The application of models to predict the behaviour of chemicals in the aquatic environment will assume increasing importance as the sophistication of river pollution management increases. A field validation of a model which enables such predictions, the US EPA EXAMS II model, is reported. The study was carried out on a stretch of a UK lowland river, the River Calder in West Yorkshire, and utilised a sewage treatment works (STW) effluent discharge as a point source of the two chemicals, aniline and lindane, modelled. Concentrations of aniline and lindane were measured in samples of water, suspended particulates and sediments taken from the river and STW effluent and the measured results compared with those predicted by the EXAMS model. Good agreements were generally obtained between the model predictions and the measured values for the water and bed sediment, but the levels measured in the suspended particulates were significantly higher than those predicted. The most likely explanation for this discrepancy was that the equilibrium partitioning approach employed by EXAMS was inappropriate for the suspended particulate associated chemicals. However, since the majority (>>95%) of both aniline and lindane in the water column was in the dissolved phase, this was not a significant drawback to the use of EXAMS for the prediction of fate and behaviour.
