Cross-phylum extrapolation of the Daphnia magna chronic biotic ligand model for zinc to the snail Lymnaea stagnalis and the rotifer Brachionus calyciflorus

We investigated if the chronic zinc biotic ligand model (BLM) developed earlier for the arthropod Daphnia magna could be extrapolated to predict chronic ecotoxicity of zinc as a function of water chemistry to two species from other phyla, i.e. the mollusc Lymnaea stagnalis and the rotifer Brachionus calyciflorus. We chronically exposed these two species to zinc in six natural surface waters. These water covered a wide range of pH (6.8–8.3), dissolved organic carbon (1.2–12.7 mg/L) and Ca (8.8–118 mg/L). Across all waters tested, the 28d-EC10s (200–1629 μg Zn/L) and EC50s (382–2026 μg Zn/L) for L. stagnalis spanned a 8.1-fold and 5.3-fold range, respectively. The 2d-EC10s (142–550 μg Zn/L) and 2d-EC50s (195–1104 μg Zn/L) for B. calyciflorus spanned a 3.9-fold and 5.7-fold range, respectively. The data indicated that higher pH and higher concentrations of Ca and DOC were generally associated with lower toxicity (higher ECx values). Furthermore, the chronic Zn BLM for D. magna, when calibrated only to reflect the intrinsic sensitivity of L. stagnalis and B. calyciflorus, was able to predict all ECx values with a less than 1.6-fold error, which demonstrates that the chronic D. magna Zn BLM can be extrapolated to other invertebrate phyla. This lends further support to the use of the chronic Zn BLM to account for bioavailability of zinc in aquatic risk assessment and the derivation of environmental quality standards.