A banned chemical known commonly as HCH (or alpha-hexachlorohexane) used fifteen years ago in Asia has been detected in significant amounts here in Canada, say U of T scientists.
Researchers in the Department of Chemistry, led by Dr. Frank Wania, discovered this while using a new tracking method to monitor the spread and degradation of chemicals. Dr. Wania and his team established a network of air sampling stations spanning from the Arctic to Central America and from Newfoundland to Vancouver Island. Each station consists of polymer resins (pellets of a lightweight plastic material) that absorb pollutants. The stations detected high concentrations of HCH in the atmosphere of Sable Island off the coast of Nova Scotia and Newfoundland. This banned chemical was last used approximately fifteen years ago in Asian countries, including China and India.
HCH is considered moderately toxic to mammals. The low doses of this chemical detected by Dr. Wania are not harmful, but they do prove the usefulness of Dr. Wania’s new chemical detection system. “Although we are no longer concerned about alpha-HCH itself, it is a good test case that allows us to understand why situations of elevated exposure occur in unexpected places. The network gave us the opportunity to get an idea of the spatial variability of the air concentrations of these contaminants across North America,” said Dr. Wania. These stations also allow researchers to determine whether computer predictions of the long range transport and accumulation behaviour of contaminants are correct.
Dr. Wania and his team concluded that temperature affects the spread and degradation of chemicals. “Temperature plays an important role in the global transport and distribution of a chemical. Warm temperatures enhance evaporation into the atmosphere and speed up degradation, whereas cold temperatures encourage deposition from the atmosphere and retard the degradation of chemicals,” said Dr. Wania. Thus the pesticide in question travelled across natural atmospheric and water flows across the planet until it reached eastern Canada, where it was slowed and finally traped by cold temperatures.
The findings are also significant with regards to the Stockholm Convention, part of the UN Environmental Programme’s global protocol for the regulation of persistent organic pollutants. This protocol applies to twelve substances that are toxic, accumulate in tissue, and can travel long distances; the protocol can be applied to other chemicals that have this combination of properties. “We hope that our work can contribute to establishing whether a chemical has long range transport potential or not. This method is a relatively cheap tool to monitor the effectiveness of the Stockholm Convention – to check whether the chemicals are indeed no longer used and whether the concentrations are decreasing as a result.”
