A new study analysing 97 chemical compounds in 18 river sites across 5 European countries has uncovered significant variation in how quickly commercial chemicals biodegrade in freshwater. While nearly all compounds broke down in at least one location, only two showed no measurable biodegradation at any site. These findings challenge the reliability of current persistence assessments under the EU’s REACH regulation, which rely heavily on standardised biodegradation testing.

Researchers found that environmental and regional factors, such as total organic carbon and clay content, influence biodegradation but don’t fully explain the variability. Compounds that biodegrade quickly tend to show lower spatial variation, suggesting that they may require testing at fewer sites. In contrast, slowly degrading compounds – those closer to being classified as persistent – need broader testing to ensure accurate assessments.

The study calls for refined testing strategies, including site prioritisation based on environmental indicators, and recommends extending similar research to other aquatic environments. These insights are key for improving the robustness of chemical risk assessments and protecting Europe’s freshwater ecosystems.