Trends and seasonality in α- and γ-hexachlorocyclohexane in western Canadian surface waters (1975–94)

Surface water monitoring results (1975–94) for α-hexachlorocyclohexane (α-HCH) and γ-hexachlorocyclohexane (γ-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 the prairie provinces, including agricultural and non-agricultural areas. Decreasing trends in α-HCH concentration and detection frequency were found at all sites, likely related to decreased use of technical HCH world-wide. Inter-site α-HCH detection frequency was comparable and intra-site seasonal variability was minimal at agricultural and non-agricultural locations, providing evidence of long-range atmospheric transport. γ-HCH concentration and detection frequency did not change significantly during the study period at most sites, consistent with relatively static use patterns in western Canada. γ-HCH detection frequency was higher, and seasonality more pronounced, at agricultural sites than at non-agricultural sites, suggesting that γ-HCH present in prairie surface waters was related to regional, rather than global, use of lindane.