Trends and seasonality in alpha- and gamma-hexachlorocyclohexane in western Canadian surface waters (1975-94)

Surface water monitoring results (1975-94) for alpha-hexachlorocyclohexane (alpha-HCH) and gamma-hexachlorocyclohexane (gamma-HCH, lindane) from nine sites in the Canadian prairie provinces were examined for long-term trends and seasonality. The monitoring sites represented four major ecozones of th e prairie provinces, including agricultural and non-agricultural areas. Dec reasing trends in alpha-HCH concentration and detection frequency were foun d at all sites, likely related to decreased use of technical HCH world-wide . Inter-site alpha-HCH detection frequency was comparable and intra-site se asonal variability was minimal at agricultural and nonagricultural location s, providing evidence of long-range atmospheric transport. gamma-HCH concen tration and detection frequency did not change significantly during the stu dy period at most sites, consistent with relatively static use patterns in western Canada. gamma-HCH detection frequency was higher, and seasonality m ore pronounced, at agricultural sites than at non-agricultural sites, sugge sting that gamma-HCH present in prairie surface waters was related to regio nal, rather than global, use of lindane. (C) 1998 Elsevier Science Ltd. All rights reserved.