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HCHs are a family of manmade organic compounds - there are no natural sources. Emissons of HCHs occur through its manufacture, use, storage and transport. They are persistent organochlorine pollutants. Elevated levels of γ-HCH detected in the atmosphere over the Canadian Prairies are consistent with the continuing use of lindane as a seed treatment. However, atmospheric concentrations of α-HCH show a uniform distribution across the continent - because α-HCH is no longer used in North America, there are no primary source `hot spots', and it has become more evenly spread through the atmosphere. Particularly high concentrations of α-HCH, however, were found in Atlantic Canada, the area of North America furthest removed from Asian source regions (China and India, as well as the Soviet Union were among the major users of α-HCH before it was banned). While it was in use, α-HCH was dispersed worldwide by atmospheric and oceanic circulation. Although, once emissions ceased, it was rapidly lost from other oceans through degradation and evaporation, α-HCH was preserved in the Arctic Ocean because low temperatures and ice cover greatly reduced the loss processes. Now, as outflow from the Arctic moves south (as the Labrador Current) along the east coast of Canada, α-HCH evaporates from these waters. The evaporation rate increases as the waters move south and temperatures rise, resulting in the high atmospheric concentrations observed at Newfoundland and Sable Island. |