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SPATIAL VARIATION OF DISINFECTION BY-PRODUCT CONCENTRATIONS: IMPLICATIONS FOR MINIMIZING EXPOSURE MISCLASSIFICATION
Evans, A., Michael Wright, Z. Rivera-Núñez, AND A. Meyer. SPATIAL VARIATION OF DISINFECTION BY-PRODUCT CONCENTRATIONS: IMPLICATIONS FOR MINIMIZING EXPOSURE MISCLASSIFICATION. Presented at American College of Epidemiology (ACE), Louisville, KY, September 21 - 24, 2013.
PURPOSE: Many epidemiological studies of disinfection by-products (DBPs) rely on system average DBP concentrations as surrogates of personal exposures. Here we examine the potential effect of exposure misclassification from spatial variability on the association between mean birth weight (BWT) and trihalomethane (THM4) concentrations. METHODS: Preliminary results from an epidemiological study of 144 public water systems (PWSs) in Massachusetts (1996-2004) were compared to data from PWSs with low spatial variability (LSV). A PWS had LSV if same day sample concentrations across different locations were ≤20 μg/L. RESULTS: Overall multivariate linear regression results showed no change in mean BWT for THM4 (-1 to +5g) and slight reductions in mean BWT for THMBr (-8 to -10g) exposure quintiles, compared to the lowest quintiles (10 µg/L and 2 µg/L). Compared to all 144 PWSs, mean BWT changed by 72% and 45% for THM4 (+8 to +14g) and THMBr (-8 to -22g), respectively, when restricted to PWSs with LSV (n=36). CONCLUSION: Although it is unclear whether the more pronounced BWT differences are entirely due to exposure misclassification, this restriction approach could help minimize the potential impact of spatial variability on effect estimates in epidemiological studies. Future research will examine the impact of haloacetic acid spatial variability, and will explore alternative methods to define low spatial variability for different DBPs.
URLs/Downloads:ACE_2013_EM DBP SV_FOR CLEARANCE.DOCX
Record Details:Record Type: DOCUMENT (PRESENTATION/POSTER)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL CENTER FOR ENVIRONMENTAL ASSESSMENT