While snails undergo involuntary sex changes, the government dithers, forgetting about the precautionary principle and human health.
by Delores Broten
Tributyl tin (TBT), a substance still commonly painted on the hulls of large ships to repel barnacles and weeds, although banned for non-aluminium small boats, should be fast-tracked for virtual elimination by the Canadian government, says the World Wildlife Fund.
TBT is a highly persistent pesticide that accumulates in the food chain and disrupts the endocrine system of wildlife species. Research shows that in humans, organotins like TBT can disrupt the function of cells that fight infection. A US study this year identified significant levels of organotins in random blood samples.
TBT is toxic to fish, shellfish and plants at concentrations in the parts per billion to parts per trillion range. The Canadian Council of Ministers of the Environment Water Quality Guideline for TBT is 1 part per trillion for marine environments but this guideline has no legal force. TBT kills shellfish larvae at less than one part per billion, and causes oyster shell deformities such as "chambering, thickening and balling," according to Environment Canada.
Female snails in Atlantic Canada and throughout the Strait of Georgia suffer from "imposex," the development of male sex organs. A 1994 survey found 100% imposex in some species at Mission Creek on the Sunshine Coast, Parksville, Campbell River, Bold Point and Granite Bay on Quadra Island, as well as some deformity at other sites. This effect has been well known in southern France and England since the 1970s.
Until 1987, TBT was also used as an anti-fouling agent on farmed salmon net cages. Assorted related organotins are also used as stabilizers in PVC, industrial cooling water slimicides, anti-mould agents in paints, and wood preservatives.
Ten years ago, an international ban on the use of TBT for small boats under 25 metres reduced the flow of TBT to the marine environment, but TBT contamination in major harbors has not declined.
Marine mammals such as dolphins and beluga whales are contaminated with TBT on both the Atlantic and Pacific coasts.
High levels of TBT are found in the sediment of Canada's major marine and freshwater harbours and shipyards, from Vancouver to Halifax. Levels in Vancouver's Burrard Inlet are the second highest on record worldwide. Sediments in small craft harbours, now devolved to community control, remain contaminated.
TBT is found in sewage sludge in Winnipeg, Toronto and Hamilton, possibly leaching from PVC plastic pipe.
The International Maritime Organization (IMO) wants a voluntary global phase out of TBT anti-fouling paints, but there will be no effective action until 2003 or later. The IMO says alternatives to TBT paint include copper-based coatings and silicon-based paints, which make the surface of the ship slippery so that sea life will be easily washed off. Underwater cleaning systems would avoid having to put the ship into dry dock for cleaning the hull, while ultrasonic or electrolytic devices may also work.
Many pesticides, including TBT, have been on the Canadian market for decades without reevaluation. WWF is calling for amendments to Canada's 30-year-old pesticide law.
* Sources: "Tributyl Tin: The Case for Virtual Elimination in Canada" (WWF) 1999; IMO News/Internet June 1999; "Fact Sheet: Organotin Compounds in the Aquatic Environment of British Columbia," Environment Canada 1996; "Neogastropad Imposex for Monitoring Recovery from Marine TBT Contaminaton," Tester et al, Environmental Toxicology and Chemistry, pp. 560-67, 1996.