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CHEMINFO Record Number: 240
CCOHS Chemical Name: Benzidine


Chemical Name French: Benzidine
Chemical Name Spanish: Bencidina
CAS Registry Number: 92-87-5
UN/NA Number(s): 1885
RTECS Number(s): DC9625000
EU EINECS/ELINCS Number: 202-199-1
Chemical Family: Aromatic amine / aromatic primary amine / diphenylamine / aromatic diamine / diphenyl diamine / benzidine
Molecular Formula: C12-H12-N2
Structural Formula: NH2-C6H4-C6H4-NH2


Appearance and Odour:
White, grayish-yellow or reddish grey crystalline powder or crystals; darkens on exposure to air and light.

Odour Threshold:
Information not available

Warning Properties:
Information not available

Uses and Occurrences:
Benzidine is no longer produced for commercial use in Canada and the United States. Its use is banned in several countries and severely curtailed in others. Any benzidine production must be for in-house use only. Historically, benzidine was largely used in the production of dyes, especially azo dyes which were used in the leather, textile and paper industries. It was also used as a detector of blood, hydrogen peroxide and nicotine, as a rubber compounding agent, in the manufacture of plastic films and in organic synthesis.(2)


White, grayish-yellow or reddish gray crystalline powder or crystals; darkens on exposure to air and light. Can probably burn if strongly heated. Can decompose at high temperatures forming toxic gases, such as nitrogen oxides. VERY TOXIC. May be fatal if swallowed and harmful if absorbed through the skin. CANCER HAZARD - can cause cancer. MUTAGEN - May cause genetic damage, based on animal information.


Effects of Short-Term (Acute) Exposure

Inhalation of benzidine vapour is unlikely to occur at normal temperatures, because it has a very low vapour pressure. However, many historical occupational exposures involved inhalation of airborne dust or vapours from heating of materials. Despite the fact that benzidine had significant historical use, no effects of short-term inhalation exposure were located in the literature.

Skin Contact:
There is no human or animal information available regarding the potential for skin irritation of benzidine.
Benzidine is readily absorbed through the intact skin, although the effects of exposure are unknown.(2)

Eye Contact:
There is no human or animal information available regarding the potential for eye irritation of benzidine.

No human information is available. Acute toxicity studies in animals indicate that benzidine is toxic by ingestion (based on the LD50s in mice and rats). However, toxic effects were not described in the report. Occupational oral exposure to benzidine is unlikely.

Effects of Long-Term (Chronic) Exposure

Skin Sensitization:
There is not enough information available to conclude that benzidine is a skin sensitizer.
A 32 year-old doctor developed recurrent skin problems on the hands and face. Patch testing with benzidine produced a very strong reaction. He was exposed to benzidine powder during an analytical technique. Previous history of allergies was not discussed.(21)
In the testing of 4600 patients over a 5- year period, 5.02% (231 cases) demonstrated sensitization to benzidine. Of those sensitized, 208 cases (88.05%) also had occupational dermatitis (dry, red, itchy skin). A unique positive patch test reaction was reported for 153 cases (66%), whereas 78 people (34%) reacted positively to benzidine as well as other allergens.(22) It is not known if the individuals who tested positive to benzidine were occupationally exposed to benzidine or if they were predisposed to developing allergic reactions.


Benzidine is one of the most potent known human carcinogens, with the principal target organ being the bladder. In virtually all occupational studies reported, there was an increase in bladder cancer.(2) The International Agency for Research on Cancer (IARC) has concluded that there is sufficient evidence for carcinogenicity in humans.(3,4)
Since the use of benzidine ceased before current protocols for reporting of carcinogenicity data were established, many studies lack detail, but the results are conclusive. A comprehensive study of Chinese workers exposed to benzidine between 1972-1977 showed 17.5 times more deaths in the exposed population than in the general population. Increases in bladder cancer were dose-related. Smoking further increased the incidence of cancer.(10) In an Italian study of workers exposed to benzidine-based dyes between 1922 and 1970, there was an overall increase in bladder cancer of 30.4 times. There were smaller increases in upper digestive and respiratory tract cancers.(11) In a review of 1030 cases of bladder cancer, 30% could be associated with exposure to benzidine or its dye derivatives.(2)

The International Agency for Research on Cancer (IARC) has concluded that this chemical is carcinogenic to humans (Group 1).

The American Conference of Governmental Industrial Hygienists (ACGIH) has designated this chemical as a confirmed human carcinogen (A1).

The US National Toxicology Program (NTP) has listed this chemical as a known human carcinogen.

This chemical is regulated by the US Occupational Safety and Health Administration (OSHA) as a carcinogen.

Teratogenicity and Embryotoxicity:
No human or animal information is available.

Reproductive Toxicity:
No human or animal information is available.

Benzidine is considered mutagenic based on animal studies. It has caused mutagenicity in live animals in a wide variety of tests. Chromosomal analysis was conducted on white blood cells (lymphocytes) from workers exposed to benzidine-based dyes. There was a statistically significant increase in chromosome aberrations (primarily chromatid breaks) in both smokers and non-smokers.(12)

Toxicologically Synergistic Materials:
No information is available.

Potential for Accumulation:
Benzidine is well absorbed by inhalation, oral and dermal routes of exposure and is distributed fairly widely throughout the body. The metabolism of benzidine is complex involving a number of alternate pathways in different organs and different species. This probably accounts for the different target organs in different species. Although small amounts of benzidine may be retained in body fat, significant accumulation does not appear to occur. Benzidine and its metabolites are probably excreted for the most part in the urine and/or feces within several days after absorption. Benzidine-based dyes are metabolized to benzidine, primarily in the digestive tract.(2)


Take proper precautions to ensure your own safety before attempting rescue (e.g. wear appropriate protective equipment). Remove source of contamination or move victim to fresh air. Obtain medical attention immediately.

Skin Contact:
Avoid direct contact. Wear chemical protective clothing, if necessary. As quickly as possible, remove contaminated clothing, shoes, and leather goods (e.g. watchbands, belts). Quickly and gently blot or brush away excess chemical. Wash gently and thoroughly with water and non-abrasive soap for 20 minutes or until chemical is removed. Obtain medical advice immediately. Discard contaminated clothing, shoes and leather goods.

Eye Contact:
Avoid direct contact. Wear chemical protective gloves, if necessary. Do not allow victim to rub eye(s). Let the eye(s) water naturally for a few minutes. Have victim look right and left, and then up and down. If particle/dust does not dislodge, flush with lukewarm, gently flowing water for 5 minutes or until particle/dust is removed, while holding eyelid(s) open. If irritation persists, obtain medical attention. DO NOT attempt to manually remove anything stuck to eye(s).

NEVER give anything by mouth if victim is rapidly losing consciousness, is unconscious or is convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water to dilute material in stomach. Obtain medical attention immediately.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures except under minor instances of inhalation or skin contact.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
Not available. Probably very high.

Lower Flammable (Explosive) Limit (LFL/LEL):
Not available

Upper Flammable (Explosive) Limit (UFL/UEL):
Not available

Autoignition (Ignition) Temperature:
Not available

Sensitivity to Mechanical Impact:
Probably not sensitive.

Sensitivity to Static Charge:
Information not available.

Combustion and Thermal Decomposition Products:
Carbon monoxide, carbon dioxide, nitrogen oxides, ammonia.

Fire Hazard Summary:
This material can probably burn if strongly heated. During a fire, irritating/toxic nitrogen oxides may be generated.

Extinguishing Media:
Carbon dioxide, dry chemical powder, alcohol foam, polymer foam, water spray or fog.

Fire Fighting Instructions:
Evacuate area and fight fire from a safe distance or a protected location. Approach fire from upwind to avoid hazardous vapours and toxic decomposition products. The flashpoint of this material is not available, but is probably very high. If the material is burning, water spray, fog or foam can be used to extinguish fires involving benzidine. Water or foam may cause frothing. However, a water spray or fog that is gently applied to the surface of the liquid, preferably with a fine spray of fog nozzle, will cause frothing that will blanket and extinguish the fire. Solid streams of water may be ineffective and spread material. If products other than benzidine are burning, extinguish fire using extinguishing agent(s) suitable for the surrounding fire.
If possible, isolate materials not yet involved in the fire and protect personnel. Move containers from fire area if it can be done without risk. Otherwise, use water spray to keep fire-exposed containers cool, absorb heat, protect exposed material and flush spills away and prevent exposures.
Benzidine and its decomposition products are very hazardous to health. Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (Bunker Gear) will not provide adequate protection. A full-body encapsulating chemical resistant suit with positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 184.23

Conversion Factor:
1 ppm = 7.52 mg/m3; 1 mg/m3 = 0.133 ppm at 25 deg C (calculated)

Physical State: Solid
Melting Point: 115-120 deg C (239-248 deg F) when slowly heated; 128 deg C (262 deg F) when anhydrous and rapidly heated.(5,13)
Boiling Point: 400-401 deg C (752-754 deg F) at 98.7 kPa (2)
Relative Density (Specific Gravity): 1.25 at 20 deg C (water = 1) (2)
Solubility in Water: Sparingly soluble (40 mg/100 mL) at 12 deg C; slightly soluble in hot water (940 mg/100 mL at 100 deg C) (2)
Solubility in Other Liquids: Soluble in hot ethanol (20 g/100 mL); moderately soluble in absolute ethanol (7.7 g/100 mL) and diethyl ether (2g/100 mL).(2)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 1.34-1.81 (2)
pH Value: Not applicable
Basicity: Weak base; pKb1 = 9.03 (K1 = 9.3X10(-10)), pKa1 = 4.97; pKb2 = 10.25 (K2 = 5.6X10(-11)), pKa2 = 3.75 (15)
Vapour Density: 6.36
Vapour Pressure: 6.66X10(-5) kPa (5X10(-4) mm Hg) at 25 deg C (2)
Saturation Vapour Concentration: 0.66 ppm at 25 deg C (calculated)
Evaporation Rate: Negligible at ambient temperatures (14)
Critical Temperature: Information not available


Normally stable. Turns brownish-red on exposure to air and light.(13,14)

Hazardous Polymerization:
Does not occur

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

STRONG OXIDIZING AGENTS (e.g. nitric acid), STRONG ACIDS (e.g. sulfuric acid) - May react violently.(14)
RED FUMING NITRIC ACID - Will ignite spontaneously. Certain metal oxides promote this ignition.(16)

Hazardous Decomposition Products:
None reported

Conditions to Avoid:
Air, light, heat

Corrosivity to Metals:
Not reported. Benzidine is slightly basic.

Stability and Reactivity Comments:
Benzidine undergoes reactions characteristic of primary aromatic amines.(3)


LD50 (oral, rat): 566 mg/kg (1)
LD50 (oral, mouse): 214 mg/kg (1)

Effects of Short-Term (Acute) Exposure:

There is no animal information on the effects of short term exposure to benzidine. In a six-week study, mice were exposed orally to a related chemical, benzidine dihydrochloride. Some changes were seen in bone marrow, liver, spleen and kidney.(2)

Effects of Long-Term (Chronic) Exposure:

Oral administration of benzidine to rabbits (13 or 26 mg/kg/day) and dogs (approx. 8 mg/kg/day) once a day for 20 to 128 days, caused wasting (atrophy) and inflammation of the muscular walls of the heart. Cirrhosis of the liver and kidney injury were observed in the rabbits, while blood was seen in the urine of both rabbits and dogs. Cirrhosis of the liver has also been reported in carcinogenicity studies in rabbits. Recurrent episodes of bladder inflammation (cystitis) were observed in 7 dogs fed benzidine for 6 days/week for 5 years (17.6 to 26.4 mg/kg/day). Benzidine was determined to be toxic to the immune system in an oral study on mice.(2) Liver, kidney, spleen and brain changes were observed in mice exposed to a related chemical, benzidine dihydrochloride (equivalent to 2.5 to 26.5 mg/kg/day of benzidine) in their drinking water from 40 to 80 weeks. Benzidine dihydrochloride (equivalent to 1.8 mg/kg/day benzidine) also caused central nervous system damage in mice exposed for their lifetime.(2)

In almost every animal study on benzidine or the related benzidine dihydrochloride, there was a substantial increase in the incidence of cancer by any route of exposure.(2,3,4,5) The target organs vary in different species. Tumours were caused in the bladder (in dogs and possibly rabbits), liver (in rats, mice and hamsters), and bile duct (in hamsters).(2) IARC has concluded that there is sufficient evidence of carcinogenicity in animals.(3,4) In a large study, there was a dose-related increase in cancer (primarily liver) in mice exposed to benzidine dihydrochloride in drinking water throughout their lifespan.(5) Female rats were exposed orally intermittently over a period of 30 days to doses totalling 12-50 mg/rat. Although not all animals survived to the 9 month termination, and not all data were reported, this study is important because the incidence of mammary gland tumours was over 50% in treated animals compared to 2% in controls.(2,5) Hamsters fed benzidine or benzidine dihydrochloride in food for their lifetime showed a high incidence (over 50%) of liver or bile duct tumours for both treated groups compared to no liver tumours in controls.(2,5) Four of 7 dogs given benzidine orally for 5 years, developed bladder cancer between 18 months and 10 years.(2,5)

Benzidine is such a strong mutagen both in in vitro and in vivo tests that it is often used as a positive control in evaluating test systems.(6,7,8) Oral administration of benzidine to rats and mice has induced micronuclei in bone marrow and fetal liver cells, DNA binding and adducts, DNA damage, and unscheduled DNA synthesis in somatic cells.
Mice were orally dosed with 16 mg/kg/day (cited as 80 ppm) radiolabelled benzidine in drinking water for 1 week. One group of each sex was sacrificed at 0, 1 and 7 days following the end of treatment. Substantial covalent binding to liver DNA was observed.(27) Male dogs were orally dose with 11 mg/kg (cited as 60 microM/kg) and then killed after 1, 2 or 7 days. DNA adducts were detected in liver cells on day 2. Radioactivity was detected in bladder epithelium DNA on day 2. However, due to its low specific activity, benzidine binding was too low to perform adduct analysis.(24) Unscheduled DNA synthesis was observed in the liver cells of male rats orally dose with 200 mg/kg in corn oil.(Ashby et al. 1988) Male rats (3/group) were orally dosed with 200 mg/kg in corn oil. A significant elevation in unscheduled DNA synthesis was observed in liver cells at 12 hours.(29) DNA damage and unscheduled DNA repair were observed in the liver cells of male rats orally treated with 200 mg/kg.(25) Male mice were given single oral doses of 160 mg/kg. A statistically significant increase in DNA damage was observed in all organs studied (stomach, liver, kidney, bladder, lung, brain and bone marrow), except the colon.(31) Male mice were orally dosed 3 times with 150 or 300 mg/kg or once with 900 mg/kg in corn oil. A clear positive response for micronuclei in bone marrow cells was obtained for all 3 test protocols.(28) Mice were orally exposed to 300 mg/kg in corn oil. For males, micronuclei were scored in bone marrow at 24, 48 and 72 hrs after single oral doses. For evaluation of transplacental effects, pregnant mice were administered benzidine on day 15-16 of pregnancy. Micronuclei were evaluated in the bone marrow of mothers and in fetal livers at several time intervals between 12 and 24 hours after single oral doses. Micronuclei were significantly increased in male mice at 24 and 48 hours. Benzidine caused no increase in micronuclei of mothers at any of the selected time intervals. In fetal livers, the incidence of micronucleated polychromatic erythrocytes was significantly increased at all intervals except 12 hours.(26) Oral doses of 40 and 200 mg/kg were administered 1, 2 or 3 times to male mice. A significant response for micronuclei induction was observed.(30) There were no sperm-head abnormalities in mice following 5 injections of benzidine into the body cavity (intraperitoneal).(2) This route of exposure is not considered relevant to occupational situations.
In rodent cells in vitro, benzidine has caused cell transformation in hamster and mouse embryo cells and induced chromosomal aberrations, sister chromatid exchanges, unscheduled DNA synthesis and DNA strand breaks.(2,4,5,9) It is mutagenic to bacteria and yeast.(2,4,5,9)


Selected Bibliography:
(1) Back, K.C., et al. Reclassification of materials listed as transportation health hazards. Report No. TSA-20-72-3. US Department of Transportation, 1972
(2) Toxicological Profile for Benzidine. DRAFT. Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services, 1993
(3) IARC Monographs on the evaluation of the carcinogenic risk of chemicals to humans. Vol. 29. IARC, 1982. p. 149-183, 391-398
(4) IARC Monographs on the evaluation of carcinogenic risks to humans. Suppl. 7. IARC, 1987. p. 58, 123-125
(5) Carcinogenicity. Vol. III. Summary reviews of the scientific evidence. The Toxicology of chemicals - Series one. Publication No. EUR 13765 EN. Commission of the European Communities, 1991. p. 101-110
(6) Arlett, C.F., et al. The third UKEMS collaborative trial. Mutagenesis. Vol. 5, suppl. (1990). p. 1-88
(7) Xing, W.J., et al. A comparison of SCE test in human lymphocytes and Vicia faba: a hopeful technique using plants to detect mutagens and carcinogens. Mutation Research. Vol. 241 (1990). p. 109-113
(8) Hellmer, L., et al. An evaluation of the E. coli K-12 uvrB/recA DNA repair host-mediated assay: I. In vitro sensitivity of the bacteria to 61 compounds. Mutation Research. Vol. 272, no. 2 (Oct. 1992). p. 145-160
(9) Waters, E. The genotoxicity of benzidine and 4- dimethylaminoazobenzene: a survey of the literature. In: Comparative genetic toxicology: the second UKEMS collaborative study. Edited by J.M. Parry, et al. VCH Publishers, 1985. p. 9-37
(10) Bi, W., et al. Mortality and incidence of bladder cancer in benzidine-exposed workers in China. American Journal of Industrial Medicine. Vol. 21 (1992). p. 481-489
(11) Piolatto, G., et al. Bladder cancer mortality of workers exposed to aromatic amines: an updated analysis. British Journal of Cancer. Vol. 63 (1991). p. 457-459
(12) Mirkova, E.T., et al. The genetic toxicity of the human carcinogens benzidine and benzidine-based dyes: chromosomal analysis in exposed workers. Progress in Clinical and Biological Research. Vol. 340, part C (1990). p. 397-405
(13) The Merck index; an encyclopedia of chemicals, drugs and biologicals. 11th ed. Merck and Co., Inc., 1989. p. 168
(14) Chemical safety sheets: working safely with hazardous chemicals. Kluwer Academic Publishers, 1991. p. 98
(15) Ullmann's encyclopedia of industrial chemistry. 5th revised ed. Vol. A3. VCH Verlagsgesellschaft, 1985. p. 539-551
(16) Bretherick, L. Bretherick's handbook of reactive chemical hazards. 4th ed. Butterworths, 1990. p. 846, 1153
(17) NIOSH pocket guide to chemical hazards. NIOSH, June 1994. p. 26-27
(18) Report on Carcinogens. 11th ed. US Department of Health and Human Services, Public Health Service, National Toxicology Program
(19) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 2nd ed. Van Nostrand Reinhold, 1993. p. 51
(20) European Communities (EC). Commission Directive 2004/73/EC. Apr. 29, 2004
(21) Baer, R.L. Benzidine as cause of occupational dermatitis in a physician. Journal of the American Medical Association. Vol. 129 (1945). p. 442-443
(22) Grimalt, F., et al. Cutaneous sensitivity to benzidine. Dermatosen. Vol. 2, no. 4 (1981). p. 95-97
(23) Ashby, J., et al. UDS activity in the rat liver of the human carcinogens benzidine and 4-aminobiphenyl, and the rodent carcinogens 3,3'-dichlorobenzidine and direct black 38. Mutagenesis. Vol. 3, no. 1 (Jan. 1988). p. 69-71
(24) Beland, F.A., et al. Arylamine-DNA adducts in vitro and in vivo: their role in bacterial mutagenesis and urinary bladder carcinogenesis. Environmental Health Perspectives. Vol. 49, suppl. 125 (1983). p. 125-134
(25) Bermudez, E., et al. Detection of DNA damage in primary cultures of rat hepatocytes following in vivo and in vitro exposure to genotoxic agents. Environmental Mutagenesis. Vol. 4, no. 6 (1982). p. 667-679
(26) Cihák, R., et al. Benzidine and 3,3'-dichlorobenzidine (DCB) induce micronuclei in the bone marrow and the fetal liver of mice after gavage. Mutagenesis. Vol. 2, no. 4 (July 1987). p. 267-269
(27) Martin, C.N., et al. Covalent binding of benzidine and N-acetylbenzidine to DNA at the C-8 atom of deoxyguanosine in vivo and in vitro. Cancer Research. Vol. 42, no. 7 (July 1982). p. 2678-2686
(28) Mirkova, E. Activity of the human carcinogens benzidine and 2-naphthylamine in triple- and single-dose mouse bone marrow micronucleus assays: results for a combined test protocol. Mutation Research. Vol. 234, no. 3-4
(June 1990). p. 161-163
(29) Mirsalis, J.C., et al. Detection of genotoxic carcinogens in the in vivo-in vitro hepatocyte DNA repair assay. Environmental Mutagenesis. Vol. 4, no. 5 (1982). p. 553-562
(30) Parton, J.W., et al. The evaluation of a multiple dosing protocol for the mouse bone-marrow micronucleus assay using benzidine and 2,6-xylidine. Mutation Research. Vol. 234, no. 3-4 (June 1990). p. 165-168
(31) Sasaki, Y.F., et al. The alkaline single cell gel electrophoresis assay with mouse multiple organs: results with 30 aromatic amines evaluated by the IARC and U.S. NTP. Mutation Research. Vol. 440, no. 1 (Mar. 1999). p. 1-18

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1994-08-22

Revision Indicators:
Sampling 1995-12-01
Respiratory guidelines 1995-12-01
Resistance of materials 1995-12-01
Protective equipment 1995-12-01
WHMIS (proposed class) 1997-07-01
US Transport 1998-03-01
TLV comments 1998-08-01
EU Class 2000-05-01
EU Risk 2000-05-01
EU Safety 2000-05-01
TDG 2002-05-27
First aid skin 2003-05-16
Personal hygiene 2003-05-26
Long-term exposure 2004-01-27
Emergency overview 2004-01-27
WHMIS health effects 2004-01-27
PEL final comments 2004-01-29
Toxicological info 2004-02-09
Mutagenicity 2004-02-09
Reproductive toxicity 2004-02-09
WHMIS detailed classification 2004-02-09
WHMIS classification comments 2004-02-09
Handling 2004-04-08
EU classification 2005-01-16
EU comments 2005-01-16
Bibliography 2005-02-02

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