Models to Evaluate the direct Release of Cosmetic Ingredients into natural waters: Summary of the MERCI framework.

Reliable environmental exposure assessment requires fit-for-purpose tools capable of characterizing the magnitude, frequency, and duration of chemical releases under realistic use conditions. While established regulatory models, such as the European Union System for the Evaluation of Substances (EUSES), support screening-level assessment of cosmetic ingredients released down-the-drain, direct release scenarios are not addressed within current chemical safety frameworks. To address this gap, we present MERCI (Models to Evaluate the direct Release of Cosmetic Ingredients into natural waters), which is an iterative, tiered exposure assessment framework, that can be used to derive predicted environmental concentrations (PECs) from, for example, UV-filters used in sunscreen products released directly into marine and freshwater systems. The MERCI Framework integrates existing environmental fate and transport models within a transparent structure that aligns model selection with problem formulation, regulatory objectives, data availability, and resource considerations. Lower tiers apply standardized, conservative assumptions consistent with regulatory screening practices, while higher tiers incorporate increasing environmental realism, including refined emission estimates and site-specific hydrodynamics to reduce uncertainty and address complex questions. The framework is intended to be iterative, enabling users to select and refine tools as needed to support decision-making, prioritize data generation, and strengthen confidence in environmental risk assessments. As regulatory expectations and scientific understanding evolve, MERCI provides a scalable, adaptable pathway to integrate direct-release exposure scenarios, particularly those associated with the direct release of UV-filters used in sunscreen products, into chemical safety evaluations.