Disparities in potential nitrate exposures within Iowa public water systems†

Abstract

Nitrates (measured as nitrate-nitrogen) in drinking water exceeding the maximum contaminant level (MCL) of 10 mg L⁻¹ can cause significant health risks, such as methemoglobinemia. Even long-term exposure to concentrations below the MCL can also increase the risks of cancer. Iowa, a major agricultural producer, has grappled with decades-long nitrate pollution in its water systems due to intensive farming practices and animal feeding operations. To help in developing interventions and policies to protect public health, this study delves into long-term nitrate levels in 871 Iowa public water systems (PWSs) between 2012 and 2022 and examines sociodemographic disparities in potential nitrate exposure in drinking water. Average nitrate concentration in Iowa's PWSs increased between 2012 and 2016, reaching an average peak of 3 mg L⁻¹ in 2016. 2.5% of 871 PWSs are classified as ‘high-risk’, with nitrate concentrations consistently exceeding 5 mg L⁻¹ over the study period, primarily in eastern and western Iowa, where animal feeding operations are concentrated. The absence of nitrate removal processes at these PWSs contributes to the sustained elevated levels. On average, 7.4% of the state's population served by PWSs has been exposed to nitrate levels consistently exceeding 5 mg L⁻¹ in the past decade. Disparities exist among various sociodemographic groups, with statistically significant higher exposure rates (10.1%, 9.6%, 9.2%, and 8.7%) observed for people whose incomes are below the federal poverty threshold ($26 496/year), older adults (65 years and above), people of colour, and children (5 years and younger). These disparities are particularly concerning as these populations often lack the resources to address the consequences of water contamination. Our study highlights inequities in Iowa's PWSs concerning potential nitrate exposures and underscores a need for nitrate remediation in specific areas. Addressing these disparities is crucial to safeguarding the health of vulnerable populations and promoting environmental justice in water management.