Society of Environmental Toxicology and Chemistry

4.04 - Environmental Hazard and Risk Assessment of UVCBs and Complex Mixtures: From Scientific Challenges to Regulatory Solutions

Description

Keywords: Animal Alternatives, Environmental Chemistry, Regulatory Science

Under the REACH Regulation, three main substance types are defined: mono-constituent, multi-constituent, and Substances of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs). UVCBs and More than One Constituent Substances (MOCS) are increasingly prevalent in industrial applications, from petrochemicals and essential oils to resins and polymers. However, their inherent complexity presents major scientific and regulatory challenges, particularly for environmental hazard and risk assessment. Standard environmental fate and ecotoxicity test methods were designed for well-defined, single-component chemicals and often prove insufficient for complex substances, with limitations related to variability, analytical constraints, and constituent-driven behaviour. This session aims to bring together researchers, regulators, and industry experts to discuss strategies and innovations for assessing the environmental fate, hazard, and risk of UVCBs and other complex mixtures. Contributions are invited that address: - Advances in analytical characterization and grouping approaches (e.g., read-across, NAMs, whole-substance testing); - Novel experimental designs and adapted protocols for UVCBs and difficult-to-test substances; - Challenges in test preparation, exposure control, and analytical monitoring, including strategies to capture key constituents; - Use and validation of alternative and non-animal methods (in vitro, in silico, omics-based tools) aligned with 3Rs principles; - Approaches to address environmental fate, bioavailability, persistence, and other challenging endpoints (e.g., PBT, PMT, vPvB, vPvM); - Testing and assessment strategies comparing whole-substance vs. constituent-based evaluations; - Case studies illustrating regulatory applications under REACH, Biocidal Product Regulation, and other frameworks. Particular emphasis will be placed on approaches that bridge scientific robustness with regulatory applicability under REACH, OECD guidelines, and global frameworks. The session also offers a forum to reflect on recent guidance developments (e.g., ECHA’s approach for UVCBs, new OECD guidances) and propose pragmatic paths forward for regulatory-relevant fate and effects studies. By fostering dialogue across sectors and disciplines, this session aims to catalyse collaborations and promote consistent, science-based approaches for UVCB and complex mixture assessment in the environmental domain.

Chairs

Kevin Bonnot   Firmenich SA Belgium
Simon Gutierrez  Ricardo-AEA Ltd Spain
Romanas Cesnaitis ECHA Finland
Sandrine Deglin HESI Global United States