Mobility in the context of exposure-based assessment of chemicals for drinking water resources protection.

In order to protect European Union (EU) drinking water resources from chemical contamination, criteria for identifying persistent, mobile and toxic (PMT) chemicals and very persistent and very mobile (vPvM) chemicals under the EU REACH Regulation were proposed by the German Environment Agency (Umweltbundesamt - UBA). Additionally, new hazard classes for PMT and vPvM substances into the revised EU classification, labelling and packaging (CLP) Regulation are intended. Therefore, a reliable approach for identification of potential drinking water resource contaminants is needed. The scientific basis of the property-based PMT/vPvM criteria, focusing on mobility which dictates the migration of chemicals drinking water sources, was evaluated and a critical analysis of the deviation of sorption metrics from simple behaviour was carried out. Based on our evaluation, a K oc may be used for non-ionic substances on a screening level only, requiring a higher tier assessment. It is considered inappropriate for hydrophilic and ionisable chemicals, particularly for soils with low organic carbon (OC) contents. The non-extractable residues (NER) formation is complex and not well understood but remains significant in limiting the mobility of chemicals through soils and sediments. In order to inform the EU commission´s work on the introduction of new hazard classes for PMT and vPvM substances into the European legislation, the derivation of a tiered approach is proposed which utilises the weight of evidence available, with adoption of appropriate higher tier models commensurate with the nature of the substance and the data available. This article is protected by copyright. All rights reserved. Integr Environ Assess Manag 2022;00:0-0. © 2022 SETAC.