Priority Substances List Assessment Report for Non-pesticidal organotin compounds

Synopsis

Non- pesticidal organotin compounds (notably mono- and di- methyltin, butyltin, and octyltin compounds) are not manufactured in Canada. They are imported, however, mainly for use as poly(vinyl chloride) (PVC) stabilizers and are also used as industrial catalysts. Data identified for 1984 indicate that approximately 290 tonnes of methyltin compounds, 1020 tonnes of butyltin compounds, and a much smaller quantity of octyltin compounds were imported to Canada. More recent data have not been identified.

Based on limited fate information, non-pesticidal organotin compounds are expected to exist predominantly in the aquatic environment. The mono- and di- alkyltin compounds are water-soluble and are not expected to volatilize from water in significant quantities. They undergo biodegradation and photolysis in water and are not expected to persist for long periods. Mono- and di- methyltin and mono- and di- butyltin have been detected in water and sediment at several locations in Canada. However, the sources of these compounds to the environment are uncertain. The methyltin compounds may have resulted from the natural methylation of tin or from anthropogenic sources. The butyltin compounds were primarily degradation products of the pesticide tributyltin, the antifouling use of which has been regulated in Canada since 1989. Leaching of organotin-stabilized PVC pipe by water could also be a source of organotin entry into the Canadian environment.

The assessment of effects on the environment focused on aquatic biota since they are the most likely to be exposed to non-pesticidal organotin compounds. There is limited information on the toxicity of most of these compounds to organisms in both the freshwater and marine environments. Nonetheless, it was possible to compare estimated effects thresholds to environmental concentrations for the mono- and di- methyltin and mono- and di- butyltin compounds. None of the effects thresholds was exceeded by environmental concentrations found in areas where contamination was suspected, indicating that these compounds are unlikely to cause harmful effects to freshwater or marine biota in Canada. Exposure to mono-and dioctyltin compounds is unlikely since they have not been found in Canada or elsewhere in any environmental medium. Although toxicity data for the octyltin compounds are lacking, it is unlikely that they would cause harmful effects to aquatic biota.

The non-pesticidal organotin compounds that were assessed are not volatile and are not expected to contribute to phenomena such as ozone depletion, global warming, or the formation of ground-level ozone.

Available data are insufficient to serve as a basis for estimation of the exposure of the general population to any of the non-pesticidal organotin compounds. Available data on the toxicity of these compounds in experimental animals and humans are also limited.

Based on these considerations, the Minister of the Environment and the Minister of National Health and Welfare have concluded that non-pesticidal organotin compounds do not constitute a danger in Canada to the environment or to the environment on which human life depends. Therefore, non-pesticidal organotin compounds are not considered to be "toxic" as defined under Paragraphs 11(a) and 11(b) of the Canadian Environmental Protection Act (CEPA). However, the Ministers have concluded that it is not possible to assess whether any of the non-pesticidal organotin compounds constitutes a danger in Canada to human life or health as defined under Paragraph 11(c) of CEPA.