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REVIEWS AND ANALYSES

When Does Nitrate Become a Risk for Humans?

^a Soil Science Dep., Rothamsted Research, Harpenden, Herts AL5 2JQ, United Kingdom
^b Derriford Hospital, Brest Rd, Derriford, Plymouth, PL6 5AA, United Kingdom
^c Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE, 68583 USA
^d Dep. of Health Risk Analysis and Toxicology, University Maastricht, P.O. Box 616, 6200 MD the Netherlands
^e Netherlands Environmental Assessment Agency, P.O. Box 303, 3720 AH Bilthoven, the Netherlands
^f Service de rhumatologie, Centre Hospitalier Universitaire de Caen, 14033 Caen Cedex, France
^g Center for Global Food Issues, Hudson Inst., PO Box 202, Churchville, VA 24421 USA
^h Dep. of Plant Sciences, Univ. of California, Davis, CA, 95616 USA

^* Corresponding author (cvankessel{at}ucdavis.edu).

Received for publication April 10, 2007. Is nitrate harmful to humans? Are the current limits for nitrate concentration in drinking water justified by science? There is substantial disagreement among scientists over the interpretation of evidence on the issue. There are two main health issues: the linkage between nitrate and (i) infant methaemoglobinaemia, also known as blue baby syndrome, and (ii) cancers of the digestive tract. The evidence for nitrate as a cause of these serious diseases remains controversial. On one hand there is evidence that shows there is no clear association between nitrate in drinking water and the two main health issues with which it has been linked, and there is even evidence emerging of a possible benefit of nitrate in cardiovascular health. There is also evidence of nitrate intake giving protection against infections such as gastroenteritis. Some scientists suggest that there is sufficient evidence for increasing the permitted concentration of nitrate in drinking water without increasing risks to human health. However, subgroups within a population may be more susceptible than others to the adverse health effects of nitrate. Moreover, individuals with increased rates of endogenous formation of carcinogenic N-nitroso compounds are likely to be susceptible to the development of cancers in the digestive system. Given the lack of consensus, there is an urgent need for a comprehensive, independent study to determine whether the current nitrate limit for drinking water is scientifically justified or whether it could safely be raised.