Fluxes of HCH isomersα- andγ-HCH dynamics were determined in four industrial U.K. rivers feeding the North Sea, Sampling was conducted weekly basis over a 2-year period. This was complemented by discrete studies of events where two hourlysampling periods were used to investigate the fine time scale dynamics of fluxes. Two intensively industrialized rivers had average isomer concentrations of ~20 ng L{sup}-1 for both isomers, while average concentrations in the two less industrializedrivers ranged between 1.5 and 5.0 ng L{sup}-1. α-HCH concentrations showed no strong temporal patterns on any river, which contrasts withγ-HCH levels that increased considerably during late summer/early autumn following sustained periods of low riverflow. Sampling during high river flow events on rivers with differing HCH pollution histories both showed the same dynamics in HCH isomer concentrations.γ-HCH concentrations decreased 4-fold during events whileα-HCH concentrations stayed constant. Theincreases inγ-HCH concentrations under low flow conditions and the rapid dilution of this isomer during events indicate thatγ-HCH has current inputs to these river systems. It was calculated that these four rivers export 30.8 kg yr{sup}-1 ofγ-HCH and14.8kg yr{sup}-1 ofα-HCH to the North Sea.
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