In the 50th anniversary edition of American Laboratory, I nominated science-based regulation as the most significant advance in the period. The examples were generally big science, but in a less conspicuous example, science-based regulation is beginning to trickle down to the family farm. In California, water supplies serving more than 25 people are regulated as municipal water supplies. But until recently, drinking water supplying less than 25 people was nearly ignored.
As illustrated in Figure 1, the small water supplies are often in rural areas associated with agriculture and ranching. Water supplies for farmhouses can be contaminated with nitrates and nitrites in wastewater runoff or effluent from septic systems.
Human toxicity of nitrate and nitrite anions is dependent upon concentration and the age of the patient. For infants, three factors combine to increase risk of nitrate toxicity: 1) the body weight is low, 2) the diet is high in water, and 3) the immature digestive system favors reduction of nitrate to nitrite. Excessive nitrite in the digestive tract of newborns can lead to methemoglobinemia. With early diagnosis and therapy, the impact of methemoglobinemia can be mitigated, at least partially.
For adults, most of the risk and hence focus is on nitrate. Nitrate itself is not carcinogenic. However, it has been classified as a procarcinogen, since it may react with amines or amides to form N-nitroso groups from amines or amides. More than 100 N-nitroso compounds have been tested for carcinogenicity in animals,1 and 75–80% of them were classified as carcionogenic (NAS 1977).
Anecdotal reports warn that excessive boiling of water for infant formula can concentrate nitrate due to water evaporation.
Nitrate concentration in drinking water is measured either in terms of the amount of nitrogen present or in terms of both nitrogen and oxygen. The federally accepted concentration is less than 10 mg/L nitrate nitrogen, which corresponds to 45 mg mg/L for nitrate. Common usage focuses on a concentration of 10 mg/L. Dosing studies indicate that this concentration has little margin of safety for toxicity, especially for infants.
Remediation program in California
To ensure nitrate data is available to well users, the California State Water Resources Control Board mandated that each of the nine Regional Water Boards require annual monitoring of nitrate and nitrite (N&N) as nitrogen for all on-farm drinking water wells. This effort has been initiated in the Central Valley and is directed to spread to the rest of the state in five years. The collected data on N&N will be available to the public and used by the Water Boards to develop water quality protection programs.
Assay methods: Ion chromatography of anions
Assay of anions by ion chromatography is well accepted globally. The technology is nearly 40 years old and is accepted by the U.S. EPA as Method 300.1 (see Table 1). Run time was 15 minutes for eight anions including nitrate, nitrite, sulfate, phosphate, and chloride. Sample prep is often direct injection of a 5- or 10-µL sample aliquot without dilution. What could be simpler?
Another option is to assay nitrate and nitrite photometrically as a few samples or in multiple-well plates. Several vendors, such as Cayman Chemical (Ann Arbor, MI), offer kits to assay nitrates in water and biological fluids including urine, serum, and saliva. The assay enzymatically reduces nitrate to nitrite with nitrate reductase. A Griess reagent is added, which couples with nitrogen oxide to produce an azo dye. Absorbance is measured at 540 nm. For modern labs, the major difficulty is the development of the color, and hence signal grows with time. Color development time is usually about 30 min, which can create scheduling problems.
Prognosis
Going forward, the nitrates in drinking water wells will be an emerging global concern for small water systems. Water supplies for ranch animals could also have a nitrate/nitrite problem. Lab staff should promote public awareness of the potential problem and help guide remediation programs.
References
- https://www.ewg.org/research/pouring-it/health-effects-nitrate-exposure
- https://assets.thermofisher.com/TFS-Assets/CMD/Application-Notes/AU-196-IC-Anions-Municipal-Drinking-Water-EPA-AU70979-EN.pdf
Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]