A new report suggests the Environmental Protection Agency should consider lowering the legal limit in drinking water for nitrates, a chemical often connected to fertilizer use.
People who drink water with elevated, but not illegal, levels of nitrates could be at an increased risk of kidney, ovarian and bladder cancer, the nonprofit Environmental Working Group asserts. But a University of Iowa researcher who studies nitrate contamination says the connection to cancer is inconsistent and other chemicals may be involved.
Nitrates are found in fertilizer and manure, and often wash off of farm fields and into drinking-water sources. High nitrates are an expensive problem for rural towns and cities like Des Moines, Iowa, which sued counties that are upstream of the river that provides its water supply.
The legal limit for nitrates is set at 10 parts per million to prevent blue baby syndrome in infants, a condition where their blood cannot absorb enough oxygen. The EWG’s report looked at water quality measurements from 50,000 utilities across the U.S., finding 118 water systems over the legal limit of 10 ppm. But there were 1,683 water systems — mostly in rural, farming communities in the Corn Belt and in California — over 5 ppm.
The nonprofit points to a conclusion from the National Cancer Institute, which says studies have shown an increased risk of some cancers with high rates of ingestion of nitrates from water or food. One example is a 2003 study that looked at data from Iowa residents with 5 ppm of nitrates in their water. It concluded there may be an increased risk of colon cancer but only among specific groups, like people who also eat a lot of meat, which can also be a source of nitrates.
“The EPA should really be taking a hard look at the legal limit for nitrates and possibly lowering it,” says Craig Cox, who works on agriculture and water quality issues at EWG.
But University of Iowa epidemiologist Peter Weyer, who studies nitrate contamination, has looked at the issue of nitrates and cancer. While one study he did showed a risk of bladder cancer in women in Iowa due to nitrates, he says other studies did not find the same connection.
“We can’t definitively say the nitrate is what’s causing the problem we’re seeing,” Weyer says. “It looks that way based on the research we’ve done, but we’re continuing the research.”
Weyer says he suspects other chemicals like pesticides or byproducts from disinfecting the water may play a role in cancers.
This story has been corrected to show that Weyer suspects byproducts from disinfecting water, not disinfectants, may play a role in an elevated cancer risk.