Nitrate pollution and the public health crisis in SE Minnesota
Written by Isaac Conrad, MCEA water program intern, summer 2023
Looking out across the landscape of southeastern Minnesota, you’ll find miles of picturesque rolling hills, dramatic bluffs, and hidden caves. Cold springs flow into clear streams, cutting through the land only to disappear into sinkholes a few miles downhill. It’s easy to forget that the features that make this area - known as the karst region - so beautiful, also make it vulnerable. An intimate relationship exists between its streams and rivers and the groundwater that hundreds of thousands rely on for drinking water. Contamination at the surface quickly seeps into the ground, moving through fractured bedrock and contaminating underground aquifers.
Over 500,000 Minnesotans are facing a drinking water crisis fueled largely by agricultural nitrate pollution from fertilizer and manure seeping into surface and groundwater sources.1 The nitrate pollution is largely driven by industrial agricultural practices, like Concentrated Animal Feeding Operations (CAFOs) and row crops. Concern in vulnerable regions like the karst is growing, as levels of nitrate in public and private wells climb to concentrations that pose a wide variety of health risks, including some cancers.
To get a better sense of how this issue has played out in southeast Minnesota, I spoke to two public health experts, Dr. Aleta Borrud and Dr. Katie Loth. As Minnesota practitioners, they have both a personal and professional investment in guaranteeing that all Minnesotans have access to clean drinking water at their tap.
Established in 1962, the current federal safe drinking water limit for nitrate - 10 milligrams per liter (mg/L) - was set to address the increased cases of methemoglobinemia, also known as blue baby syndrome. According to Dr. Aleta Borrud, a retired Mayo Clinic physician with decades of experience in the karst region, the condition occurs when nitrate limits the ability of hemoglobin in blood to carry oxygen. As for effects on the extremely susceptible infants? “Blue hands, blue feet, and can’t breathe,” states Dr. Borrud.
But the current nitrate limit isn’t protective enough, Dr. Borrud said. “I do think [the nitrate limit] should be revisited, given the fact that we know that for pregnant women, the risks for adverse outcomes during pregnancy happen at much lower levels, and particularly for agricultural communities across the US, the exposure means that we may see increased cases of colorectal cancer, thyroid disease, and the potential for all these other adverse effects.”
Recent research – including a meta-analysis of 27 peer-reviewed studies2 – has concluded that exposure to nitrate levels well below the 10 mg/L threshold can lead to a variety of health outcomes, which can be broadly classified as cancers or pregnancy and birth complications. How does nitrate contribute to these health outcomes? “When you ingest nitrates, bacteria in the gut convert them to what we call N-nitroso compounds, which we know to be carcinogenic (causes cancer) and teratogenic (causes birth defects),” says Dr. Borrud.
“[Studies] did find that with nitrate levels over 5 mg/L, not 10 mg/L, 5 mg/L, there was an increased risk of thyroid cancer, ovarian cancer, and bladder cancer,” emphasizes Dr. Borrud. The data Dr. Borrud references comes from the Iowa Women’s Health Study—a series of studies including over 38,000 women that found statistically significant increases in the risk for thyroid cancer,3 ovarian cancer,4 and bladder cancer5 when women were regularly exposed to nitrate levels above 5mg/L in their drinking water.
Elevated risk for colorectal cancer begins at nitrate levels of just 1 mg/L, with statistically significant increases in risk beginning at 3.87 mg/L. These findings come from very large epidemiological studies, one from Spain and Italy6 and the other from Denmark.7 According to Borrud, “We don’t do studies like this in the US.” The studies are some of “the largest and most definitive” studies on the issue.
Beyond cancers, a growing body of research suggests that elevated levels of nitrate also contribute to pregnancy complications and birth defects. “We do know that there’s neural tube defects, like cleft palate or anencephaly—leading to no brain development, spinal cord defects, or spina bifida,” explains Dr. Borrud. Her claims are backed by a study of over 4,000 women finding that mothers of children with spina bifida, limb deficiency, cleft palate, and cleft lip were, respectively, 2.0, 1.8, 1.9, and 1.8 times more likely than control mothers to ingest more than 5.42 mg of nitrate daily.8
“The one thing that’s still not clear but suspected is that there might be nitrate-related cases of preterm births, low birth weights, and spontaneous abortions,” shares Dr. Borrud. That relationship becomes more clear when analyzing the literature. Adverse pregnancy outcomes like spontaneous abortion, fetal death, premature births, low-birth weights, and congenital malformations can begin around 1 mg/L.9, 10, 11Nitrate in drinking water is associated with 1.4% of low-birth weight cases, 5.3% of very preterm birth cases, and 2.7% of neural tube defect cases annually.12
None of these conditions are easily treatable, “especially when you think about birth defects, or the loss of a pregnancy or pre term birth,” says Dr. Borrud. The medical and emotional toll of these nitrate-attributable conditions is significant, and that doesn’t even take into consideration the economic burden of treatment. “The medical costs of treating multiple cancers, that we find out about decades down the road, that’s huge.”
“The medical costs of treating multiple cancers, that we find out about decades down the road, that’s huge.” - Dr. Borrud
Just how huge? Using the 2014 dollar, the annual economic costs of treating nitrate-attributable neural tube defects ranges from $24-32 million annually. Very preterm births - those that occur between 28 and 32 weeks gestation - cost $116 million annually, and indirect costs of nitrate-attributable low birth weights range from $172-232 million annually. Treating nitrate attributable cancers may cost between $250 million and $1.5 billion annually. When considering the economic costs of the lost years of life, the US loses $1.3-6.5 billion annually.12
When asked how families in the karst should respond to this drinking water crisis, Dr. Katie Loth, an Assistant Professor of Family Medicine and Community Health at the University of Minnesota Medical School, said, “I think testing your water is a big piece of it. The safety of your water can change over time — both seasonally and with the integrity of your well. So make it something that becomes part of your health patterns.”
“I think testing your water is a big piece of it. The safety of your water can change over time — both seasonally and with the integrity of your well. So make it something that becomes part of your health patterns.” - Dr. Katie Loth
But testing the water isn’t enough, emphasized Dr. Loth, and it’s certainly not only the burden of impacted families to develop strategies for responding to test results. “I think people sometimes are afraid to test their tap water, because if it's not safe to drink, and they can't afford the solution to make it safe, then what do they do?” State and local governments need to provide impacted families the resources they need to respond, like free testing, bottled water, treatment system options, and more.
Agriculture has long been, and still is, a central part of life for communities across Minnesota, and the karst region of southeast Minnesota is a perfect example of that; however, state regulators must quickly wrestle with what to do with industrial agriculture’s consequences for drinking water. That said, addressing the failures of modern agricultural practices to protect surface and groundwater is a complicated endeavor, as it’s both political and personal for communities all across the state.
Yet Dr. Loth reminds us, “It's only going to become more important that we tackle this as climate change begins to impact things more. There's a lot of politics that go into this, but at the end of the day, this is health, right? And everybody wants their kids to be healthy, and their kids’ kids to be healthy, and to be able to grow up safely. People should have the capability of drinking water at the kitchen sink, raising healthy children, and living into old age, and if we can come together around those issues rather than thinking about some of the other stuff, I think that would be a good place to start.”
Over 500,000 Minnesotans face a drinking water crisis fueled largely by agricultural nitrate pollution from fertilizer and manure seeping into surface and groundwater sources.
The problem has reached crisis proportions in Southeastern Minnesota, where industrial agricultural practices like Concentrated Animal Feedlot Operations combined with the region’s porous geography leave water supplies particularly vulnerable to nitrate pollution
Consuming nitrate-contaminated drinking water is linked to a host of concerning health harms, including some cancers, birth defects and pregnancy complications.