Tracking down the public-health implications of nitrogen pollution

Claudine Benmar in Grist summarizes some of the effects of nitrogen: ….Nitrate – a compound of nitrogen and oxygen -- is the most common chemical contaminant in groundwater. That isn't surprising when you consider its many sources: sewage overflows, fertilizer runoff, animal waste, and decaying organic material in soil. Nitrate is also found in foods, notably processed, preserved meats like bacon and naturally in green, leafy vegetables like spinach and celery. The list of health afflictions possibly linked to nitrate overexposure includes infant death, miscarriage, birth defects, diabetes, thyroid disease, and cancer.

….Once ingested, nitrate reacts with digestive bacteria to form nitrite. Nitrite changes hemoglobin, the oxygen-carrying protein in the blood, into methemoglobin, which can't carry oxygen. In infants, whose bodies convert nitrate to nitrite more readily, this can cause methemoglobinemia or "blue-baby syndrome," in which a child turns blue from the lack of oxygen and can die.

Nitrites can also react with other chemicals in the body to form what's known as N-nitroso compounds, linked in animal studies to birth defects and cancer. The scientific evidence linking environmental nitrate exposure to health problems is still murky. "There's some smoke," says Alan Townsend, assistant professor of ecology at the University of Colorado, Boulder. "How big the fire is, I don't know. But there's something there."

Between 10 and 20 percent of groundwater sources exceed the federal Maximum Contaminant Level (MCL) of 10 parts per million for nitrate, Townsend says. The Safe Drinking Water Act requires public water supplies to test for nitrates and take action if they exceed the MCL. But small, private wells often aren't regulated. The Environmental Protection Agency estimates that 16 percent of Americans get their drinking water from wells that are vulnerable to nitrate contamination.

…A study published last summer in the journal Southwest Hydrology estimated that California farmers applied 740,000 tons of nitrogen to 6.7 million acres of irrigated farmland in 2007. Of that, 110 pounds per acre aren't used by the plants. Some escapes into the air, but an estimated 80 pounds of nitrogen (as nitrate) per acre per year seeps into the groundwater…..

The original caption to this spellbinding shot by Ansel Adams: Farm, farm workers, Mt. Williamson in background, Manzanar Relocation Center, California