John C. Kissel

Pesticide take-home pathway among children of agricultural workers: Study design, methods, and baseline findings

Farmworkers are exposed to pesticides and may take home pesticide residues to their families. In this paper, self-reported pesticide exposure and home practices to reduce the amount of pesticide residues taken home were examined among 571 farmworkers. Urine samples from a subsample of farmworkers and children and dust samples from households and vehicles also assessed pesticide exposure. Overall, 96% of respondents reported exposure to pesticides at work. Many employers did not provide resources for hand washing. Farmworkers’ protective practices to keep pesticide residues out of the home were at a low level. In a subset of respondents, pesticide levels above the limit of quantitation were seen in the urine of children and adults and in house and vehicle dust. The results support the take-home pathway of pesticide exposure. Ways must be found to reduce this pesticide exposure among children of farmworkers.

Comparison of organophosphorus pesticide metabolite levels in single and multiple daily urine samples collected from preschool children in Washington State

A total organophosphorus pesticide exposure study was conducted in Washington State in 1998 in a sample population of 13 children aged 2.5–5.5 years. The children were roughly split between rural and suburban populations and had been previously identified as having potentially elevated organophosphorus pesticide exposures. One component of the study was urine collection and analysis. Urine samples were collected from each subject up to four times in 24 h in two different seasons. Samples were collected at specific time points: before bed, first morning void, after lunch, and before dinner. Urine samples were analyzed initially for the six nonspecific dialkylphosphate (DAP) metabolites and subsequently for eight specific metabolites including malathion dicarboxylic acid (MDA), 3,5,6-trichloro-2-pyridinol (TCPy), and paranitrophenol (PNP). Relatively large percentages of the urine samples contained quantifiable amounts of two of the nonspecific DAP metabolites (DMTP—97%; DETP—67%), and three of the specific metabolites (MDA (71%), TCPy (79%), and PNP (96%)). A percent deviation analysis was employed to determine which of the spot sample time points was the best predictor of the estimated volume-weighted daily average. Of the four spot samples collected, first morning void samples were consistently found to be the best predictors of weighted-average daily metabolite concentration. This finding also held when the data were creatinine-adjusted. The results of this analysis suggest that if spot sampling is to be conducted as part of a biological monitoring study, first morning void samples should be preferentially collected.

Strategies for assessing children's organophosphorus pesticide exposures in agricultural communities

Children can be exposed to pesticides from multiple sources and through multiple pathways. In addition to the standard pathways of diet, drinking water and residential pesticide use, children in agricultural communities can be exposed to pesticides used in agricultural production. A research program on children and pesticides was established at the University of Washington (UW) in 1991 and has focused on two major exposure pathway issues: residential proximity to pesticide-treated farmland and transfer of pesticides from the workplace to the home (paraoccupational or take-home exposure). The UW program selected preschool children of agricultural producers and farm workers in the tree fruit region of Washington state as a population that was likely to have elevated exposures from these pathways. The organophosphorus (OP) pesticides were selected as a common class of chemicals for analysis so that issues of aggregate exposure and cumulative risk could be addressed. This paper provides an overview of key findings of our research group over the past 8 years and describes current studies in this field. Soil and housedust concentrations of OP pesticides were elevated in homes of agricultural families (household members engaged in agricultural production) when compared to non-agricultural reference homes in the same community. Dialkyl phosphate metabolites of OP pesticides measured in childrens urine were also elevated for agricultural children when compared to reference children and when compared to children in the Seattle metropolitan area. Proximity to farmland was associated with increased OP pesticide concentrations in housedust and OP pesticide metabolites in urine. Current studies include a community-based intervention to reduce parental transfer of pesticides from the workplace, and a systematic investigation of the role of agricultural spray drift in childrens exposure to pesticides.

Uncertainty in estimated half-lives of PCBS in humans: impact on exposure assessment

Estimates of the half-lives of PCBs in humans derived from successive body burden measurements are reviewed and found to vary widely whether based on congener-specific or aggregate data. Variability due to differences in physiological processes among individuals and in congener properties is to be expected, but does not appear to be a complete explanation. Very short half-lives (i.e. < 1 year) are unlikely for those congeners most frequently found in human blood because the exposures required to sustain observed body burdens are too large to be easily explained. Very long half-lives ( > 10 years) may be artifacts of confounding by ongoing exposures (a common effect at low body burdens) and are also suspect. The loss of significant quantities of PCBs from the blood of occupationally exposed persons with half-lives of 2-6 years is comparatively well documented (i.e. has been observed in studies with relatively large numbers of subjects and high initial body burdens). Therefore, very long half-lives must be limited to subsets of congeners or of populations if they occur at all. The impact of the use of fixed estimates of half-lives drawn from the tails of the observed range on the evaluation of regulatory standards is shown to be substantial.

Biologic Monitoring to Characterize Organophosphorus Pesticide Exposure among Children and Workers: An Analysis of Recent Studies in Washington State

We examined findings from five organophosphorus pesticide biomonitoring studies conducted in Washington State between 1994 and 1999. We compared urinary dimethylthiophosphate (DMTP) concentrations for all study groups and composite dimethyl alkylphosphate (DMAP) concentrations for selected groups. Children of pesticide applicators had substantially higher metabolite levels than did Seattle children and farmworker children (median DMTP, 25 μg/L; p < 0.0001). Metabolite levels of children living in agricultural communities were elevated during periods of crop spraying. Median DMTP concentrations for Seattle children and farmworker children did not differ significantly (6.1 and 5.8 μg/L DMTP, respectively; p = 0.73); however, the DMAP concentrations were higher for Seattle children than for farmworker children (117 and 87 nmol/L DMAP, respectively; p = 0.007). DMTP concentrations of U.S. children 6–11 years of age (1999–2000 National Health and Nutrition Examination Survey population) were higher than those of Seattle children and farmworker children at the 75th, 90th, and 95th percentiles. DMTP concentrations for workers actively engaged in apple thinning were 50 times higher than DMTP concentrations for farmworkers sampled outside of peak exposure periods. We conclude that workers who have direct contact with pesticides should continue to be the focus of public health interventions and that elevated child exposures in agricultural communities may occur during active crop-spraying periods and from living with a pesticide applicator. Timing of sample collection is critical for the proper interpretation of pesticide biomarkers excreted relatively soon after exposure. We surmise that differences in dietary exposure can explain the similar exposures observed among farmworker children, children living in the Seattle metropolitan area, and children sampled nationally.

The mismeasure of dermal absorption

The results of dermal absorption experiments are routinely and often exclusively reported in terms of fractional absorption. However, fractional absorption is not generally independent of skin loading conditions. As a consequence, experimental outcomes are commonly misinterpreted. This can lead in turn to poor estimation of exposures under field conditions and inadequate threat assessment. To aid interpretation of dermal absorption-related phenomena, a dimensionless group representing the ratio of mass delivery to plausible absorptive flux under experimental or environmental conditions is proposed. High values of the dimensionless dermal number (NDERM) connote surplus supply (i.e., flux-limited) conditions. Under such conditions, fractional absorption will generally depend on load and should not be assumed transferable to other conditions. At low values of NDERM, dermal absorption will be delivery-limited. Under those conditions, high fractional absorption is feasible barring maldistribution or depletion due to volatilization, washing, mechanical abrasion or other means. Similar logic also applies to skin sampling and dermal toxicity testing. Skin surface sampling at low NDERM is unlikely to provide an appropriate measure of potential dermal dose due to depletion, whereas dermal toxicity testing at high NDERM is unlikely to show dose dependence due to saturation.

Residential arsenic and lead levels in an agricultural community with a history of lead arsenate use

Lead arsenate (PbHAsO4) was used as an insecticide in Washington fruit orchards from 1905 to 1947. We examined exposure potential for children living in an agricultural community with historic PbHAsO4 use. Soil and housedust samples were collected from 58 residences. Families were asked about land use history, age of home, and remodeling activities. Median concentrations of arsenic were higher in housedust than in soil (9.0 and 4.2 microg/g, respectively; P=0.05), as were lead concentrations (129 and 46 microg/g, respectively; P=0.0001). Significant associations were observed between indoor and outdoor levels of each metal, indicating track-in as an important exposure pathway. Homes on or near land use for pear or apple production between 1905 and 1947 had significantly higher soil (P=0.005) and housedust (P=0.004) lead, and soil arsenic (P=0.04) than did the other homes. Homes more than 30 years old had significantly higher soil and housedust lead than did newer homes (P=0.01). Homes remodeled within the past two years had significantly higher soil (P=0.01) and housedust (P=0.04) lead. Child doses extrapolated from these data indicate that 36% of homes had soil or dust arsenic levels above the minimum risk level estimated by the Agency for Toxic Substances and Disease Registry. None of the measured lead levels exceeded current US Environmental Protection Agency guidelines. Public health education programs focused on residential hygiene would be of value in areas of historic PbHAsO4 use.

Composition and variability of leachate from recent and aged areas within a municipal landfill

A leachate study was conducted at a large, operating, regional municipal solid waste (MSW) landfill near Seattle, Washington, to examine differences in composition and emission rates between old and new areas of the fill. The landfill began operation in 1966, was receiving approximately 2000 tpd of MSW and had 30×10 6 m 3 (∼12×10 6 tonnes) waste in place at the time of this study. The two areas studied had average ages of 3.7 and 16 years, and contained 5.7×10 6 and 2.04×10 6 tonnes of MSW, respectively. Variations in flow rate, total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), Fe, and Mn were monitored over a 3-month period in the winter and spring of 1992. Increases in flow driven by precipitation caused gradually increasing leachate mass emissions from the aged fill. The rate of mass emission increase with increasing flow from the new fill was more than three times higher than that from the old fill. Leachate flow through the old fill appeared more channelized, resulting in diluting effects with increasing percolation. In leachate from the new fill concentrations were essentially independent of flow. Overall, mass emissions per unit waste mass in place decreased with increasing waste age for TDS and Mn, indicating that these components were leachable independent of degradation processes. Mass emissions per unit waste mass in place increased with increasing waste age for COD, TOC, and Fe, which typify components that increase in availability for leaching with increasing age and progressing stage of decomposition

Para Niños Saludables: A Community Intervention Trial to Reduce Organophosphate Pesticide Exposure in Children of Farmworkers

Background Exposure to organophosphate (OP) pesticides is an occupational hazard for farmworkers and affects their children through the take-home pathway. Objectives We examined the effectiveness of a randomized community intervention to reduce pesticide exposure among farmworkers and their children. Methods We conducted a baseline survey of a cross-sectional sample of farmworkers (year 1) in 24 participating communities. Communities were randomized to intervention or control. After 2 years of intervention, a new cross-sectional survey of farmworkers was conducted (year 4). Farmworkers with a child 2–6 years of age were asked to participate in a substudy in which urine was collected from the farmworker and child, and dust was collected from the home and the vehicle driven to work. Results The median concentration of urinary metabolites was higher in year 4 than in year 1 for dimethylthiophosphate (DMTP) and dimethyldithiophosphate in adults and for DMTP for children. There were significant increases within both the intervention and control communities between year 1 and year 4 (p < 0.005); however, the differences were not significant between study communities after adjusting for year (p = 0.21). The dust residue data showed azinphos-methyl having the highest percentage of detects in vehicles (86% and 84% in years 1 and 4, respectively) and in house dust (85% and 83% in years 1 and 4, respectively). There were no significant differences between intervention and control communities after adjusting for year (p = 0.49). Conclusions We found no significant decreases in urinary pesticide metabolite concentrations or in pesticide residue concentrations in house and vehicle dust from intervention community households compared with control community households after adjusting for baseline. These negative findings may have implications for future community-wide interventions.

Investigation of Dermal Contact with Soil in Controlled Trials

A series of laboratory, greenhouse, and field experiments have been conducted at the University of Washington to improve the empirical grounding of dermal/soil pathway risk calculations. This article presents results from controlled trials, conducted in a greenhouse, in which volunteers engaged in activities in soil amended with a fluorescent marker. Activities included transplanting of bedding plants and laying of pipe by adults and childrens play. Soil contact on hands, forearms, lower legs, and faces was examined using both fluoro-metric and gravimetric measurements. Results provide information on pre- and postactivity loadings, the extent of contact associated with the selected activities, and the effects of clothing, activity duration, and soil moisture. Preactivity loadings were consistent with previously reported observations. Following activity, skin coverage was found to be substantially incomplete except on hands. Local soil loadings may therefore deviate markedly from mean values obtained by w...