Trends in agricultural pesticide (atrazine, lindane, simazine) concentrations in the Thames Estuary

Trends in the concentrations of atrazine, lindane and simazine in the estuary of the River Thames between 1988 and 1997 were examined using linear regression methods to determine whether attempted reductions in pesticide discharges had improved estuarine water quality. Concentrations of all the studied pesticides declined over the period, despite the influences of drought induced reductions in freshwater flow from the Thames catchment. Measures to control pesticide discharges resulted in dramatic reductions (>90%) of the triazines atrazine and simazine, and a 73% reduction in lindane. Achieved reductions in the Thames compare favourably with those recorded for the Humber Estuary. Measured concentrations in the Thames Estuary are now similar to those found in other UK and European estuaries, suggesting that the Thames Estuary is no longer of special concern. Although worries have been expressed about possible long-term exposure effects on estuarine fauna of sublethal levels of the studied pesticides, current measured concentrations are below literature-reported chronic threshold values. Current levels, therefore, do not appear to pose significant ecotoxicological risks to exposed estuarine biota.