Technical report 123

Recommendation

In summary, the Task Force recommends that the ERA of ionisable organic compounds emphasise a need for projecting robust and reliable estimates and/or measurements of bioavailability. Specifically:

• Testing strategies, particularly those aimed at quantifying KOW, DOW and KOC need to ensure that they account for the potential for ionisation during the test, and the implications of ionisation with respect to modelling Clocalwater within the EU TGD framework are appropriately captured.
• With regard to analytical methods, the finalisation of OECD test guideline 122 for measuring pKa, KOW and DOW is encouraged.
• The use of QSARs to estimate KOW, DOW, and KOC need to be checked for their applicability towards the chemical under investigation. Based on observations from data scrutinised within this report, greater confidence in estimation methods appear to be warranted for acids than for bases.
• It is recommended that users compare output from more than one estimation method, for instance between SPARC and ACD with respect to estimates of DOW.
• There is a need for a wider debate regarding the relevance of regulatory triggers, such as KOW, in screening ionisable organic chemicals for their potential to be persistent and bioaccumulative.
• Are there surrogates, other than octanol, that could be better used as a metric for bioaccumulation.

Given the recent interest in ionisable organic compounds, such as those used as APIs, it is of great importance to improve mechanistic understanding of their sorption to various environmental matrices. Research is thus needed to transition current understanding, which is largely based on interactions associated with neutral organic compounds with organic carbon, to an improved framework for assessing the electronic interactions of a charged molecule with charged solid surfaces. In particular:

• Encourage updates to ERA tools, such as SimpleBox and SimpleTreat, to better project concentrations of ionisable organic compounds.

• To complement knowledge gained towards an improved assessment of exposure, there is a need to encourage support to address the relevance of ecotoxicological testing strategies for ionisable organic compounds.