ERA of ionisable compounds

risk, hazard and precaution miniexposure pathways miniRisk, hazard and precaution /
Environmental fate and behaviour

Chemicals Programme Manager Henk Vrijhof

Administrative Assistant: Sonia Pulinckx


The release of “ionisable compounds’ (where behaviour depends on pH, ionic strength, etc) into the environment presents the risk assessor with particular problems. The Scientific Committee, therefore, established a task force 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. This should improve our ability to better predict the environmental concentration of ionisable compounds in aquatic environments.

The work of this task force may also help to define a generic model environment with appropriate soil and water properties, and other parameters required for effective environmental risk assessment of ionisable compounds. This should include identification of the key parameters needed to better predict the BCF of ionisable compounds.

A scoping meeting on pharmaceuticals in the environment held in March 2009 highlighted several topics that are of interest to the pharmaceutical industry. Environmental risk assessment (ERA) of ionisable compounds was one of three topics that scored the highest.

Terms of reference

  • Conduct a literature review to identify the availability of partitioning property data for ionisable compounds, specifically pKa, Kow, Dow, Koc, 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 PEC of ionisable compounds in aquatic environments based on the relationship between pH, pKa, and their partitioning properties.
  • Can recommendations be made regarding what pH and soil properties are most desirable for predicting environmental concentrations, i.e. is it possible to define a generic model environment for use in a predictive risk assessment?
  • Identify the key parameters needed to better predict the BCF of ionisable compounds.
  • How might information obtained through improved estimates of PEC be used to assess the aquatic risk of ionisable compounds? What are the key factors and relationships (e.g. between BCF and LC50) which would improve the risk assessment of ionisable compounds?

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