Pyrethroids Fact Sheet

Source of Exposure

Pyrethroids are an increasingly important class of insecticides based on the amount used. Commercially available pyrethroids include permethrin, cypermethrin, cyfluthrin, deltamethrin and cyhalothrin. Exposure to the general population is from crop residues on food, which is generally low. Other exposures are from manufacture or agricultural use and from products such as flea and lice shampoos. Pyrethroids are not very volatile and when they are detectable at all in indoor air following indoor use, are found in very low concentrations.

Disposition

The low toxicity of pyrethroids in mammals is due largely to their rapid biotransformation by ester hydrolysis and/or hydroxylation. Many of the available formulations of pyrethroids contain piperonyl butoxide which inhibits cytochrome P-450 increasing the insecticidal efficacy by slowing the biotransformation in insects. The elimination half time of pyrethroid metabolites averages about 6 hours. This indicates an elimination time of about 30 hours.

Due to the short half life probabilities of finding the compounds of interest in analysis are increased by analyzing for the metabolites of the actual parent compounds. This also eliminates the possibility of any positive result being caused by environmental contamination of the sample.

Toxic Levels

The primary adverse effects of pyrethroids are their allergenic properties. The pyrethroids are markedly less likely to cause allergic response than pyrethrum (pyrethrin). Many cases of contact dermatitis and respiratory allergy have been reported. Persons sensitive to ragweed pollen are particularly prone to such reactions. The LD50 ratio for mammals to insects is 1400. Acute toxicity in rats has been seen to cause aggressive sparring, sensitivity to external stimuli, and fine tremor progressing to gross whole-body tremor and prostration. The Food and Agriculture Organization of the United Nations/World Health Organization joint meeting on pesticide residues estimated the acceptable daily intake for various pyrethroids including:

Deltamethrin 10 µg/kg body weight
Cypermethrin 50 µg/kg
Permethrin 50 µg/kg

Specimen Required

Urine:   At lest 20 ml
Note:   Sent in a glass container with Teflon lined cap.
Permethrin   50 µg/kg

Methodology

Run by Gas Chromatography Mass Spectrometry Reporting limits are 10 ng/ml.

Interpretation of results

The presence of the following compounds indicate exposure to:

Cis-DCCA -  Cyfluthrin, a-cypermethrin, cypermethrin, permethrin
Trans-DCCA -  Cyfluthrin, Cypermethrin, permethrin
Cis-DBCA -  Deltamethrin
m-PBA -  Cyhalothrin, a-cypermethrin, cypermethrin, permethrin, deltamethrin

References

- Aldridge, W.N.: Toxicology of pyrethroids. In Miyamoto, J. and Kearney, P.C. (eds.): Pesticide Chemistry: Human Welfare and the Environment, Vol. 3 Mode of Action, Metabolism and Toxicology, Pergamon Press, Oxford, 1983, PP. 485-90.

- Narahashi, T.: Interaction of pyrethroids and DDT-like compounds with the sodium channels in the nerve membrane. In Miyamoto, J. and Kearney, P.C. (eds.): Pesticide Chemistry: Human Welfare and the Environment, Vol. 3 Mode of Action, Metabolism and Toxicology, Pergamon Press, Oxford, 1983, PP. 109-14.

- Cassaret and Doull’s Toxicology, The Basic Science of Poisons, 3rd ed.: Klassen, Curtis D., Amdur, Mary O., Doull, John (eds.): Macmillan Publishing Co., New York, 1986, p.553.

- Pesticides Residues in Food: Joint Report of the FAO Working Party on Pesticide Residues. Series. Rome: Food and Agriculture Organization of the United Nations, 1964-1995.