The authors found that 99% of community water systems (CWSs) in the United States do not exceed the maximum contaminant level for nitrate specified by the Environmental Protection Agency (10 milligrams per liter).
Hispanic residents more often lived in areas serviced by CWSs that had average nitrate concentrations of 5 mg/L or above.
Dr. Laurel Schaider, lead author of the study said: "We hypothesized that Hispanic Americans might have higher nitrate in their drinking water because many US farmworkers are Hispanic, and agriculture is a major source of nitrate pollution.
However, we saw these associations even after we adjusted our statistical model to take into account agricultural land use.
These results suggest that there may be additional reasons why Hispanic residents in the US have higher nitrate in their drinking water."
Dr. Schaider added: "Our findings suggest that programs intended to help low-income and small public water supplies may not be adequately assisting communities with higher proportions of Hispanic residents, who are more likely to live in areas with high nitrate and thus may be at greater risk of the associated harmful health effects."
Systems relying on groundwater had higher nitrate concentrations compared to systems relying on surface water and were more likely to have high levels of nitrate.
In order to gain a better understanding of nitrate exposure and whether it may be associated with specific demographic factors, the authors compiled nitrate data on 616,591 samples collected from 39,466 CWSs across the United States between 2010 and 2014.
The authors suggest that previous evidence of possible health effects associated with nitrate concentrations of 5 mg/L and above in drinking water raises concerns for the 5.6 million Americans served by public water supplies with average nitrate concentrations above this level.
More information: Laurel A. Schaider et al, Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water?, Environmental Health (2019).