The science of exposure assessment is relatively new and evolving rapidly with the advancement of sophisticated methods for specific measurements at the picogram per gram level or lower in a variety of environmental and biologic matrices. Without this measurement capability, environmental health studies rely on questionnaires or other indirect means as the primary method to assess individual exposures. Although we use indirect methods, they are seldom used as stand-alone tools. Analyses of environmental and biologic samples have allowed us to get more precise data on exposure pathways, from sources to concentrations, to routes, to exposure, to doses. They also often allow a better estimation of the absorbed dose and its relation to potential adverse health outcomes in individuals and in populations. Here, we make note of various environmental agents and how best to assess exposure to them in the National Children’s Study—a longitudinal epidemiologic study of children’s health. Criteria for the analytical method of choice are discussed with particular emphasis on the need for long-term quality control and quality assurance measures.

Epidemiologic studies increasingly rely on improved exposure assessments to characterize pesticide exposures in agricultural populations. A subset of private pesticide applicators in the AHS epidemiological cohort was monitored around the time of their agricultural use of 2,4-D and chlorpyrifos to assess exposure levels and potential exposure factors. Measurements included pre- and post-application urine samples, and patch, hand wipe, and personal air samples. Broadcast or hand spray application methods were used by applicators for 2,4-D products. Chlorpyrifos products were applied using spray applications and in-furrow application of granular products. Geometric mean (GM) values for 69 2,4-D applicators were 7.8 and 25 µg/L in pre- and post-application urine, respectively (p < 0.05 for difference); 0.39 mg for estimated hand loading; 2.9 mg for estimated body loading; and 0.37 µg/m3 for concentration in personal air. Significant correlations were found between all media for 2,4-D. GM values for 17 chlorpyrifos applicators were 11 µg/L in both pre- and post-application urine for the 3,5,6-trichloro-2-pyridinol metabolite, 0.28 mg for body loading, and 0.49 µg/m3 for air concentration. Only 53% of the chlorpyrifos applicators had measureable hand loading results; their median hand loading was 0.02 mg. Factors associated with differences in 2,4-D measurements included application method and glove use; and, for hand spray applicators, use of adjuvants, equipment repair, duration of use, and contact with treated vegetation. Spray applications of liquid chlorpyrifos products were associated with higher measurements than in-furrow granular product applications. This study provides information on exposures and possible exposure determinants for several application methods commonly used by farmers in the cohort and will provide information to assess and refine exposure classification in the Agricultural Health Study. Results may also be of use in pesticide safety education for reducing exposures to applied pesticides.

A deterministic model was developed to identify the critical input parameters needed to assess dietary intakes of young children. The model was used as a framework for understanding the important factors in data collection and data analysis. Factors incorporated into the model included transfer efficiencies of pesticide from surfaces to food, transfer efficiencies of pesticide from surfaces to hands to food, and more accurate microactivity data related to contact frequency for the three variables of interest Ð hands, surfaces, and food. Results from range -finding measurements of transfer efficiencies using an aqueous pesticide solution of a mixture of malathion, diazinon, and chlorpyrifos sprayed on the surfaces indicate that a higher pesticide transfer occurred from hard surfaces to food ( hardwood, plastic ) , with low transfer from soft surfaces ( carpet, cloth ) . Six children, all less than 4 years old, were videotaped to obtain realistic contact frequency and times for the interaction of hands, surfaces, and foods during eating meals and snacks while in their homes or day care centers. The time range of eating events varied from about 2 to 55 min, with an average of about 20 min. The average number of contact frequencies between food and hands was 19 times for each eating event, with a range of 10 ± 40. Contacts between the surface and hand were about the same as the food and hands. Contacts between foods and surfaces ranged from 0 to 32, but only five or less of the contacts per eating event were associated with surfaces other than eating utensil. The children's microactivity data collected during the eating events, together with the laboratory results from the transfer studies, were provided as input into a Monte Carlo simulation of the dietary ingestion model. Simulation results indicate that children's handling of the food could contribute 20 ± 80% of the total dietary intake of pesticides. Dietary exposure due to residues in the food before handling accounted for 16% and 47%, respectively, of the total mean intake from simulations for a child's consumption of an apple or banana. These results indicated that transfer efficiencies for foods on various surfaces typically found in homes as well as children's hand contacts with the food and surfaces are important as determinants of dietary exposure. Journal of Exposure Analysis and Environmental Epidemiology ( 2000 ) 10, 710 ± 722.

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