Nitrates in drinking water and methemoglobin levels in pregnancy: a longitudinal study.

BACKGROUND: Private water systems are more likely to have nitrate levels above the maximum contaminant level (MCL). Pregnant women are considered vulnerable to the effects of exposure to high levels of nitrates in drinking water due to their altered physiological states. The level of methemoglobin in the blood is the biomarker often used in research for assessing exposure to nitrates. The objective of this study was to assess methemoglobin levels and examine how various factors affected methemoglobin levels during pregnancy. We also examined whether differences in water use practices existed among pregnant women based on household drinking water source of private vs. public supply. METHODS: A longitudinal study of 357 pregnant women was conducted. Longitudinal regression models were used to examine changes and predictors of the change in methemoglobin levels over the period of gestation. RESULTS: Pregnant women showed a decrease in methemoglobin levels with increasing gestation although <1% had levels above the physiologic normal of 2% methemoglobin, regardless of the source of their drinking water. The multivariable analyses did not show a statistically significant association between methemoglobin levels and the estimated nitrate intake from tap water among pregnant women around 36 weeks gestation (ß = 0.046, p = 0.986). Four women had tap water nitrate levels above the MCL of 10 mg/L. At enrollment, a greater proportion of women who reported using water treatment devices were private wells users (66%) compared to public system users (46%) (p < 0.0001). Also, a greater proportion of private well users (27%) compared to public system users (13%) were using devices capable of removing nitrate from water (p < 0.0001). CONCLUSION: Pregnant women potentially exposed to nitrate levels primarily below the MCL for drinking water were unlikely to show methemoglobin levels above the physiologic normal. Water use practices such as the use of treatment devices to remove nitrates varied according to water source and should be considered in the assessment of exposure to nitrates in future studies.

A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes.

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.

Hazardous substances events associated with the manufacturing of chemicals and allied products.

This report describes events involving the acute release of hazardous substances reported to the Hazardous Substances Emergency Events Surveillance (HSEES) system for 1993-2000. HSEES, maintained by the Agency for Toxic Substances and Disease Registry (ATSDR), collects data on the industries/services associated with events. This analysis focuses on fixed-facility events that occurred during the manufacturing of chemicals and allied products (i.e. categorized according to the 1990 Industrial Classification System (ICS) of the US Bureau of the Census). This is the most frequently reported industry category in the surveillance system, with over 12000 events (28% of all events and 35% of fixed-facility events). Further classification found that the majority (71%) of these events involved the manufacturing of industrial and miscellaneous chemicals (ICS code 192), and 21% plastics, synthetics, and resins (ICS code 180). A total of 2676 persons reported injuries in 307 fixed-facility events. Most of the injured persons were employees (42%), followed by the general public (38%), students (15%), and responders (5%). Thirty-five percent of all injured persons and 46% of all injured employees had respiratory symptoms. Releases frequently occurred in processing vessels, and the majority was due to equipment failure. A review of the data indicates that manufacturers of chemicals and allied products could help reduce morbidity and mortality by taking preventive actions such as performing regular maintenance of processing equipment, regular training of employees and encouraging them to wear respiratory protection, and educating the public on what to do in the event of a release from these facilities.

A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes.

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 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. 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. 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.

Counterterrorism planning using the Hazardous Substances Events Surveillance system.

The Hazardous Substances Emergency Events Surveillance (HSEES) system was developed in 1990 and is maintained by the Agency for Toxic Substances and Disease Registry, a public health agency within the United States Department of Health and Human Services. HSEES data can be used for hazard vulnerability assessments. Baseline patterns of hazardous substance releases can be used by local emergency planning committees to (1) identify substances that cause serious injuries, (2) improve monitoring and control of access, and (3) assess the preparedness of responding agencies. HSEES is an active surveillance system that can be useful in the early detection of unusual occurrences involving hazardous substances.

A review of nitrates in drinking water: maternal exposure and adverse reproductive and developmental outcomes

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 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. 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. 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.

Nesta revisão, apresentamos um estudo sobre exposição materna aos nitratos na água potável e possíveis reações adversas ao desenvolvimento reprodutivo, no caso dos Estados Unidos. O padrão de uso de nitratos na água potável é baseado em estudos retrospectivos e leva em conta níveis que protegem os bebês contra a metemoglobinemia. Mas nenhum fator de segurança foi construído a partir desse padrão, sendo que os níveis atuais foram construídos e exigidos apenas para os sistemas públicos de distribuição de água. Estudos com animais encontraram efeitos reprodutivos adversos e advindos das altas doses de nitrato ou nitrito na água. A evidência epidemiológica sobre a relação de exposição-resposta direta entre o nível de nitratos na água potável e efeitos adversos não está clara. No entanto, algumas notificações sugerem associação entre exposição a nitratos na água potável e abortos espontâneos, restrições ao crescimento intrauterino e vários defeitos de nascença. As incertezas nos estudos epidemiológicos incluem a falta de avaliação da exposição individual que excluiria confundir a exposição com outros fatores. Concluimos que a literatura atual não provê suficiente evidência de uma relação causal entre exposição a nitratos na água potável e efeitos reprodutivos adversos.