Rolling Revision of the WHO Guidelines for Drinking-Water Quality ...

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Methaemoglobinaemia is a rare condition which can have several causes. Certain chemicals such as perchlorates, sulphonamides, aniline dyes (Adam, 1980., in Terblanche, 1991) can convert Hb to metHb. Inherited metabolic deficiencies of, for example, NADH diaphorase (Kumar et al., 1989) can also induce formation of metHb. The toxicity of nitrate to humans is mainly attributable to its reduction to nitrite. The major biological effect of nitrite in humans is its involvement in the oxidation of normal Hb to metHb, which is unable to transport oxygen to the tissues. The normal metHb level in humans is less than 2%, and less than 3% in infants under three months of age. At a metHb concentration of 5% of normal Hb no external signs or symptoms are generally noted. The reduced oxygen transport becomes clinically manifest when the metHb concentration is between 5 and 10% (Knotek and Schmidt, 1964). Hypoxic signs and symptoms may develop at about 20%, while death results at 50% metHb or higher (Shuval and Gruener, 1977). The Hb of young infants is more susceptible to metHb formation than that of older children and adults. This higher susceptibility is believed to be the result of the large proportion of foetal Hb still present in the blood of infants. Foetal Hb is more easily oxidised to metHb. In addition, there is a deficiency in the metHb reductase responsible for the reduction of metHb back to Hb. The net result is that a dose of nitrite causes a higher metHb formation in young infants than in adults. Young infants are also more at risk from exposure to nitrate because of a relatively high intake of nitrate and, under certain conditions, a higher reduction of nitrate to nitrite by gastric bacteria due to the low production of gastric acid (Speijers et al., 1989; WHO, 1996). The higher reduction of nitrate to nitrite in young infants is not well understood, but it appears that gastrointestinal infections increase the risk of higher yield of nitrite and thus a higher metHb formation (ECETOC, 1988; Speijers et al., 1989; Möller, 1995; Schuddeboom, 1955; WHO, 1996). Other groups particularly susceptible to metHb formation include pregnant women and people deficient in glucose-6-phosphate dehydrogenase or metHb reductase (Speijers et al., 1989). Adults and children above the age of three months Clinical cases of adult methaemoglobinaemia due to consumption of nitrate contaminated water have never been reported (Bruningfann and Kaneene, 1993). This is attributed to lower gastric acidity which inhibits nitrate-reducing bacteria and greater enzyme activity resulting in faster transformation of metHb to Hb. However, cases of methaemoglobinaemia have been reported in adults consuming high doses of nitrate by accident or as a medical treatment. Fatalities have been reported after single intakes of 4-50 g of nitrate (equivalent to 67-833 mg of nitrate per kg of body weight) (Speijers et al., 1989; WHO, 1996). Many of these occurred among special risk groups in whose members gastric acidity was reduced. Toxic doses (with metHb formation as a criterion for toxicity) ranged from 2-9 g (equivalent to 33-150 mg of nitrate perkg of body weight) (WHO, 1996). In a controlled study, an oral dose of 7- 10.5 g of ammonium nitrate and an intravenous dose of 9.5 g of sodium nitrate did not cause increased metHb levels in adults, although vomiting and diarrhoea occurred (Speijers et al., 1989; WHO, 1996).
Accidental human intoxications have been reported as a result of the presence of nitrite in food. The oral lethal dose for humans was estimated to range from 33-250 mg of nitrite per kg of body weight, the lower doses applying to children and elderly people. Toxic doses giving rise to methaemoglobinaemia ranged from 0.4-200 mg kg – 1 of body weight (WHO, 1996). Another source of information with respect to nitrite toxicity in humans is the use of sodium nitrite as a medication for vasodilation or as an antidote in cyanide poisoning. Doses of 30 - 300 mg per person (equivalent to 0.5-5 mg kg –1 of body weight) were reported not to cause toxic effects (WHO, 1996). Few cases of methaemoglobinaemia have been reported in older children. A correlation study among children aged one to eight years in the USA showed that there was no difference in metHb levels between 64 children consuming high-nitrate well water (22-111 mg of nitrate-nitrogen per litre) and 38 children consuming lownitrate water (
Page 1 and 2: WHO/SDE/WSH/04.08/56 Rolling Revisi
Page 3 and 4: List of contents Chapter 1 Origin o
Page 5 and 6: 7.3 Soil and organic matter 7.4 Sit
Page 7 and 8: Table 1.1 Trend in nitrate concentr
Page 9 and 10: NH4 + + 1.5 O2 --> NO2 - + H2O + 2
Page 11 and 12: In developed countries, urban groun
Page 13 and 14: Saharan Africa correlate with popul
Page 15 and 16: through microbial denitrification a
Page 17 and 18: Figure 1.7 From overproduction to r
Page 19 and 20: total emissions is between 0.2 and
Page 21 and 22: 1999 Marker species for identifying
Page 23 and 24: NEERI 1991 Water Mission Report on
Page 25 and 26: Chapter 2 Human Exposure and Risk a
Page 27 and 28: of nitrogen fertiliser or manure. O
Page 29 and 30: nitrate and nitrite concentrations
Page 31 and 32: methaemoglobinaemia observed in inf
Page 33: 2.3.4 Reproductive and development
Page 37 and 38: of nitrates, nitrites and N-nitroso
Page 39 and 40: McKnight et al. (1999) suggest that
Page 41 and 42: nitrate in the etiology of the hype
Page 43 and 44: Gonzalez, C.A., Sanz, J.M., Marcos,
Page 45 and 46: Lagerstedt, E., Jacks, G. and Sefe,
Page 47 and 48: thyroids of rats.] Schrifte für Ge
Page 49 and 50: Northern China. Agriculture, Ecosys
Page 51 and 52: top soil ⎫ ⎫ ⎫ ⎪ ⎪ ⎪
Page 53 and 54: nitrate is not of significance. Den
Page 55 and 56: Figure. 3.4: Nitrate concentration
Page 57 and 58: observed in various parts of the wo
Page 59 and 60: groundwater recharge as a result of
Page 61 and 62: oxygen, are quickly displaced to gr
Page 63 and 64: Chapter 4 Treatment and disposal of
Page 65 and 66: 4. Formulation and implementation o
Page 67 and 68: the sludge. Table 4.3 Permissible a
Page 69 and 70: sewage quality, higher requirements
Page 71 and 72: In all types of organic fertilisers
Page 73 and 74: • Use of maintenance-free enginee
Page 75 and 76: (Chan and Guterstam, 1996). Constru
Page 77 and 78: Staatsministeriums für Landesentwi
Page 79 and 80: und Grundwasserbeschaffenheit bei n
Page 81 and 82: Figure 5.1 Calculation of the nitro
Page 83 and 84: in an accumulation of organic nitro
Page 85 and 86:
EF = (PW/FKRZ) * 100 Where EF = exc
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groundwater zone, due to capillary
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This information may help to optimi
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Figure 5.7 Potential rate of minera
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Figure 5.8 Cumulative NH3 emissions
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5.3.5 Grassland farming Compared wi
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In order to calculate the optimum a
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5.5 References Arbeitsgemeinschaft
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21. Belastungen der Oberflächengew
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Rejesus, R.M. and Hornbaker, R.H. 1
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Chapter 6 Water treatment processes
Page 107 and 108:
Nitrate-selective resins also add l
Page 109 and 110:
6.2.2 Heterotrophic denitrification
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small reactor volumes and areas. Th
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2. NO - 2 + 2AL + 3H2O → NH3 + 2A
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denitrification in cooler climates
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Chapter 7 Problem evaluation and ma
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inputs from point sources, land run
Page 121 and 122:
most commonly used methods for anal
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sulphuric acid to 1 litre of sample
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The nitrite produced is determined
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concentrations of NO - 3-N, dilutio
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Figure 7.4 Actions required in the
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7.5 References Ballance, R. 1996a P
Page 133:
ions. Part 1: Method for water with
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