Arsenic in drinking water is a major contributor to U.S. exposure

April 26, 2023
New research evaluates the link between drinking water arsenic levels and arsenic biomarkers in urine, finding that arsenic in public systems and private wells is a major contributor to total measured arsenic exposure.

A new study finds that water arsenic levels are linked to higher urinary arsenic among the U.S. population for users of both private wells and public water systems, according to a press release by the University of South Florida.

Long-term exposure to arsenic even at low and moderate levels can increase the risk of cancer and other types of chronic disease. While drinking water along with diet is a major source of arsenic for the general population, the contribution of arsenic in drinking water to total arsenic exposure has been unclear in U.S. populations, especially at less than high levels in public water supplies.

The researchers evaluated the association between arsenic in private wells and public water supplies using urinary arsenic biomarkers within U.S. populations. Their findings are published in the journal Environmental Research.

“To date, no nationwide study had evaluated the link between drinking water arsenic with arsenic biomarkers in urine to assess how drinking water contributes to arsenic exposure for both regulated community water systems (CWS) and unregulated private wells,” said Maya Spaur, a PhD candidate in environmental health sciences at Columbia Mailman School of Public Health.

The U.S. Department of Health and Human Services Agency for Toxic Substances and Disease Registry includes arsenic as a potent carcinogen and toxicant associated with numerous adverse health outcomes, ranking it number one on their substance priority list. The U.S. Environmental Protection Agency (EPA) regulates arsenic in public drinking water supplies and sets the maximum contaminant level (MCL) allowable in public water systems. However, differences in CWS arsenic concentrations persist across the U.S.

In 2006, the EPA reduced allowable maximum contaminant levels from 50 µg/L to 10 µg/L. However, based solely on risk to health, the EPA set an MCL goal (MCLG) of 0 µg/L. In addition to community water systems, arsenic exposure from drinking water is also a major concern for approximately 40 million U.S. residents reliant on private well water. However, private wells are not subject to EPA’s MCL or other federal regulations.

To conduct the study, the researchers evaluated 11,088 participants from the 2003-2014 National Health and Nutrition Examination Survey (NHANES). For each participant, the researchers assigned private well and CWS arsenic levels according to county of residence using estimates previously derived by EPA and the U.S. Geological Survey. Participants also completed an in-person interview, dietary recall, and physical examination.

The average recalibrated urinary dimethylarsinate (rDMA), the main metabolite of arsenic excreted in urine was 2.52 µg/L among private well users and 2.64 µg/L among CWS users. Urinary rDMA was highest among participants in the West and South, and among Mexican American, other Hispanic, and non-Hispanic other participants. Urinary rDMA levels were 25% and 20% higher comparing the highest to the lowest third of the population distribution of CWS and private well arsenic, respectively.

“We found that higher private well and public water arsenic levels were linked to higher urinary arsenic among NHANES participants,” noted Spaur. “We further observed very similar relationships between water arsenic and urinary arsenic for both regulated public water supplies and unregulated private wells, but did see differences by region with the strongest associations in the South and West, and among Mexican American participants. Our findings show that water arsenic, including in public water, is a major contributor to total arsenic as measured in urine.”