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The following information relevant to Poisons Centres has been extracted from the CHEMINFO database produced by CCOHS. Complete CHEMINFO records also contain comprehensive hazard control and regulatory information. For more information about the complete CHEMINFO database contact CCOHS.

CHEMINFO Record Number: 314
CCOHS Chemical Name: Pyrethrin I

Chrysanthemum monocarboxylic acid pyrethrolone ester
Pyrethrolone, chrysanthemum monocarboxylic acid ester
(+)-Pyrethronyl (+)-trans-chrysanthemate
Pyr├ęthrine I

CAS Registry Number: 121-21-1
Other CAS Registry Number(s): 3903-69-3 39668-01-4
RTECS Number(s): GZ1725000
EU EINECS/ELINCS Number: 204-455-8
Chemical Family: Pyrethrins (natural) and pyrethroids (synthetic)
Molecular Formula: C21-H28-O3


Appearance and Odour:
Viscous liquid or oil

Odour Threshold:
No data. Pyrethrin I has a very low vapour pressure.

Warning Properties:
Information not available

Composition and purity depend on the method of preparation. Pyrethrin I may be extracted from natural pyrethrins, reconstituted from component alcohols and acids obtained from the natural material or synthesized (2).

Uses and Occurrences:
Pure pyrethrin I is used primarily in laboratories for research on pyrethroid insecticides. Pyrethrin I makes up about 35% of the active ingredients in natural extracts of pyrethrins used in commercial formulations. It is the major insecticidal ingredient of these extracts.



Effects of Short-Term (Acute) Exposure

No animal or human information is available for pyrethrin I.
Based on data available for natural pyrethrins (of which pyrethrin I is a major component) and on ease of metabolism in animals, health effects are unlikely by inhalation.

Skin Contact:
Irritation or injury from short-term exposure appears unlikely.

Eye Contact:
Based on animal testing of pure pyrethrin I and natural pyrethrins, mists and dusts might cause some degree of eye irritation.
No data available to indicate whether eye injury would occur.

Accidental ingestion of large amounts might result in nausea, vomiting, convulsions and other signs of disturbance of the central nervous system.

Effects of Long-Term (Chronic) Exposure

Based on similarity to natural pyrethrins and on ease of metabolism, chronic effects are not expected with normal use and handling of pyrethrin I. It seems unlikely to cause skin sensitization or respiratory sensitization.

No information available. Related pyrethrins are not carcinogenic.

The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.

The American Conference of Governmental Industrial Hygienists (ACGIH) has no listing for this chemical.

Pyrethrin I makes up 35% of pyrethrum (natural pyrethrins), which has an ACGIH carcinogenicity designation of A4 (not classifiable as a human carcinogen).

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
No information available. Animal tests on natural pyrethrins showed no teratogenic or embryotoxic effects.

Reproductive Toxicity:
No information available

No information available

Toxicologically Synergistic Materials:
In animal testing, a pyrethrin "synergist" (piperonyl butoxide) did not enhance the acute toxicity of pyrethrins to rats.

Potential for Accumulation:
Pyrethrins are rapidly broken down in the body and are unlikely to accumulate.


If symptoms are experienced, remove source of contamination or move victim to fresh air. Obtain medical advice immediately.

Skin Contact:
Remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). Gently blot or brush away excess chemical quickly. Wash gently and thoroughly with water and non-abrasive soap. If irritation persists, obtain medical advice immediately. Completely decontaminate clothing, shoes and leather goods before reuse, or discard.

Eye Contact:
Gently blot or brush away excess chemical quickly. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 20 minutes, by the clock, holding the eyelid(s) open. If irritation persists, obtain medical attention immediately.

Never give anything by mouth if victim is rapidly losing consciousness, or is unconscious or 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. If vomiting occurs naturally, rinse mouth and repeat administration of water. Obtain medical advice immediately.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).

Consult a physician and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.

All first aid procedures should be periodically reviewed by a physician familiar with the material and its conditions of use in the workplace.


Flash Point:
No data. For natural pyrethrins, flash point has been reported as 82-88 deg C (180-190 deg F) (open cup).

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

Extinguishing Media:
Carbon dioxide, dry chemical powder, alcohol foam, polymer foam.

Fire Fighting Instructions:
Treat as combustible liquid. Cool exposed containers.


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


Molecular Weight: 328.4

Conversion Factor:
Not applicable

Melting Point: No data
Boiling Point: Decomposes without boiling at normal pressure; boils at reduced pressure (146-150 deg C at 0.0005 mm Hg); decomposes at 170 deg C at 0.1 mm Hg.
Relative Density (Specific Gravity): No data
Solubility in Water: Practically insoluble
Solubility in Other Liquids: Soluble in ethyl alcohol, petroleum ether, kerosene, carbon tetrachloride, ethylene dichloride and nitromethane.
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: Not applicable
Vapour Density: Not applicable
Vapour Pressure: Extremely low
Saturation Vapour Concentration: Not applicable
Evaporation Rate: Extremely low
Critical Temperature: Not applicable


Stable when protected from air and light. Oxidizes readily and becomes inactive in air and light.

Hazardous Polymerization:
Does not occur.

Incompatibility - Materials to Avoid:
STRONG OXIDIZING AGENTS - May cause fire and explosions.

STRONG BASES - Breakdown (hydrolysis) occurs. The reaction may be vigorous.

Hazardous Decomposition Products:
Insufficient information

Corrosivity to Metals:


LD50 (oral, rat): 260-420 mg/kg (1,2,4,6)
LD50 (iv, rat): 5 mg/kg (1,2,4)
The differences between oral and iv (intravenous) toxicities are presumably due to rapid breakdown of pyrethrin I in the body when given orally (1).
Some rats survived total oral doses of 450 to 2000 mg/kg administered in 2-6 portions over 12-54 hours (ref. 2, page 128).

METABOLISM: Studies with rats and mice showed rapid multiroute oxidation of pyrethrin I. Within 48 hours, 46% of metabolites appeared in the urine and 0.3% in expired CO2. Some unmetabolized pyrethrin I was found in the feces (3,4).

IRRITATION: Irritating to eyes and mucous membranes. No permanent damage to the eyes appears to have been reported (5).


Selected Bibliography:
(1) Gosselin, R.E., et al. Clinical toxicology of commercial products. 5th ed. Williams & Wilkins, 1984. p. III-352 - III-355
(2) Casida, J.E. Pyrethrum : the natural insecticide. Academic Press, 1973
(3) Hutson, D.H. The metabolic fate of synthetic pyrethroid insecticides in mammals. Progress in Drug Metabolism. Vol. 3 (1979). p. 215-252
(4) Hayes, W.J. Pesticides studied in man. Williams and Wilkins, 1982. p. 75-80
(5) Grant, W.M. Toxicology of the eye. 3rd ed. Charles C. Thomas, 1986. p. 774
(6) RTECS record for cyclopropanecarboxylic acid, 2,2-dimethyl-3-(2-methylpropenyl)-, ester with 4-hydroxy- 3-methyl-2-(2,4-pentadienyl)-2-cyclopenten-1-one. Date of last update 8806
(7) Schwope, A.D., et al. Guidelines for the selection of chemical protective clothing. 3rd ed. Vol. 1 : field guide. American Conference of Governmental Industrial Hygienists, February 1987. p. 122
(8) NIOSH pocket guide to chemical hazards. June, 1994. p. 270-271
(9) European Communities. Commission Directive 98/98/EC. December 15, 1998

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: 1988-10-20

Revision Indicators:
PEL-TWA 1993-03-01
Trans PEL-TWA 1993-04-01
TDG 1994-03-01
Sampling 1996-01-01
Protective equipment 1996-01-01
EU number 1996-01-01
US transport 1996-01-01
Respiratory guidelines 1996-01-01
Resistance of materials 1996-01-01
TLV comments 1996-09-01
EU Class 2000-05-01
EU Risk 2000-05-01
EU Safety 2000-05-01
Bibliography 2000-05-01
UN/NA No 2002-12-18
Carcinogenicity 2003-07-24

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