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CHEMINFO Record Number: 311
CCOHS Chemical Name: Pyrethrins

Chrysanthemum cinerareaefolium

Chemical Name French: Pyrèthre
Chemical Name Spanish: Piretrinas

Trade Name(s):

CAS Registry Number: 8003-34-7
Other CAS Registry Number(s): 12768-73-9
RTECS Number(s): UR4200000
Chemical Family: Pyrethrins (natural) and pyrethroids (synthetic)
Molecular Formula: C(20-22)-H(28,30)-O(3,5)


Appearance and Odour:
Yellow to brown, viscous liquid or oil depending on state of purity.

Odour Threshold:
Not available

Warning Properties:
Information not available

Pyrethrins are naturally occurring insecticides derived from chrysanthemum flowers. The refined extract contains 6 active components (pyrethrin I and II, cinerin I and II, and jasmolin I and II) as well as impurities which are mainly fatty acids. The refined extracts are usually 20% pyrethrins and 80% petroleum distillate. /Products for household use usually contain pyrethrins concentrations below 1%; other formulations may have up to 9% pyrethrins. Almost all formulations contain a synergist--usually piperonyl butoxide or MGK 264. /This material is often only a small percentage of pesticide formulations. The overall physical, chemical and toxic characteristics of the product may depend on other ingredients such as solvents.

Uses and Occurrences:
Ingredient of insecticidal sprays for use in households, food-storage warehouses, animal facilities and factories and on domestic and farm animals; garden and indoor plant sprays; control of insects in fruit, vegetable, field crop, and vine cultivation.



Effects of Short-Term (Acute) Exposure

Inhalation is probably the main route of occupational exposure to pyrethrins. Animal studies indicate very low toxicity by inhalation, and there are no reports of health effects despite extensive use of pyrethrin products.
Other ingredients in pyrethrin formulations such as solvents may cause toxic effects.

Skin Contact:
Pyrethrins may be non-irritating or only mildly irritating to the skin. Skin absorption of pyrethrins is very low (4a).
Patch tests of 200 individuals with a pyrethrin product produced no effects on any volunteers during initial or follow-up exposure 12 days later (4a,4b).

Eye Contact:
No reports of eye injury despite extensive use of natural pyrethrins. Minimal effects were observed in animal tests.

A researcher who took doses up to 50 mg by mouth reported only numbness of tongue and lips (4a).
Accidental ingestion could result in nausea, vomiting, convulsions and stimulation of the nervous system. Fatal oral dose for humans is estimated at 1-2 g/kg (9).

Effects of Long-Term (Chronic) Exposure

Pyrethrins have been in use as insecticides for many years with no reports of chronic health effects. Animal data supports this.
No chronic effects are expected from normal use and handling of pyrethrins.

RESPIRATORY SENSITIZATION: There are reports of acute allergic, anaphylactic and asthmatic reactions following exposure to unrefined pyrethrum dust. However, in a study using refined pyrethrins (currently used), there was no asthma or serious reaction following exposure.
Fourteen allergic (asthmatic) individuals were exposed to pyrethrins aerosol: 7 experienced no reaction; 5 had dryness or itching of nose and throat; 2 experienced mild temporary eye irritation (4b).

There is one documented case of hypersensitivity pneumonitis resulting from prolonged domestic exposure to a currently used pyrethrins product (10).

SKIN SENSITIZATION: Refined pyrethrins currently used are not primary irritants or skin sensitizers (4a,4b). No cases of skin sensitization were observed in patch testing with 200 volunteers (4a,4b). There were no medically documented cases of allergy in one company with an 18-year history of manufacturing and packaging pyrethrins-containing products (4b).

There are many reports of severe dermatitis from contact with unrefined pyrethrum. Symptoms include itching, swelling, reddening and painful deeply-cracked skin. The effects are aggravated by sweating and exposure to sunlight (4a).

Skin tests show that about one half of persons sensitive to ragweed are also sensitive to unrefined pyrethrum. However, persons sensitive to ragweed or unrefined pyrethrum are very rarely sensitive to refined pyrethrum (4a,4b).

No evidence of carcinogenicity from animal testing. No human data available.

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 designated this chemical as not classifiable as a human carcinogen (A4).


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

Teratogenicity and Embryotoxicity:
Based on animal tests, no teratogenic or embryotoxic effects are expected.

Reproductive Toxicity:
Insufficient information available

No human information or laboratory testing information available.

Toxicologically Synergistic Materials:
In animal testing, a pyrethrin "synergist" (piperonyl butoxide) did not enhance the acute toxicity of pyrethrins to rats (3,4a,4c).

Potential for Accumulation:
Pyrethrins are rapidly broken down in the body. It is thought that this is the reason for their low toxicity in animal studies (7,8).


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 occurs, 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 advice 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:
NOTE: Other ingredients in pyrethrins formulations might cause toxic effects and require specific first aid measures.

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:
May be combustible. One source reports flash point as 82-88 deg C (180-190 deg F) (open cup) (2).

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:
Acrid smoke and fumes may be emitted.

Extinguishing Media:
(Pyrethrum or pyrethrin-containing products): Carbon dioxide, dry chemical powder, alcohol foam, polymer foam.

Fire Fighting Instructions:
Cool fire-exposed containers. The flammability of pyrethrum-containing products depends on the solvent in these products. Select extinguishing media and prepare fire fighting procedures appropriate for the product as a whole.


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


Molecular Weight: Complex mixture. Six active components with MW 316-374

Conversion Factor:
Not applicable

Melting Point: Not available
Boiling Point: Not available
Relative Density (Specific Gravity): Not available
Solubility in Water: Practically insoluble
Solubility in Other Liquids: Readily soluble in alcohols, acetone, carbon tetrachloride, ethylene dichloride, nitromethane, kerosene, petroleum ether.
Coefficient of Oil/Water Distribution (Partition Coefficient): Not available
pH Value: Not applicable
Vapour Density: Not applicable
Vapour Pressure: Essentially zero at 20 deg C
Saturation Vapour Concentration: Not applicable
Evaporation Rate: Practically zero
Critical Temperature: Probably not applicable


Stable if isolated 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 fires and explosions.

STRONG BASES - Hydrolysis (chemical breakdown) occurs. The reaction may be vigorous.

Hazardous Decomposition Products:
None reported.

Corrosivity to Metals:


ACUTE TOXICITY: A wide range of LD50 values have been reported.
LD50 (oral, rat): 200-1500 mg/kg (4a)
Range may reflect differing purities. Highly refined extracts tend to be less toxic, suggesting that impurities may be more toxic than pyrethrins.
LD50 (oral, rat): 480 mg/kg (commercial solution) (4a)
LD50 (oral, rat): 584 mg/kg (pale extract) (4a)
Commercial solution and pale extract are commonly used in pesticide formulations.

LD50 (dermal, rat): greater than 1350 mg/kg
LD50 (dermal, rabbit): greater than 5000 mg/kg (4a)

Rats exposed to high concentrations in air (6000 mg/m3 for 30 minutes or 2000 mg/m3 for 1 hour) were not killed. There was minor lung injury.

EYE IRRITATION (rabbit): A 1% pyrethrum solution was not immediately irritating, but a blister appeared in the conjunctiva (tender tissue around the eye) after 6 hours (4a).
SKIN: Application of a 1% pyrethrum solution did not cause skin sensitization in guinea pigs (4a).
CHRONIC EXPOSURE: Daily 30-minute inhalation exposures of dogs and rats at 16 mg/m3 for 27-85 days produced no significant effects and no excess mortality (4a).
Dogs and rats were fed diets containing up to 5000 ppm pyrethrins for up to 2 years. At levels above 1000 ppm, there was some liver damage. Gross toxic effects were excitation, salivation, fever, tremors, convulsions, laboured breathing and paralysis (4a,4b).
CARCINOGENICITY: No detailed studies have been reported. In the chronic studies discussed above, no unusual incidence of tumours was noted (4b).
REPRODUCTION: Rats ingesting 5000 ppm pyrethrins in their diet produced litters of normal weight and size with no pathological changes. Significant growth depression during nursing was reported (4b).
Dogs given a diet containing 5000 ppm pyrethrins for 21 days after mating had litters of reduced size and weight; no other toxic effects were reported (4a).
No toxic or teratogenic effects were reported among rabbits or their offspring following treatment with pyrethrins at 90 mg/kg/day during pregnancy (4a,4b).
A small increase in resorptions was reported in rats fed up to 100 mg/kg/day on days 6-15 of pregnancy. This result was not significant compared to the overall control group (12).

PYRETHRINS IN COMBINATION WITH PIPERONYL BUTOXIDE: Piperonyl butoxide increases the toxicity of pyrethrins in insects by 30-100 times (3,5). However, in acute and chronic studies in rats, piperonyl butoxide did not significantly increase the toxicity of pyrethrins (3,4a,4c).


Selected Bibliography:
(1) Documentation of the threshold limit values and biological exposure indices. 5th ed. ACGIH, 1986. p. 506
(2) NIOSH pocket guide to chemical hazards. NIOSH, June 1994. p. 270-271
(3) Hayes, W.J. Pesticides studied in man. Williams and Wilkins, 1982. p. 75-81
(4) Casida, J.E., ed. Pyrethrum : the natural insecticide. Academic Press, 1973. p. 123-142 (4a); p. 167-176 (4b); p. 177-194 (4c)
(5) Dandliker, W.B., et al. Effect of pesticides on the immune response. Envir. Sci. and Tech. Vol. 14, no. 2 (1980). p. 204-210
(6) Wester, R.C., et al. Human in vivo percutaneous absorption of pyrethrin and piperonyl butoxide in RID formulation. Neurotox. Vol. 5, no. 4 (1984). p. 72
(7) Soloway, S.B. Naturally occurring insecticides. Envir. Health Pers. Vol. 14 (Apr. 1976). p. 109-117
(8) Hutson, D.H. The metabolic fate of synthetic pyrethroid insecticides in mammals. Progress in Drug Metabolism. Vol. 3 (1979). p. 215-252
(9) Gosselin, R.E., et al. Clinical toxicology of commercial products. 5th ed. Williams and Wilkins, 1984. p. III-352 - III-355
(10) Carlson, J.E., et al. Hypersensitivity pneumonitis due to pyrethrum. JAMA Vol. 237, no. 16 (1977). p. 1718-1719
(11) Selection, Care, and Use of Respirators (CSA Standard Z94.4-M1982). Canadian Standards Association, 1982
(12) Khera, K.S., et al. Teratogenicity study on pyrethrum and rotenone (natural origin) and ronnel in pregnant rats. Journal of Toxicology and Environmental Health. Vol. 10 (1982). p. 111-119
(13) Schwope, A.D. Guidelines for the selection of chemical protective clothing. 3rd ed. American Conference of Governmental Industrial Hygienists, February 1987. p. 122
(14) RTECS record for pyrethrum. Date of last update 8810
(15) 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
Respiratory guidelines 1995-11-01
Sampling 1996-01-01
US transport 1996-01-01
Respiratory guidelines 1996-01-01
Resistance of materials 1996-01-01
TLV-TWA 1996-09-01
TLV comments 1996-09-01
EU Class 2000-05-01
EU Risk 2000-05-01
EU Safety 2000-05-01
EU Comments 2000-05-01
Bibliography 2000-05-01
UN/NA No 2002-12-20
Carcinogenicity 2003-07-24

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