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 in dustry. This study aims to establish the concentrations and mobility of per methrin within rivers in the Humber catchment, which contain some of the hi ghest 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) inte nsive 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. Sed iments were extracted by supercritical fluid extraction and all samples wer e analysed by gas chromatography with mass spectrometry, Results demonstrated the presence of permethrin in 'whole waters' and sedim ents, 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 riv er-discharge. Isomer ratios (trans:cis) give retention times of permethrin in different components of the system as 'whole water' < suspended sediment s <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 Che mical Industry.