State of the Science on Metals Bioavailability Modeling

Chris Schlekat, Bill Stubblefield and Kathryn Gallagher, Workshop Co-Chairs

A SETAC Technical Workshop titled “Bioavailability-based Aquatic Toxicity Models for Metals” was held 3–8 December 2017 in Pensacola, Florida, USA.  Forty experts from academia, business and government sectors from seven countries in North America, Europe and Australia participated in the week-long workshop. Post-doctoral researchers and one graduate student were among the participants, providing an early career perspective to the workshop. 

The influence of water chemistry parameters on the aquatic toxicity of metals was first documented in the middle of the 20th century. This knowledge led to the development of metals water quality standards and criteria based on water hardness in the 1980s, beginning in the USA and gaining acceptance elsewhere in the world shortly thereafter. Recognition that water chemistry parameters other than water hardness affect metal toxicity contributed to the development and regulatory application of mechanistic-based approaches like the Biotic Ligand Model in the 2000s. Since then, alternative modeling approaches have been developed, including empirical approaches like Multiple Linear Regression models. Considering the current availability of several scientifically defensible approaches, the SETAC Technical Workshop was held to take stock of the current state of the science of metals bioavailability models, to evaluate the performance of the models, and to identify best practices in the use of these models in the determination and application of bioavailability-based effects concentrations for metals that are intended to protect aquatic life (e.g., criteria and standards).

Participants at the SETAC Technical Workshop, 3–8 December, in Pensacola.

Participants were divided among five workgroups that addressed the following issues:

1. State of the science of metals bioavailability models (Workgroup chairs: Bill Adams, Red Cap Consulting, and Dave Mount, US Environmental Protection Agency)
2. Considerations for developing mechanistic-based bioavailability models (Workgroup chairs: Chris Wood, University of British Columbia, and Chris Mebane, US Geological Survey)
3. Considerations for developing empirical bioavailability models (Workgroup chairs: Kevin Brix, Ecotox, and Russ Erickson, US Environmental Protection Agency)
4. Validation of bioavailability-based models (Joe Meyer, Applied Limnology Professionals, and Emily Garman, NiPERA)
5. Application of metals bioavailability models in the determination of thresholds for aquatic life protection (Jenny Stauber, Commonwealth Scientific and Industrial Research Organization, and Eric Van Genderen, International Zinc Association)

The workshop resulted in several high-level recommendations regarding the development of metals bioavailability models and their use:

1. All bioavailability models should be informed by mechanistic understanding of metal toxicity and of metal speciation
2. The development of simplified tools is feasible as long as the tools have mechanistic links
3. All models should undergo qualitative and quantitative validation, and be applied within appropriate application ranges of water chemistry
4. Different models can be used for different situations; the critical aspect is that the choice of the most appropriate model needs to be transparently communicated. 

In conclusion, the outcomes of the workshop provide a solid basis for developing and applying bioavailability models for metals that reflect the state of the science, are flexible in terms of how they reflect influences of site-specific water chemistry, and are straightforward in terms of their application. Given that the scientific principles governing metal bioavailability are universal, the conclusions and recommendations from the workshop can support expanded incorporation of metal bioavailability information into regulatory frameworks around the world. 

The following communications are anticipated to disseminate the outcome of the workshop:

• A collection of publications to be submitted to the SETAC journal Environmental Toxicology and Chemistry
• A workshop summary that will be published by SETAC
• A presentation at the SETAC Europe 28th Annual Meeting, which will be held from 13–17 May in Rome, Italy, and a dedicated session at the SETAC North America 39th Annual Meeting from 4–8 November in Sacramento, California

For more information, please contact Chris Schlekat, Bill Stubblefield or Kathryn Gallagher.

Authors’ contact information: cschlekat@nipera.org, Bill.Stubblefield@oregonstate.edu and Gallagher.Kathryn@epa.gov

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