Water Quality Standards

Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. - Geneva, World Health Organization, 1993. pp. 69-70.

The dichlorobenzenes (DCBs) are widely used in industry and in domestic products such as odour-masking agents, chemical dyestuffs, and pesticides. Sources of human exposure are predominantly air and food.

1,2-Dichlorobenzene

1,2-DCB is of low acute toxicity by the oral route of exposure. Oral exposure to high doses of 1,2-DCB affects mainly the liver and kidneys. The balance of evidence suggests that 1,2-DCB is not genotoxic, and there is no evidence for its carcinogenicity in rodents.

A TDI of 429 µg/kg of body weight was calculated for 1,2-DCB by applying an uncertainty factor of 100 (for inter- and intraspecies variation) to a NOAEL of 60 mg/kg of body weight per day for tubular degeneration of the kidney identified in a 2-year mouse gavage study with administration 5 days per week. This gives a guideline value of 1000 µg/litre (rounded figure) based on an allocation of 10% of the TDI to drinking-water. This value far exceeds the lowest reported taste threshold of 1,2-DCB in water (see Acceptability aspects).

1,3-Dichlorobenzene

There are insufficient toxicological data on this compound to permit a guideline value to be proposed, but it should be noted that it is rarely found in drinking-water.

1,4-Dichlorobenzene

1,4-DCB is of low acute toxicity, but there is evidence that it increases the incidence of renal tumours in rats and of hepatocellular adenomas and carcinomas in mice after long-term exposure. IARC has placed 1,4-DCB in Group 2B.

1,4-DCB is not considered to be genotoxic, and the relevance for humans of the tumours observed in animals is doubtful. It is therefore valid to calculate a guideline value using the TDI approach. A TDI of 107 µg/kg of body weight was calculated by applying an uncertainty factor of 1000 (100 for inter- and intraspecies variation and 10 because a LOAEL was used instead of a NOAEL and because the toxic end-point is carcinogenicity) to a LOAEL of 150 mg/kg of body weight per day for kidney effects identified in a 2-year rat study (administration 5 days per week). A guideline value of 300 µg/litre (rounded figure) is proposed based on an allocation of 10% of the TDI to drinking-water. This value far exceeds the lowest reported odour threshold of 1,4-DCB in water (see Acceptability aspects).