Occurrence and mobility of the insecticide permethrin in rivers in the Southern Humber catchment, UK

The synthetic pyrethroid insecticides cis- and trans-permethrin are widely used, particularly in sheep-dips and for mothproofing within the textile industry. This study aims to establish the concentrations and mobility of permethrin within rivers in the Humber catchment, which contain some of the highest densities of wool-scouring activity in the world. Our approach was to utilise three different surveys: (a) weekly and storm-responsive sampling of 'whole waters' in the rivers Aire, Ouse, Don, Trent and Calder; (b) intensive sampling of 'whole waters' and suspended sediments in the rivers Aire (0.5h) and Calder (1h); (c) a bed-sediment survey of the River Calder. Sediments were extracted by supercritical fluid extraction and all samples were analysed by gas chromatography with mass spectrometry, Results demonstrated the presence of permethrin in 'whole waters' and sediments, particularly in the rivers Aire and Calder, and at concentrations in the bed-sediment likely to cause ecotoxicological effects to benthic macro-invertebrates. Mass-balance calculations indicated some loss of permethrin from the water column during transport, with the greatest losses at low river-discharge. Isomer ratios (trans:cis) give retention times of permethrin in different components of the system as 'whole water' < suspended sediments <bed-sediments, with estimates of 4-26 days for suspended sediments and a maximum of 103-125 days for surface bed-sediments. (C) 2000 Society of Chemical Industry.