Excess Nitrogen and Human Health

Nitrate concentrations have not declined substantially since the early 1970s. In many streams and aquifers in North America, Europe, and Asia they have risen appreciably, but this rise has not been accompanied by any clearly discernible damage to human health. In the United States commercial fertilizers (whose overall use is now, as we have seen, much higher than in the late 1960s) are the primary nonpoint source of nitrogen in water. Excessive nitrate levels have been present in water wells throughout the American Midwest for more than two decades. Concentrations above the maximum contaminant limit (MCE) are particularly common in the Corn Belt states, as well as in North Dakota and Kansas.  

Rising nitrate concentrations in four of the world s major rivers. 

Effects progress from cyanosis (blue baby syndrome) to shortness of breath and eventual asphyxiation (chemical suffocation) as the blood turns chocolate brown. Fortunately, an infant treated in a timely manner with ascorbic acid or methylene blue will experience a complete recovery, and adequate intake of vitamin C provides 

But even if nitrates were to be unequivocally implicated in the etiology of some cancers, their intake in drinking water would be only a part of the problem. Most of the nitrates that we take in (about four-fifths of the total daily intake in the United States) do not come from water but from vegetables, above all from beets, celery, spinach, lettuce, and radishes, and our bodies may synthesize daily an amount that matches that total, or even surpasses it.  

The most recent review of the epidemiological evidence merely extends the inconclusive verdict although no firm links have been found between dietary intakes of nitrate and stomach, brain, esophageal, and nasopharyngeal cancers, an association caimot be ruled out. In contrast to these continuing epidemiological uncertainties, the undesirable impacts of water-borne reactive nitrogen on aquatic ecosystems have 

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