Drinking Water Sources and Water Quality in the Agricultural Health Study

Abstract

BACKGROUND AND AIM: Drinking water contaminants have been associated with adverse health effects. However, little is known about exposures in agricultural communities where farm practices and well use may enhance exposures to specific contaminants. We describe the exposure assessment and exposure distributions for common drinking water contaminants by water source in an agricultural population. METHODS: We used questionnaire data from the Agricultural Health Study (AHS), a cohort of licensed pesticide applicators (mostly farmers) and their spouses in Iowa (IA) and North Carolina (NC) to ascertain drinking water source at enrollment (1993-1997). For users of public water supplies (PWS), we linked participants’ geocoded addresses to monitoring data for regulated contaminants, including five haloacetic acids (HAA5), total trihalomethanes (TTHM), and nitrate-nitrogen (NO₃-N). For private well users, we estimated nitrate levels using previously developed random forest models based on well depth, land use, soil characteristics, nitrogen inputs, and other relevant factors. RESULTS:We assigned drinking water source for 84% (N=74,919) of AHS participants; approximately 70% in IA and 75% in NC used private wells. Median nitrate concentrations (mg/L NO₃-N) in PWS were higher in IA (0.8, interquartile range (IQR): 0.2-3.1) than NC (0.5, IQR: 0.5-0.6), while median concentrations of HAA5 (µg/L) and TTHM (µg/L) were higher in NC (HAA5: 12.1, IQR: 3.8-33.4; TTHM: 35.4, IQR: 8.8-54.7) than IA (HAA5: 4.3, IQR: 3.0-10.5; TTHM: 13.0, IQR: 3.7-32.3). Private well nitrate concentrations in IA (1.5, IQR: 0.8-4.9) and NC (1.9, IQR: 1.4-2.5) were higher than in PWS. A larger proportion of private wells exceeded the 10mg/L regulatory limit in IA (12%) than NC (1%). CONCLUSIONS:Drinking water nitrate levels were higher for private well users and in IA PWS, while TTHM and HAA5 levels were higher in NC PWS. This work will facilitate future analyses of the health effects of drinking water contaminants in the AHS. KEYWORDS: Water quality, Exposure assessment, Environmental epidemiology