An extensive study on the presence of nine organotin compounds (OTs) in a freshwater foodweb was made, using newly developed analytical procedures in order to obtain insight in accumulation and degradation processes. Tributyltin (TBT), Triphenyltin (TPT) and their degradation products were detected. Zebra mussels, eel, roach, bream, pike, perch, and pike perch and cormorant showed high OT body concentrations. At the lower trophic levels, phenyltin concentrations were higher in benthic species while butyltin concentrations were higher in pelagic species. This indicates that TBT is passed on primarily via the water, while TPT is passed on to a larger extent via the sediment. At the higher trophic levels, net bioaccumulation of TPT was greater than that of TBT, resulting in relatively higher TPT concentrations. High concentrations of biodegradation products of TBT, but not of TPT, were found in the livers of fish and birds, which indicates that TBT is more easily metabolized than TPT. A comparison with literature data of fish lethal body concentrations revealed that fish in the field may be endangered. With birds, the highest concentrations of OTs were present in liver and kidney and not in subcutaneous fat, which confirms that OTs accumulate via different mechanisms than traditional lipophilic compounds. As a whole the OT concentrations found in the foodweb may be considered to be quite alarming.

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Tributyltin (TBT) measurements in a food web in the freshwater Lake Westeinder are used to calibrate an integrated fate and bioaccumulation model with special attention given to exposure pathways. The Dutch ban on antifouling paints containing TBT is simulated with a load reduction scenario. By integrating Monte-Carlo sampling with a calibration procedure, probability distributions of TBT concentrations in the food web are matched to the measured variation in TBT concentrations. Subsequently, these distributions are used for a dynamic risk analysis of TBT accumulation in water, sediment, and the food web in the whole lake and a typical marina. Model predictions indicate a fast decrease of concentrations in water, suspended matter, and the zebra mussel Dreissena polymorpha. TBT concentrations in sediment, chironomids, amphipods, and benthivorous fish are predicted to decrease at a much slower rate. Simulations indicate that TBT in the sediment contributes significantly to uptake of TBT by several species. The relative proportion of sediment uptake increases for (partly) benthivorous fish after TBT load reduction. The model predicts low bioaccumulation risks for the whole lake, but substantial risks of TBT are calculated for fish and zooplankton in marinas, both before and during load reduction.

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