Are ready biodegradation tests effective screens for non-persistence in all environmental compartments?

Background Persistence assessment is a cornerstone of chemical hazard and risk assessment in numerous regulatory frameworks, as the longevity of a substance in the environment relates to exposure and ultimately the risk it poses. A chemical that is readily biodegradable is commonly assumed to undergo rapid and ultimate biodegradation under most environmental conditions. Ready biodegradability tests (RBT), such as the OECD 301 test series, are used to quickly screen out non-Persistent substances and focus regulatory scrutiny on the most hazardous substances. The stringency of the RBT as a screen for all environmental compartments is paramount to ensure that there are no readily biodegradable yet Persistent substances. To assess this stringency in practice, we here describe a systematic comparison of substances with both RBT data and biodegradation simulation test data for soil, sediment, or water compartments to see whether there are any substances which are readily biodegradable yet meet EU REACH regulatory Persistence criteria in any specific environmental compartment. Results A rough assembly of data extracted from the ECHA database showed that, out of 263 substances with both RBT and simulation test data, there were 19 substances that were readily biodegradable but Persistent (based on the most conservative result and after a temperature adjustment to the half-life). However, many of the underpinning simulation study information were either not high-quality guideline studies or the substances were UVCBs. To more accurately compare the RBT and simulation testing outcomes, quality criteria on the RBT and simulation tests were applied, which limited the data set to about one-third. Conclusions When examining quality-screened, temperature-adjusted simulation testing half-lives for readily biodegradable substances, there were no readily biodegradable substances that were Persistent. A side-by-side comparison of the available data supports the stringency and effectiveness of RBTs to identify non-Persistent chemicals.