September 28, 2016 by Adam Peters
Graham and I have recently published a paper comparing some of the implementation approaches which are available for bioavailability based water quality standards for metals. There has been some confusion within the technical and regulatory community because whilst there are several user-friendly bioavailability tools available for users to try, they often give different results for the same problems. The Biotic Ligand Models (BLMs) which the user-friendly bioavailability tools are based on are very complicated to use and have not always been widely available. Consequently, it has generally not been possible to compare the predictions made by the user-friendly bioavailability tools against predictions made by the BLMs. This has led to confusion about which of the user-friendly bioavailability tools provides the most reliable predictions for the range of water chemistries which are likely to be experienced within any particular river basin.
The practical implementation of metal bioavailability within national water quality monitoring networks is continuously developing as greater experience is gained within those countries who have been the first to apply bioavailability based standards. The Dutch user-friendly bioavailability tool is already in the process of being updated to include the same refinements that are used by the nickel BLM.
One issue which is clear however, is that regardless of which of the user-friendly bioavailability tools is used, is that it is much more ecologically relevant to consider bioavailability than to only take account of hardness in assessing metal toxicity. In field situations there is often no overall relationship between hardness and the sensitivity of a particular water to metals, meaning that hardness based standards can divert scarce resources towards situations which might see no real ecological benefit. The implementation of bioavailability based water quality standards for metals throughout Europe in the future should address this problem and help to identify the most important priorities for regulatory action.
The full paper is available in Environmental Toxicology and Chemistry Volume 35, Issue 10 and the full text can also be accessed here.