High nitrate levels found in agricultural Wisconsin groundwater can pose a health risk to the public and experts are urging better precautionary measures.
Nitrogenous fertilizers used to grow crops transform into nitrates and cause serious problems for agricultural counties.
The issue with nitrates
The consistent increased use of nitrogenous fertilizers and animal manure for farming practices has led to an increase in groundwater nitrate concentrations, Richard Lathrop, honorary research scientist at the University of Wisconsin Center for Limnology, said.
This increase in nitrates can cause serious health problems.
High infant nitrate intake can lead to methemoglobinemia, or ‘blue baby syndrome,’ which reduces the blood’s oxygen carrying capacity. But there are few fatal cases, Kirsti Sorsa, program manager at Public Health Madison and Dane County, said.
Other studies have shown high nitrate consumption is linked to problems in thyroid gland function, diabetes, birth defects and even cancer in children whose mothers have been exposed to high nitrate levels. Most results have not been conclusive, Sorsa said, but have encouraged pregnant women to avoid nitrates in high levels.
Sorsa said the Public Health Madison and Dane County, Department of Natural Resources and the State Historical and Geological Survey recently conducted a study that found nitrate levels are decreasing. State health has broadened the guidance for protecting babies and adults, especially pregnant women.
Where nitrates pose issues
Lathrop said the higher nitrate concentration problem in Wisconsin is mainly isolated to agricultural areas.
He said in non-agricultural areas, Wisconsin has a much lower nitrate concentration of two milligrams per liter than the health standard for nitrate concentration, which is 10 milligrams.
Higher concentrations are observed mainly in agricultural areas and areas with livestock and dairy farming.
High nitrate concentrations are usually found in shallow sources of groundwater, such as private wells or wells that are 100 to 150 feet deep. People who reside in agricultural areas or own shallow wells need to be especially careful of the increasing nitrate concentrations in their water, Sorsa said.
“Those are the most vulnerable because we can see elevated levels of nitrates,” Sorsa said.
Lathrop said Dane County is relatively safer because the fractured bedrock is covered in protective layers of glacial soils, sandstone and aquifers. By the time water from agricultural areas reaches Dane County, it is safer because it has gone through a significant amount of denitrification.
Where nitrates come from
Lathrop said corn in particular requires a lot of nitrogen to grow and causes farmers to take on a “more is better” mindset.
This eventually leads to an excessive use of nitrogenous fertilizers, Lathrop said. Much of the nitrogen is not absorbed by crops and is converted into a nitrate ion that does not bind to the soil. This seeps into the ground whenever it rains and goes into the groundwater supply, Lathrop said.
In a similar manner, animal manure is converted to nitrates that get absorbed into the regional water table, Lathrop said. Northern Wisconsin, mainly Kewaunee, Fond du Lac and Brown Counties, are most prone to nitrate pollution because of their thin soils and fractured bedrock that allow nitrates to easily infiltrate groundwater.
Future solutions
Sorsa said only a small fraction of people with private wells get their water tested because of the lack of regulations. Public water systems and municipal wells, she said, are much deeper and are unlikely to be affected.
It’s vital, Sorsa said, that more people test their water quality to avoid nitrate-related health problems.
“People should really test their water, at least annually and particularly if there are changes in the odor, taste or appearance of the water or after flooding,” Sorsa said.