Water Quality
Standards
Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. -Geneva, World Health Organization, 1993. p. 75.
The group of chemicals known as the organotins is composed of a large number of compounds with differing properties and applications. The most widely used of the organotins are the disubstituted compounds, which are employed as stabilizers in plastics, including polyvinyl chloride (PVC) water pipes, and the trisubstituted compounds, which are widely used as biocides.
The disubstituted compounds that may leach from PVC water pipes for a short time after installation are primarily immunotoxins, although they appear to be of low general toxicity. The data available are insufficient to permit the proposal of guideline values for individual dialkyltins.
Tributyltin oxide (TBTO) is widely used as a biocide in wood preservatives and antifouling paints. It is extremely toxic to aquatic life, and its use is being reduced in some countries. There are only limited exposure data; however, exposure from food, except from certain seafood, is unlikely.
TBTO is not genotoxic. One carcinogenicity study has been reported in which neoplastic changes were observed in endocrine organs, but the significance of these changes is considered questionable. The most sensitive end-point appears to be immunotoxicity, with a lowest NOAEL of 0.025 mg/kg of body weight per day in a 17-month feeding study in rats related to suppression of resistance to the nematode Trichinella spiralis. The significance to humans of this finding is not completely clear, but this NOAEL is consistent, within an order of magnitude, with other NOAELs for long-term toxicity.
A TDI of 0.25 µg/kg of body weight was calculated by applying an uncertainty factor of 100 (for inter- and intraspecies variation) to the NOAEL of 0.025 mg/kg of body weight per day for suppression of resistance to T. spiralis. The guideline value for TBTO is 2 µg/litre (rounded figure) based on an allocation of 20% of the TDI to drinking-water.
The database on the toxicity of the other trisubstituted organotin compounds is either limited or rather old. It was therefore not considered appropriate to propose guideline values for these compounds.
