Cancer Risks from Unregulated Contaminants of Public Water Systems

PROJECT SUMMARY/ABSTRACT Despite health protections of the Safe Drinking Water Act (SDWA), contaminants of concern continue to emerge in public water systems (PWS). ‘Unregulated’ contaminants are addressed in the SDWA by the Unregulated Contaminant Monitoring Rule (UCMR), which mandates sampling of PWS for a newly developed list of unregulated contaminants of concern, every five years. The UCMR program, currently in its fifth cycle, has identified contaminants in a systematic way across PWS that serve the majority of the U.S. population. Several chemicals which were frequently detected in the UCMR are suspected or known carcinogens, such as industrial chemicals 1,4-dioxane and per- and polyfluoroalkyl substances (PFAS) and metals including cobalt and chromium-6. Disinfection byproducts also continue to be a major category of concern, even as water treatment approaches change; for example, chlorate (a byproduct of chlorine dioxide disinfectant) was detected in 69% of PWS in 2014-2016. The objective of this proposed study is to examine cause-specific cancer mortality in relation to levels of unregulated contaminants in PWS. We will conduct our investigation through linkage of individual survey records from one of the largest defined cohorts in the U.S. – the Mortality Disparities in American Communities (MDAC) cohort from the U.S. Census Bureau – with measurement of unregulated contaminants in PWS from UCMR sampling. Among U.S. adults in the MDAC cohort, over a study period from 2008-2019, we will estimate associations between unregulated contaminants in PWS and cause- specific cancer mortality. Drinking water contaminants will be examined both individually and as mixtures for their associations with cancer mortality risks. Our study will be the first of its kind to leverage mandated PWS monitoring results through linkage with individual-level cohort data in an examination of cancer risks from unregulated drinking water contaminants. Given the geographic representation of our study to the U.S. population, the size of the study population (>3 million adults), and the resolution of exposures to PWS service areas, this project will provide a realistic overview of the contribution of particular unregulated contaminants on cancer mortality and a high potential for translation to policy.