The U.S. Environmental Protection Agency (EPA) is resuming its assessment of nitrates and nitrites in drinking water, which was suspended in 2018 after the Trump administration deprioritized the chemicals for evaluation under EPA’s Integrated Risk Information System (IRIS). In June 2023, EPA reversed the decision.

Nitrates and nitrites are pervasive contaminants in surface water and groundwater in the U.S. Studies have suggested an association between the chemicals and cancer, thyroid harm, birth defects, preterm birth and low birth weight, and type 2 diabetes.

The IRIS nitrate assessment has not been updated in more than three decades. In light of mounting evidence of the chemicals’ harm to human health, IRIS set the process in motion for the reevaluation of nitrites and nitrates in 2015, three years prior to the Trump administration decision that halted their assessment.

In 2023, IRIS decided to reevaluate nitrates and nitrites upon the request of the EPA Office of Water—Region 5, and the EPA Office of Children’s Health Protection, in order to inform a review of federal drinking water regulations.