Evaluation of current copper bioavailability tools for soft freshwaters in Sweden

• 1530 Swedish fresh water lakes and rivers was modeled.
• Toxicity using three different biotic ligand models was calculated.
• Problems were noticed applying current BLM's on Swedish soft waters.
• The models calibration interval was not suitable for the fresh waters investigated.
• Calculated EQS/WQC exceeded recommended Swedish limits regarding Cu.

The Water Framework Directive (WFD) in Europe calls for an improved aquatic ecological status. Biotic ligand models (BLM) have been suggested as a possible tool assisting in the regulatory process. The aim of this study was therefore to investigate the applicability of BLM under the WFD to set environmental quality standards (EQS), in particular regarding copper in Swedish freshwaters of which many are softer than those used for model calibration. Three different BLMs, one acute and two chronic, were applied to water chemistry data from 926 lakes and 51 rivers (1530 data entries) and evaluated with respect to their calibration range for input parameters. In addition, the predicted no-effect concentration (PNEC) for copper was calculated. From the 1530 data entries, 750 ended up outside of the BLM calibration range, when looking at the chemical parameters Ca2+, alkalinity, pH and DOC, primarily due to low carbonate alkalinity. Furthermore, the calculated Cu PNECs were higher than the suggested Swedish limit for Cu (4 µg L−1) in surface waters for 98% and 99% of the cases concerning lakes and rivers, respectively. To conclude, our findings show that water chemical characteristics outside of the calibration ranges are quite common in Sweden and that the investigated models differ in how they calculate toxicity concerning Cu under these conditions. As a consequence, additional work is required to validate the BLMs by use of bioassays with representative species of soft waters. Such results will show if these models can be used outside of their calibration ranges and also which of the models that gives the most reliable results.

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