EWG water atlas links water pollution to heavy fertilizer use in Illinois, Iowa, Minnesota and Wisconsin

MINNEAPOLIS – The Environmental Working Group today unveiled its innovative water atlas, which shows a close link between heavily fertilized cropland in four Upper Mississippi River Basin states – Illinois, Iowa, Minnesota and Wisconsin – and nutrient pollution endemic to the region’s waterways and drinking water supply.

“EWG’s water atlas relies on thousands of data sources to give people the ability to visualize where the worst nitrate and phosphorus pollution occurs in counties with large applications of fertilizer,” said Soren Rundquist, EWG’s director of spatial analysis. “It’s a great resource for anyone concerned about farming’s impact on water quality.”

Nitrate and phosphorus are the main components of the commercial fertilizer and manure farmers use to provide nutrients to crops – mostly soybeans and corn, in the four states included in the water atlas. Without careful farm management of fertilizer and manure, excess phosphorus and nitrate run off fields into streams, rivers and lakes or seep through the soil into groundwater.

The water atlas’s two interactive maps incorporate phosphorus and nitrate data from 8,200 state and federal water monitors and nitrate data from 3,794 community water systems serving 19 million people in the four states. The maps reveal high levels of phosphorus pollution in counties with intensive fertilizer use throughout the Upper Mississippi River Basin.

In Illinois, Iowa, Minnesota and Wisconsin, 80 percent of surface water monitors and 83 percent of groundwater monitors with elevated phosphorus levels of at least 100 micrograms per liter, or ug/L, were located in counties where more than 70 percent of cropland is fertilized.

Excess phosphorus in freshwater feeds algae blooms. Not all algae outbreaks are toxic, but those that are can harm humans and animals. And even algae blooms that are not toxic can make waterways unfit for fishing and swimming.

The water atlas confirms previous EWG investigations revealing that drinking water nitrate contamination is a serious and worsening problem. In the four states, 86 percent of the water systems contaminated with nitrate levels at half or more of the federal legal limit are located in counties where at least 70 percent of the cropland is fertilized.

Under the 1974 federal Safe Drinking Water Act, the legal limit for nitrate (measured as nitrogen) in community water systems is 10 milligrams per liter, or mg/L. But more recent studies show strong evidence of an increased risk of colon and rectal cancers, thyroid disease and neural tube birth defects at levels of 5 mg/L or even lower.

More than 2.8 million people are served by water systems that tested at or above 5 mg/L at least once over the eight-year period covered by the records used for the water atlas. One out of every 400 water systems detected nitrate at or above 10 mg/L at least once. These systems serve more than 490,000 people, with 32 percent of them in Minnesota and 29 percent in Iowa, followed by Wisconsin, with 22 percent, and Illinois, with 17 percent.

Nitrogen and phosphorus runoff from agriculture in these four states is the primary cause of a notorious annual hypoxic zone off the coasts of Louisiana and Texas. During the summer, that part of the Gulf of Mexico is effectively dead, with devastating effects on Gulf fisheries and ecosystems – and the maps show the pollution problem persists.

“As EWG’s water atlas clearly demonstrates, surface and groundwater resources are vulnerable to heavy fertilizer use in Illinois, Iowa, Minnesota and Wisconsin,” Rundquist said.


The Environmental Working Group is a nonprofit, non-partisan organization that empowers people to live healthier lives in a healthier environment. Through research, advocacy and unique education tools, EWG drives consumer choice and civic action. Visit www.ewg.org for more information.

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