Temporal and spatial patterns in alpha- and gamma-hexachlorocyclohexane concentrations in industrially contaminated rivers

Fluxes of HCH isomers alpha- and gamma-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 hourly sampling periods were used to investigate the fine time scale dynamics of fluxes. Two intensively industrialized rivers had average isomer concentrations of similar to 20 ng L-1 for both isomers, while average concentrations in the two less industrialized rivers ranged between 1.5 and 5.0 ng L-1. alpha-HCH concentrations showed no strong temporal patterns on any river, which contrasts with gamma-HCH levels that increased considerably during late summer/early autumn following sustained periods of low river flow. Sampling during high river flow events on rivers with differing HCH pollution histories both showed the same dynamics in HCH isomer concentrations. gamma-HCH concentrations decreased 4-fold during events while alpha-HCH concentrations stayed constant. The increases in gamma-HCH concentrations under low flow conditions and the rapid dilution of this isomer during events indicate that gamma-HCH has current inputs to these river systems. It was calculated that these four rivers export 30.8 kg yr(-1) of gamma-HCH and 14.8 kg yr(-1) of alpha-HCH to the North Sea.