Pyrethroid Pesticides Overview
Pyrethroid pesticides are synthetic analogues of pyrethrins, which are natural chemicals found in chrysanthemum flowers. Pyrethroid pesticides are used to control a wide range of insects in public and commercial buildings, animal facilities, warehouses, agricultural fields, and greenhouses. They are also applied on livestock to control insects. In agriculture, cypermethrin, cyfluthrin, and deltamethrin have been used frequently on cotton. Pyrethroid insecticides are the most common active ingredient in commercially available insect sprays and are also used as structural termiticides. Certain pyrethroid insecticides (such as permethrin, resmethrin, and sumithrin) are also registered for use in mosquito-control programs in the United States. Outside the U.S., deltamethrin has been used for indoor protection against mosquitoes that carry malaria, in some situations replacing the use of DDT. About two million pounds of permethrin and one million pounds of cypermethrin have been applied annually (U.S. EPA, 2006a, 2006b). Permethrin is also used in skin lotions and shampoos as medical treatments for lice and scabies. Pyrethroid pesticides are generally formulated as complex mixtures of different chemical isomers, solvent oils, and synergists, such as piperonyl butoxide. Pyrethroid pesticides have low volatility, bind to soils, and are rarely detected in ground waters (USGS, 2007). Generally, they are not persistent in the environment due to their rapid degradation within days to several months. This class of pesticides has low toxicity in birds and mammals, but pyrethroids are highly toxic to fish and some aquatic invertebrates, so usage is restricted near water (U.S.EPA, 2012).
The general population may be exposed to pyrethroid insecticides primarily from the ingestion of food or from residential use. Estimated intakes from diet and drinking water are below recommended limits. Dermal exposure with the potential for inadvertent ingestion may occur when lotions or shampoos are applied to treat lice or scabies. Pesticide applicators can be exposed to pyrethroid pesticides via dermal and inhalation routes from powders and liquid formulations. Pyrethroids are not well absorbed through the skin (ATSDR, 2003; Woollen et al., 1992). After absorption from inhalation or ingestion, pyrethroids are rapidly metabolized, by either ester hydrolysis or hydroxylation, followed by conjugation, and then eliminated over several days in urine and bile (Kuhn et al., 1999; Leng et al., 1997; Soderlund et al., 2002; Woollen et al., 1992). Unmetabolized pyrethroids have been measured in breast milk, but may be poorly transferred across the placenta (ATSDR, 2003; WHO, 2005).
Human health effects from pyrethroid pesticides at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Compared with other classes of insecticides such as organochlorines, organophosphorus, or carbamate pesticides, pyrethroid pesticides have less acute toxicity in animals and people. They are ranked as having moderate acute oral toxicity. Adverse effects from large doses are related to the action of pyrethroids on the nervous system, where these chemicals prolong sodium channel opening when a nerve cell is depolarized (Shafer et al., 2005; Soderlund et al., 2002). Possible other additional actions on neuroreceptors and other ion channels may also explain some pyrethroid effects. Human cases of systemic poisoning are rare and usually result from accidental exposure or intentional ingestion of pyrethroid insecticides. Signs and symptoms of acute pyrethroid poisoning after massive ingestions include agitation, hypersensitivity, tremor, salivation, choreoathetosis, and seizures (ATSDR, 2003; Ray et al., 2000; Soderlund et al., 2002). Concomitant exposure to organophosphorus insecticides may increase pyrethroid toxicity by slowing metabolic clearance of the pyrethroid. In California, cyfluthrin was the most frequent pyrethroid associated with symptomatic effects (irritant respiratory and dermal effects, paresthesias) reported in agricultural workers from 1996 to 2002 (Spencer and O'Malley, 2006). Transient dermal paresthesias have been reported among pesticide applicators after direct contact with certain types of pyrethroid pesticides. No relationship of indoor air or housedust concentrations of permethrin and irritant symptoms was found in a study of urban residents in 80 private homes (Berger-Preiss et al., 2002).
In developing rodents, neurochemical changes in cholinergic, dopaminergic, and catecholaminergic pathways and behavioral changes have been demonstrated at subacute and subchronic doses for some pyrethroid pesticides (Aziz et al., 2001; Elwan et al., 2006; Eriksson and Fredriksson, 1991; Lazarini et al., 2001; Shafer, et al., 2005). The pyrethroids in general use are not considered teratogenic or to have significant reproductive toxicity (ATSDR, 2003; WHO, 2005), though a few pyrethroid pesticides and some metabolites have shown weak or inconsistent estrogenic effects on standardized assays (ATSDR, 2003; Garey and Wolff, 1998; Go et al., 1999; Hu et al., 2003; Kim et al., 2004; Kunimatsu et al., 2002; McCarthy et al., 2006; Moniz et al., 2005). Generally, the pyrethroids are not considered genotoxic in in vitro testing or carcinogenic in animal testing (WHO, 2005). IARC considers deltamethrin and permethrin as not classifiable as to their human carcinogenicity. Additional information about pesticides is available from U.S. EPA at http://www.epa.gov/pesticides and from ATSDR at http://www.atsdr.cdc.gov/toxprofiles/index.asp#H.
There are about 30 different pyrethroid pesticides in use. The table shows the urinary pyrethroid metabolites measured in the National Biomonitoring Program.
|Pyrethroid Insecticides Metabolites in the National Biomonitoring Program|
|Pyrethroid (CAS number)||Urinary metabolite (CAS number)|
|Cyfluthrin (68359-37-5)||4-Fluoro-3-phenoxybenzoic acid (77279-89-1)|
cis-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (55701-05-8)
trans-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (55701-03-6)
|Deltamethrin (52918-63-5)||cis-3-(2,2-Dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid|
|3-Phenoxybenzoic acid (3739-38-6)|
CAS No. 68359-37-5
The chemical 4-fluoro-3-phenoxybenzoic acid is a specific metabolite of the pyrethroid insecticide cyfluthrin. Cyfluthrin accounted for one-third of pyrethroid-related worker illnesses reported in California from 1996-2002; most of which were dermal and respiratory irritations (Spencer and O'Malley, 2006). Cyfluthrin is rapidly metabolized and eliminated from the body. Following an indoor application exposure, the mean elimination half-life of cyfluthrin from the plasma was 16 hours (Williams et al., 2003).
Degradation of cyfluthrin to 4-fluoro-3-phenoxybenzoic acid occurs in the environment. Thus, the presence of 4-fluoro-3-phenoxybenzoic acid in urine not only reflects the metabolic transformation of cyfluthrin, but it can also reflect direct exposure to 4-fluoro-3-phenoxybenzoic acid formed in the environment.
Urinary levels of 4-fluoro-3-phenoxybenzoic acid reflect recent exposure to cyfluthrin or its environmental degradate. Urinary levels of 4-fluoro-3-phenoxybenzoic acid were generally below the limit of detection (0.2 μg/L) in the U.S. representative subsample in NHANES 2001-2002 (CDC, 2009). In an analysis of 217 urine specimens from a nonrandom sample of United States residents, Baker et al. (2004) reported a geometric mean concentration of 4-fluoro-3-phenoxybenzoic acid of 0.95 µg/L. Studies in Germany of 396 children and adolescents (Becker et al., 2006) and 1177 urban adults and children (Heudorf et al., 2001) showed that urinary levels of 4-fluoro-3-phenoxybenzoic acid at the 95th percentile ranged from either slightly higher or lower than the detection limit in the U.S. representative 2001-2002 NHANES subsample (CDC, 2009). Urinary levels for adults and children in these studies were similar (Heudorf et al., 2001, 2006) and estimated daily intakes based on urinary levels in children were considered to be below acceptable daily intakes (Heudorf et al., 2004).
In 57 volunteers entering areas previously spot-sprayed with various pyrethroid pesticides (including cyfluthrin), median urinary levels of 4-fluoro-3-phenoxybenzoic acid were slightly less than the limit of detection in the NHANES 2001-2002 subsample (CDC, 2009; Leng et al., 2003). Seven individuals participating in floor exercises on cyfluthrin treated carpet demonstrated a rise in the urinary excretion of 4-fluoro-3-phenoxybenzoic acid in the 72 hours following the activity (Williams et al., 2003).
Finding a measurable amount of 4-fluoro-3-phenoxybenzoic acid in urine does not imply that the level will result in an adverse health effect. Biomonitoring studies of 4-fluoro-3-phenoxybenzoic acid in urine provide physicians and public health officials with reference values so that they can determine whether other people have been exposed to higher levels of cyfluthrin than levels found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for pyrethrins and pyrethroids. September 2003. Available from URL: http://www.atsdr.cdc.gov/toxprofiles/tp.asp?id=787&tid=153. 12/28/12
Aziz MH, Agrawal AK, Adhami VM, Shukla Y, Seth PK. Neurodevelopmental consequences of gestational exposure (GD14-GD20) to low dose deltamethrin in rats. Neurosci Lett 2001;300(3):161-165.
Baker SE, Olsson AO, Barr DB. Isotope dilution high-performance liquid chromatography-tandem mass spectrometry method for quantifying urinary metabolites of synthetic pyrethroid insecticides. Arch Environ Contam Toxicol 2004;46(3):281-288.
Becker K, Seiwert M, Angerer J, Kolossa-Gehring M, Hoppe HW, Ball M, et al. GerES IV pilot study: assessment of the exposure of German children to organophosphorus and pyrethroid pesticides. Int J Hyg Environ Health 2006;209(3):221-233.
Berger-Preiss E, Levsen K, Leng G, Idel H, Sugiri D, Ranft U. Indoor pyrethroid exposure in homes with woollen textile floor coverings. Int J Hyg Environ Health 2002;205(6):459-472.
Centers for Disease Control and Prevention (CDC). Fourth National Report on Human Exposure to Environmental Chemicals. 2009. [online] Available at URL: http://www.cdc.gov/exposurereport/. 12/28/12
Elwan MA, Richardson JR, Guillot TS, Caudle WM, Miller GW. Pyrethroid pesticide-induced alterations in dopamine transporter function. Toxicol Appl Pharmacol 2006;211(3):188-197.
Eriksson P, Fredriksson A. Neurotoxic effects of two different pyrethroids, bioallethrin and deltamethrin, on immature and adult mice: changes in behavioral and muscarinic receptor variables. Toxicol Appl Pharmacol 1991;108(1):78-85.
Garey J, Wolff MS. Estrogenic and antiprogestagenic activities of pyrethroid insecticides. Biochem Biophys Res Commun 1998;251(3):855-859.
Go V, Garey J, Wolff MS, Pogo BG. Estrogenic potential of certain pyrethroid compounds in the MCF-7 human breast carcinoma cell line. Environ Health Perspect 1999;107(3):173-177.
Heudorf U, Angerer J, Drexler H. Current internal exposure to pesticides in children and adolescents in Germany: urinary levels of metabolites of pyrethroid and organophosphorus insecticides. Int Arch Occup Environ Health 2004;77(1):67-72.
Heudorf U, Angerer J. Metabolites of pyrethroid insecticides in urine specimens: current exposure in an urban population in Germany. Environ Health Perspect 2001;109(3):213-217.
Heudorf U, Butte W, Schulz C, Angerer J. Reference values for metabolites of pyrethroid and organophosphorous insecticides in urine for human biomonitoring in environmental medicine. Int J Hyg Environ Health 2006;209(3):293-299.
Hu JY, Wang SL, Zhao RC, Yang J, Chen JH, Song L, et al. [Effects of fenvalerate on reproductive and endocrine systems of male rats] Zhonghua Nan Ke Xue 2002;8(1):18-21. (in Chinese)
Kim IY, Shin JH, Kim HS, Lee SJ, Kang IH, Kim TS, et al. Assessing estrogenic activity of pyrethroid insecticides using in vitro combination assays. J Reprod Dev 2004;50(2):245-255.
Kuhn K, Wieseler B, Leng G, Idel H. Toxicokinetics of pyrethroids in humans: consequences for biological monitoring. Bull Environ Contam Toxicol 1999;62:101-108.
Kunimatsu T, Yamada T, Ose K, Sunami O, Kamita Y, Okuno Y, et al. Lack of (anti-) androgenic or estrogenic effects of three pyrethroids (esfenvalerate, fenvalerate, and permethrin) in the Hershberger and uterotrophic assays. Regul Toxicol Pharmacol 2002;35(2 Pt 1):227-237.
Lazarini CA, Florio JC, Lemonica IP, Bernardi MM. Effects of prenatal exposure to deltamethrin on forced swimming behavior, motor activity, and striatal dopamine levels in male and female rats. Neurotoxicol Teratol 2001;23(6):665-673.
Leng G, Leng A, Kuhn KH, Lewalter J, Pauluhn J. Human dose-excretion studies with the pyrethroid insecticide cyfluthrin: urinary metabolite profile following inhalation. Xenobiotica 1997;27(12):1273-1283.
Leng G, Ranft U, Sugiri D, Hadnagy W, Berger-Preiss E, Idel H. Pyrethroids used indoors—biological monitoring of exposure to pyrethroids following an indoor pest control operation. Int J Hyg Environ Health 2003;206(2):85-92.
McCarthy AR, Thomson BM, Shaw IC, Abell AD. Estrogenicity of pyrethroid insecticide metabolites. J Environ Monit 2006;8(1):197-202.
Moniz AC, Cruz-Casallas PE, Salzgeber SA, Varoli FM, Spinosa HS, Bernardi MM.
Behavioral and endocrine changes induced by perinatal fenvalerate exposure in
female rats. Neurotoxicol Teratol 2005;27(4):609-14.
Ray DE, Forshaw PJ. Pyrethroid insecticides: poisoning syndromes, synergies, and therapy. J Toxicol Clin Toxicol 2000;38:95-101.
Shafer TJ, Meyer DA, Crofton KM. Developmental neurotoxicity of pyrethroid insecticides: critical review and future research needs. Environ Health Perspect 2005;113(2):123-36.
Soderlund DM, Clark JM, Sheets LP, Mullin LS, Piccirillo VJ, Sargent D, et al. Mechanisms of pyrethroid neurotoxicity: implications for cumulative risk assessment. Toxicology 2002;171:3-59.
Spencer J, O'Malley M. Pyrethroid illnesses in California, 1996-2002. Rev Environ Contam Toxicol 2006;186:57-72.
U.S. Environmental Protection Agency (U.S. EPA). Permethrin, resmethrin, d-phenothrin (Sumithrin): synthetic pyrethroids for mosquito control. Updated September 12, 2012. Available at URL: http://www.epa.gov/mosquitocontrol/Synthetic_Pyrethroids.html. 12/28/12
U.S. Environmental Protection Agency (U.S. EPA). Permethrin Facts (Reregistration Eligibility Decision Fact Sheet). June 2006a. Available at URL: http://www.epa.gov/oppsrrd1/REDs/factsheets/permethrin_fs.htm. 12/28/12
U.S. Environmental Protection Agency (U.S. EPA). Reregistration Eligibility Decision for Cypermethrin. June 2006b. Available at URL: http://www.epa.gov/oppsrrd1/REDs/cypermethrin_red.pdf. 12/28/12
U.S. Geological Survey (USGS). Pesticides in the Nation's Streams and Ground Water, 1992–2001. March 2006, Revised February 15, 2007. Available at URL: http://pubs.usgs.gov/circ/2005/1291/. 12/28/12
Williams RL, Bernard CE, Krieger RI. Human exposure to indoor residential cyfluthrin residues during a structured activity program. J Expo Anal Environ Epidemiol 2003;13(2):112-119.
Woollen BH, Marsh JR, Laird WJ, Lesser JE. The metabolism of cypermethrin in man: differences in urinary metabolite profiles following oral and dermal administration. Xenobiotica 1992;22(8):983-991.
World Health Organization (WHO). Pesticide and Evaluation Scheme. Safety of pyrethroids for public health use. 2005. Available at URL: http://whqlibdoc.who.int/hq/2005/WHO_CDS_WHOPES_GCDPP_2005.10.pdf. 12/28/12