Toxicokinetics of pyrethroids in humans: consequences for biological monitoring

Environmental exposure to pyrethroid pesticides in a nationally representative sample of U.S. adults and children: The National Health and Nutrition Examination Survey 2007-2012

Pyrethroids are an important class of insecticides, and thousands of tons of these compounds are used in the United States every year. This study characterized exposures to pyrethroids and assessed demographic, socioeconomic, and lifestyle factors that modulate pyrethroid exposure using data from the National Health and Nutrition Examination Survey (NHANES) 2007-2012, a nationally representative survey of the non-institutionalized population of the United States. Urinary levels of commonly used biomarkers of pyrethroid exposure, including 3-phenoxybenzoic acid (3-PBA), 4-fluoro-3-phenoxybenzoic acid (F-PBA), and cis-dibromovinyl-dimethylcyclopropane carboxylic acid (DBCA), were determined by liquid chromatography-tandem mass spectrometry. The detection rate of 3-PBA, a nonspecific metabolite of several pyrethroids, was 78.1% in adults (N = 5233) and 79.3% in children (N = 2295). The detection rates of all other pyrethroid metabolites were <10%. The median urinary level of 3-PBA in adults was 0.47 μg/L (interquartile range, 0.14-1.22 μg/L). For children, the median urinary level was 0.49 μg/L (interquartile range, 0.17-1.29 μg/L). Age, gender, family income-to-poverty ratio (PIR), levels of physical activity, alcohol intake, and body mass index were associated with 3-PBA levels in adults. In children, age, gender, race/ethnicity, and PIR were associated with 3-PBA levels. 3-PBA levels also differed significantly across NHANES cycles, with higher levels observed in NHANES 2011-2012. Geometric mean 3-PBA levels in U.S. adults were 0.41 μg/L in NHANES 2007-2008, 0.41 μg/L in NHANES 2009-2010, and 0.66 μg/L in NHANES 2011-2012. In U.S. children, geometric mean 3-PBA levels were 0.40 μg/L in NHANES 2007-2008, 0.46 μg/L in NHANES 2009-2010, and 0.70 μg/L in NHANES 2011-2012. These results demonstrate that pyrethroid exposures remain a current environmental health concern and lay the foundation for further preclinical and epidemiological studies assessing human health risks associated with pyrethroids.

Wastewater-based epidemiology to assess human exposure to pyrethroid pesticides

Pesticides are active substances with potentially adverse effects on human health, and therefore great effort is addressed to study the relation between their widespread use and the effects on humans. To track human exposure to pesticides, novel approaches are needed to give additional information on exposure at population level. In this study, a novel application of Wastewater-Based Epidemiology (WBE) was developed to measure the intake of pyrethroid pesticides in a population. Three human urinary metabolites of pyrethroids were selected and validated as biomarkers of exposure by evaluating their sources and stability in wastewater. They were measured by liquid chromatography-tandem mass spectrometry in raw urban wastewater collected from the wastewater treatment plants of six Italian cities. Their concentrations were used as biomarkers to back-calculate the intake of pyrethroid pesticides in the population. WBE results were in line with the urinary biomarker levels of biomonitoring studies considering dilution in wastewater. Significant differences in the metabolites levels were observed among different cities. Seasonal variations in human intake of pyrethroids were also seen, as expected, with higher intakes during spring/summer. Intakes in the six cities were compared with the acceptable daily intake (ADI) and it was concluded that some of the populations examined might face significant health risks. Results confirm that this method can provide supplementary information to biomonitoring studies and can be a valuable tool for obtaining objective, direct information on the real levels of exposure to pyrethroids of different populations.

Temporal variability of pyrethroid metabolite levels in bedtime, morning, and 24-h urine samples for 50 adults in North Carolina

Pyrethroid insecticides are widely used to control insects in both agricultural and residential settings worldwide. Few data are available on the temporal variability of pyrethroid metabolites in the urine of non-occupationally exposed adults. In this work, we describe the study design and sampling methodology for the Pilot Study to Estimate Human Exposures to Pyrethroids using an Exposure Reconstruction Approach (Ex-R study). Two major objectives were to quantify the concentrations of several pyrethroid metabolites in bedtime, first morning void (FMV), and 24-h urine samples as concentration (wet weight), specific-gravity (SG) corrected, creatinine (CR) corrected, and excretion rate values for 50 Ex-R adults over a six-week monitoring period and to determine if these correction approaches for urine dilution reduced the variability of the biomarker levels. The Ex-R study was conducted at the United States Environmental Protection Agency's Human Studies Facility in Chapel Hill, North Carolina USA and at participants' homes within a 40-mile radius of this facility. Recruitment of participants and field activities occurred between October 2009 and May 2011. Participants, ages 19-50 years old, provided daily food, activity, and pesticide-use diaries and collected their own urine samples (bedtime, FMV, and 24-h) during weeks 1, 2, and 6 of a six-week monitoring period. A total of 2503 urine samples were collected from the study participants. These samples were analyzed for the pyrethroid metabolites 3-phenoxybenzoic acid (3-PBA), cis/trans-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane carboxylic acid (cis/trans-DCCA), and 2-methyl-3-phenylbenzoic acid (MPA) using high performance liquid chromatography/tandem mass spectrometry. Only 3-PBA was frequently detected (>50%) in the adult urine samples. Median urinary 3-PBA levels were 0.88 ng/mL, 0.96 ng/mL-SG, 1.04 ng/mg, and 1.04 ng/min for concentration, SG-corrected, CR-corrected, and excretion rate values, respectively, across all urine samples. The results showed that median urinary 3-PBA concentrations were consistently the lowest in FMV samples (0.77 ng/mL, 0.68 ng/mL-SG, 0.68 ng/mg, and 0.58 ng/min) and the highest in 24-h samples (0.92 ng/mL, 1.06 ng/mL-SG, 1.18 ng/mg, and 1.19 ng/min) across all four methods. Intraclass correlation coefficient (ICC) estimates for 3-PBA indicated poor reproducibility (<0.22) for all urine sample types and methods over a day, week, and six weeks. Correcting for urine sample dilution, based on either SG, CR or urine output, introduced additional measurement variability both between- and within-individuals. These results indicate that a single measure of urinary 3-PBA was not sufficient to characterize average exposure regardless of sample type, correction method, and time frame of collection. In addition, the study results can be used to inform the design of exposure characterization strategies in relevant environmental epidemiology studies in the future.

Time profiles and toxicokinetic parameters of key biomarkers of exposure to cypermethrin in orally exposed volunteers compared with previously available kinetic data following permethrin exposure

Biomonitoring of pyrethroid exposure is largely conducted but human toxicokinetics has not been fully documented. This is essential for a proper interpretation of biomonitoring data. Time profiles and toxicokinetic parameters of key biomarkers of exposure to cypermethrin in orally exposed volunteers have been documented and compared with previously available kinetic data following permethrin dosing. Six volunteers ingested 0.1 mg kg(-1) bodyweight of cypermethrin acutely. The same volunteers were exposed to permethrin earlier. Blood samples were taken over 72 h after treatment and complete timed urine voids were collected over 84 h postdosing. Cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acids (trans- and cis-DCCA) and 3-phenoxybenzoic acid (3-PBA) metabolites, common to both cypermethrin and permethrin, were quantified. Blood and urinary time courses of all three metabolites were similar following cypermethrin and permethrin exposure. Plasma levels of metabolites reached peak values on average ≈ 5-7 h post-dosing; the elimination phase showed mean apparent half-lives (t½ ) for trans-DCCA, cis-DCCA and 3-PBA of 5.1, 6.9 and 9.2 h, respectively, following cypermethrin treatment as compared to 7.1, 6.2 and 6.5 h after permethrin dosing. Corresponding mean values obtained from urinary rate time courses were peak values at ≈ 9 h post-dosing and apparent elimination t½ of 6.3, 6.4 and 6.4 h for trans-DCCA, cis-DCCA and 3-PBA, respectively, following cypermethrin treatment as compared to 5.4, 4.5 and 5.7 h after permethrin dosing. These data confirm that the kinetics of cypermethrin is similar to that of permethrin in humans and that their common biomarkers of exposure may be used for an overall assessment of exposure.

A novel toxicokinetic modeling of cypermethrin and permethrin and their metabolites in humans for dose reconstruction from biomarker data

To assess exposure to pyrethroids in the general population, one of most widely used method nowadays consists of measuring urinary metabolites. Unfortunately, interpretation of data is limited by the unspecified relation between dose and levels in biological tissues and excreta. The objective of this study was to develop a common multi-compartment toxicokinetic model to predict the time courses of two mainly used pyrethroid pesticides, permethrin and cypermethrin, and their metabolites (cis-DCCA, trans-DCCA and 3-PBA) in the human body and in accessible biological matrices following different exposure scenarios. Toxicokinetics was described mathematically by systems of differential equations to yield the time courses of these pyrethroids and their metabolites in the different compartments. Unknown transfer rate values between compartments were determined from best fits to available human data on the urinary excretion time courses of metabolites following an oral and dermal exposure to cypermethrin in volunteers. Since values for these coefficients have not yet been determined, a mathematical routine was programmed in MathCad to establish the possible range of values on the basis of physiological and mathematical considerations. The best combination of parameter values was then selected using a statistic measure (reliability factor) along with a statistically acceptable range of values for each parameter. With this approach, simulations provided a close approximation to published time course data. This model allows to predict urinary time courses of trans-DCCA, cis-DCCA and 3-PBA, whatever the exposure route. It can also serve to reconstruct absorbed doses of permethrin or cypermethrin in the population using measured biomarker data.

Evaluation of pyrethroid exposures in pregnant women from 10 Caribbean countries

Pyrethroid pesticides are commonly used in tropical regions such as the Caribbean as household insecticides, pet sprays, and where malaria is endemic, impregnated into mosquito-repellent nets. Of particular concern is exposure during pregnancy, as these compounds have the potential to cross the placental barrier and interfere with fetal development, as was shown in limited animal studies. The objective of this study was to evaluate exposure to pyrethroids to pregnant women residing in 10 English-speaking Caribbean countries. Pyrethroid exposures were determined by analyzing five pyrethroid metabolites in urine samples from 295 pregnant women: cis-DBCA, cis-DCCA, trans-DCCA, 3-PBA, and 4-F-3-PBA. Pyrethroid metabolite concentrations in Caribbean pregnant women were generally higher in the 10 Caribbean countries than levels reported for Canadian and U.S. women. In Antigua & Barbuda and Jamaica participants the geometric mean concentrations of cis-DBCA was significantly higher than in the other nine countries together (p<0.0001 and <0.0012 respectively). For cis- and trans-DCCA, only Antigua & Barbuda women differed significantly from participants of the other nine Caribbean countries (p<0.0001). Urinary 4-F-3-PBA and 3-PBA levels were significantly higher in Antigua & Barbuda (p<0.0028 and p<0.0001 respectively) as well as in Grenada (p<0.0001 and p<0.007 respectively). These results indicate extensive use of pyrethroid compounds such as permethrin and cypermethrin in Caribbean households. In Antigua & Barbuda, the data reveals a greater use of deltamethrin. This study underscores the need for Caribbean public health authorities to encourage their populations, and in particular pregnant women, to utilize this class of pesticides more judiciously given the potentially adverse effects of exposure on fetuses and infants.

Determination of the pyrethroid insecticide metabolite 3-PBA in plasma and urine samples from farmer and consumer groups in northern Thailand

In this study, the enzyme-linked immunosorbent assays (ELISA) were modified to detect 3-PBA in plasma (including the adducted form) and urine among a large group of consumers and farmers in an agricultural area. The samples were collected on the same day in the morning from 100 consumers (50 females, 50 males) and 100 farmers (50 females, 50 males) in the Fang district, Chiang Mai province, northern Thailand. The ELISA was very sensitive having an IC50 value of 26.7 and 15.3 ng/mL, a limit of quantitation of 5 and 2.5 ng/mL and a limit of detection of 1.08 and 1.94 ng/mL for plasma and urine, respectively. These methods had low (< 5%) intra- and inter-assay coefficients of variation. The extraction technique satisfactorily eliminated the matrix effect from samples before ELISA analysis, yielding good recoveries (85.9-99.4% and 87.3-98.0%, respectively). For the volunteer study, the detection rate for plasma 3-PBA was 24% in consumers and 42% in farmers, but the median and range values were similar (median 5.87 ng/mL, range 5.16-8.44 ng/mL in consumers and 6.27 ng/mL, range 4.29-9.57 ng/mL in farmers). The rate of detection in the urine was similar (76% and 69%, in consumers and in farmers), yet the median concentration was significantly higher in farmers (8.86 μg/g creatinine in consumers vs 16.1 μg/g creatinine in farmers) and the range also much wider in farmers (1.62-80.5 μg/g creatinine in consumers and 0.80-256.2 μg/g creatinine in farmers). There was no correlation between plasma 3-PBA and urinary 3-PBA concentrations in the study presumably because plasma 3-PBA is a measure of cumulative exposures while urinary 3-PBA reflects acute exposures. In addition, metabolism and excretion of pyrethroids varies by individual. Nevertheless, this study demonstrated that these volunteers were exposed to pyrethroids. To our knowledge, this is the first report that compared plasma 3-PBA and urinary 3-PBA in a large group of volunteers. The ELISA method provided higher sample throughput with lower cost as compared to the instrumental analysis.

Urinary concentrations of metabolites of pyrethroid insecticides in textile workers, Eastern China

Pyrethroid insecticides have been applied in the production of cotton, wool and textile. In order to examine whether textile workers are exposed to pyrethroid insecticides, we recruited 50 textile workers in two textile plants in Eastern China. Their urine samples were collected for the measurement of pyrethroid metabolites: cis- and trans-isomers of 2,2-dichlorovinyl-2,2-dimethylcyclopropane-1-carboxylic acid (cis-Cl2CA and trans-Cl2CA) and 3-phenoxybenzoic acid (3-PBA). Our results showed that textile workers were exposed to high levels of pyrethroid insecticides. cis-Cl2CA and 3-PBA were dominant metabolites with concentrations of 0.17-261μg/L, while concentrations of trans-Cl2CA were in the range of 0.26-11μg/L. Levels of three metabolites were in a descending order: cis-Cl2CA, 3-PBA, and trans-Cl2CA. Levels of the metabolites were associated with ages and job responsibilities of textile workers. Sewing workers, cutting workers, machine operators, reorganizers, and older workers were more likely in contact with pyrethroid insecticides in the textile production. trans- to cis-Cl2CA ratios might indicate that exposure of textile workers was via dermal absorption and inhalation.

Effects of early life permethrin exposure on spatial working memory and on monoamine levels in different brain areas of pre-senescent rats

Pesticide exposure during brain development could represent an important risk factor for the onset of neurodegenerative diseases. Previous studies investigated the effect of permethrin (PERM) administered at 34 mg/kg, a dose close to the no observable adverse effect level (NOAEL) from post natal day (PND) 6 to PND 21 in rats. Despite the PERM dose did not elicited overt signs of toxicity (i.e. normal body weight gain curve), it was able to induce striatal neurodegeneration (dopamine and Nurr1 reduction, and lipid peroxidation increase). The present study was designed to characterize the cognitive deficits in the current animal model. When during late adulthood PERM treated rats were tested for spatial working memory performances in a T-maze-rewarded alternation task they took longer to choose for the correct arm in comparison to age matched controls. No differences between groups were found in anxiety-like state, locomotor activity, feeding behavior and spatial orientation task. Our findings showing a selective effect of PERM treatment on the T-maze task point to an involvement of frontal cortico-striatal circuitry rather than to a role for the hippocampus. The predominant disturbances concern the dopamine (DA) depletion in the striatum and, the serotonin (5-HT) and noradrenaline (NE) unbalance together with a hypometabolic state in the medial prefrontal cortex area. In the hippocampus, an increase of NE and a decrease of DA were observed in PERM treated rats as compared to controls. The concentration of the most representative marker for pyrethroid exposure (3-phenoxybenzoic acid) measured in the urine of rodents 12 h after the last treatment was 41.50 μg/L and it was completely eliminated after 96 h.

The relation between dietary habits and urinary levels of 3-phenoxybenzoic acid, a pyrethroid metabolite

Concerns about pesticide exposure through food consumption have increased during the past several years. Pyrethroids are applied as insecticides throughout the world. Human metabolism of pyrethroids results in urinary metabolites that are suitable for biological monitoring. The objective of our study was to investigate the relation between food consumption and urinary levels of 3-phenoxybenzoic acid (3-PBA), a general metabolite of pyrethroids, in a non-occupational exposed adult population from the IDI-IRCCS, Rome, Italy. Information on socio-demographic characteristics, smoking, diet and self-reported household pesticide exposure was collected. Urinary 3-PBA level of each subject was measured and adjusted by urinary creatinine. We found that people consuming both raw and cooked vegetables five times weekly or more had higher mean levels of 3-PBA in urine (1.03 μg/g creatinine versus 0.52 μg/g creatinine; p=0.009 and 0.99 μg/g creatinine versus 0.58 μg/g creatinine; p=0.01, respectively) than subjects consuming less than five times weekly. In a multivariate model, after adjusting for age, sex, BMI, smoking and household insecticide exposure, high intake of raw vegetables (OR: 5.31; 95%CI: 1.32-21.3) and high intake of cooked vegetables, in particular cruciferous (OR: 4.67; 95%CI: 1.07-20.5) and leafy vegetables (OR: 6.88; 95%CI: 1.50-31.7), were associated with high urine 3-PBA levels (≥0.70 μg/g creatinine). The results of this study suggest that part of the variation in pyrethrois intake is explained by vegetable intake.

A pilot study of workplace dermal exposures to cypermethrin at a chemical manufacturing plant

Exposure during the manufacture of pesticides is of particular concern due to their toxicity and because little is known about worker exposure, since most studies have focused on end-use application within agriculture or buildings. Even though dermal exposure can be expected to dominate for pesticides, little is known about workplace dermal exposures or even appropriate methods for their assessment. The current study begins to address this gap by evaluating alternative methods for assessing dermal exposure at a chemical manufacturing plant. For this pilot study, eight workers were recruited from a U.S. plant that produced the pesticide cypermethrin. Exposure was evaluated using three approaches: (1) survey assessment (questionnaire), (2) biological monitoring, and (3) workplace environmental sampling including ancillary measurements of glove contamination (interior and exterior). In each case, cypermethrin was quantified by enzyme-linked immunosorbent assay (ELISA). Environmental measurements identified two potential pathways of cypermethrin exposure: glove and surface contamination. Workplace exposure was also indicated by urine levels (specific gravity adjusted) of the parent compound, which ranged from 35 to 253 μg/L (median of 121 μg/L) with no clear trend in levels from pre- to post-shift. An exploratory analysis intended to guide future studies revealed a positive predictive association (Spearman correlation, p ≤ 0.10) between post-shift urine concentrations and a subset of survey questions evaluating worker knowledge, attitudes, and perceptions (KAP) of workplace dermal hazards, i.e., personal protective equipment self-efficacy, and inverse associations with behavior belief and information belief scales. These findings are valuable in demonstrating a variety of dermal exposure methods (i.e., behavioral attributes, external contamination, and biomarker) showing feasibility and providing measurement ranges and preliminary associations to support future and more complete assessments. Although these pilot data are useful for supporting design and sample size considerations for larger exposure and health studies, there is a need for validation studies of the ELISA assay for quantification of cypermethrin and its metabolites in urine.

Review of pesticide urinary biomarker measurements from selected US EPA children's observational exposure studies

Children are exposed to a wide variety of pesticides originating from both outdoor and indoor sources. Several studies were conducted or funded by the EPA over the past decade to investigate children’s exposure to organophosphate and pyrethroid pesticides and the factors that impact their exposures. Urinary metabolite concentration measurements from these studies are consolidated here to identify trends, spatial and temporal patterns, and areas where further research is required. Namely, concentrations of the metabolites of chlorpyrifos (3,5,6-trichloro-2-pyridinol or TCPy), diazinon (2-isopropyl-6-methyl-4-pyrimidinol or IMP), and permethrin (3-phenoxybenzoic acid or 3-PBA) are presented. Information on the kinetic parameters describing absorption and elimination in humans is also presented to aid in interpretation. Metabolite concentrations varied more dramatically across studies for 3-PBA and IMP than for TCPy, with TCPy concentrations about an order of magnitude higher than the 3-PBA concentrations. Temporal variability was high for all metabolites with urinary 3-PBA concentrations slightly more consistent over time than the TCPy concentrations. Urinary biomarker levels provided only limited evidence of applications. The observed relationships between urinary metabolite levels and estimates of pesticide intake may be affected by differences in the contribution of each exposure route to total intake, which may vary with exposure intensity and across individuals.

Percutaneous absorption and exposure assessment of pesticides

Dermal exposure to a diverse range of chemicals may result from various uses. In order to assess exposure and estimate potential risks, accurate quantitative data on absorption are required. Various factors will influence the final results and interpretations of studies designed to assess the ability of compounds to penetrate the skin. This overview will discuss skin penetration by pesticides, emphasizing key parameters to be considered from the perspective of exposure assessment.

Effect of permethrin insecticide on rat polymorphonuclear neutrophils

Polymorphonuclear neutrophils are professional phagocytes whose efficacy depends on a multicomponent NADPH oxidase for generating superoxide anions and bacterial killing. They can be primed and activated by different agents that can impair oxidative burst and phagocytosis with opposite effects: reduced capability to destroy bacteria or hyperactivation that induces the generation of large quantities of toxic reactive oxygen species, which can damage surrounding tissue and participate in inflammation. The present study was designed to evaluate the effect of sub-chronic (60 days) permethrin treatment (1/10 DL(50)) on rat polymorphonuclear neutrophils respiratory burst. The results show that permethrin treatment increases superoxide anion production (33 times) and the activity of hydrogen peroxide-myeloperoxidase system (67 times). In vitro experiments suggest that this effect can be related to permethrin priming and to physico-chemical changes at the plasma membrane level of neutrophils. The antioxidant supplementation with Vitamin E and coenzyme Q(10) can protect against the abnormal respiratory burst in rat treated with permethrin. The in vitro studies show that neutrophil apoptosis begins soon after 1h of incubation with permethrin (0.725% of total cells) or its metabolites (3-phenoxybenzyl alcohol, 3-phenoxybenzaldehyde and 3-phenoxybenzoic acid 1.36, 2.26 and 1.3 of total cells, respectively) and that the level of apoptotic cells is very low. In conclusion, immunotoxicity of permethrin measured in rats could prompt future studies on the consequences of chronic insecticide exposure.

The attribution of urban and suburban children's exposure to synthetic pyrethroid insecticides: a longitudinal assessment

Despite the widespread use of synthetic pyrethroid insecticides that led to common exposure in the population, very few studies have been conducted to quantitatively assess human, particularly, children's, long-term exposures to pyrethroid insecticides. The objective of the Children Pesticide Exposure Study - Washington (CPES-WA) was to establish the longitudinal exposure profiles for pyrethroid insecticides in a cohort of children living in an urban and suburban community using urinary pyrethroid metabolites as exposure biomarkers. The results from this analysis will allow us to examine potential risk factors in relation to the elevated pyrethroid insecticide exposure in children. A total of 23 children, aged 3-11 years, who only consumed conventional diets were enrolled in this 1-year study. We provided organic food items to children for 5 consecutive days in the summer and fall sampling seasons. We measured urinary metabolites for the synthetic pyrethroid insecticides in urine samples that were collected twice daily during each of the four sampling seasons. 3-phenoxybenzoic acid was frequently detected in the urine samples with mean and median daily volume-weighted average levels of 1.5 and 1.2 microg/l, followed by trans-2,2-(dichloro)-2-dimethylvinylcyclopropane carboxylic acid (1.4 and 1.0 microg/l) and cis-2,2-(dichloro)-2-dimethylvinylcyclopropane carboxylic acid (0.5 microg/l, and non-detected). When we took into account season, age, sex, diet, and self-reported residential use of pyrethroid insecticides in a linear mixed-effects model, the results suggested that the combination of the use of pyrethroid insecticides in the household, dietary intake, and seasonal differences play a significant role in predicting children's exposure to synthetic pyrethroid insecticides. We found CPES-WA children were continuously exposed to pyrethroid insecticides through their diets all year long, and this chronic exposure pattern was periodically modified by episodes of relatively high exposures from residential uses. Future research should be devoted to enhancing our understanding of the complexity of pyrethroid insecticide exposure patterns.

An observational study of 127 preschool children at their homes and daycare centers in Ohio: environmental pathways to cis- and trans-permethrin exposure

The potential exposures of 127 preschool children to the pyrethroid insecticides, cis- and trans-permethrin, in their everyday environments were examined. Participants were recruited randomly from 127 homes and 16 daycare centers in six Ohio (OH) counties. Monitoring was performed over a 48-h period at the children's homes and/or daycare centers. Samples collected included soil, carpet dust, indoor air, outdoor air, diet, hand wipes, surface wipes, transferable residues, and urine. The environmental samples were analyzed for the cis and trans isomers of permethrin, and the urine samples were analyzed for the pyrethroid urinary metabolite, 3-phenoxybenzoic acid (3-PBA), by gas chromatography/mass spectrometry. The isomers were detected most often in the dust (100%) and hand wipe (>78%) samples collected at both homes and daycare centers. The median levels of cis-permethrin (470 and 1010 ng/g) were higher than the median levels of trans-permethrin (344 and 544 ng/g) in the dust samples at both the children's homes and daycare centers, respectively. In the children's hand wipe samples, the median levels of cis- and trans-permethrin were similar, ranging from 0.03 to 0.04 ng/cm(2), at both locations. The urinary metabolite 3-PBA was detected in 67% of the children's urine samples. The median urinary 3-PBA concentration for the children was 0.3 ng/mL, and the maximum value for one child was 33.8 ng/mL. The primary route of the children's exposure to the combined isomers was through dietary ingestion, followed by indirect ingestion. In addition, our calculated aggregate absorbed doses of permethrin accounted for about 60% of the excreted amounts of 3-PBA found in the children's urine. In conclusion, these children were potentially exposed to low levels of permethrin from several sources, and through several pathways and routes.

A longitudinal approach to assessing urban and suburban children's exposure to pyrethroid pesticides

We conducted a longitudinal study to assess the exposure of 23 elementary school-age children to pyrethroid pesticides, using urinary pyrethroid metabolites as exposure biomarkers. We substituted most of the children's conventional diets with organic food items for 5 consecutive days and collected two daily spot urine samples, first morning and before bedtime voids, throughout the 15-day study period. We analyzed urine samples for five common pyrethroid metabolites. We found an association between the parents' self-reported pyrethroid use in the residential environment and elevated pyrethroid metabolite levels found in their children's urine. Children were also exposed to pyrethroids through their conventional diets, although the magnitude was smaller than for the residential exposure. Children's ages appear to be significantly associated with pyrethroids exposure, which is likely attributed to the use of pyrethroids around the premises or in the facilities where older children engaged in the outdoor activities. We conclude that residential pesticide use represents the most important risk factor for children's exposure to pyrethroid insecticides. Because of the wide use of pyrethroids in the United States, the findings of this study are important for both children's pesticide exposure assessment and environmental public health.

Mechanisms of pyrethroid neurotoxicity: implications for cumulative risk assessment

The Food Quality Protection Act (FQPA) of 1996 requires the United States Environmental Protection Agency to consider the cumulative effects of exposure to pesticides having a 'common mechanism of toxicity.' This paper reviews the information available on the acute neurotoxicity and mechanisms of toxic action of pyrethroid insecticides in mammals from the perspective of the 'common mechanism' statute of the FQPA. The principal effects of pyrethroids as a class are various signs of excitatory neurotoxicity. Historically, pyrethroids were grouped into two subclasses (Types I and II) based on chemical structure and the production of either the T (tremor) or CS (choreoathetosis with salivation) intoxication syndrome following intravenous or intracerebral administration to rodents. Although this classification system is widely employed, it has several shortcomings for the identification of common toxic effects. In particular, it does not reflect the diversity of intoxication signs found following oral administration of various pyrethroids. Pyrethroids act in vitro on a variety of putative biochemical and physiological target sites, four of which merit consideration as sites of toxic action. Voltage-sensitive sodium channels, the sites of insecticidal action, are also important target sites in mammals. Unlike insects, mammals have multiple sodium channel isoforms that vary in their biophysical and pharmacological properties, including their differential sensitivity to pyrethroids. Pyrethroids also act on some isoforms of voltage-sensitive calcium and chloride channels, and these effects may contribute to the toxicity of some compounds. Effects on peripheral-type benzodiazepine receptors are unlikely to be a principal cause of pyrethroid intoxication but may contribute to or enhance convulsions caused by actions at other target sites. In contrast, other putative target sites that have been identified in vitro do not appear to play a major role in pyrethroid intoxication. The diverse toxic actions and pharmacological effects of pyrethroids suggest that simple additivity models based on combined actions at a single target are not appropriate to assess the risks of cumulative exposure to multiple pyrethroids.