Article

by Carey Gillam

New research out of Iowa adds to a wide body of evidence showing that when pregnant women are exposed to nitrates in drinking water, it raises the risks of problematic birth outcomes, including low birth weights and pre-term birth.

The study, published June 25 in PLOS Water, found that the risks persist even when exposures are lower than the regulatory standard for allowable levels.

It comes as the US farm state wrestles with near-record levels of nitrates in prominent waterways, and as residents increasingly question high levels of cancer and other health problems occurring across Iowa.

Nitrate levels have been so high recently in key Iowa rivers that in June, public health officials banned about 600,000 businesses and homeowners in central Iowa from watering lawns to limit demands on utility operations seeking to filter nitrates from water for household use.

When asked by local media about the study and the state’s struggle with the high nitrate levels, Polk County Health Director Juliann Van Liew was quoted by local media as saying that pregnant women “may want to consider alternative drinking sources when we’re in these sustained rates.”

Ties to agriculture

Farm operations are considered largely to blame for nitrate contamination, both because of the runoff of fertilizer applied to fields of corn and other crops, and the runoff of liquified manure generated by large livestock operations that is also often spread on farm fields. The runoff carries nitrates and phosphorus into surface and groundwaters, and ultimately into drinking water.

In addition to concerns about impacts on babies before and after they are born, a growing body of literature indicates potential associations between nitrates and an increased risk of cancer.

“Iowa is a huge agriculture state and we have a lot of health problems here,” said Jason Semprini, assistant professor at the University of Iowa and author of the new study. “People really want to know how their health is being impacted.”

Last year, the Iowa Environmental Council (IEC) and 12 other organizations called for the Environmental Protection Agency (EPA) to take steps to cut harmful nitrate pollution found in water supplies in Northeast Iowa.

The petition highlighted the fact that for many years, nitrate concentrations found in thousands of private wells and some public water sources have exceeded the federal limit of 10 milligrams per liter for drinking water, which the EPA set more than 30 years ago.

This summer, the IEC and the Harkin Institute at Drake University launched an initiative to study the “relationship between environmental risk factors and cancer rates”, and said researchers would be looking at nitrates and pesticides used in farming as key suspected culprits, among other factors.

A separate study is due to be released on Tuesday looking at broad agricultural pollution of Iowa waters.

“The nitrate levels are making it extremely difficult for public water suppliers to treat and deliver drinking water that meets the current regulatory limits,” said Colleen Fowle, IEC water program director.

“As Dr. Semprini and other researchers have published, more evidence is emerging about the links between long-term, low-level nitrate concentrations below the federal regulatory limit in drinking water and adverse health outcomes, such as cancer, thyroid disease, preterm labor, and birth defects,” Fowle said. “It is becoming clear that safe and clean drinking water is a basic human right that cannot be taken for granted.”

Analyzing more than 300,000 births

In his new paper, Semprini examined 357,741 Iowa birth records from 1970 to 1988, the last year that the records provided county-level location data, which allowed him to link births to nitrate measurements in public drinking water supplies within 30 days of conception.

Consistent with studies done elsewhere, Semprini said he found that prenatal nitrate exposure “at levels far below the current EPA standard of 10 mg/L, significantly increases risks of adverse birth outcomes such preterm birth and low birth weight.”

The evidence “should motivate greater scholarly and policymaking attention for understanding and mitigating the potential adverse effects of exposure to nitrate in our drinking water,” according to Semprini.