis
2.2.3.4 X-ray fluorescence
2.2.3.5 Other methods
2.2.3.6 Comparability of methods
3. SOURCES OF MANGANESE IN THE ENVIRONMENT
3.1. Natural occurrence
3.2. Industrial production and consumption
3.2.1. Uses
3.2.2. Contamination by waste disposal
3.2.3. Other sources of pollution
4. ENVIRONMENTAL LEVELS AND EXPOSURE
4.1. Air
4.1.1. Ambient air
4.1.2. Air in workplaces
4.2. Water
4.3. Soil
4.4. Food
4.5. Total exposure from environmental media
5. TRANSPORT AND DISTRIBUTION IN ENVIRONMENTAL MEDIA
5.1. Photochemical and thermal reactions in the lower atmosphere
5.2. Decomposition in fresh water and seawater
5.3. Atmospheric washout and rainfall
5.4. Run-off into fresh water and sea water
5.5. Microbiological utilization in soils
5.6. Uptake by soil and plants
5.7. Bioconcentration
5.8. Organic manganese fuel additives
6. METABOLISM OF MANGANESE
6.1. Absorption
6.1.1. Absorption by inhalation
6.1.2. Absorption from the gastrointestinal tract
6.2. Distribution
6.2.1. Distribution in the human body
6.2.2. Distribution in the animal body
6.2.3. Transport mechanisms
6.3. Biological indicators of manganese exposure
6.4. Elimination
6.5. Biological half-times
6.5.1. Man
6.5.2. Animals
7. MANGANESE DEFICIENCY
7.1. Metabolic role of manganese
7.2. Manganese deficiency and requirements in man
7.3. Manganese deficiency in animals
8. EXPERIMENTAL STUDIES ON THE EFFECTS OF MANGANESE
8.1. Median lethal dose
8.2. Effects on specific organs and systems
8.2.1. Central nervous system
8.2.2. Respiratory system
8.2.3. Liver
8.2.4. Cardiovascular effects
8.2.5. Haematological effects
8.3. Effects on reproduction
8.4. Carcinogenicity
8.5. Mutagenicity and chromosomal abnormalities
8.6. Miscellaneous effects
8.7. Toxicity of organic manganese fuel additives
8.8. Mechanisms and toxic effects
9. HUMAN EPIDEMIOLOGICAL AND CLINICAL STUDIES
9.1. Occupational exposure and health effects
9.2. General population exposure and health effects
9.3. Clinical studies
9.3.1. Pathomorphological studies
9.3.2. Therapeutic studies
9.4. Susceptibility to manganese poisoning
9.5. Interaction
10. EVALUATION OF THE HEALTH RISKS TO MAN FROM EXPOSURE TO
MANGANESE AND ITS COMPOUNDS
10.1. Relative contributions of air, food and water to total
intake
10.1.1. General population
10.1.2. Occupationally-exposed groups
10.2. Manganese requirements and deficiency
10.3. Effects in relation to exposure
10.3.1. General population
10.3.2. Occupationally-exposed groups
10.3.2.1 Effects on the central nervous system
10.3.2.2 Manganese pneumonia
10.3.2.3 Nonspecific effects on the respiratory
tract
10.3.2.4 Diagnosis of manganese poisoning and
indices of exposure
10.3.2.5 Susceptibility and interaction
10.4. Organomanganese compounds
10.5. Conclusions and recommendations
10.5.1. Occupational exposure
10.5.2. General population exposure
REFERENCES
NOTE TO READERS OF THE CRITERIA DOCUMENTS
While every effort has been made to present information in the
criteria documents as accurately as possible without unduly delaying
their publication, mistakes might have occurred and are likely to
occur in the future. In the interest of all users of the environmental
health criteria documents, readers are kindly requested to communicate
any errors found to the Division of Environmental Health, World Health
Organization, Geneva, Switzerland, in order that they may be included
in corrigenda which will appear in subsequent volumes.
In addition, experts in any particular field dealt with in the
criteria documents are kindly requested to make available to the WHO
Secretariat any important published information that may have
inadvertently been omitted and which may change the evaluation of
health risks from exposure to the environmental agent under
examination, so that the information may be considered in the event of
updating and re-evaluation of the conclusions contained in the
criteria documents.
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR MANGANESE
Members
Dr M. Cikrt, Institute of Hygiene and Epidemiology, Prague,
Czechoslovakia
Dr G J. van Esch, Toxicology and Food Chemistry, National Institute of
Public Health, Bilthoven, Netherlands (Chairman)
Dr G. F. Hueter, Environmental Research Center, US Environmental
Protection Agency, Research Triangle Park, NC, USA
Dr I. C. Munro, Toxicology Research Division, Bureau of Chemical
Safety, Department of National Health and Welfare, Ottawa,
Ontario, Canada (Rapporteur)
Dr H. Oyanguren, Institute of Occupational Health and Air Pollution,
National Health Service, Santiago, Chile
Dr M. Saric, Institute of Medical Research and Occupational Health,
Zagreb, Yugoslavia
Dr S. Sigan, Sysin Institute of General and Community Hygiene, Moscow,
USSR
Dr N. Skvortsova, Laboratory for Air Pollution Control, Sysin
Institute of General and Community Hygiene, Moscow, USSR
Professor M. Tati, Department of Public Health, Gifu University
Medical School, Gifu, Japan
Dr I. Ulanova, Institute of Industrial Hygiene and Occupational
Diseases, Moscow, USSR (Vice-Chairman)
Representatives of other agencies
Dr H. M. Mollenhauer, Division of Geophysics, Global Pollution and
Health, United Nations Environment Programme, Nairobi, Kenya
Dr D. Djordjevic, Occupational Health and Safety Branch, International
Labour Organisation
Mrs M. Th. van der Venne, Health Protection Directorate, Commission of
the European Communities, Luxembourg
Secretariat
Dr Y. Hasegawa, Medical Officer, Control of Environmental Pollution
and Hazards, World Health Organization, Geneva, Switzerland
Dr H. de Koning, Scientist, Control of Environmental Pollution and
Hazards, World Health Organization, Geneva, Switzerland
Dr J. E. Korneev, Scientist, Control of Environmental Pollution and
Hazards, World Health Organization, Geneva, Switzerland
Dr G. E. Lambert, Scientist, Occupational Health, World Health
Organization, Geneva, Switzerland
Dr B. Marschall, Medical Officer, Occupational Health, World Health
Organization, Geneva, Switzerland
Dr V. B. Vouk, Chief, Control of Environmental Pollution and Hazards,
World Health Organization, Geneva, Switzerland (Secretary)
ENVIRONMENTAL HEALTH CRITERIA FOR MANGANESE
A WHO Task Group on Environmental Health Criteria for Manganese
met in Geneva from 22 to 26 September 1975. Dr B. H. Dieterich,
Director, Division of Environmental Health, opened the meeting on
behalf of the Director-General. The Task Group reviewed and revised
the second draft Of the criteria document and made an evaluation of
the health risks from exposure to manganese and its compounds.
The first and second drafts of the criteria document were
prepared by Dr P. S. Elias of the Department of Health and Social
Security, London, England. The first draft was based on national
reviews received from the national focal points for the WHO
Environmental Health Criteria Programme in Bulgaria, Japan, New
Zealand, the United Kingdom, the USA, and the USSR. The second draft
was prepared according to comments received from national focal points
in Canada, Chile, Czechoslovakia, Greece, Japan, Netherlands, New
Zealand, Poland, Sweden, the USA, and the USSR; and from the
Commission of the European Communities, the Food and Agriculture
Organization of the United Nations, the Ethyl Corporation, the
International Union of Biological Sciences, the International Union of
Pure and Applied Chemistry, the United Nations Economic Commission for
Europe, and the World Meteorological Organization. Dr P. S. Elias and
Dr I. C. Munro, Bureau of Chemical Safety, Department of National
Health and Welfare, Ontario, Canada, assisted the Secretariat in the
preparation of a third draft, which was distributed for comments to
the Task Group members. Additional comments on this draft were
received from Dr R. J. M. Horton, US Environmental Protection Agency,
Research Triangle Park, USA, and Professor M. Piscator, the Karolinska
Institute, Stockholm, Sweden. Following the recommendations made by a
WHO Consultative Group on the application of environmental health
criteria, Bilthoven, Netherlands, 2-5 May 1977, a final draft was
prepared by Dr H. Nordman, Institute of Occupational Health, Helsinki,
Finland, taking into consideration the comments of members of the Task
Group and of Professor P. S. Papavasiliou, the New York Hospital
Centre-Cornell Medical Center, New York, USA, and Professor M.
Piscator.
The collaboration of these institutions, organizations, and
individual experts is gratefully acknowledged. The Secretariat wishes
to thank, in particular, Dr P. S. Elias, Dr. I. C. Munro, and Dr H.
Nordman for their help in the various phases of preparation of the
document.
This document is based on original publications listed in the
reference section but much valuable information was also obtained from
publications reviewing and evaluating the essentiality and toxicity of
manganese, including those by Cotzias (1958, 1962), Stokinger (1962),
Schroeder et al. (1966), Suzuki et al. (1973a, 1973b, 1973c), WHO
(1973), WHO Working Group (1973), US Environmental Protection Agency
(1975), International Agency for Cancer Research (1976), and Saric
(1978). Owing to unforseen circumstances, it has not been possible to
update the document beyond 1978.
Details of the WHO Environmental Health Criteria Programme,
including some terms frequently used in the documents, can be found in
the general introduction to the Environmental Health Criteria
Programme published together with the environmental health criteria
document on mercury (Environmental Health Criteria 1, Mercury, Geneva,
World Health Organization, 1976) and now available as a reprint.
Financial support for the publication of this criteria document
was kindly provided by the Department of Health and Human Services
through a contract from the National Institute of Environmental Health
Sciences, Research Triangle Park, North Carolina, USA -- a WHO
Collaborating Centre for Environmental Health Sciences.
1. SUMMARY AND RECOMMENDATIONS FOR FURTHER STUDIES
1.1 Summary
1.1.1 Analytical methods
Numerous analytical methods are available for the quantitative
determination of manganese in environmental media and biological
samples. The method the most frequently used is atomic absorption
spectroscopy, which appears to be sufficiently sensitive for most
analytical purposes. The way in which biological and environmental
samples are procured and stored, prior to analysis, has an important
bearing on the accuracy and validity of the results. For example, in
air sampling, it is important to ensure that respirable particulate
matter is collected. In the collection of biological samples with a
low manganese content, contamination may constitute a major
difficulty.
1.1.2 Sources and pathways of exposure
Manganese is one of the more abundant elements in the earth's
crust and is widely distributed in soils, sediments, rocks, water, and
biological materials. The major sources of man-made environmental
pollution by manganese arise in the manufacture of alloys, steel, and
iron products. Other sources include mining operations, the production
and use of fertilizers and fungicides, and the production of synthetic
manganese oxide and dry-cell batteries. Organomanganese fuel
additives, though only a minor source at present, could significantly
increase exposure, if they come into widespread use. Average manganese
concentrationsa in soils range from about 500 to 900 mg/kg and
concentrations in sea water range from 0.1 to 5 µg/litre. Surface
waters may have a manganese content of 1-500 µg/litre, but in areas
where high concentrations of manganese occur naturally, levels may be
considerably higher. Average manganese levels in drinking water range
from 5 to 25 µg/litre.
Manganese is present in all foodstuffs, usually at concentrations
below 5 mg/kg. However, concentrations in certain cereals, nuts, and
shellfish can be much higher, exceeding 30 mg/kg in some cases. Levels
in finished tea leaves may amount to several hundred mg/kg.
Manganese has been found in measurable quantities in practically
all air samples of suspended particulate matter. Annual average levels
in ambient air in unpolluted urban and rural areas vary from 0.01 to
0.07 µg/m3. However, in areas associated with the manganese industry,
a Throughout the document, the term concentration refers to mass
concentration, unless otherwise stated.
annual averages may be higher than 0.5 µg/m3, and have occasionally
exceeded 8 µg/m3. About 80% of the manganese in suspended particulate
matter is associated with particles having a mass median equivalent
diameter (MMED)b of less than 5 µm, i.e., particles within the
respirable range. This association with small particles favours the
widespread airborne distribution of manganese.
1.1.3 Essentiality of manganese
Manganese is an essential trace element for both animals and man.
It is necessary for the formation of connective tissue and bone, and
for growth, carbohydrate and lipid metabolism, the embryonic
development of the inner ear, and reproductive functions. Some
specific biochemical functions of manganese have been discovered such
as the catalysing of the glucosamine-serine linkages in the synthesis
of the mucopolysaccharides of cartilage.
Estimates from intake and balance studies in man show that the
daily requirement for adults is 2-3 mg/day and that of pre-adolescent
children, at least 1.25 mg/day. Manganese deficiency states, which
have been detected in a wide variety of animals, have been described
only once in man, in association with vitamin K deficiency and the
accidental omission of manganese from the diet. A distinctly negative
manganese balance is found in newborn infants, the metal being
excreted from stores that have accumulated in the tissues during fetal
life. However, deficiency symptoms have not been detected.
1.1.4 Magnitude of environmental exposure
Food is the major source of manganese for man. Daily intake
ranges from 2 to 9 mg, depending on the relative consumption of foods
with a high manganese content, especially cereals and tea. In young
children and up to the age of adolescence, the daily intake is about
0.06-0.08 mg/kg body weight; for breastfed and bottlefed infants, it
is only about 0.002-0.004 mg/kg body weight. Daily intake with
drinking water may range from a few micrograms to 200 µg, the average
intake being about 10-50 µg/day.
b Mass median equivalent diameter: equivalent diameter above and
below which the weights of all larger and smaller particles are
equal.
The daily intake of manganese in the air by the general
population in areas without manganese emitting industries is below
2 µg/day. In areas with major foundry facilities, intake may rise to
4-6 µg/day and in areas associated with ferro- or silicomanganese
industries it may be as high as 10 µg, with 24-h peak values exceeding
200 µg/day.
1.1.5 Metabolism
The respiratory and gastrointestinal tracts constitute the major
routes of absorption of manganese. Quantitative data are not
available, but it seems unlikely that the skin is an important route
of absorption for inorganic manganese compounds, although
organomanganese compounds can be absorbed by this route.
The extent of absorption of manganese following inhalation is
unknown. A certain proportion of inhaled manganese particles is
cleared by mucociliary action and swallowed, and is available for
gastrointestinal absorption. The small amount of information available
concerning the gastrointestinal absorption of manganese in man
indicates that the absorption rate in healthy adults is below 5% but
that it is higher in anaemic subjects. This is supported by data from
studies on mice and rats. There is little information on
gastrointestinal absorption in infants and children and not much is
known about the mechanism of absorption from the gastrointestinal
tract.
In studies on experimental animals, preloading with high dietary
levels of manganese caused a decrease in the rate of absorption and
young rats appeared to have a considerably higher absorption rate than
adult rats.
The total manganese body burden for a man of 70 kg is about
10-20 mg. It is transported in the plasma bound to a beta1-globulin,
most likely transferrin, and is widely distributed throughout the
body. Manganese concentrates in tissues rich in mitochondria, the
highest concentrations being found in the liver, pancreas, kidney, and
the intestines. It can also penetrate both the blood-brain barrier and
the placenta. The disappearance half-time for manganese from the whole
body is about 37 days and the half-time in the brain appears to be
longer than that for the whole body. Tissue concentrations in man are
remarkably stable throughout life. Variable excretion is known to play
an important role in the homeostasis of manganese, but recent studies
have shown that the variability of absorption is also important.
Inorganic manganese is mainly eliminated in the faeces. The
principal route of excretion is with the bile, part of which is
reabsorbed in the enterohepatic circulation. To some extent, manganese
is also excreted with the pancreatic juice and through the intestinal
wall; the importance of these routes may increase under abnormal
conditions such as biliary obstruction or increased manganese
exposure. It has been shown that only about 0.1-1.3% of the daily
intake of inorganic manganese is normally excreted in the urine.
However, larger amounts are excreted through the kidney following
exposure to organomanganese tricarbonyl compounds, indicating that
these compounds, which are used as additives in gasoline, are
metabolized in the body.
1.1.6 Effects on experimental animals
The toxic effects of manganese on the central nervous system have
been induced in various animal species, including the rat and monkey,
mainly by the administration of manganese dioxide or dichloride.
Exposure of a monkey to manganese dioxide aerosol, by inhalation, at
concentrations of 0.6-3.0 mg/m3, for 95 1-h periods over 4 months,
induced typical signs of central nervous system effects. Parenteral
administration of manganese dioxide or dichloride also induced signs
of central nervous system disturbance but oral administration produced
fewer effects, presumably because of poor gastrointestinal absorption.
Histopathological lesions found in intoxicated animals included
degenerative changes, primarily in the striatum and pallidum, but
lesions in the subthalamic nucleus, cortex, cerebrum, cerebellum, and
the brain stem have also been observed. It has been shown that
manganese causes depletion of dopamine, and probably serotonin, in the
basal ganglia of monkeys, rabbits, and rats. These biochemical
findings may explain, at least in part, the neurotoxic effects of
manganese.
Inflammatory changes were produced in rats by intratracheal
administration of manganese dioxide at concentration of 0.3 mg/m3 for
5-6 h daily, over 4 months; mottling was seen on the pulmonary
radiographs of monkeys exposed to the same compound by inhalation
(0.7 mg/m3). Sulfur dioxide was found to act synergistically with
manganese dioxide on the respiratory tract of guineapigs.
Biochemical and histopathological changes have been reported in
other organ systems, notably the liver. Testicular changes have been
demonstrated in the rat after intravenous administration of
permanganate at 50 mg/kg body weight and in the rabbit after
administration of manganese dichloride at 3.5 mg/kg. Intraperitoneal
injections of manganese(II) sulfate (10 mg/kg body weight, 15
injections) in mice increased the incidence of lung rumours; however,
the carcinogenic, mutagenic, and teratogenic potential of manganese
needs further investigation.
1.1.7 Effects on man
1.1.7.1 Occupational exposure
Chronic manganese poisoning is a hazard in the mining and
processing of manganese ores, in the manganese alloy and dry-cell
battery industries, and in welding. The disorder is characterized by
psychological and neurological manifestations, the neurological signs
closely resembling those that occur in other extrapyramidal disorders,
notably parkinsonism. Autopsy reports on cases of chronic manganese
poisoning have shown that lesions of the central nervous system are
most severe in the striatum and pallidum, and may also be found in the
substantia nigra. In one case, post-mortem analysis revealed a reduced
concentration of dopamine. This finding combined with animal data and
the fact that a precursor of dopamine, 3-hydroxy L-tyrosine (L-dopa),
has been effective in the treatment of chronic manganese poisoning
implicates the dopaminergic pathway in the etiology of extrapyramidal
manifestations of the disease.
Individual susceptibility to the adverse effects of manganese
varies considerably. The minimum dose that produces effects in the
central nervous system is not known, but signs of adverse effects may
occur at manganese concentrations in air ranging from 2 to 5 mg/m3.
Although an increased incidence of pneumonia has repeatedly been
reported in manganese workers, it is not possible to establish any
exposure-effect relationships from available data. It may be that
particle size distribution and the type of manganese compound are more
important than the mass concentration of manganese in air. This may
also be true for the nonspecific effects on the respiratory tract
reported in manganese workers. Smoking appears to act synergistically
with manganese in causing such effects.
The early diagnosis of manganese poisoning is difficult in the
absence of reliable biological indicators of exposure. Repeated
screening for subjective symptoms and thorough clinical examinations
should be undertaken at regular intervals together with measurements
of manganese in blood and urine. Measurement of manganese levels in
faeces may serve as a useful guide to exposure.
With better understanding of the pathophysiology of manganese
poisoning, new drugs have been introduced for its treatment. In many
cases, the use of the dopamine precursor L-dopa, has been successful.
The use of chelating agents has also been reported to have a
beneficial effect, although sometimes only temporarily and mainly in
the early stages of poisoning. This treatment cannot be expected to
bring about any improvement in cases where structural neurological
injury has already occurred.
1.1.7.2 Community exposure
Adverse effects have been reported in populations, in areas
associated with manganese-processing plants. In 1939, increased
morbidity and mortality due to lobar pneumonia were reported from
Sauda in Norway, where a ferro- and silicomanganese plant was
operating. The mortality rate was positively correlated with the
amount of manganese alloy produced. Manganese was reported to occur in
the ambient air as Mn (II, III) oxide (Mn3O4) at manganese
concentrations of up to 45 µg/m3. In another study, a higher
prevalence of nose and throat symptoms and lowered respiratory
function were registered in schoolchildren exposed to manganese
concentrations in air ranging from 4 to 7 µg/m3 (5-day mean values)
compared with an unexposed control group. However, short-time sampling
(1-h) of the factory smoke, down-wind, yielded a maximum level of
260 µg/m3.
A 4-year study performed in a population living in the vicinity
of a ferromanganese plant indicated that even a manganese exposure of
only 1 µg/m3 might be connected with an increase in the rate of acute
respiratory disease. However, it is possible that some other factors,
which were not sufficiently controlled, might have influenced the
results.
In one study, the incidence of abortions and stillbirths was
reported to be higher in wives of workers exposed to manganese for
10-20 years than in a control group. The study is difficult to
evaluate as factors such as the occupations of the wives were not
reported.
1.1.8 Organomanganese compounds
There are two groups of organomanganese compounds of
toxicological importance. Manganese ethylene-bis-dithiocarbamate
(Maneb) is used as a fungicide on edible crops. Toxicologically, the
manganese fraction is of little importance, whereas the organic
portion is part of a larger problem concerning this type of fungicide.
The manganese tricarbonyl compounds constitute the other group of
organomanganese compounds of toxicological significance. These are
used as additives in unleaded petrol (gasoline) and future widespread
use seems likely. After combustion, only a small fraction of the
compound is emitted and this undergoes rapid photodecomposition to
form compounds that, so far, have not been satisfactorily identified.
Exposure to manganese tricarbonyl compounds is therefore likely to
constitute an occupational hazard but community exposure to the parent
compound will remain very small, even if the use of these compounds
increases. Nevertheless, widespread use would result in increased
community exposure to inorganic manganese and to other possible
combustion products. Rats, hamsters, and monkeys have been exposed
experimentally to combusted methylcyclopentadienyl manganese
tricarbonyl (MMT) at concentrations of manganese in air ranging from
12 to 5000 µg/m3 for various periods ranging up to 66 weeks without
any adverse effects. However, tissue levels of manganese increased in
monkeys exposed to a manganese concentration in air of 100 µg/m3.
1.2 Recommendations for Further Studies
1.2.1 Analytical methods
There is a need for interlaboratory comparison to determine the
accuracy of methods available for the estimation of manganese.
Additional studies are required to determine particle size in airborne
manganese particulate matter, so that total intake through the
respiratory pathway can be estimated more precisely.
1.2.2 Environmental exposure
More precise data are needed on manganese intake, especially by
inhalation. A better understanding of the translocation of manganese
in the environment and factors that affect this process is required
and its potential for bioaccumulation in environmental compartments
should be explored in more depth.
1.2.3 Metabolism
Chemobiokinetic studies are necessary to identify, more
precisely, the mechanisms involved in the uptake and clearance of
manganese from the gastrointestinal tract and the respiratory system
in both experimental animals and exposed populations and to obtain a
better understanding of factors that affect these processes. Tissue
levels at which adverse effects are observed should be established and
special attention should be paid to the role of nutritional status and
age in the metabolism of manganese.
1.2.4 Experimental animal studies
More information is needed on the long-term, low-level effects of
manganese in order to develop dose-response data. Further studies are
also necessary on the neurotoxicity and potential carcinogenicity,
teratogenicity, and mutagenicity of manganese and on factors that
might affect toxicity such as nutrition, age, disease state, and the
presence of other pollutants.
Not enough is known about the essentiality of manganese as a
nutrient and more studies are needed on the biochemical role of this
metal to obtain a better understanding of toxic mechanisms and to
develop a rational basis for the treatment of manganese intoxication.
1.2.5 Epidemiological and clinical studies in man
Studies are required to elucidate the dose-effect and
dose-response characteristics of manganese with particular emphasis on
the effects of long-term, low-level, inhalation exposure on the
respiratory and central nervous systems. Interactions with other
pollutants, diet, age, and general health status should be studied in
more detail. The effects of manganese on the cardiovascular system,
particularly its effects on blood pressure and the myocardium, need to
be more fully understood. Reliable diagnostic procedures for manganese
intoxication should be established, paying particular attention to the
development of methods for its early detection. Additional studies are
necessary to assess the embryotoxic potential of manganese and its
compounds in communities exposed to elevated levels of manganese in
air. Organomanganese compounds may come into widespread use as fuel
additives. This would result in increased exposure of the general
population to manganese and probably to other combustion products of
the additive. Thus, the potential hazards to public health of the use
of organomanganese fuel additives should be examined by means of
carefully conducted controlled and epidemiological studies.
2. PROPERTIES AND ANALYTICAL METHODS
2.1 Chemical and Physical Properties of Manganese and its Compounds
Manganese, Mn (atomic number Z = 25; relative atomic mass Ar =
54.938) is an element of the VIIb group of the periodic table of
elements, together with technetium and rhenium. It belongs to the
first series of d-block transition elements which also contains
titanium, vanadium, chromium, nickel, and copper. Because of their
electron configuration, transition elements have some characteristic
properties: they are all metals; they exist in a variety of oxidation
states; and they form many coloured and paramagnetic compounds.
Several transition elements have an important role in biological
systems.
In the elemental state, manganese is a white-grey, brittle, and
reactive metal with a melting point of 1244°C and a boiling point of
1962°C. It is the most common transition metal after iron and
titanium. It can form compounds in a number of oxidation states, the
most important being +2, +3, and +7.
Manganous (Manganese(II), Mn2+) salts are mostly water-soluble,
with the exception of the phosphate and carbonate, the solubilities of
which are rather low. Dihalides of manganese include MnF2, MnCl2,
MnBr2, and MnI2. Addition of OH- ion to the Mn2+ solutions gives
the gelatinous white hydroxide Mn(OH)2. MnO and MnS are also known.
The MnII complexes are generally weakly coloured (pale pink). Mn2+
is in many ways similar to Mg2+, and can replace it in some
biological molecules.
Mn3O4 (hausmannite) contains both MnII and MnIII, i.e., MnII
MnIII2O4. The manganic Mn(III) ion (Mn3+) easily hydrolyses in weak
acid solutions into Mn2+ and MnO2. Manganese(III) and manganese(IV)
complexes seem to be important in photosynthesis.
Manganese dioxide (MnO2), found naturally as pyrolusite, is the
most important manganese (II) compound. It is insoluble in water and
in cold acids. The little-known manganese(IV) ion occurs in blue
"hypomangamates".
Manganese(VI) exists in the deep green manganate ion, MnO42-,
which is stable only in very basic solutions. Otherwise, it breaks
down to give the permanganate ion MnO4- and MnO2. The permanganate
ion is the best known form of MnVII. Permanganate, which is a good
oxidant in basic solutions, is reduced to Mn2+ in acid solutions.
The properties of some inorganic manganese compounds are
summarized in Table 1.
Table 1. Chemical and physical properties of manganese and some manganese compoundsa
Chemical Relative atomic Melting Boiling
Compound formula or molecular point point Solubility
mass (°C) (°C)
Manganese Mn 54.94 1244 1962 Decomposes in cold and hot
water; soluble in dilute acid.
(II) acetate Mn(C2H3O2)2 173.02 Soluble in cold water
(decomposes); soluble in
alcohol.
(II) carbonate MnCO3 114.95 decomposes Soluble in cold water;
soluble in dilute acids.
dichloride MnCl2 125.84 650 1190 Soluble In cold and hot water,
and in alcohol.
(II) nitrate Mn(NO3)2 . 4H2O 251.01 25.8 1294 Soluble in cold and hot water,
and in alcohol.
(II, III) oxide Mn3O4 228.81 1705 Soluble In hydrochloric acid.
dioxide MnO2 86.94 -0.535 Soluble In hydrochloric acid.
(III) oxide Mn2O3 157.87 -0.1080 Soluble In acid.
(II) metasilicate MnSiO3 131.02 1323 Insoluble In water and
hydrochloric acid.
(II) sulfate MnSO4 151.00 700 850 Soluble in cold and hot water, and
(decomposes) in alcohol.
Table 1. (contd).
Chemical Relative atomic Melting Boiling
Compound formula or molecular point point Solubility
mass (°C) (°C)
(III) sulfate Mn2(SO4)3 398.06 160 Decomposes in water, soluble in
hydrochloric acid, and
dilute sulfuric acid.
(II) sulfide MnS 87.00 decomposes Soluble In cold water, dilute
acid, and alcohol.
(IV) sulfide MnS2 119.07 decomposes Decomposes in hydrochloric acid.
Potassium KMnO4 158.00 decomposes < 240 Soluble in cold and hot water,
permanganateb in sulfuric acid, alcohol, and
acetone. Decomposes in alcohol.
a From: Weest (1974).
b From: Stokinger (1962).
Manganese may form a variety of complexes particularly in the +2
state. The +1 state is present in hexacyano complexes such as
K5Mn(CN)6, which exist also with manganese in the +3 state,
K3Mn(CN)6.
Manganese forms various organometallic compounds such as
Mn2(CO)10, sodium pentacarbonylmanganate (NaMn (CO)5), and
manganocene (C5H5)2Mn. However, of major practical interest is
methylcyclopentadienyl manganese tricarbonyl (CH3C5H4Mn(Co)3),
often referred to as MMT, Cl-2 or Ak-33X (antiknock 33X), which has
been used as an additive in fuel oil, as a smoke inhibitor, and as an
antiknock additive in petrol, usually as a supplement to
tetraethyllead.
2.2 Sampling and Analysis
2.2.1 Collection and preparation of samples
Nonmetallic sampling systems should be used for the collection of
environmental materials, and suitable precautions should be taken to
avoid contamination during the analytical process.
Filters for ambient air particulates must be chosen with care so
that trace amounts of manganese in the filter material do not distort
the results. Generally the air sampling techniques chosen will depend
on the purpose of the investigation. High-volume air samplers and
centripeters are expensive, require power points, and are unsuitable
for large-scale monitoring at multiple sites. The use of standard
deposit gauges is limited to the collection of particles larger than
5 µm; particles with a smaller diameter are deposited only by
impaction. In Japanese studies, a high-volume air sampler is used for
suspended particulate matter, and a cyclone type low-volume air
sampler for suspended particulate matter with a particle size of 10 µm
or less (Environment Agency, Japan, 1972).
Sphagnum moss techniques are useful for comparing fallout in
different areas or for studying seasonal variations in one area.
Continuous sampling drawing measured air volumes through filter paper,
or dry deposition on filter papers protected from the rain combined
with rain water collecting, may also be used. According to normal
practice in emission studies, sampling for manganese at stationary air
pollution sources is carried out isokinetically, using a sampling
train that will remove manganese efficiently. In the source sampling
method used by the US Environmental Protection Agency (1971), it is
possible to analyse the particulates collected in the probe, on the
filter, and in the water impingers.
Manganese is emitted in automobile exhaust in the form of
particulate matter. Concentrations vary according to the natural
manganese levels in the fuel and to the concentration of
manganese-containing additives, if present. Exhaust particulates may
be collected by total or proportional sampling of the hot exhaust or
by proportional sampling of the exhaust mixed with air, which allows
cooling and condensation of the compounds of greater relative atomic
mass associated with short-time ambient exhaust particulates. The
second method provides a more realistic assessment of the mass and
composition of the primary exhaust particulates. Collection using this
technique can be carried out using a single filter, multiple filter,
beta gauge (Dresia & Spohr, 1971), or particulate-size-fractionating
devices. Gaseous samples may be collected either by the cold-trap
technique or on chromatographic columns.
The following considerations are important in the sampling of
water for manganese analysis: (a) selection of sampling sites; (b)
frequency of sampling; (c) sampling equipment; and (d) sample
preparation (Brown et al., 1970). Usually, little or no sample
preparation is required but freeze-drying operations can be used.
Aqueous samples should be filtered immediately on collection,
using a membrane or other suitable filtering material if
differentiation between soluble and particulate phases is to be
attempted. Once the particulates are collected on a filter, the
analytical problems are similar to those of air analysis. Special
precautions are required in the handling and storage of solid and
aqueous samples with regard to the choice of equipment and containers.
Because of the extremely low concentration of manganese in some
biological tissues and body fluids, contamination of the samples
constitutes a major difficulty, a fact which is often overlooked or
underestimated. It seems likely that the wide variation in manganese
concentrations reported, for instance, in serum (section 6.2.1) can
portly be explained by contamination.
Steel equipment is considered unsuitable for tissue biopsy, and
quartz or glass knives have been suggested as alternatives; the use of
a laser beam has also been discussed (Becker & Maienthal, 1975).
Versieck et al. (1973a) reported that the radioactivated Menghini
needles used in liver biopsy could cause up to 30% manganese
contamination. It has also been suggested that skin-pricking is
inferior to venepuncture in the drawing of blood samples because of
the possible introduction of tissue manganese into the sample
(Papavasiliou & Cotzias, 1961). Single transfer of blood through
conventional steel needles has caused serious contamination of samples
(Cotzias et al., 1966), and the use of platinum-rhodium alloy needles
with Kel-F hubs has been proposed to overcome this problem (Becker &
Maienthal, 1975).
A considerable contamination problem may arise in the presence of
some anticoagulants. Bethard et al. (1964) reported a manganese
concentration in heparin of 3.56 µg/ml whereas acid-citrate-dextrose
contained only 0.002 µg/ml. Consequently, when heparin was used as an
anticoagulant, the manganese concentration was 0.17 ± 0.03 µg/ml
compared with 0.00014 µg/ml when acid-citrate-dextrose was used.
Sampling of hair may be complicated by the fact that manganese is
associated with melanin-containing structures, black and brown hair
containing much higher concentrations of manganese than white hair
(Cotzias et al., 1964).
2.2.2 Separation and concentration
Special procedures are not normally necessary for the separation
of manganese from other metals prior to the analysis or concentration
of samples. Chromatographic methods for the determination of manganese
have been reviewed by Fishbein (1973).
2.2.3 Methods for quantitative determination
2.2.3.1 Optical spectroscopy
Trace metals, including manganese, have been determined
spectroscopically by a number of research workers. With suitable
variations in sample preparation, the available standard spectroscopic
methods can be used equally well for mineral ores, air particulates,
or biological samples (Cholak & Hubbard, 1960; Tipton, 1963;
Angelieva, 1969, 1970, 1971; Bugaeva, 1969; Carlberg et al., 1971; El
Alfy et al., 1973; Pépin et al., 1973). The advantages of spectroscopy
are that it can be applied to most elements with a satisfactory
specificity and sensitivity and that it can be used for the
simultaneous determination of several elements (US Environmental
Protection Agency, 1972, 1973). Drawbacks of the emission
spectroscopic assay include the exacting nature of the method, which
necessitates the use of highly qualified personnel, the cost of the
instrument, the complexity of the method, and the detection limits,
which are too high to detect metals occurring in low concentrations
(Thompson et al., 1970).
2.2.3.2 Atomic absorption spectroscopy
This is the most commonly used method of determining manganese at
present, because the procedure is relatively simple and fast and the
sensitivity is high. The application to ambient air samples has been
described by Thompson et al. (1970), Begak et al. (1972), and Muradov
& Muradova (1972). The method is fairly free from interference except
for possible matrix effects, which can generally be avoided. Any
silica extracted from glass-fibre filters can cause interference
unless removed by the addition of calcium to the solution, prior to
analysis (Slavin, 1968). Atomic absorption methods have also been used
to determine manganese in water and other materials. Little or no
preparation of the sample solution is required (Thompson et al., 1970;
Tichy et al., 1971; US Environmental Protection Agency, 1974).
The advantage of flameless atomizers is that the determination
can be carried out with high sensitivity using only a small sample.
The method was initiated by L'vov (1961) to avoid interference caused
by reactions in the flame. However, the precision of the results is
not necessarily good since atomizing can easily be altered by various
conditions such as the type of the sample which, for instance, may
stick to the wall of the boat. These difficulties are especially
significant when directly atomizing biological samples. Graphite
furnace or carbon rod techniques can be used for the direct analysis
of water samples, although matrix interference must be checked for and
eliminated. Concentration of fresh water can be achieved simply by
evaporation. Other variants have been developed for biological
substrates, foodstuffs, soils, and plant materials (Ajemian & Whitman,
1960; Suzuki, 1968; Suzuki et al., 1968; Obelanskaja et al., 1971; Bak
et al., 1972; Van Ormer & Purdy, 1973).
An atomic absorption assay using direct aspiration of the sample
into the burner has been described for the determination of
methylcyclopentadienyl manganese tricarbonyl (MMT) in gasoline. The
drawback of this method is that it does not discriminate between MMT
and other manganese compounds (Bartels & Wilson, 1969).
Atomic absorption methods can be classified, according to the
type of sample or sample solution to be applied to the atomizer, into
(a) the direct method, in which the sample or sample solution is
used directly; and (b) the solvent-extraction method in which a
clean-up and concentration process by solvent extraction is carried
out before atomizing. The gross matrix effects of saline waters
necessitate a preliminary extraction, which usually entails a
concentration procedure. Chelating ion-exchange (Riley & Taylor, 1968)
and solvent extraction are also often used (Hasegawa & Ijichi, 1973).
2.2.3.3 Neutron-activation analysis
This method has a high specificity and sensitivity for very low
concentrations of manganese as well as several other elements (Dams et
al., 1970). However, the user must be aware that neutron-activation of
biological samples may result in the production of isotopes that
interfere with the determination of manganese. Irradiated samples are
treated by a chemical separation process with a certain amount of
manganese carrier and then determined by gamma-spectroscopy. The
1810.7 Kev gamma line of 56Mn is measured. This method can be used to
check the accuracy of results obtained by other analytical methods and
for the determination of manganese at very low concentrations in a
small number of samples. It is essential to collect particulate matter
on filters that have a very low trace element content (ashless filter
paper). Variations of this method have been used for determining
manganese concentrations in blood and serum (Cotzias et al., 1966) and
in plants (Hatamov et al., 1972).
2.2.3.4 X-ray fluorescence
The use of X-ray fluorescence spectroscopy provides a means for
the non-destructive analysis of elements in sediments and
particulates.
X-ray fluorescence can also be used to determine manganese in
solutions, if the sample is prepared by freeze-drying. Birks et al.
(1972) have made a complete elemental analysis with high sensitivity
in 100 seconds using multichannel analysers with 14-24 crystals. The
necessity of distinguishing unreactive, structurally incorporated
manganese in particulates and sediments from the more reactive
absorbed, biogenic, and hydrogenic phases was discussed in a paper by
Chester & Hughes (1967), who proposed a selective acid-leaching
technique for this purpose. Manganese in water was determined by
Watanabe et al. (1972), using a nickel carrier, with a limit of
detection of 0.03 µg. Another method that has been developed for the
analysis of various elements including manganese, is proton-induced
X-ray emission analysis (Johansson et al., 1975). Manganese in dust
samples collected by an impactor was detected at nanogram levels using
this method.
2.2.3.5 Other methods
The periodate method is the classical wet chemical method of
analysing air samples for manganese (American Conference of
Governmental Industrial Hygienists, 1958). The advantage of this
method is that it can be used in almost any chemical laboratory with
relatively simple equipment, but the sensitivity (0.1 mg/m3) is
rather poor in comparison with that of other methods (Peregud &
Gernet, 1970). This technique has also been widely used for
determining total manganese in the soil but it is considered to give a
poor estimate of the manganese available to plants.
The permanganate method is the most commonly used method for the
analysis of manganese in water samples. Interference caused by
manganese in the glassware has to be eliminated when the manganese
level in the sample is low, and prior removal of organic material may
be necessary. However, not all forms of manganese likely to occur in
water can be measured by the permanganate method (e.g., the complexes
of trivalent manganese and manganese dioxide), and an improved, simply
performed formaldoxime method has been developed for the analysis of
both water and soils (Samohvalov et al., 1971; Cheeseman & Wilson,
1972).
A rapid drop quantitative method, developed for determining
manganese in the air of the working environment, is based on the
colour reaction of manganese ions with potassium ferricyanide. The
method is specific and results compare well with those obtained by
emission spectroscopy (Muhtarova et al., 1969).
A kinetic method based on the ability of manganese to catalyse
the atmospheric oxidation of the morin-beryllium complex has been
developed for the determination of manganese in atmospheric
precipitates (Morgen et al., 1972). Polarography can be used for
determining manganese in industrial waste waters with a sensitivity of
0.05 mg/litre. Chromium interference can be removed by phosphate
precipitation (Bertoglio-Riolo et al., 1972). A similar method for
analysing animal foodstuffs, organs, and tissues has been developed
for samples weighing only 2 g. Interference caused by iron can be
avoided by precipitating it with a mixture of ammonium chloride and
ammonium hydroxide (Usovic, 1967). An alternative method for the
determination of manganese in biological material is electron
paramagnetic resonance spectroscopy (Cohn & Townsend, 1954; Miller et
al., 1968).
Spark source mass spectroscopy is probably a suitable method for
the determination of manganese in petrol (US Environmental Protection
Agency, 1975). Cyclopentadienyl manganese tricarbonyl can be
determined by treating the sample with nitric and sulfuric acid and
subsequently converting the manganese to permanganate (Byhovskaja et
al., 1966).
2.2.3.6 Comparability of methods
As already stated, atomic absorption spectroscopy combined, when
necessary, with a separation solvent procedure, can be applied to most
environmental samples. Each of the other methods described has its
particular advantages and characteristics and can be used according to
the need for sensitivity and to the type of sample. Studies such as
that of Harms (1974) on the comparison of data from several different
analytical methods are useful. The inter-comparison of analytical
techniques carried out under the responsibility of EURATOMa also
provides interesting information. In this study, good agreement was
obtained when neutron-activation analysis, X-ray fluorescence,
emission spectroscopy, and atomic absorption spectroscopy were
compared for the determination of manganese.
a EURATOM (unpublished data, 1974) Chemical analysis of airborne
particulates: intercomparison and evaluation of analytical
techniques. In: Guzzi, G., ed. Minutes of the Meeting held at
Ispra, Italy, 8-9 July 1974, Ispra Establishment, Chemistry
Division, Joint Research Centre of the European Communities,
33 pp.
3. SOURCES OF MANGANESE IN THE ENVIRONMENT
3.1 Natural Occurrence
Manganese is widely distributed in nature but does not occur as
the free metal. The most abundant compounds are the oxide (in
pyrolusite, brannite, manganite, and hausmannite), sulfide (in
manganese blonde and hauserite), carbonate (in manganesespar), and the
silicate (in tephroite, knebelite, and rhodamite). It also occurs in
most iron ores in concentrations ranging from 50-350 g/kg, and in many
other minerals throughout the world.
A rough estimate of the average concentration of manganese in the
earth's crust is about 1000 mg/kg (NAS-NRC, 1973). Manganese
concentrations in igneous rock may range from about 400 mg/kg in
low-calcium granitic rock to 1600 mg/kg in ultrabasic rock and
sedimentary rocks. Deep sea sediments contain concentrations of about
1000 mg/kg (Turekian & Wedepohl, 1961). It has been reported that the
manganese content of coal ranges from 6 to 100 mg/kg (Ruch et al.,
1973) and that of crude oil from 0.001 to 0.15 mg/kg (Bryan, 1970).
In soil, manganese concentrations depend primarily on the
geothermal characteristics of the soil, but also on the environmental
transformation of natural manganese compounds, the activity of soil
microorganisms, and the uptake by plants.
Although the principal ores are only slightly soluble in water,
gradual weathering and conversion to soluble salts contribute to the
manganese contents of river and sea water. Considerable amounts of
manganese are present in deposits in large areas of the oceans in the
form of nodules. These are formed continuously at a rate of several
million tonnes per year (Schroeder et al., 1966). The average
concentration of manganese in these nodules is about 200 mg/kg (Zajic,
1969) with a range of about 150-500 mg/kg (Schroeder et al., 1966).
3.2 Industrial Production and Consumption
Elemental manganese was isolated in 1774, though the oxide has
been used in the manufacture of glass since antiquity. The total world
production of manganese, which was 18 million tonnes in 1969, rose to
about 27 million tonnes in 1975. However, consumption, which had risen
by 20% between 1970 and 1975, dropped by 3% in 1975 (Mineral Yearbook,
1975, 1977).
Fumes, dust, and aerosols from metallurgical processing, mining
operations, steel casting (Mihajlov, 1969) and metal welding and
cutting, (Erman, 1972), mainly in the form of manganese oxide are the
principal sources of environmental pollution. Emissions into the
atmosphere from blast and electric furnaces vary considerably
depending on the process involved and the degree of control exercised.
Dust from the handling of raw materials in metallurgical processing
and other manufacturing activities probably makes only a small
contribution to the atmospheric concentration of manganese. Calculated
emission factors for manganese are given in Table 2.
Table 2. Emission factors for manganese
Mining 0.09 kg/tonne of manganese mined
Processing
manganese metal 11.36 kg/tonne of manganese processed
ferromanganese
blast furnace 1.86 kg/tonne of ferromanganese produced
electric furnace 10.86 kg/tonne of ferromanganese produced
silicomanganese
electric furnace 31.55 kg/tonne of silicomanganese produced
Reprocessing
carbon steel
blast furnace 10.22 kg/1000 tonnes of pig iron produced
open-hearthfurnace 23.18 kg/1000 tonnes of steel produced
basic oxygen furnace 20.00 kg/1000 tonnes of steel produced
electric furnace 35.45 kg/1000 tonnes of steel produced
cast iron 150.00 kg/1000 tonnes of cast iron
welding rods 7.27 kg/tonne of manganese processed
nonferrous alloys 5.45 kg/tonne of manganese processed
batteries 4.54 kg/tonne of manganese processed
chemicals 4.54 kg/tonne of manganese processed
Consumer uses
coal 3.50 kg/tonne of coal burned
From: Davis & Associates (1971).
3.2.1 Uses
Over 90% of the manganese produced in the world is used in the
making of steel, either as ferromanganese, silicomanganese, or
spiegeleisen. Manganese is also used in the production of nonferrous
alloys, such as manganese bronze, for machinery requiring high
strength and resistance to sea water, and in alloys with copper,
nickel, or both in the electrical industry. In dry-cell batteries,
manganese is used in the form of manganese dioxide, which is also used
as an oxidizing agent in the chemical industry. Many manganese
chemicals, eg., potassium permanganate, manganese(II) sulfate,
manganese dichloride, and manganese dioxide are used in fertilizers,
animal feeds, pharmaceutical products, dyes, paint dryers, catalysts,
wood preservatives and, in small quantities, in glass and ceramics.
Some of these uses contribute to environmental pollution.
3.2.2 Contamination by waste disposal
The disposal of liquid and solid waste products containing
manganese may contribute to the contamination of land, water courses,
and soil. For example, sludges and various waste waters containing
manganese are used in the production of micronutrient fertilizers
(Eliseeva, 1973) and manganese slurries have been used in the
production of clay blocks for road construction. Information
concerning the degree of pollution arising from the incineration of
refuse containing manganese is not available.
3.2.3 Other sources of pollution
The emission of manganese from motor vehicles powered by petrol
that does not contain manganese additives has been estimated to
average 0.03-0.1 mg/km (Moran et al., 1972; Gentel et al., 1974a;
Gentel et al., 1974b).
Methylcyclopentadienyl manganese tricarbonyl (MMT) was initially
marketed in the USA as a supplement to tetraethyl lead in an antiknock
preparation. During the 1960s, it was introduced as a fuel-oil
combustion improver and as a smoke suppressant for gas turbines using
liquid fuels. In 1974, it came into commercial use as a fuel additive
in unleaded petrol in the USA; in 1976 about 20% of the fuel was
unleaded, and 40% of this amount contained MMT at an average
concentration of 10.56 mg/litre (0.04 g/US gallon) (Ethyl Corporation,
private communication). The use of MMT is likely to increase during
the coming years. At the manufacturer's recommended maximum level of
MMT (a manganese concentration of 33 mg/litre),a the emission of MMT
is approximately 0.62-3.1 µg/km (1-5 µg/mile); levels of about
0.62-1.55 µg/km (1-2.5 µg/mile) have been reported in lubrication oil
(Hurn et al., 1974). This low emission rate together with the fact
that MMT rapidly undergoes photochemical decomposition (section 5.8)
suggests that exposure to the parent compound through the exhaust gas
would be low.
Taking data on lead emissions in exhaust gas as a model, it has
been calculated that the use of MMT in petrol might result in the
emission of 0-0.25 µg of manganese per m3 of air, with a median of
0.05 µg/m3, and that the organic component of this would be about
1.2 × 10-5 µg/m3 (Ter Haar et al., 1975). This is not far from the
estimate of 0.05-0.2 µg/m3 made by Keane & Fisher, (1968). It has
been reported that 50% of emitted manganese particles have a mass
median diameter (MMD) of 0.5 µm or less (Moran, 1975).
At the 1975 SAE Automobile Engineering Meeting, it was claimed
that the use of manganese in petrol resulted in increased total
particulate emissions that could not be totally accounted for on the
basis of increased manganese content (Moran, 1975). This was disputed
at the same meeting by Desmond (1975), who argued that the figures
presented by Moran (1975) for increased total particulate emissions
were compatible with the theoretical maximum emissions of Mn3O4
resulting from combustion of the manganese in the fuel.
It appears that the use of MMT in petrol causes increased
emission of hydrocarbons (Gentel et al., 1974b; Hurn et al., 1974;
Kocmond et al., 1975). However, there is no conclusive evidence to
indicate that MMT decreases the efficiency of catalysts (Faggan et
al., 1975; Moran, 1975).
It is possible that MMT in petrol increases aldehyde emissions,
though the data so far available are conflicting (Ethyl Corporation,
1974; Gentel et al., 1974b; Hurn et al., 1974). Too little information
is available to draw any conclusions with regard to the effects of MMT
in petrol on the emission of polynuclear aromatic hydrocarbons. Tests
performed by the Ethyl Corporation (1974) showed a decrease in
benzo(a)pyrene concentrations in exhaust gas. A similar decrease in
benzo(a)pyrene concentrations was reported by Lerner (1974) using an
analogous compound, cyclopentadienyl manganese tricarbonyl. In one
study, it was shown that MMT in petrol could decrease atmospheric
visibility (Kocmond et al., 1975). Results of other studies conducted
by the Ethyl Corporation (1971) indicated that comparatively high
concentrations of manganese in air were needed to influence the
reaction converting sulfur dioxide to sulfuric acid and sulfates.
Thus, the reaction rate was unchanged at a manganese concentration of
4 µg/m3 and no effect was detectable at a concentration of 36 µg/m3,
when the humidity was below 70%.
a In June 1977, the manufacturer reduced the recommended maximum
level of manganese in petrol to 16 mg/litre, bringing about a
corresponding cut in the estimated emission levels (Ethyl
Corporation, private communition).
The effects of MMT in petrol on the emission of carbon monoxide
and oxides of nitrogen are not clear (Moran, 1975).
Another organic manganese compound, manganese
ethylene-bis-dithiocarbamate (Maneb), is used as a fungicide.
A large-scale investigation was made in Japan using a pilot
plant, equipped with a desulfurization device containing activated
manganese dioxide, to explore its influence on manganese levels in the
surrounding environment. The operation of the device increased the
manganese level in air by an average value of 0.002 µg/m3 (Ministry
of International Trade and Industry & Ministry of Health and Welfare,
1969).
Minor uses of manganese compounds in the manufacture of linoleum
and calico printing and in the manufacture of matches and fireworks
may be an additional source of environmental contamination.
4. ENVIRONMENTAL LEVELS AND EXPOSURE
4.1 Air
4.1.1 Ambient air
The natural level of manganese in air is low. A concentration in
air of 0.006 µg/m3 at a height of 2500 m and an annual average
concentration of 0.027 µg/m3 at 823 m were reported by Georgii et al.
(1974). In rural areas, manganese levels in air may range from 0.01 to
0.03 µg/m3 (US Environmental Protection Agency, 1973).
Because nearly all the manganese emitted into the atmosphere is
in association with small particles, it may be distributed over
considerable distances. According to Lee et al. (1972), about 80% of
manganese emitted into the atmosphere is associated with particles
with a mass median equivalent diameter of less than 5 µm and about 50%
with particles of less than 2 µm. Thus, most of the particles are
within the respirable range.
A survey of manganese concentrations in suspended particulate
matter, conducted during the period 1957-1969 at some 300 urban and
300 nonurban sites in the USA, has been summarized by the US
Environmental Protection Agency (1975). Annual average manganese
concentrations ranged from less than 0.099 µg/m3 for about 80% of the
sites to more than 0.3 µg/m3 for about 5% of the sites (Table 3). In
areas associated with local ferromanganese or silicomanganese
industries such as Johnstown, Charleston, and Niagara Falls, the
annual average concentrations ranged upwards from 0.50 µg/m3
(Table 4). The average 24-h concentrations in such places can exceed
10 µg/m3 and may present an important health risk. Urban centres
without major foundry facilities, such as New York, Los Angeles, and
Chicago, exhibited annual average manganese concentrations in air
ranging from 0.03 to 0.07 µg/m3, whereas in cities with these
facilities, such as Pittsburg, Birmingham, and East Chicago, values
ranged from 0.22 to 0.30 µg/m3 (US Environmental Protection Agency,
1973). These concentrations are in agreement with those found in other
studies from the USA (Brar et al., 1970; Lee et al., 1972). The
highest reported annual average concentration of 8.3 µg/m3, was
measured in Kanawha Valley, West Virginia, during 1964-65. The major
source of pollution was a ferromanganese plant situated in a nearby
area (US Environmental Protection Agency, 1975).
Manganese values from air sampling sites in the United Kingdom
during 1971-1972 ranged from 0.004 to 0.049 µg/m3; Keane & Fisher
(1968) reported mean manganese concentrations of 0.013-0.033 µg/m3 in
relatively unpolluted areas of the United Kingdom.
Table 3. Number of National Air Surveillance Network (NASN) stations within selected
annual average manganese concentration intervals, 1957--1969a
Concentration interval (µg/m3)
Year <0.099 0.100-0.199 0.200-0.299 >0.300 Total
1957- No. stations 76 29 10 13 128
1963 % 59.4 22.7 7.8 10.2 100
1964 No. stations 68 12 6 7 93
% 73.1 12.9 6.5 7.5 100
1965 No. stations 132 14 5 6 157
% 84.1 8.9 3.2 3.8 100
1966 No. stations 113 8 4 3 128
% 88.3 6.3 3.1 2.3 100
1967 No. stations 121 13 4 4 142
% 85.2 9.2 2.8 2.8 100
1968 No. stations 126 11 2 6 145
% 86.9 7.6 1.4 4.1 100
1969 No. stations 169 23 9 8 209
% 80.9 11.0 4.3 3.8 100
1957- No. stations 805 110 40 47 1002
1969 % 80.4 11.0 4.0 4.7 100
a From: US Environmental Protection Agency (1975).
Table 4. National Air Surveillance Network (NASN) stations with annual
average manganese concentrations greater than 0.5 µg/m3a
Manganese concentration (µg/m3)
Year Station Average Max. quarterly Max. 24-h
1958 Charleston, W.VA 0.61 1.10 7.10
1959 Johnstown, PA 2.50 5.40 7.80
Canton, OH 0.72 1.10 2.20
1960 Gary, Ind. 0.97 3.10
1961 Canton, OH 0.57 2.90
Philadelphia, PA 0.70 >10.00
1963 Johnstown, PA 1.44 6.90
Philadelphia, PA 0.62 3.70
1964 Charleston, W.VA 1.33 >10.00
1965 Johnstown, PA 2.45 3.90
Philadelphia, PA 0.72 1.70
Lynchburg, VA 1.71 2.50
Charleston, W.VA 0.60 1.70
1966 Niagara Falls, NY 0.66 1.30
1967 Knoxville, TN 0.81 1.50
1968 Johnstown, PA 3.27 14.00
1969 Niagara Falls, NY 0.66 1.30
Johnstown, PA 1.77 2.10
Philadelphia, PA 0.50 1.30
a From: US Environmental Protection Agency (1975).
In the Federal Republic of Germany, manganese concentrations were
found to range from 0.08 to 0.16 µg/m3 in different areas of
Frankfurt, with a maximum 24-h concentration of 0.49 µg/m3 (Georgii &
Müller, 1974), whereas in a residential area of Munich levels of
0.030-0.034 µg/m3 were reported, with 0.06-0.27 µg/m3 in a street
with heavy traffic (Bouquiaux, 1974).
The Environment Agency, Japan (1975) reported an annual mean
manganese concentration in the air of Japanese cities of about
0.02-0.80 µg/m3 with maximum 24-h concentrations of 2-3 µg/m3
(Environment Agency, Japan, 1975). Studies are also available from a
district in Kanazawa, Japan, close to a plant using electric furnaces
for the production of manganese alloys. Average levels during 1970
varied from 1.1 to 9.8 µg/m3, when measured over 2-day periods at a
point 300 m from the emitting source. Unpolluted areas of the same
city showed average levels of 0.035 µg/m3 during the period
1968-1970 (Itakura & Tajima, 1972). When manganese concentrations were
measured at underground shopping districts adjoining subway stations
in Tokyo, Osaka, and Nagoya, open-air concentrations of
0.042-0.074 µg/m3 and subway concentrations of 0.040-0.353 µg/m3
were found, indicating that heavy subway traffic on railway lines
containing manganese as a ferroalloy may increase manganese exposure
(Japan Environmental Sanitation Centre, 1974).
Thus, it can be concluded that annual average levels for
manganese in ambient air in nonpolluted areas range from approximately
0.01 to 0.03 µg/m3, while in urban and rural areas without
significant manganese pollution, annual averages are mainly in the
range of 0.01-0.07 µg/m3. With local pollution near foundries, this
level can rise to an annual average of 0.2-0.3 µg/m3 and in the
presence of ferro- and silicomanganese industries, to over 0.5 µg/m3.
The data available are not adequate for drawing valid conclusions with
respect to trends in ambient manganese concentrations.
4.1.2 Air in workplaces
In recent years, most of the industrialized countries have
established occupational exposure limits for manganese. Thus, working
conditions have improved and earlier reports of excessive exposure to
manganese do not always represent more recent conditions. This should
be borne in mind when considering the information presented in this
section.
According to one report (Ansola et al., 1944a), Chilean manganese
miners were exposed to manganese concentrations in air of
62.5-250 mg/m3. However in a later study in a Chilean mine, Schuler
et al. (1957) reported a concentration range of 0.5-46 mg/m3, the
highest levels being found in connection with the drilling of pure,
dry ore and the drilling of manganese-bearing rock. Manganese
concentrations of up to 926 mg/m3 of air were found in Moroccan mines
(Rodier, 1955). Flinn et al. (1940) recorded a manganese concentration
of 173 mg/m3 in an ore-crushing mill in the USA but a much later
survey of dust levels in the air of a ferromanganese crushing plant in
the United Kingdom (as measured by personal sampling devices) showed
manganese concentrations of 0.8-8.6 mg/m3. The device of one man
cleaning down the crusher showed an exceptionally high concentration
of 44.1 mg/m3. When levels in air were measured at fixed sampling
points, they ranged from 8.6 to 83.4 mg/m3 (Department of Health &
Social Security, unpublished data).a
In an electric steel foundry in Japan, manganese concentrations
ranged from 4.0 to 38.2 mg/m3 around an electric furnace and from 4.9
to 10.6 mg/m3 around the mouth of the kiln (Ueno & Ohara, 1958).
In studies in the USSR reported by Mihajlov (1969), manganese
concentrations in air of 0.3 mg/m3 or more were found in 98% of 1905
samples collected in the furnace area of a steel shop, during the
period 1948-1983. The levels reached 1.8-2.4 mg/m3 during melting
operations and increased to as much as 10 mg/m3, when the molten
steel was being poured. Additional data on manganese concentrations in
air can be found in section 9.1.
Few studies have included details of the size distribution of
manganese dust, which is of importance in the evaluation of dust
absorption following inhalation. Akselsson et al. (1975) reported
manganese concentrations of up to 3 mg/m3 in the breathing zone of
welders. The highest concentrations were associated with particles
ranging in size from 0.1 to 1.0 µm. This is in agreement with the
finding that 80% of particles from a ferromanganese furnace ranged in
size from 0.1 to 1.0 µm (Sullivan, 1969). In studies by Smyth et al.
(1973), more than 99% of the particles in airborne fume around a blast
furnace were smaller than 2 µm and 95% of airborne dust particles at a
crushing and screening plant were smaller than 5 µm.
4.2 Water
Manganese may be present in fresh water in both soluble and
suspended forms. However, in most reported studies, only total
manganese has been determined.
Surface waters of various American lakes were found to contain
from 0.02 to 87.5 µg of manganese per litre with a mean of
3.8 µg/litre (Kleinkopf, 1960). In two other studies the contents of
large rivers in the USA ranged from below the detection limit to
185 µg/litre (Durum & Haffty, 1961; Kroner & Kopp, 1965). A range of
0.8-28.0 µg/litre was found in Welsh rivers (Abdullah & Royle, 1972).
Manganese concentrations at 37 river sampling sites in the United
Kingdom (Department of Health and Social Security, 1975 --
unpublished) and in the Rhine and the Maas and their tributaries
(Bouquiaux, 1974) ranged from 1 to 530 µg/litre. There are some
reports indicating a seasonal variation in the manganese contents of
rivers (Bescetnova et al., 1968; Kolesnikova et al., 1973) and inshore
waters, manganese levels being lowest during the winter months
(Morris, 1974). High manganese concentrations reaching several
mg/litre have been found in waters draining mineralized areas
(Kolomijeeva, 1970; Department of Health and Social Security, 1975 --
unpublished) and in water contaminated by industrial discharges
(Kozuka et al., 1971).
a Department of Health and Social Security (1975) Environmental
health criteria for manganese and its compounds: Review of work
in the United Kingdom, 1967-1973.
In the USSR, groundwater not associated with manganese-bearing
rock, contained manganese concentrations ranging from 1 to
250 µg/litre (Kolomijeeva, 1970). A comparatively high average
concentration of 0.55 mg/litre was reported in a study of 6329
untreated samples of groundwater in Japan (Kimura et al., 1069) and
concentrations ranging from 0.22 to 2.76 mg/litre were found in deep
well water in the Takamatsu City area (Itoyama, 1971).
An average concentration of manganese in seawater of 0.4 µg/litre
was reported by Turekian (1969). In other studies on the manganese
contents of sea water in the North Sea, the Northeast Atlantic, the
English Channel, and the Indian Ocean, concentrations ranged from 0.03
to 4.0 µg/litre with mean values of 0.06-1.2 µg/litre. In estuarine
and coastal waters of the Irish Sea and in waters along the North Sea
shores of the United Kingdom, values ranging from 0.2 to 25.5 µg/litre
have been reported with mean values of 1.5-6.1 µg/litre (Topping,
1969; Preston et al., 1972; Jones et al., 1973; Bouquiaux, 1974).
Manganese concentrations in treated drinking-water supplies in
100 large cities in the USA ranged from undetectable to 1.1 mg/litre,
with a median level of 5 µg/litre; 97% of the supplies contained
concentrations below 100 µg/litre (Durfor & Becker, 1964). According
to a US Public Health Service survey quoted by Schroeder (1966),
manganese levels in tap water from 148 municipal supplies ranged from
0.002 to 1.0 mg/litre, with a median level of 10 µg/litre. Mean
concentrations of manganese in drinking-water in the Federal Republic
of Germany were reported to range from 1 to 63 µg/litre (Bouquiaux,
1974).
4.3 Soil
The average concentration of manganese in soils is probably about
500-900 mg/kg (NAS/NRC, 1973). Earlier analyses are of doubtful value,
as errors arising from contamination and interference with other
substances were not fully appreciated (Mitchell, 1964). The
significance of manganese levels in soils depends largely on the type
of compounds present and on the characteristics of the soil such as
the pH and the redox potential. Accumulation usually occurs in the
subsoil and not in the surface, 60-90% of manganese being found in the
sand fraction of the soil. In well-drained areas, the manganese
contents of stream sediments and of parent rocks and soils have been
found to be comparable. In areas of poorly-drained, peaty gleys and
podzols, stream sediments may be greatly enriched. For example, stream
sediments from poorly drained Welsh moorlands with rock and soil
concentrations of 540 mg/kg and 300 mg/kg, respectively, contained an
excess of 1% manganese (Nichol et al., 1967).
Soddy-podzolic soils in the USSR contained manganese
concentrations of 21-200 mg/kg, chernozem soils, up to 6400 mg/kg, and
boggy soils, 10-500 mg/kg. Mobile manganese in the USSR soils varied
from 23 to 149 mg/kg (Vasilevskaja & Bogatyrev, 1970). In Belgium,
loess formation in a forest region contained manganese concentrations
of 113-450 mg/kg. In a semi-industrialized region, concentrations
ranging from 135 to 320 mg/kg were found, while in sandy uncultivated
soil, concentrations ranged from 30 to 43 mg/kg (Bouquiaux, 1974).
4.4 Food
The manganese contents of various foodstuffs vary markedly
(Table 5).
In cereal crops from the USSR, manganese concentrations varied
from 2 to 100 mg/kg wet weight, concentrations in pulse crops ranged
from 0.36 to 32 mg/kg, and those in root crops from 0.2 to 15 mg/kg;
beet crops contained up to 37 mg/kg (Aljab'ev & Dmitrienko, 1971;
Musaeva & Kozlova, 1973).
The edible muscle tissue of 8 common commercial species of fish
in New Zealand was reported by Brooks & Rumsey (1974) to have mean
concentrations of manganese ranging from 0.08 to 1.15 mg/kg wet
weight. Similar values (0.03-0.2 mg/kg wet weight) were found in North
Sea fish. In cod and plaice, most values were lower than 0.1 mg/kg.
Shellfish may concentrate manganese. Scallops, oysters, and mussels
dredged from Tasman Bay contained average manganese levels of 111 mg,
8 mg, and 27 mg/kg dry weight, respectively (Brooks & Rumsey, 1965).
High concentrations of manganese have been found in tea including
levels of 780-930 mg/kg in the finished leaves (Nakamura & Osada,
1957) and 1.4-3.6 mg/litre in liquid tea (Nakagawa, 1968).
In most human studies, the average daily intake of manganese, via
food, by an adult has been reported to be between 2 and 9 mg/day.
Values of about 2.3-2.4 mg/day have been reported from the Netherlands
(Belz, 1960) and the USA (Schroeder et al., 1966). North et al. (1960)
obtained an average daily intake of 3.7 mg for 9 American college
women, and Tipton et al. (1969), using the duplicate portion method,
reported 50-week, mean daily intakes of 3.3 and 5.5 mg, respectively,
for two American adult males. Similarly, an average intake of
4.1 mg/day was reported from a Canadian composite diet (Méranger &
Smith, 1972). In a study by Soman et al. (1969), also using the
duplicate portion method, the average manganese intake for Indian
adults was 8.3 mg/day, while the intake from drinking-water ranged
from 0.004 to 0.24 mg/day. These results agree well with previously
reported values for Indian adults on a rice diet (9.81 mg of
manganese/day) and on a wheat diet (9.61 mg of manganese/day) (De,
1949).
Table 5. Manganese levels in some foodstuffs
Category Manganese (mg/kg wet weight)
Shroeder et al. (1966) Guthrie (1975)
Cereals
barley, meal 17.8 9.9
corn 2.1 3.8
rice, polished 1.5 9.6
unpolished 2.1 32.5
rye 13.3 34.6
wheat 5.2-11.3 13.7-40.3
Meat and poultry < 0.1-0.8 < 0.1-2.7
Fish < 0.1 0.1-0.5
Dairy products
milk 0.2 0.5
butter 1.0 0.1
Eggs 0.5 0.3
Vegetables
beans 0.2 1.8
peas 0.6 2.6
cabbage 1.1 0.8
spinach 7.8 1.8
tomatoes 0.3 0.2-0.6
Fruit
apples 0.3 0.2-0.3
oranges 0.4 0.3
pears 0.3 0.1-0.4
Nuts
walnuts 7.5 19.7
The daily intake of manganese by bottlefed and breastfed infants
is very low because of the low concentrations of manganese in cow's
milk and, especially, in breast milk (McLeod & Robinson, 1972a).
Widdowson (1969) reported a daily intake of 0.002 mg/kg body weight
for 1-week-old babies. Values of a similar order of magnitude
(0.002-0.004 mg/kg) have been reported for the first 3 months of life
by Belz (1960) and McLeod & Robinson (1972a). When a child is
established on a mixed food regimen after 3-4 months of age, the
intake increases considerably (McLeod & Robinson, 1972a).
Belz (1960) reported a daily intake of 1.7 mg for children aged
7-9 years, and Schlage & Wortberg (1972) reported intakes of
1.4 mg/day for 6 children aged 3-5 years, and 2.2 mg/day for 5
children aged 9-13 years, corresponding to 0.08 mg and 0.06 mg/kg body
weight, respectively. Day-to-day intake varied considerably, the
maximum intake being 10 times the minimum. Similar values for daily
intake were obtained by Alexander et al. (1974) for 8 children aged
between 3 months and 8 years; the mean intake was 0.06 mg/kg body
weight.
4.5 Total Exposure from Environmental Media
Based on annual average air concentrations and a respiratory rate
of 20 m3/day, an estimate of the daily exposure to manganese of
populations living in areas without manganese-emitting industries
would be less than 2 µg/day. For populations living in areas with
major foundry facilities, the value is likely to be about 4-6 µg,
while in areas associated with ferromanganese or silicomanganese
industries, the exposure may rise to 10 µg, and 24-peak values may
exceed 200 µg.
Considering the manganese concentrations in the vast majority of
drinking-water supplies, and assuming a water intake of 2 litres per
day, the average daily intake of manganese with drinking-water would
be about 10-50 µg with a range of about 2-200 µg. Although the
variation is considerable, an intake exceeding 1.0 mg/day would be
exceptional.
The daily intake of manganese from food appears to be 2-9 mg.
Some European and American studies suggest a likely range of 2-5 mg,
while in countries where grain and rice make up a major portion of the
diet, the intake is more likely to be in the range of 5-9 mg. The
consumption of tea may substantially add to the daily intake.
The average intake for children from a very early age up to
adolescence is about 0.06-0.08 mg/kg body weight whereas for breastfed
or bottlefed infants intake is only about 0.002-0.004 mg/kg body
weight.
5. TRANSPORT AND DISTRIBUTION IN ENVIRONMENTAL MEDIA
5.1 Photochemical and Thermal Reactions in the Lower Atmosphere
Atmospheric manganese compounds seem to promote the conversion of
sulfur dioxide to sulfuric acid (Coughanowr & Krause, 1965; Matteson
et al., 1969; Ethyl Corporation, 1971; McKay, 1971). However, the
concentration of manganese required to achieve this conversion and the
significance of its effect remain unknown. The available evidence
seems to indicate that a higher concentration of atmospheric manganese
than is normally observed would be necessary.
Manganese dioxide reacts with nitrogen dioxide, in the
laboratory, to form manganous nitrate (Schroeder, 1970). There is the
possibility that such a reaction might occur in the atmosphere but
further studies are needed before any conclusion can be reached.
5.2 Decomposition in Fresh Water and Seawater
All water contains manganese derived from soil and rocks.
Manganese in seawater is found mostly as manganese dioxide (MnO2),
some of which is produced from manganese salts by several species of
bacteria common to soils and ocean muds. The aqueous chemistry of
manganese is complex. Mobilization of manganese is favoured by low Eh
and/or pH conditions. Thus acid mine-drainage waters can give rise to
high environmental concentrations of dissolved manganese. Mitchell
(1971) showed that mobilization was greatly enhanced in acid, poorly
drained podzolic soils and groundwaters. It was suggested by Nichol et
al., (1967) that, in acid waterlogged soils, manganese passes freely
into solution and circulates in the groundwaters but that it is
precipitated on entering stream waters with average pH and Eh, thus
giving rise to stream sediments enriched with manganese.
Particulate material suspended in natural waters may contain an
appreciable proportion of manganese. Preston et al., (1972) found that
67-84% of the total manganese in shoreline and offshore areas of the
British Isles was associated with particulate matter that contained
manganese levels of several hundred mg/kg. Levels of particulate
manganese present in ocean waters are low in comparison with levels of
dissolved manganese. However, much larger amounts of particulate
manganese occur in estuarine and river waters, where resuspension of
bottom material may occur. Spencer & Sachs (1970) found that organic
particulate matter in the Gulf of Maine was predominantly regenerated
in the water column and that the amount of manganese transported to
the sediments in this way was negligible.
In deep-sea sediments, manganese is concentrated in the form of
both crustal material and coastal and shelf sediments. The composition
of manganese nodules on the ocean floors is related to factors such as
water composition, sedimentation rates, volcanic influences, and
organic productivity. Regional variations have also been observed,
especially in the Atlantic Ocean (Elderfield, 1972).
5.3 Atmospheric Washout and Rainfall
On the basis of samples taken at 32 stations in the USA, Lazrus
et al., (1970) concluded that the manganese in atmospheric
precipitation was derived mainly from human activity. The average
manganese concentration in the samples was 0.012 mg/kg. These data do
not show the immediate influence of major sources of industrial
emissions.
5.4 Run-off into Fresh Water and Seawater
Aerosols, pesticides, limestone and phosphate fertilizers,
manures, sewage sludge, and mine wastes have all been identified as
possible sources of soil contamination that can add to the manganese
burden of fresh water and seawater (Lagerwerff, 1967). The
concentrations of trace elements in soil additives are generally low
and do not significantly affect the total manganese content of soil
(Swaine, 1962; Mitchell, 1971).
5.5 Microbiological Utilization in Soils
Manganese cycles in the soil have been proposed involving di-,
tri-, and tetravalent manganese. Divalent manganese is transformed
through biological oxidation to the less available trivalent form and
later, through dismutation, the Mn+++ form is biologically reduced
to Mn++. A dynamic equilibrium may exist between all forms. The
oxidizing power of higher oxides increases with acidity and thus
reduction by organic matter is more likely at low pH values. If the
oxygen tension is low, biological reduction can take place at any pH
value. Bacterial oxidation is very slow or absent in very acid soils
and Mn++ predominates; organic matter can reduce the higher oxides.
In alkaline soils, the divalent form nearly disappears bacterial
oxidation is rapid and reduction by organic matter is slow. In
well-aerated soils with a pH of more than 5.5, soil microorganisms can
oxidize the divalent form rapidly. The rates of exchange between the
various forms are not known at the present time but there is a very
pronounced seasonal variation. This is probably due to oxidation and
reduction induced by microbial action. The manganous form predominates
in summer and the manganic form in winter, though the opposite is said
to be true for alkaline soils (Zajic, 1969).
5.6 Uptake by Soil and Plants
It appears that plants mainly absorb manganese in the divalent
state and that the availability of soil manganese is closely
influenced by the activity of microorganisms that can alter pH and
oxidation reduction potentials. Reducing the soil pH or the soil
aeration by flooding or compaction favours the reduction of manganese
to the Mn++ form and thereby increases its solubility and
availability to plants. Heavy fertilization of acid soils without
liming (particularly with materials containing chlorides, nitrates, or
sulfates) may also increase manganese solubility and availability.
Under some conditions of pH and aeration, the addition of organic
compounds to soil can increase the chemical reduction of manganese and
its uptake by plants. In a study by NAS/NRC (1973), it was shown that
the capacity of plants to absorb manganese varied according to
species. For example, in 20 different species of flowering plants, the
absorption capacity of some species was 20-60 times greater than that
of the species with the lowest capacity for absorbing the element
(NAS/NRC, 1973).
Areas with low manganese concentrations in the soil (below
500 mg/kg) are associated with low manganese levels in the herbage
(30-70 mg/kg dry weight) (Department of Health & Social Security, 1975
-- unpublished). Liming has been shown to reduce the availability of
manganese in soils; on plots with pH values ranging from 5.0 to 7.0,
the average manganese content of clover fell from 55 to 12 mg/kg and
that of rye grass from 104 to 13 mg/kg, alter liming (Reith, 1970).
Nitrogen applications consistently reduce the availability of
manganese. Organic material associated with a high pH can produce
organic complexes of divalent manganese leading to insufficient
available manganese for susceptible plants such as peas or cereals.
Aging of manganese oxides reduces their availability. Manganese
toxicity in plants may occur in soils containing manganese levels
exceeding 1000 mg/kg dry weight; this generally occurs in very acid
soils and can usually be remedied by liming (Mitchell, 1971). It
should be noted that the total manganese content of soil is of little
biological significance, since only a small amount is present in an
available form.
The uptake of manganese by barley p.!ants is stimulated by the
presence of microorganisms, which also appear to break down
EDTA-manganese chelates (Barber & Lee, 1974). On a dry-weight basis,
perennial rye and timothy grass have been shown to have about three
times the manganese content of lucerne, and rather more than
tetraploid red clover. Under deficiency conditions, plants destined
for herbage contained manganese concentrations of less than 10 mg/kg
dry weight (Fleming, 1974).
5.7 Bioconcentration
Terrestrial mammals may concentrate available manganese up to a
factor of 10, whereas fish and marine plants concentrate it by factors
of 100 and 100 000, respectively. Porphyra spp. in the Irish Sea
contained 13-93 mg/kg dry weight and Fucus spp. from British coasts
contained 33-190 mg/kg dry weight (Preston et al., 1972).
All vegetation appears to concentrate manganese to some extent,
the greatest degree of concentration taking place. in new growth and
seeds. Surface enrichment occurs through plant uptake and leaf
shedding.
Aquatic and terrestrial food chains have not been fully
determined for manganese. Variations reported in manganese
concentrations in foods may be caused by a number of factors, such as
the level and availability of manganese in the soil and water, the use
of agricultural chemicals, species differences in uptake, and
variations in sampling techniques and analyses.
The form in which manganese exists in animal and plant tissues is
not known.
5.8 Organic manganese fuel additives
In the petrol engine, over 99% of the methylcyclopentadienyl
manganese tricarbonyl (MMT) is combusted, the principal combustion
product being Mn3O4 (Ethyl Corporation, 1974; Moran, 1975).
According to available studies, less than 0.5% of MMT itself is likely
to be emitted with the exhaust gas (Ethyl Corporation, 1974; Hurn et
al., 1974). The emitted MMT is rapidly decomposed photochemically and
has an atmospheric half-time of only a few minutes, at the most (Ter
Haar et al., 1975). The photolytic decomposition products of MMT are
not well known. Nearly all the manganese in this compound is converted
by photochemical decomposition to a mixture of solid manganese oxides
and carbonates; manganese carbonyl compounds do not appear to be
formed (Ter Haar et al., 1975).
6. METABOLISM OF MANGANESE
6.1 Absorption
The main routes of absorption of manganese are the respiratory
and gastrointestinal tracts. Absorption through the skin is not
considered to occur to any great extent (Rodier, 1955).
6.1.1 Absorption by inhalation
Little is known about the absorption of manganese through the
respiratory system. The absorption of some metals and metallic
compounds was considered by the Task Group on Metal Accumulation
(1973) and certain of the basic principles outlined in that group's
report can be applied to inhaled metals in general. Particles small
enough to reach the alveolar lining of the lung (less than a few
tenths of a micrometre in diameter) are eventually absorbed into the
blood. Mucociliary clearance, which differs with each individual,
affects the degree of particle deposition in the lung. Furthermore, in
studies by Hubutija (1972), it was shown that deposition of inhaled
manganese oxide dust depended on the electrical charge carried, up to
33% more positively charged dust being deposited than negatively
charged dust. As a certain percentage of inhaled manganese particles
cleared by mucociliary action may be swallowed (Mena et al., 1969),
absorption from the gastrointestinal tract should also be considered
(Mouri, 1973).
6.1.2 Absorption from the gastrointestinal tract
Not much is known about the mechanisms of absorption of manganese
from the gastrointestinal tract. From in vitro studies using the
everted sac method, it would seem that manganese may be actively
transported across the duodenal and ileal segments of the small
intestine (Cikrt & Vostal, 1969). Results of studies in man and the
rat on the interrelationship between manganese and iron absorption
have indicated that intestinal absorption of manganese takes place by
diffusion in iron-overload states and by active transport in the
duodenum and jejunum in iron-deficiency states (Thomson et al., 1971).
Few quantitative data are available concerning absorption from
the gastrointestinal tract in man. Mena et al. (1969) studied
gastrointestinal absorption in 11 healthy, human subjects, each of
whom received 100 µc (3.7 MBq) of radioactive manganese dichloride
(54MnCl2) using 200 µg of manganese dichloride (55MnCl2) as a
carrier. About 3 ± 0.5% of the amount administered was found to be
absorbed. There were individual variations showing a five-fold
difference between the lowest and highest values of absorption. The
reported rate of absorption did not take into account reabsorption
into the enterohepatic circulation, but the authors considered this
underestimation to be small.
The rate of absorption may be influenced by such factors as
dietary levels of manganese and iron, the type of the manganese
compound, iron deficiency, and age. Thus, in the study just described,
Mena et al., found an absorption of 7.5 ± 2.0% in 13 patients with
iron-deficiency anaemia. They also found that, in 6 miners with high
tissue levels of manganese, an increase in the rate of excretion of
manganese was accompanied by an increase in iron excretion. This
interrelationship may further aggravate a pre-existing anaemia, thus
increasing the rate of manganese absorption and may be a relevant
factor in occupational exposure to manganese. Similarly, Thomson et
al. (1971), using duodenal perfusion with a manganese dichloride
solution containing a manganese concentration of 0.5 µg/ml, noted an
increased rate of absorption in iron-deficient patients that could be
inhibited by adding iron to the solution.
Figures for gastrointestinal absorption in infants and young
children are not available.
Most studies on animals have indicated a gastrointestinal
absorption of less than 4%. Suzuki (1974) reported an intestinal
absorption of only 0.5-2.0% in mice fed dietary levelsa of manganese
dichloride of 20-2000 mg/kg.
However, when rats were given 0.1 mg of radioactive manganese
orally, 3-4% of the dose was absorbed (Greenberg et al., 1943).
Similar results were obtained by Pollack et al. (1965), who reported
an absorption of 2.5-3.5% in rats given an oral dose of radioactive
manganese dichloride (54MnCl2). Thus, absorption data for the adult
rat agree with the figure obtained for the absorption of manganese
dichloride in man. However, Mena (1974) reported that intestinal
absorption in the young rat was of the order of 70% compared with 1-2%
in the adult rat.
In a study by Abrams et al. (1976), rats were given dietary
levels of manganese ranging from 4 to 2000 mg/kg for about 2 weeks,
followed by a single oral dose of radioactive manganese (54Mn).
Absorption of 54Mn was significantly lower in rats receiving high
dietary levels (1000-2000 mg/kg) than in animals receiving the lowest
level (4 mg/kg).
Ethanol given to fasting rats in doses of 4 g/kg body weight
increased absorption of manganese from the gastrointestinal tract and
resulted in a two-fold increase in uptake of manganese in the liver.
Furthermore, in vitro experiments indicated a four-fold increase in
the transmural migration of manganese (Schafer et al., 1974). It has
long been known that calcium in the diet can reduce the amount of
manganese absorbed by poultry, probably by reducing the amount of
manganese available for absorption (Wilgus & Patton, 1939).
However, recent studies suggest that calcium may, under certain
circumstances, enhance gastrointestinal absorption of manganese.
Lassiter et al. (1970) noted a higher rate of absorption in rats fed a
dietary level of calcium of 6 g/kg for 21 days before oral dosing with
54Mn, compared with rats receiving a level of only 1 g/kg. In studies
on sheep, the same authors found that phosphoric acid, mixed into the
ground hay at a concentration of 15 g/kg, decreased gastrointestinal
absorption of the stable manganese in the hay.
In rats, the enterohepatic circulation appears to be of
importance. Intraduodenal administration of manganese that had been
excreted into the bile resulted in about 35% absorption, whereas only
15% of an equivalent dose of manganese dichloride administered
intraduodenally was absorbed (Cikrt, 1973). This indicates that
manganese present in bile is in a form that is more easily absorbed
than manganese dichloride.
6.2 Distribution
6.2.1 Distribution in the human body
Manganese is an essential element for man and animals and thus
occurs in the cells of all living organisms. Concentrations of
manganese present in individual tissues, particularly in the blood,
remain constant, in spite of some rapid phases in transport,
indicating that such amounts may be considered characteristic for
these particular organs irrespective of the animal species (Cotzias,
1958).
The total manganese body burden of a standard man of 70 kg has
been estimated to be about 10-20 mg (Underwood, 1971; WHO Working
Group, 1973; Kitamura et al., 1974). Thus, tissue concentrations will
frequently be below the µg/kg level. In general, higher manganese
concentrations can be expected in tissues with a high mitochondria
content (Maynard & Cotzias, 1955; Thiers & Vallee, 1957), with the
exception of the brain which contains only low concentrations (Maynard
& Cotzias, 1955). There also appears to be a tendency towards higher
concentrations in pigmented tissues such as dark hair or pigmented
skin (van Koetsveld, 1958; Cotzias et al., 1964).
a The approximate relation between concentration in diet in mg/kg
(ppm) and mg per kg body weight per day is given for a number of
animal species in Nelson (1954).
Table 6. Manganese in human tissues (mg/kg wet weight)
Tissue Kehoe et al. (1940) Tipton & Cook (1963)a Kitamura (1974)
(emission spectroscopy) (emission spectroscopy) (atomic absorption)
aorta -- 0.11 --
brain 0.30 0.27 0.25
fat -- -- 0.07
heart 0.32 0.22 0.19
intestine 0.35 -- --
kidney 0.60 0.90 0.58
liver 2.05 1.30 1.20
lung 0.22 0.19 0.21
muscle -- 0.06 0.08
ovary -- 0.16 0.19
pancreas -- 1.18 0.74
spleen -- 0.13 0.08
testis -- 0.13 0.20
trachea -- 0.19 0.22
rib -- -- 0.06
a Values calculated using the given ash percentage wet weight
and the median value of manganese in tissue ash.
Table 6 gives the results of 3 studies on the manganese contents
of various tissues in people without any known occupational or other
additional exposure to manganese. Two are studies on adults from the
USA (Kehoe et al., 1940; Tipton & Cook, 1963). In a study by Kitamura
(1974) performed on 15 Japanese males and 15 females who had died in
accidents, the highest concentrations of manganese were found in the
liver, pancreas, kidney, and intestines. Comparatively high
concentrations were also found in the suprarenal glands.
From birth to 6 weeks, infants have relatively higher tissue
concentrations of manganese than older children, especially in tissues
normally associated with low manganese levels. However, after about 6
weeks of age, no accumulation of manganese appears to take place with
increasing age (Schroeder et al., 1966). This is in agreement with the
study of Dobrynina & Davidjan (1969), who reported that manganese did
not accumulate with age, and that the manganese content of the lung
actually decreased with increasing age. Anke & Schneider (1974) also
found a statistically significant decrease in the kidney content of
manganese beginning at about 60 years of age; they reported a slightly
higher mean concentration in females (4.4 mg/kg) than in males
(3.8 mg/kg). With respect to manganese concentrations in the liver,
Widdowson et al. (1972) reported that there was no consistent change
with age in 30 fetuses from 20 weeks' gestation to full-term, but
that, generally, manganese concentrations in full-term livers were
7-9% higher than concentrations in adult livers. Studies by Schroeder
et al. (1966) and Widdowson et al. (1972) confirmed that human
placental transfer of manganese takes place.
Table 7. Concentrations of manganese in the whole blood of people without occupational
exposure to manganese
Number of Mean Range
subjects (µg/100 ml) (µg/100 ml) Method Reference
14 0.844 n.r.a neutron Cotzias et al.
activation (1966)
19 n.r. 0.86-1.45 neutron Cotzias & Papavasiliou
activation (1962)
7 1.16 0.90-1.45 neutron Papavasiliou & Cotzias
activation (1961)
18 2.4 n.r. neutron Bowen (1956)
activation
232 3.47b n.r. spectrographic Horiuchi et al.
(1967)
47 4.0 n.r. spectrographic Butt et al. (1964)
12 4.6 2.2-7.9 spectrographic Cholak & Hubbard (1960)
13 7.6 4.0-15.0 colorimetric Barborik & Sehnalova
(1967)
30