Enhanced ready biodegradability screening tests for the evaluation of potential PBT substances

In persistence assessment enhanced ready biodegradation tests (eRBT) are aimed to close the gap between screening tests and complex simulation tests. However, only few data from these tests are available and neither guidance on the design and interpretation of eRBTs, nor suitable validity criteria have been established so far. In a practical testing programme 5 compounds with controversial degradation data have been tested in 4 test series including prolongation to 60 days and use of different inocula (activated sludge, final effluent from a STP), flask sizes, and endpoints (CO₂, O₂, DOC). The drug ibuprofen and the intermediate 4-fluorophenol were biodegraded by >60% within 28 days within a 10-day-window and therefore are considered as readily biodegradable and in conclusion fulfilling the criteria for "not persistent". The mean mineralization of the pesticide synergist piperonylbutoxide and the antioxidant octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate achieved 20%-50% (="potentially P"). The mineralization of the cosmetic ingredient cis-13-docosenonamide (Erucamide) was between 36%-64% after 60 days with activated sludge and 21% with the effluent from the STP. Diethylene glycol reached the pass level of 60% mineralization within 28 days in all test series without always meeting the 10-day window, and thus proved to be a suitable reference substance for eRBTs. Based on the results of the study several recommendations for the test design, the evaluation and the interpretation of eRBTs are made. However, a broader data set is required and further enhancements such as the quality and amount of the inoculum should also be considered in future research.