The need for a consistent approach to account for transformation products when deriving environmental quality...

Environmental quality standards (EQS) derived under the European Water Framework Directive represent legally binding limits for chemicals in the environment. These EQS are typically based on ecotoxicity data for the chemical only, following the published EQS technical guidance. Recent proposed EQS derivations for the pharmaceuticals carbamazepine and clarithromycin have deviated from this by incorporating ecotoxicity and exposure data for their transformation products (TPs). The published technical guidance lacks consideration of TPs in EQS derivation, which is manifested in inconsistencies between these chemicals, such as the use of additional assessment factors and the proposed application of the EQS to the sum of the measured parent and TPs rather than just the parent chemical. To resolve these inconsistencies, we have developed an evidence-driven approach to illustrate how TP considerations could be incorporated into the EQS derivation process in a repeatable and transparent manner and to utilize all the relevant and reliable data for effects and exposures. As the precedent has now been set by the European Commission that TPs may be considered in EQS derivations, we recommend that this approach be further developed and incorporated into an upcoming revision to the technical guidance to ensure that future derivations by regulators and nonregulatory environmental risk assessors and practitioners are consistent and scientifically robust.