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Development and validation of a chronic Pb bioavailability model for the freshwater rotifer Brachionus calyciflorus

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We investigated the univariate effects of Ca, pH and DOC on chronic (48h) Pb toxicity to the freshwater rotifer Brachionus calyciflorus. High pH (8.2) and higher concentrations of DOC were protective against filtered Pb toxicity, whereas Ca was not. However, expressed as free Pb2+ ion, Pb2+ toxicity increased with increasing DOC concentration, indicating that Pb‐Fulvic Acid (FA) complexes may be bioavailable and may contribute to toxicity. Two different bioavailability models were developed. The pH effect was modeled as a single site competition effect by H+ (log KHBL = 7.14). In the first model, we considered only this H+ effect, in a second model we also incorporated a log‐linear FA bioavailability effect (SFA = 0.602). Both models predicted chronic Pb toxicity for most waters used for model development within 2‐fold error. To validate the predictive capacities of the models, chronic Pb toxicity to B. calyciflorus was tested in 5 natural and a reference water. Both models consistently underestimated Pb toxicity in these natural waters, due to a shift in rotifer sensitivity to Pb between the development and the validation test series. However, optimizing the intrinsic sensitivity in the models specific for the validation test series resulted in reasonable predictions of Pb toxicity in the natural waters. The second, more complex model predicted chronic Pb toxicity most accurately. The protective effects of water chemistry on Pb toxicity to Brachionus are comparable to those observed for Ceriodaphnia. However, the developed Brachionus models were not able to predict chronic Pb toxicity to the rotifer Philodina rapida accurately. It remains unclear why the influence of water chemistry on chronic Pb toxicity appears to be different between two rotifer species. This article is protected by copyright. All rights reserved

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