Water Quality Standards

Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. - Geneva, World Health Organization, 1993. pp. 65-66.

Xylenes are used in blending petrol, as a solvent, and as a chemical intermediate. They are released to the environment largely via air.

Concentrations of up to 8 µg/litre have been reported in surface water, ground water, and drinking-water. Levels of a few milligrams per litre were found in ground water polluted by point emissions. Exposure to xylenes is mainly from air, and exposure is increased by smoking.

Xylenes are rapidly absorbed by inhalation. Data on oral exposure are lacking. Xylenes are rapidly distributed in the body, predominantly in adipose tissue. They are almost completely metabolized and excreted in urine.

The acute oral toxicity of xylenes is low. No convincing evidence for teratogenicity has been found. Long-term carcinogenicity studies have shown no evidence for carcinogenicity. In vitro as well as in vivo mutagenicity tests have proved negative.

A TDI of 179 µg/kg of body weight was derived using a NOAEL of 250 mg/kg of body weight per day based on decreased body weight in a 103-week gavage study in rats (administration 5 days per week), applying an uncertainty factor of 1000 (100 for intra- and interspecies variation and 10 for the limited toxicological end-point). This yields a guideline value of 500 µg/litre (rounded figure), allocating 10% of the TDI to drinking-water. This value exceeds the lowest reported odour threshold for xylenes in drinking-water (see Acceptability aspects).