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Drinking-Water Nitrate and Health--Recent Findings and Research Needs

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

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