LRI-ECO42 – Fate-directed Toxicity Testing and Risk Assessment of UVCBs

Background

Environmental toxicity information serves two roles in the assessment of a substance for environmental safety and regulatory requirements. The data are used to assess ecotoxicity but also to derive Predicted No-effect Concentrations (PNECs) for environmental risk assessment. In the context of fate and exposure assessment, substance properties (e.g. vapour pressure, water solubility, log K_ow, log K_oc) and information on biodegradation are needed to estimate the distribution of releases in environmental compartments and to calculate Predicted Environmental Concentrations (PECs) for each compartment. For conventional risk assessment of single substances, these PECs would be compared to PNECs based on aquatic toxicity testing. This process is relatively well established for single chemicals, well-defined substances and simple mixtures.

Multi-constituent substances (MCSs) and substances of unknown or variable composition, complex reaction products or biological materials (UVCBs) pose particular challenges for conventional hazard and risk assessment (see ECHA Guidance for identification and naming of substances under REACH and CLP for more detail). UVCB substances are comprised of individual constituents, each of which may possess different physico-chemical and fate properties. Of 11,998 registered substances in REACH, 10% are multi-constituent and 21% are UVCBs (ECHA Read-Across Assessment Framework), which includes petroleum substances, fragrances/essential oils, pine resins, and surfactants. Risk assessment for multi-constituent substances is hampered by the fact that toxic effects of complex substances cannot be linked to specific constituents; standard guidelines for risk assessment of single chemicals are therefore not applicable. It is known that UVCB substances cannot be sufficiently identified by their chemical composition, which creates the complications for testing using standard guideline methodologies. In addition, the risk assessment of such substances as traditional hazard and exposure assessments for the whole substance, in most cases is not possible. Furthermore, fate and hazard of the different constituents in the environment will be determined by their specific physicochemical properties, but the Unknown and potentially Variable composition of these substances adds a level of uncertainty which is difficult to address by both producers and regulators.

The recent RIFM/ECETOC UVCB Workshop (02-04 November 2016, Florida, USA) highlighted the need to account for complex substance exposure and fate in order to perform more relevant toxicity testing, and raised questions on the impact this type of testing would have on risk assessment outcomes (Salvito and Galay-Burgos, 2017). Aquatic toxicity data for UVCBs can be generated from testing known individual components or testing water accommodated fractions (WAFs) generated from the whole substance. In order to quantify toxicity for classification purposes, the WAF method was developed, although data are considered of limited value for whole substance risk characterisation. In order to lower this uncertainty, a coupled fate and effects approach is envisioned, where the biodegradation of a complex substance is investigated and subsequently toxicity testing is performed on the remaining sample/constituents. In this way, fate of constituents is accounted for by design, thereby increasing the environmental relevance of toxicity testing. Within the Workshop, the attendees, including the regulatory authorities (i.e., ECHA, ECCC, USEPA), were interested in developing this approach, including the development of data/case studies to support its future use.