Exposure Misclassification: Temporal and Spatial Variability in Estimates of Individual Species and Mixtures of Disinfection Byproducts

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Disinfection of drinking water is a public health advance, but the potential risk of unintended consequences of disinfection byproduct (DBP) formation remains unclear. Over 600 DBPs have been identified to date, although most have not been analytically quantified in disinfected drinking water. Some DBP exposures occur through multiple routes which can complicate exposure assessment in epidemiological studies especially based on aggregate data derived from routinely-collected monitoring data. Therefore it is important to quantify the spatiotemporal variability in occurrence to minimize measurement error and exposure misclassification. In the absence of biomonitoring data, concentration-based exposure scores based on routinely-collected monitoring data can be spatial water system averages or location-specific estimates. However, intra-water system variation in DBP concentrations results from formation and degradation processes occurring over space and residence time. Temporal variability can also occur from diurnal variation to longer-term trends such as seasonality noted for trihalomethanes (THMs) and haloacetic acids (HAAs). Temporally averaged data may estimate lifetime exposure for cancer outcomes or trimester-specific windows for developmental effects, but they ill fully account for the potential impact of peak exposures. Although the DBP surrogacy issue is beyond the scope here, data availability limitations may preclude examination and delineation of potential risk for individual DBPs or DBP mixtures especially when the measurement error structures can vary due to use of aggregate exposure estimates. With few DBPs regulated or routinely measured, this review will characterize strengths and limitations of existing approaches based on HAAs and THMs and will offer evidence from simulations and sensitivity analyses and offer recommendations to help address the aforementioned challenges. Disclaimer: The views expressed in this abstract are those of the author and do not necessarily reflect the views or policies of the U.S. EPA. Keywords: Water, water quality, disinfection byproducts, environmental epidemiology