Using biotic ligand models to help implement EQS for metals

By accounting for bioavailability in assessing metal compliance against an EQS, it is possible to provide the most environmentally and ecologically relevant metric of metal risk. This consideration of bioavailability removes, or at least reduces, many of the confounding issues related to the assessment of metal compliance, such as ambient background concentrations, forms of differing toxicity and the alteration of those forms in response to water quality. Biotic ligand models (BLMs) enable chemical and biological interactions to be taken into account; a BLM relates, through water chemistry, the toxicity of the metal to a dissolved concentration, which can then be used in compliance assessment. Unlike many other speciation-based approaches, the BLMs have been rigorously tested in the laboratory and field, and routinely predict ecological effects to many aquatic taxa across a wide range of water chemistries to within a factor of two, an acceptable level of variability within routine ecotoxicity testing. This collaborative project has developed and tested a simple, user-friendly version of the copper BLM with the purpose of providing a rapid screening tool to fit into Environment Agency monitoring and assessment systems. This model is not intended to replace the existing BLM, but to deliver a method requiring quick, low resource input, high data throughput and rapid interpretation of monitoring data. This project effectively transforms BLMs from the preserve of researchers into practical and accessible tools for regulators and stakeholders.

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