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Public water supplies are routinely monitored for nitrate levels, and whenever these supplies exceed the nitrate standard, public notification via broadcast and print media is required. The current drinking water standard and health advisory level of 10 mg/L NO₃⁻ N (equivalent to 10 parts per million NO₃⁻-N or 45 parts per million NO₃⁻ ) is based only on the non cancer health effects related to infantile methemoglobinemia (Kross et al.,1993). Concentrations over 3 mg/L nitrate nitrogen are usually considered indicative of anthropogenic pollution (Madison& Brunett, 1985, Kross et al.,1993).

The presence of nitrogen in the form of nitrates indicates older events of pollution and does not represent an immediate threat(Karavoltsosa, et al.,2008). SO₄²⁻ and NO₃⁻ together represent the major ionic derivatives of industrial and traffic emissions(Evans et al.,2006).

Much of adults' nitrate intake may come from their diet, particularly green vegetables. With children, water intake is proportionately much more important, and often the dominant input ( Kross et al.,1993).

The drinking water standard for nitrate was set primarily to prevent infant cyanosis, or methemoglobinemia (blue baby syndrome), a temporary blood disorder that reduces the ability of an infant's bloodstream to carry oxygen through the body which could have long-term developmental or neurological effects. (Kross et al.,1993). Infants younger than 6 months are particularly sensitive to nitrate-induced methemoglobinemia because of many reasons: (1) they have a low capacity to reduce MetHb back to normal Hb (WHO, 1998); (2) they consume more water relative to their body weight than adults (US EPA, 1991), and thus have a higher relative exposure to nitrate when drinking formula or other drinks made with contaminated water; (3) a large proportion of Hb in infants is in the form of fet al., Hb, which is more readily oxidized to MetHb than adult Hb (WHO, 1998); (4) the gastric environment in infants is more alkaline than in adults, providing optimal conditions for growth of bacteria that promote MetHb formation (WHO, 1996); and (5) gastroenteritis with vomiting and diarrhea, which is more common in infants than adults, enhances conditions for MetHb formation (ECETOC, 1988; Wright et al., 1999). (Sadeq et al.,2007). If excess nitrate concentration is determined, the well water should not be used in preparing infant formula or otherwise consumed by infants, particularly those less than 6 months of age ( Kross et al.,1993).

Two cross-sectional studies were carried out in Sale´ , Morocco to determine the prevalence of methemoglobinemia among 411 infants and children aged 1–7 years in two adjacent areas that were similar in terms of the air quality, available vegetables and medicines but different in terms of the drinking water quality (nitrate contaminated well water versus municipal water). The prevalence of methemoglobinemia among study children was 36.2% in the exposed area, and 27.4% in the non-exposed area ( Sadeq, et al., 2007).

Some evidence exists from epidemiological studies that high nitrate ingestion is involved in the etiology of human cancer. High nitrate levels in groundwater have been associated with increased rates of non-Hodglin's lymphoma in a Nebraska study. Boiling of water contaminated with nitrate is not effective and, in fact, actually increases the concentration of nitrate because of evaporation(Kross et al.,1993).

References:

Evans, C., Coombes, P. and Dunstan, R. (2006): Wind, rain and bacteria: The effect of weather on the microbial composition of roof-harvested rainwater. Water Research 40, 37-44.



Kross, B., Hallberg, G., Bruner, R., Cherryholmes, K. and Johnson, J. (1993): The Nitrate Contamination of Private Well Water in Iowa. American Journal of Public Health,(83), 270-272.

Madison, R.J., Brunett, J.O.(1985): Overview of the occurrence of nitrate in ground water of the United States. In: National Water Summary 1984. Reston, Va: US Geological Survey; 1985:93-105. Water-Supply Paper2275.



Sadeqa, M., Moeb, C., Attarassic, B., Cherkaouid, I., ElAouada, R.,and Idrissia, L.(2007): Drinking water nitrate and prevalence of methemoglobinemia among infants and children aged 1–7 years in Moroccan areas.Int. J. Hyg. Environ. Health ] (]]]]) ]]]–]]]





World Health Organization (WHO) (1984): Guidelines for Drinking Water Quality, Health Criteria andOther Supporting Information. Vol. 2. Geneva: WHO.



World Health Organization (WHO) (1986):Information and Training for Low-Cost Water Supply andSanitation-Wells and Hand Pumps. Washington DC, USA: WHO.



World Health Organization (WHO) (1996): Guidelines for Drinking Water Quality: Health Criteria and Other Supporting Information. Vol 2. Geneva: WHO.



World Health Organization (WHO) (1997): Guidelines for Drinking Water Quality: Surveillance and Control of Community Supply. 2nd edn. Vol. 2. Geneva: WHO.



World Health Organization(2004):Guidelines for Drinking-water Quality. Third Edition,ISBN,Geneva.



World Health Organization(2004): Guidelines for Drinking-water Quality.Vol.1: 3 rd ed. Printed in China by Sun Fung.

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