May 7, 2021 by Adam Peters


Adam Peters co-chaired a discussion session on the Importance of Chemical Speciation and Bioavailability in Hazard Assessment, Risk Assessment and Regulation of Metals in Multi-Stressor Environmental Conditions.

There was a diverse range of presentations associated with this session that broadly covered a number of general themes. One of these issues is considering how changes in climate can result in changes to the release, transport, and availability of metals in the environment. These issues raised the importance of considering the effects of other stressors in addition to metal toxicity in understanding how ecosystems respond to contamination.

Another important and related issue that was covered in the discussions is the effects of chemical mixtures, and whilst there has been some progress made in recent years in terms of understanding the effects of mixtures of metals there has been relatively little progress in developing our understanding of mixtures of metals and organic chemicals. There was some interesting discussion about how best to identify the most important combinations of substances and the principal factors that emerged from the discussion were the significance of the exposures of the different substances in the environment, and the ecological relevance of their interactions. Many of the potential combinations of substances are not present together at environmentally and ecotoxicologically important concentrations, and the combined effects of many of the potential combinations of substances are either of limited ecological relevance or their effects can be adequately predicted based on the assumption of simple additive toxicity.

One example of a combination of metals and organic chemicals that was cited as an example that has received some attention in the past is the interactions of several trace metals with EDTA and similar chelating agents of anthropogenic origin. Both metals and EDTA are relatively common components of wastewater effluents and often interact with each other to form relatively stable metal-EDTA complexes that can significantly affect the fate and toxicity of the metals. This also highlighted the fact that the mixtures may not necessarily increase the toxicity of the individual components, and in the example of the interactions between metals and EDTA the resulting metal-EDTA complexes are generally less toxic, but more mobile, than the metals alone. wca have published a paper on this topic which is available here.