Drinking water sources and water quality in a prospective agricultural cohort

Abstract

We describe drinking water sources and water quality for a large agricultural cohort. We used questionnaire data from the Agricultural Health Study (N = 89,655), a cohort of licensed pesticide applicators 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 contaminant monitoring data [five haloacetic acids (HAA5), total trihalomethanes (TTHM), and nitrate-nitrogen (NO3-N)]. We estimated private well nitrate levels using random forest models accounting for well depth, soil characteristics, nitrogen inputs, and other predictors. We assigned drinking water source for 84% (N = 74,919) of participants. Among these, 69% of IA and 75% of NC participants used private wells; 27% in IA and 21% in NC used PWS. Median PWS nitrate concentrations (NO3-N) were higher in IA [0.9 mg/L, interquartile range (IQR): 0.4–3.1 mg/L] than NC (0.1 mg/L, IQR: 0.1–0.2 mg/L), while median HAA5 and TTHM concentrations were higher in NC (HAA5: 11.9 µg/L, IQR: 5.5–33.4 µg/L; TTHM: 37.7 µg/L, IQR: 10.7–54.7 µg/L) than IA (HAA5: 5.0 µg/L, IQR: 3.7–10.7 µg/L; TTHM: 13.0 µg/L, IQR: 4.2–32.4 µg/L). Private well nitrate concentrations in IA (1.5 mg/L, IQR: 0.8–4.9 mg/L) and NC (1.9 mg/L, IQR: 1.4–2.5 mg/L) were higher than PWS. More private wells in IA (12%) exceeded 10 mg/L NO3-N (regulatory limit for PWS) than NC (<1%). Due to the proximity of their drinking water sources to farms, agricultural communities may be exposed to elevated nitrate levels.

Ingested nitrate and nitrite and end-stage renal disease in licensed pesticide applicators and spouses in the Agricultural Health Study

“…We assigned private applicators the same drinking water source as that reported by their spouses, assuming that applicators and spouses lived together at enrollment. For those who did not report drinking water source at enrollment but provided such information in subsequent interviews, we assigned the water source using their responses in later interviews (see Manley et al [ 26 ] for details).…”

“…Water nitrate data for water systems in IA from 1987 to 2018 were obtained from the Center for Health Effects of Environmental Contamination at the University of Iowa, and data for NC from 1977 to 2018 were obtained from the North Carolina Department of Environmental Quality. Most PWS data were linked to towns by town names, and remaining PWS were linked via other approaches (e.g., internet searches, phone calls to utilities) [ 26 ]. Average exposure to nitrate, measured as nitrate-nitrogen (NO 3 -N, milligram/liter (mg/L)), was computed by averaging annual PWS measurements across years that participants lived in their residence within 1990−2000, a time period around study enrollment.…”

“…To explore potential EMM of the associations by sex, we conducted subgroup analyses among male pesticide applicators and among female spouses because the vast majority of pesticide applicators were men and almost all the spouses were women. We also explored EMM of the associations by state (IA vs. NC) to account for any differences (e.g., lifestyles, occupational and residential exposures) in populations [ 26 ] that were not captured by existing covariates. In analysis of water nitrate, we stratified by drinking water source (private well vs. PWS) to account for other potential contaminants in private wells and PWS (e.g., pesticides) between participants using these drinking water sources that could have led to adverse renal effects.…”

“…The method for developing water nitrate exposure estimates for participants in the AHS has been described elsewhere [26][27][28]. At enrollment, spouses of applicators were asked to select their primary residential drinking water source from the following choices: private well, PWS, bottled water, or some other source.…”

Corn Yield Increase Under Constant Fertilizer Did Not Reduce Nitrate Export

“…Nitrate levels even below the US Environmental Protection Agency's accepted level of 10 mg L -1 in drinking water can contribute to negative public health outcomes (Ward et al, 2018). Most Iowans get their water from private wells, which not uncommonly exceed this threshold (Manley et al, 2022). Even Des Moines Water Works, which supplies Iowa's capital, has struggled to keep nitrate levels low for decades (Lucey and Goolsby, 1993;Eller, 2022).…”