Future requirements for regulatory testing of mixtures and UVCBs

SETAC NA 2023 -- UVCB substances (Unknown, Variable composition, Complex reaction products, Biological) have many different constituents, some of which may be unknown. The composition can be variable or difficult to predict. Multi-constituent substances consists of several main constituents. Each of these main constituents will be present at a concentration of between 10% and 80% in the substance. A multi-constituent substance is named as a "reaction mass of the main constituents" present in the substance. There are differences in how we test with these two mixture categories and there are also regulatory difference between UVCBs and multi-component substances. Here we look at some of the challenges between what regulators expect and what is scientifically feasible in ecotoxicological fate and effects studies.