A silent killer is lurking in tens of millions of faucets nationwide, with families in agricultural areas of the country at greatest risk.

Groundwater contamination is occurring due to a combination of chemical fertilizers, pesticides, and animal waste. These substances are breaking down into nitrates—compounds that naturally exist in the environment but can be harmful in high concentrations. High nitrate levels can lead to methemoglobinemia, a serious and potentially fatal condition in infants, also known as blue-baby syndrome.

Consuming water with these chemicals over a long period, even if the nitrate levels are below the Environmental Protection Agency’s safety threshold of 10 mg/L, is associated with various health risks. These include thyroid, kidney, ovarian, bladder, and colon cancers, as well as DNA damage, complications during pregnancy, and increasing rates of colon cancer among young individuals.

Recent studies conducted by researchers at Des Moines University College of Health Sciences have focused on how exposure to these chemicals during pregnancy can impact the developing fetus.

Nitrate levels as low as just one percent of the EPA’s safety limit increased the risks of preterm birth and low birth weight, conditions that have been linked to a higher risk of chronic disease, learning disabilities, and mental health struggles in the baby’s future.

Dr Jason Semprini, the study’s author, said that exposure to nitrate in pregnancy causes about 15 percent as much harm as smoking during pregnancy.

‘I do not want to diminish the importance of efforts to prevent smoking during pregnancy,’ he said. ‘But, I must ask, do we give nitrates 15 percent of the attention we give to smoking?’

An estimated 60 million Americans rely on tap water that is, unbeknownst to them, laced with nitrates. They tend to live in states and rural areas where agriculture is central to the economy, such as Iowa, Nebraska, Kansas, central California, Texas, and Oklahoma.

Dr Semprini added: ‘Our work adds to the evidence base that the current regulatory threshold (more than 10mg/L) may be insufficient for protecting the in utero transmission of water-based nitrate during the first trimester of pregnancy.’

His research was published in the journal PLOS Water.  

Nitrate pollution affects larger cities, as well. An analysis by the Environmental Working Group highlighted the problem in Los Angeles, San Francisco, Denver, Miami, and the suburbs of New York City.

Drinking water in 43 states had nitrate levels of 3 mg/L or higher in major water systems, while 39 states had at least one large system with levels at or above 5 mg/L, according to the group’s latest report.

While still below the EPA’s maximum safety limit, public health experts argue the standards should be stricter.

When the safety limit was first established in the 1950s, scientists discovered that levels as low as 11 mg/L could cause blue baby syndrome.

Blue Baby Syndrome, clinically known as methemoglobinemia, is a rare but serious condition where an infant’s blood cannot carry enough oxygen, leading to a bluish skin discoloration, particularly around the lips, fingers, and toes. 

The most well-known cause is nitrate contamination in drinking water, which is sometimes mixed with formula. 

It’s very rare, with fewer than 100 cases reported in the US, but it is more common in parts of the world where well water is not tested.  

According to former Wisconsin state toxicologist Dave Belluck, the standard was set at 10, right up to the edge of safety.

‘It’s akin to a cliff,’ he said. ‘When you’re standing on the edge of the cliff, you’re safe. You take one step, and it’s just like the Road Runner.’

But Belluck dove deeper into the research that informed safety designation, finding that some infants in the study became sick at nitrate levels nearly 30 times lower, just 0.4 mg/L.

He now believes the EPA’s standards should be stricter, arguing that the science clearly shows nitrates are more harmful than previously thought.  

Other studies on the subject have come to similar conclusions. Researchers from Nova Scotia, Canada, tracked major birth defects recorded in the area between 1998 and 2006 and found they were twice as likely in areas where drinking water nitrate levels were between 1 and 5.56 mg/L.

Exposure over time to nitrates could also increase a person’s risk of a variety of cancers and the International Agency for Research on Cancer (IARC) has classified the compounds as ‘probably carcinogenic to humans’.

Long-term exposure to nitrate in water—even below EPA’s 10 mg/L limit—is linked to thyroid, kidney, ovarian, bladder, and colorectal cancers

A 2008 study of women in rural Wisconsin found that women drinking water containing 10 mg/l or more were nearly three times as likely to get a deadly cancer that affects the first part of the colon.

Even nitrate levels between one and 5.9 mg/l increased the risk of cancer by 1.4 times.

Meanwhile, in Spain and Italy, scientists identified a connection between nitrates in drinking water and colorectal cancer.

Analyzing nearly 5,400 participants, the study revealed that people who consumed more than 10 mg of nitrate per day from water – roughly equivalent to drinking two liters of water containing 5 mg/L of nitrate – had a 49 percent higher risk of colorectal cancer compared to those who drank half that amount.

In Iowa, researchers uncovered links between nitrate exposure and thyroid cancer in older women. Tracking nearly 22,000 women for decades, researchers found that those who drank water with nitrate levels above 5 mg/L for at least five years faced a 2.6 times higher risk of thyroid cancer.

And a long-term study of over 28,000 postmenopausal women in 2015 found that those with the highest nitrate levels in their public water supply (2.98 mg/L or above) had twice the risk of developing ovarian cancer compared to those with the lowest levels.

Private well users also saw a moderately elevated risk – 1.5 times – due to agricultural runoff contaminating groundwater. In total, researchers found 315 cases of ovarian cancer over 24 years of follow-up.

Nitrate is highly soluble in water, making it difficult and expensive to eliminate. Individual homes or municipal water supply systems could be fitted with reverse osmosis and ion exchange filters to remove toxins from their drinking water. Still, those are expensive and out of reach for many.

In addition to stemming from agricultural run-off, leaky septic systems can release untreated wastewater containing nitrates. Landfills, factories, and food processing plants can also leach nitrates over time.