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Re-examining “Nitrate Toxicity”: A Call for a More Rational Approach to Effluent Limits for Nitrogen in Decentralized Wastewater Treatment
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Eleventh Individual and Small Community Sewage Systems Conference Proceedings, 20-24 October 2007, Warwick, Rhode Island 701P1107cd.(doi:10.13031/2013.23980)Authors: Jason John Churchill
Keywords: Nitrate, nitrogen, methemoglobinemia, blue-baby, cancer
Increasingly, regulatory agencies are adopting restrictive rules limiting nitrogen levels in effluent discharged to land from decentralized wastewater treatment systems. These effluent limits are often modeled after the federal drinking water standard for nitrate, set at 10 mg/L nitrate-N. By law, that standard applies only to public drinking water supplies, and not to wastewater treatment system discharges. Nevertheless, restrictive effluent limits are often imposed by regulatory agencies that believe such measures are necessary to protect the public from nitrate health risks. The supposed risks include methemoglobinemia (blue-baby syndrome), increased incidence of cancer, adverse reproductive effects, and other possible effects. However, a review of published epidemiological and medical research spanning over five decades shows that convincing, reproducible scientific evidence to substantiate health-risk claims has not materialized. For example, health officials often assume that drinking-water nitrate is responsible for causing blue-baby syndrome, due to conversion of nitrate to nitrite in the infants digestive tract. That outdated theory is inconsistent with numerous observations suggesting that another factor must be responsible. In fact, compelling evidence is consistent with the emerging theory that the underlying cause of drinking-water associated blue-baby syndrome is infection by fecal microorganisms that contaminate unsanitary wells. Studies that examined the relationship between nitrate and incidence of cancer, reproductive effects, and other health effects also fail to show a strong link to nitrate as the cause. Considering that definitive evidence of nitrate health risks is conspicuously lacking, a more rational approach to setting effluent limits for waste treatment systems is needed, one that considers costs/benefits and recognizes factors that act to limit nitrogen buildup in groundwater. Such factors include nitrogen removal by soil microorganisms, and aquifer hydrogeology.
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