Development of interim guidance for the inclusion of non-extractable residues (NER) in the risk assessment of chemicals

Background

Bound residues (BR), including non-extractable residues (NER), are an important factor in PBT (Persistence, bioaccumulation and toxicity) assessment and risk assessment of chemicals. Precautionary risk assessments usually assume 100% bioavailability, i.e. all of the chemical present, is available for degradation or to have potential toxic effects on the biota. This precautionary approach generally overestimates the exposure concentration by the amount that is not available and therefore overestimates the level of risk to biota in the environment. It is also well documented that chemicals that are irreversibly bound to solids are less degradable and less toxic than the total residue would predict. Even though it is a position that has been recognised by ECPA (2000), and referenced by REACH (2008) and OECD test guidance (2002), there is no agreed guidance on how to determine what is available or not, and how it should be considered in the risk assessment.

An ECETOC workshop "Significance of Bound Residues in Environmental Risk Assessment" was held on 14-15 October 2009 in Brussels, where thirty-eight leading experts in environmental fate, ecotoxicity and environmental risk assessment participated. The workshop aimed at reviewing what is known about “bound residues', to identify what issues may exist in respect to their use and interpretation in environmental risk assessments, and to identify areas of science that require further research. The main output of this workshop (ECETOC Workshop Report No. 17) was a framework outlining a possible decision tree for improving the risk assessment of NER, together with the identification of key research needs to address gaps in the current knowledge base.Many of these research projects will take a number of years to deliver and hence there is a clear need to agree an interim approach to address the impact of NER on current risk assessments for aquatic and terrestrial organisms. To this end the Scientific Committee of ECETOC established a task force to:

1. Critically evaluate the proposed risk assessment framework developed following the ECETOC workshop and assess its utility as an interim approach for regulatory assessment of chemicals.
2. Develop suitable guidance and trigger values to enable the decision tree to be used and test the utility of the scheme using suitable case studies.
3. Provide guidance on study design to provide the appropriate quality of data needed for the risk assessment framework to function within a regulatory decision making system.

It is foreseen that the task force will complete its work by the end of 2011.