The application of the EXAMS model to estimate the likely distribution of the steroid oestrogens, 17 beta-oestradiol, oestrone and ethinyl-oestradiol in the Rivers Thames, Calder and Aire, U.K, is described. The model uses parameters estimated from laboratory measurements using material collected from each of the three rivers or from the literature. Total concentrations in the water column were predicted to be similar for 17 beta-oestradiol and oestrone and an order of magnitude less for ethinyl-oestradiol, reflecting the difference in the sewage input loads of the chemicals used in the models. Concentrations under average conditions were predicted to (a) be found mainly in the dissolved phase and (b) to vary between 0.21 and 0.37 ng l(-1) for 17 beta-oestradiol, 0.27 and 0.44 ng Tl for oestrone and 0.024 and 0.038 ng l(-1) For ethinyl-oestradiol. Under low-flow conditions,. predicted concentrations increased by a factor of 4 to 10 times the average concentrations at the point of discharge. Predicted degradation processes in the water column were only significant under low-flow conditions and volatilization was negligible. A simple assessment of the model sensitivity to selected parameters identified those that were most significant in determining the distribution of the chemicals. (C) 1999 Elsevier Science Ltd. All rights reserved.
