Footnotes

5.1.1 Disinfectants

Table 1. Intake reference values for disinfectants

1: There is no guideline value for chlorine dioxide because it breaks down rapidly and because the provisional guideline value for its major breakdown product, chlorite, is adequately protective.

5.1.2 Chlorine by-products

Table 2. Intake reference values for chlorine by-products

1: The drinking water guidelines for the four trihalomethanes (THMs) are 200 µg/litre for chloroform, 60 µg/litre for bromodichloromethane (BDCM) and 100µg/litre for both dibromochloromethane (DBCM) and for bromoform. However, the WHO advises that trihalomethanes be taken as a group, which is why national standards are normally set as total THMs. The WHO recommends that the sum of the ratio of the concentration of each trihalomethane to its respective guideline value should not exceed 1.

2: For some carcinogens, the guideline value is the concentration in drinking-water associated with an upper-bound excess lifetime cancer risk of 10-5 (one additional cancer per 100 000 of the population ingesting drinking water containing the substance at the guideline value for 70 years), computed from laboratory animal data by using a theoretical mathematical model.

3: The haloacetic acids are dominated by the chlorinated acids and the WHO has recommended guideline values of 40 µg/litre for dichloroacetic acid (DCA) and 200 µg/litre for trichloroacetic acid (TCA). The calculated guideline value for DCA is below the level that can be achieved through practical treatment methods or source control and disinfection is likely to result in the guideline value being exceeded.

4: Guideline value not reviewed in 3rd edition of guidelines. Under review, new data indicate probable significant increase in guideline value.

5: WHO has recently reviewed the 1993 guideline values for dichloroacetonitrile (DCAN) and dibromoacetonitrile (DBAN). In the case of dichloroacetonitrile (DCAN) there is evidence of a potential hazard, but the available information on health effect is limited. No TDI can be established for trichloroacetonitrile (TCAN), because available data is inadequate.

6: Because MX occurs at concentrations well below those at which toxic effects are observed and because it is difficult to measure at low concentrations, no guideline values have been established.

5.1.3 Chlorine dioxide by-products

Table 3. Intake reference values for chlorine dioxide by-products

1: The Tolerable Daily Intake (TDI) for chlorite and for chlorate has translated into a provisional drinking water guideline value, which is likely to be exceeded by disinfection.

5.1.4 Ozonation by-products

Table 4. Intake reference values for ozonation by-products

1: At present there are conflicting data regarding the exact mechanism by which bromate causes cancer in laboratory animals and how that would impact on risk assessment. The WHO has developed a drinking water guideline value of 10 µg/litre based on two approaches and taking into account the practicality of using ozone. Where bromide is present in the raw water, the guideline value can only be achieved by appropriate control of disinfection conditions.

Water Disinfectants & disinfectant by-products

Footnotes