Technical Report 123

Terms of Reference

The aim of the task force was to review the current understanding and available literature on partitioning property data of ionisable compounds at environmental relevant pHs, including estimation methods for these properties in case measured data are lacking, and that should lead to better predictions of the environmental concentration and bioavailability of ionisable compounds in aquatic environments. Members of the task force are given at the end of the report. The group adhered to the following terms of reference in compiling this report.

• Conduct a literature review to identify the availability of partitioning property data for ionisable compounds, specifically the acid dissociation constant pKa, octanol-water partition coefficient KOW, octanol-water distribution ratio DOW, organic carbon-water partition coefficient KOC, and adsorption desorption distribution coefficient Kd. Additionally, in the absence of good quality data, there will be a need to estimate these partitioning properties. Consequently, a review, summarising the various estimation methods available and their range of applicability, is required.

• Provide guidance on how to better estimate the predicted environmental concentration (PEC) of ionisable compounds in aquatic environments based on the relationship between pH, pKa, and their partitioning properties.

• Make recommendations regarding what pH and soil properties are most useful for accurately predicting environmental concentrations, i.e. it may be possible to define a generic model environment for use in a predictive ERA. It may also be possible to advise the most appropriate testing conditions.

• Identify the key parameters needed to better predict the bioavailability of ionisable compounds.

• Determine how information obtained through improved estimates of PEC might be used to assess the aquatic risk of ionisable compounds. If possible, identify the key factors and relationships between bioavailability, and ecotoxicity that would improve the ERA of ionisable compounds.