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

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analysis. Mineralisation of organic N will increase the proportion of NO - 3-N whilst denitrification will decrease soil NO - 3-N. Ideally, samples should be analysed as soon as possible after being taken. Samples should be kept refridgerated until they can be dried. They should be air-dried in thin layers (
concentrations of NO - 3-N, dilution of the sample may be necessary to avoid exceeding the separation capacity of the column. Interference from anions in the extraction solution (eg. sulphate) is minimal as long as sufficient separation exists between the NO - 3-N peak and that part of the anion. If cations interfere with nitrate determination, pre-treatment cartridges can be used which remove the cations via ion-exchange. Soluble organic matter may be absorbed onto the column, decreasing its capacity to retain anions. Addition of charcoal in the extraction procedure aids removal of such soluble organics. Whilst ion chromatography can be automated, it tends to be slower than continuous flow instruments, for example the cadmium reduction method. Cadmium reduction method Cadmium reduction procedures are both very sensitive and free from potential interference by soil cations and organic matter. The minimum reproducible concentration of NO - 3-N that could be detected in soil extracts by a manual cadmium reduction procedure was 0.014 mg NO - 3 N l -1 (Dorich and Nelson, 1984). The maximum concentration measured without dilution was 20 mg NO - 3 N l -1 . Compared to manual cadmium reduction, the automated method has the advantage of speed, allowing 20 to 120 sample extracts to be analysed per hour, depending on manufacturer and quality of equipment. Further advantages are good precision and uniformity of flow rate through the reduction column from sample to sample. However, equipment is expensive and the working concentration range for some systems is only 0 to 2 mg NO - 3-N l -1 . For soil extracts containing NO - 3-N concentrations above 2 mg l -1 , extracts must be manually diluted, the size of the sample and diluent lines on the manifold must be adjusted or a predilution loop must be added to the manifold. The working concentration range of newer automated systems has been increased to 0 to 20 mg NO - 3-N l -1 . 7.4 Situation assessment and management action Data generated by routine and frequent analysis of drinking water supplies for nitrate concentrations should be assessed immediately for compliance with the recommended health guideline or maximum allowable concentration. Whenever concentrations in excess of the limit are detected, the sampling and analytical records should be checked first to determine whether the results are due to analytical or reporting error or sample contamination. If no other cause can be found, a genuine change in water quality can be verified by repeat sampling and analysis. If the concentrations are unacceptably high appropriate action should be taken. The action taken depends on the magnitude of the problem, i.e. whether a few or very many people may be affected (see Figure 7.4). If only a few people are affected, the simplest action may be to change their water supply, at least until the source of the increased nitrate can be identified and remedial measures taken that restore the nitrate concentration to an acceptable level for drinking water. People at high risk, such as the elderly or young infants, should also be identified and an alternative source of water provided to them, such as bottled water, until the problem is solved. In the meantime, high risk groups may need to be kept well-informed about the risks and medical surveillance may even need to be put in place (Figure 7.5). Where an alternative water supply cannot be provided to populations at risk, options such as blending the high nitrate supply with purer water (in order to reduce nitrate
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WHO/SDE/WSH/04.08/56 Rolling Revisi
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List of contents Chapter 1 Origin o
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7.3 Soil and organic matter 7.4 Sit
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Table 1.1 Trend in nitrate concentr
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NH4 + + 1.5 O2 --> NO2 - + H2O + 2
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In developed countries, urban groun
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Saharan Africa correlate with popul
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through microbial denitrification a
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Figure 1.7 From overproduction to r
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total emissions is between 0.2 and
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1999 Marker species for identifying
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NEERI 1991 Water Mission Report on
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Chapter 2 Human Exposure and Risk a
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of nitrogen fertiliser or manure. O
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nitrate and nitrite concentrations
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methaemoglobinaemia observed in inf
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2.3.4 Reproductive and development
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Accidental human intoxications have
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of nitrates, nitrites and N-nitroso
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McKnight et al. (1999) suggest that
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nitrate in the etiology of the hype
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Gonzalez, C.A., Sanz, J.M., Marcos,
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Lagerstedt, E., Jacks, G. and Sefe,
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thyroids of rats.] Schrifte für Ge
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Northern China. Agriculture, Ecosys
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top soil ⎫ ⎫ ⎫ ⎪ ⎪ ⎪
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nitrate is not of significance. Den
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Figure. 3.4: Nitrate concentration
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observed in various parts of the wo
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groundwater recharge as a result of
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oxygen, are quickly displaced to gr
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Chapter 4 Treatment and disposal of
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4. Formulation and implementation o
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the sludge. Table 4.3 Permissible a
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sewage quality, higher requirements
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In all types of organic fertilisers
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• 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
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Page 85 and 86: EF = (PW/FKRZ) * 100 Where EF = exc
Page 87 and 88: groundwater zone, due to capillary
Page 89 and 90: This information may help to optimi
Page 91 and 92: Figure 5.7 Potential rate of minera
Page 93 and 94: Figure 5.8 Cumulative NH3 emissions
Page 95 and 96: 5.3.5 Grassland farming Compared wi
Page 97 and 98: In order to calculate the optimum a
Page 99 and 100: 5.5 References Arbeitsgemeinschaft
Page 101 and 102: 21. Belastungen der Oberflächengew
Page 103 and 104: Rejesus, R.M. and Hornbaker, R.H. 1
Page 105 and 106: Chapter 6 Water treatment processes
Page 107 and 108: Nitrate-selective resins also add l
Page 109 and 110: 6.2.2 Heterotrophic denitrification
Page 111 and 112: small reactor volumes and areas. Th
Page 113 and 114: 2. NO - 2 + 2AL + 3H2O → NH3 + 2A
Page 115 and 116: denitrification in cooler climates
Page 117 and 118: Chapter 7 Problem evaluation and ma
Page 119 and 120: inputs from point sources, land run
Page 121 and 122: most commonly used methods for anal
Page 123 and 124: sulphuric acid to 1 litre of sample
Page 125: The nitrite produced is determined
Page 129 and 130: Figure 7.4 Actions required in the
Page 131 and 132: 7.5 References Ballance, R. 1996a P
Page 133: ions. Part 1: Method for water with
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