SETAC Globe - Environmental Quality Through Science
  14 April 2011
Volume 12 Issue 4

Return to the Globe

3rd SETAC Europe Special Science Symposium, “Prospective and Retrospective Environmental Risk Assessment of Mixtures: Moving from Research to Regulation”

Thomas Backhaus, University of Gothenburg, Sweden; Nina Cedergreen, Royal Veterinary & Agricultural University, Denmark; Tom Hutchinson, Plymouth Marine Laboratory, UK

3rd SETAC Europe Special Science Symposium

Chemical–analytical surveys demonstrate over and over again that organisms in the environment are exposed to complex chemical cocktails. Recent eco-epidemiology studies indicate that the 'toxic pressure' due to chemical mixtures is correlated with reduced biodiversity in river catchments (Posthuma and de Zwart, ET&C 25[4]:1094-1105). Also chemical products, such as e.g. pesticides or surfactants are usually combination products, comprising active ingredients, preservatives, filling agents, etc. However, the environmental effects of chemicals are traditionally evaluated and regulated on the basis of single substances, chemical by chemical. This approach might not be sufficient, especially because the toxicity of a mixture of chemicals is usually higher than each of the individual substances.

In December 2009, the EU environment ministers therefore asked the European Commission to strengthen its work on managing the risks posed by chemical mixtures. In parallel, a range of reviews, guidelines and recommendations on how to assess risks of chemical mixtures have been compiled by academic working groups as well as national, European and international bodies (e.g., WHO or EFSA).

In order to provide an overview of the state of the art and to facilitate knowledge exchange between scientists from different disciplines, regulators and chemical industry, SETAC organized a 2-day Special Science Symposium on the issue, which was held in Brussels, 2-3 February 2011.

Presentations were given by a range of well-known experts from environmental regulation, ecotoxicological risk assessment, human health–oriented toxicology, analytical environmental chemistry. Approaches to mixture risk assessment were discussed from a retrospective as well as a prospective perspective. Retrospective studies were discussed with the aim to identify key components in a given mixture or exposure scenario, e.g., a river catchment or waste disposal site. Prospective studies on the other hand were presented with a view on predicting mixture toxicities, based on the toxicological or ecotoxicological properties of the mixture components (often termed the mode of action or MOA approach), with the aim to e.g., set environmental quality standards. All presenters kindly agreed to make copies of their presentations available online.

Obviously, the different risk assessment areas have different protection goals. However, common ground was identified in several aspects:

  1. Concentration Addition seems to be suitable for providing a scientific frame of reference and as a slightly conservative, first-tier approach for mixture hazard and risk assessment in human toxicology as well as ecotoxicology. Results from such a tier might be especially useful for informing the need for additional, more in-depth study of a particular mixture.
  2. Surprisingly little is known on the actual exposure to mixtures. Hence it is currently unclear by how much the current compound-per-compound assessment, incorporating assessment factors derived for these individual substances, might (or might not) underestimate actual environmental risks.
  3. Chemical mixtures in the environment are a special challenge for environmental risk assessment and regulation, particularly because of their organization in highly specialized silos. A clear need for overarching approaches was identified.

Last but certainly not least, we would like to take the opportunity to thank all the presenters for their time and their engaging talks! It was certainly rewarding to be around…

Authors’ contact information:;;

Return to the Globe

SETAC mission statement Contact SETAC Globe
Contact the SETAC North America office
Contact the SETAC Europe office