Bioavailability and risk assessment of metals in freshwaters: is global regulatory implementation keeping pace with...

The scientific knowledge that enables the prediction of potential aquatic ecological risks due to exposure of metals based on freshwater chemistry data has been available for several decades. As a result, ecosystems can be protected using frameworks and procedures incorporated into regulatory approaches. Yet when evaluating how freshwater risks from metals are assessed globally, it is apparent that regulatory jurisdictions differ in their progress and approaches when accounting for bioavailability. It is entirely reasonable and appropriate for a lag in time between the development of the science and its incorporation into routine regulatory environmental protection. We openly acknowledge that this is not just a regulatory challenge and take a more holistic view of the implementation of the science that informs metal bioavailability. Implementation comprises the steps required to utilize science and knowledge to enable its practical, beneficial, and routine application in regulatory decision-making. Different regulatory jurisdictions have taken varied approaches to account for metal bioavailability. We have made specific use of frameworks that utilize limit values, such as water quality guidelines, criteria, and quality standards, to illustrate the similarities and differences in the implementation of bioavailability. Approaches taken in Europe, Canada, Australia and New Zealand, and the United States were reviewed and evaluated. Although some of these approaches or parts thereof have been successful, other aspects have been less so. In this evaluation, we have identified key commonly encountered obstacles and challenges in these approaches to the implementation of metal bioavailability. Finally, we provide an evidence-driven "road map" to the successful regulatory implementation of metal bioavailability in risk assessment drawn from successful components of the approaches reviewed. The application of this framework will enable regulatory jurisdictions to readily keep pace with the science pertaining to metal bioavailability and avoid the challenges experienced by others.