National Water-Quality Assessment (NAWQA) Program
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By Mary H. Ward1, Theo M. deKok2, Patrick Levallois3, Jean Brender4, Gabriel Gulis5, Bernard T. Nolan6, and James VanDerslice7
[Environmental Health Perspectives, vol. 113, no. 11, November 2005]1Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA; 2Department of Health Risk Analysis and Toxicology, University of Maastricht, the Netherlands; 3Institut National de Santé Publique du Québec and Unité de recherche en santé publique, Centre Hospitalier Universitaire de Québec, Québec, Canada; 4Department of Health Services Research, Texas State University, San Marcos, Texas, USA; 5Department of Health Promotion Research, Southern Denmark University and Department of Public Health, University of Trnava, Slovakia; 6U.S. Geological Survey, Reston, Virginia, USA; 7Washington State Department of Health, Olympia, Washington, USA
Abstract
Human alteration of the nitrogen cycle has resulted in steadily
accumulating nitrate in our water resources. The U.S. maximum
contaminant level and World Health Organization guidelines for nitrate
in drinking water were promulgated to protect infants from developing
methemoglobinemia, an acute condition. Some scientists have recently
suggested that the regulatory limit for nitrate is overly
conservative; however, they have not thoroughly considered chronic
health outcomes. In August 2004, a symposium on drinking-water nitrate
and health was held at the International Society for Environmental
Epidemiology meeting to evaluate nitrate exposures and associated
health effects in relation to the current regulatory limit. The
contribution of drinking-water nitrate toward endogenous formation of
N-nitroso compounds was evaluated with a focus toward identifying
subpopulations with increased rates of nitrosation. Adverse health
effects may be the result of a complex interaction of the amount of
nitrate ingested, the concomitant ingestion of nitrosation cofactors
and precursors, and specific medical conditions that increase
nitrosation. Workshop participants concluded that more experimental
studies are needed and that a particularly fruitful approach may be to
conduct epidemiologic studies among susceptible subgroups with
increased endogenous nitrosation. The few epidemiologic studies that
have evaluated intake of nitrosation precursors and/or nitrosation
inhibitors have observed elevated risks for colon cancer and neural
tube defects associated with drinking-water nitrate concentrations
below the regulatory limit. The role of drinking-water nitrate
exposure as a risk factor for specific cancers, reproductive outcomes,
and other chronic health effects must be studied more thoroughly
before changes to the regulatory level for nitrate in drinking water
can be considered.
Table of Contents
INTRODUCTION
NITRATE LEVELS IN GROUNDWATER AND WATER SUPPLIES
METHEMOGLOBINEMIA
NITRATE INTAKE AND ENDOGENOUS FORMATATION OF N-NITROSO COMPOUNDS
HEALTH EFFECTS ASSOCIATED WITH DRINKING-WATER NITRATE
RECOMMENDATIONS FOR FUTURE RESEARCH
CONCLUSIONS
Report