A new report by a Washington, D.C.-based environmental group found that nitrate levels in some Minnesota public drinking water systems have increased in recent years.
The trend appears to be most prevalent in rural parts of the state, according to the Environmental Working Group’s report. And even though most of the nitrate levels surveyed fall below the federal legal limit, members of the group still say their findings are a cause for concern.
Some researchers have suggested that exposure to even minimal amounts of the compound, found in fertilizer and manure, may be a risk factor for cancer, illness and birth defects. As a result, and having released a similar report in January, the group is continuing its calls for Minnesota regulators and farmers to adopt more stringent drinking water protections.
“The more the agricultural community steps up to do this, the more the industry steps up to help farmers make the changes that they need to make, the better” said Craig Cox, Environmental Working Group vice president of agriculture and natural resources.
Nitrate is believed to enter surface water and groundwater sources as runoff leached from soil or crop fields. Water with levels below 10 milligrams per liter is considered by the U.S. Environmental Protection agency to be safe to drink.
Though nitrate can occur in water naturally, concentrations of 3 milligrams per liter are generally thought to indicate man-made contamination.
In the study released Wednesday, the Environmental Working Group analyzed state Department of Health data on 115 public water systems that reported nitrate levels of 3 milligrams per liter at least once between 1995 and 2018. Many are located in the central and southeastern parts of the state.
Average nitrate levels increased in 72 of the systems during those years, according to the study, affecting 218,000 people but falling below the federal limit. They jumped from 2.7 milligrams per liter in 1995 to 4.4 in 2018, according to the study.
But the Environmental Working Group and others have argued that research shows concentrations of 5 milligrams per liter can still pose health risks.
Twenty-four other systems reviewed for the study reported nitrate levels that exceeded the federal limit at least once between 1995 and 2018. Of those, 16 saw their nitrate levels rise in the time between those years.
According to the Minnesota Department of Health, more than 900 public drinking systems serve some 80 percent of the state population.
Through a spokesman, the Health Department said that it “constantly” works with public drinking water systems to keep nitrate levels below the federal limit. And changes to that limit — at the state and federal level — are not up for consideration.
“We often hear both that the nitrate standard of 10 mg/l is too low or not low enough, as (Environmental Working Group) concludes in their report,” department spokesman Scott Smith said. “Our toxicologists constantly review the literature and have not found evidence to modify the current number of 10 mg/L. There is not scientific consensus that exposure to nitrate below 10 mg/L results in adverse health effects.”
The Environmental Working Group could not say why levels are increasing in some of the water systems it analyzed. Cox suggested that soil composition, which can affect leaching intensity, might be a factor. Over-fertilizing could be another, he said.
State regulators have taken steps to address nitrate contamination and in September will begin to enforce what is called the Groundwater Protection Rule. It seeks to curb nitrate contamination by restricting fall crop fertilization in fragile parts of the state and preventing the further pollution of already contaminated areas.
In a statement, the Environmental Working Group criticized the rule for not extending the same restrictions to farms located near private wells, and for granting farmers near public wells an “unnecessarily drawn-out timeline” for adopting more environmentally friendly practices. Under the rule, producers near already contaminated public wells will volunteer to comply with best management practices suggested by local-and-state-organized advisory boards. Farms would be forced to comply only if they refuse to implement those practices or if nitrate levels in nearby wells increase.
The soonest that mandatory compliance would be enforced would be in three years’ time, according to the state Department of Agriculture.
Minnesota Agricultural Water Resource Center executive director Warren Formo pushed back on the Environmental Working Group’s claim that the new rule relies too heavily on volunteerism. The center is made up of 25 Minnesota agriculture producer associations.
“There are regulatory teeth in this new rule,” he said.
Farmers make judicious use of water and fertilizer, Formo said, both for the sake of preventing nitrate contamination and to produce savings.
