This paper describes the residue analysis of water and hydrosoil samples taken from two separate large-scale aquatic ecotoxicology trials designed to assess the environmental fate and effects of the pyrethroids lambda-cyhalothrin and cypermethrin. Comparison of the results demonstrates the high degree of reproducibility of the chemical residue found the day after treatment using experimental mesocosms (lambda-cyhalothrin) as opposed to an in-use farm pond (cypermethrin). Both studies showed that pyrethroid residues were rapidly lost from the water column: residues of lambda-cyhalothrin were less than 2 ng litre-l following the final application of a cumulative seasonal exposure equivalent to twelve 'drift' and six 'run-off' events, each delivering a dose equivalent to that expected from a typical event under field conditions. Hydrosoil appeared to act as a sink for pyrethroid residues and, under the stringent test conditions of the mesocosm study, lambda-cyhalothrin residues reached 3-2 pg kg-l following the seasonal exposure described above. The cypermethrin farm-pond study illustrated the localised pattern of exposure expected under natural field conditions, with site topography and cultivation practices which represent an average 'worst case'. Residues in hydrosoil reached a maximum level of approximately 25 pug kg-' in one sampling zone at one interval, and thereafter declined to a level of < 9 pg kg-' within four months.
This paper describes the development of methods suitable for the sampling and analysis of the pyrethroid insecticides lambda‐cyhalothrin and cypermethrin in natural waters. A solid‐phase water‐sampling method which avoids the requirement for transport and storage of large volumes of water is described. This method is shown to be capable of extracting trace levels (ng litre−‐1) of the title compounds from natural waters with efficiencies of at least 80%. Chromatographic analysis of processed samples by gas chromatography–electron capture detection enables determination of residues at levels of 1–2 ng litre−‐1 in water.
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