In this review we present an update on maternal exposure to
nitrates in
drinking water in relation to possible adverse reproductive and developmental effects, and also discuss
nitrates in
drinking water in the United States. The current standard for
nitrates in
drinking water is based on retrospective studies and approximates a level that protects infants from
methemoglobinemia, but no safety factor is built into the standard. The current standard applies only to public water systems.
Drinking water source was related to
nitrate exposure (i.e., private systems water was more likely than community system water to have
nitrate levels above the maximum contaminant limit). Animal studies have found adverse reproductive effects resulting from higher doses of
nitrate or
nitrite. The epidemiologic evidence of a direct exposure-response relationship between
drinking water nitrate level and adverse reproductive effect is still not clear. However, some reports have suggested an association between exposure to
nitrates in
drinking water and
spontaneous abortions,
intrauterine growth restriction, and various
birth defects. Uncertainties in epidemiologic studies include the lack of individual exposure assessment that would rule out confounding of the exposure with some other cause.
Nitrates may be just one of the contaminants in
drinking water contributing to adverse outcomes. We conclude that the current literature does not provide sufficient evidence of a causal relationship between exposure to
nitrates in
drinking water and adverse reproductive effects. Future studies incorporating individual exposure assessment about users of private wells--the population most at risk--should be considered.