Environmentally Relevant Inoculum Concentrations Improve the Reliability of Persistent Assessments in Biodegradation Screening Tests.

Standard OECD biodegradation screening tests (BSTs) have not evolved at the same rate as regulatory concerns, which now place an increased emphasis on environmental persistence. Consequently, many chemicals are falsely assigned as being potentially persistent based on results from BSTs. The present study increased test duration and increased inoculum concentrations to more environmentally relevant levels to assess their impact on biodegradation outcome and intratest replicate variability for chemicals with known environmental persistence. Chemicals were assigned to potential persistence categories based on existing degradation data. These more environmentally relevant BSTs (erBSTs) improved the reliability of persistence assignment by reducing the high variability associated with these tests and the occurrence of failures at low inoculum concentrations due to the exclusion of specific degraders. Environmental fate was determined using a reference set of 14C-labeled compounds with a range of potential environmental persistences, and full mass balance data were collated. The erBST correctly assigned five reference chemicals of known biodegradabilities to their appropriate persistence category in contrast to a standard OECD Ready Biodegradation Test (RBTs, P < 0.05). The erBST was significantly more reproducible than an OECD RBT (ANOVA, P < 0.05), with more consistent rates and extent of biodegradation observed in the erBST.