Testing the Biotic Ligand Model for Swedish surface water conditions - a pilot study to investigate the applicability of BLM in Sweden

Biotic Ligand Models (BLMs) have been developed for a number of metals (e.g. Cu, Zn, Ni), in order to account for bioavailability in metal risk assessment. The BLMs predict the bioavailable fraction of a metal in the water, based on water chemistry, and calculate site-specific PNEC-values, to which measured dissolved concentrations can be compared. Concerns have been raised that these models may not apply in the Swedish environment, due to the large difference in Swedish water chemistry compared to those European waters, for which the models have mainly been validated. IVL has, in close collaboration with industrial partners undertaken a pilot study, with the aim of testing the applicability of Biotic Ligand Models for assessing metal toxicity in Swedish waters. The study concerned the metals copper (Cu), zinc (Zn) and nickel (Ni), cadmium (Cd) and chromium (Cr). The overall conclusions of the project are that a) BLM-models can and should be applied as a natural element when assessing metal risks in Swedish waters, preferably as a sub-step in a tiered approach; b) The chemical conditions of Swedish water bodies are generally in agreement with the BLM requirements concerning the two key parameters pH and DOC, when it concerns the metals Cu, Zn, and Ni; c) Swedish national monitoring programmes should focus on routine measurements of dissolved metal concentrations, and also on measurements of DOC. If the currently used method is regarded as equivalent to filtration through a 0.45 µm filter, this should be clearly stated in the national monitoring databases; d) Models are available for Cu, Zn, and will soon be available for Ni. The BLMs are regularly improved and updated; e) Concerning chromium, BLMs are currently not available. It is therefore considered that all soluble chromium (III) is bioavailable and thus contributes to toxicity ; f) Cadmium is assessed using a hardness correction and the proposed Cd-EQSs are to be compared with dissolved monitoring data. In order to assess the model results, a validation exercise should be performed for soft waters regarding Zn, in particular for soft waters with a high pH-valueBiotic Ligand Models (BLMs) have been developed for a number of metals (e.g. Cu, Zn, Ni), in order to account for bioavailability in metal risk assessment. The BLMs predict the bioavailable fraction of a metal in the water, based on water chemistry, and calculate site-specific PNEC-values, to which measured dissolved concentrations can be compared. Concerns have been raised that these models may not apply in the Swedish environment, due to the large difference in Swedish water chemistry compared to those European waters, for which the models have mainly been validated. IVL has, in close collaboration with industrial partners undertaken a pilot study, with the aim of testing the applicability of Biotic Ligand Models for assessing metal toxicity in Swedish waters. The study concerned the metals copper (Cu), zinc (Zn) and nickel (Ni), cadmium (Cd) and chromium (Cr). The overall conclusions of the project are that a) BLM-models can and should be applied as a natural element when assessing metal risks in Swedish waters, preferably as a sub-step in a tiered approach; b) The chemical conditions of Swedish water bodies are generally in agreement with the BLM requirements concerning the two key parameters pH and DOC, when it concerns the metals Cu, Zn, and Ni; c) Swedish national monitoring programmes should focus on routine measurements of dissolved metal concentrations, and also on measurements of DOC. If the currently used method is regarded as equivalent to filtration through a 0.45 µm filter, this should be clearly stated in the national monitoring databases; d) Models are available for Cu, Zn, and will soon be available for Ni. The BLMs are regularly improved and updated; e) Concerning chromium, BLMs are currently not available. It is therefore considered that all soluble chromium (III) is bioavailable and thus contributes to toxicity ; f) Cadmium is assessed using a hardness correction and the proposed Cd-EQSs are to be compared with dissolved monitoring data. In order to assess the model results, a validation exercise should be performed for soft waters regarding Zn, in particular for soft waters with a high pH-valu