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LONGITUDINAL COHORT METHODS STUDIES
The objective of this task is to identify, develop, and evaluate simple, cost effective monitoring methods that can be used to develop exposure classifications for the proposed Longitudinal Cohort Study. Methods once evaluated should be applicable to other epidemiological studies. This project will be conducted as four concurrent subprojects.
(1) demonstrating field performance and developing uptake rates of a semipermeable membrane devise (SMPD) to collect long-term integrated samples for semivolatile organics in air,
(2) developing simple rapid methods for analyzing the SMPDs,
(3) developing rapid field or near field methods for analyzing chemical metabolites in urine,
(4) review literature to identify available but not currently used techniques for long-term integrated exposure measurements.
Accurate exposure classification tools are required to link exposure with health effects in epidemiological studies. Exposure classification for occupational studies is relatively easy compared to predicting residential childhood exposures. Recent NHEXAS (Maryland) study articles reveal that population distributions of exposure are relatively constant; however, for the majority of individuals within the study population exposures vary dramatically over time (62 subjects sampled six times during a one-year period - air, food, water, dust, and urine). Long-term, time-integrated exposure measurements would help address the problem of developing appropriate residential childhood exposure classifications. This task will investigate/or evaluate measurement methods classifying exposure, both long term integrated and screening for exposures to short half life contaminants.
Although long-term integrated exposure measurements are a critical component of exposure assessment, the ability to include these measurements into epidemiological studies is often limited by time, budget, and compliance issues. Another problem which arises when determining the sources, routes, and pathways of exposure to pesticides and other chemicals is the lag time between collection of a sample and the receipt of the results. Current methods which use laboratory analysis may take 30-60 days, or longer, to obtain results. This means that the source of exposure may be gone by the time it is discovered that the child has been exposed, given the relatively short half-lives of many compounds. Screening techniques could direct attention to the most highly exposed (to particular indicator compounds) population of children for which multiroute, multimedia monitoring would be of value. In addition, stratification of the study population (i.e., the majority of the environmental/biological samples collected from the "highly exposed population" of children) often is required, given the expense of multiroute, multimedia monitoring (numerous non-detect results are counterproductive in determining sources).