Comparison of trihalomethane exposure assessment metrics in epidemiologic analyses of reproductive and developmental outcomes
Background: Researchers have developed exposure assessment metrics for disinfection by-products (DBPs) utilizing drinking water monitoring data and accounting for spatial variability, temporal variability, water consumption, and showering and bathing time with an expectation of decreasing exposure misclassification when compared to the use of quarterly water utility monitoring data alone. Objective: We used exposure data collected for a previous study of DBPs to evaluate how the inclusion of different sources of information impact trihalomethane (THM) exposure estimates. Methods: We created and compared gestational exposure estimates to THMs based on water utility monitoring data alone, statistical imputation of daily concentrations to incorporate temporal variability, and data on personal water use and behaviors from interviews. We used Pearson correlation coefficients and ranked classifications (Kappa statistics) to compare exposure classifications. Results: Exposure estimates using measured or imputed THM concentrations or self-reported personal water use behaviors such as water consumption, bathing and showering differed substantially from those based on water utility monitoring data alone, though the ranked classifications were generally consistent across exposure metrics. (i.e., a subject with “high” exposure based on measured or imputed THM concentrations generally remained in the “high” category across exposure metrics.) The measured concentrations and imputed daily (i.e., spline regression) concentrations were highly correlated (r=0.99). The weighted kappa statistics comparing exposure estimates made using different exposure metrics ranged from 0.27to 0.89, with the highest values for the ingestion + bathing/showering metrics compared to metrics for bathing/showering only (0.76 and 0.89). As expected, bathing and showering is a primary driver of “total” THM exposure estimates. Significance: This comparison of THM exposure assessment metrics supports recent studies suggesting that water use behavior data in conjunction with quarterly sampling data may reduce some exposure measurement error and related misclassification introduced when relying on quarterly sampling data alone for estimates of THM and other volatile DBPs.