14.10.2009 - 15.10.2009

Significance of bound residues in environmental risk assessment


Bound residues, including non-extractable residues, are an important factor in PBT assessment and the 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.

Although it is a position that has been recognised and referenced by REACH (2008) and OECD test guidance (2002), there is no agreed guidance on how to determine what is available and what is not, and how information on bound residues should be interpreted in the risk assessment. As a result, it continues to be debated from a scientific and regulatory point of view.

Discussion topics

ECETOC held a 2-day workshop attended by 38 stakeholders representative of industry, academia and regulatory authorities from the USA, Canada, Europe and Asia in Brussels on 21-22 October 2009, to further this debate and to develop guidance on how to account for bound residues and bioavailability in environmental risk assessment.

Conclusions and recommendations

The conclusions, future regulatory and research needs, and a framework outlining a possible approach for advancing and improving the risk assessment of bound residues, are presented in Workshop Report 17.