Simultaneous determination of mixture mineralization and constituent-specific primary degradation in a modified ready...

Ready biodegradability screening tests are the first step in regulatory persistence assessments of chemicals. However, current ready biodegradability tests are not applicable to substances of unknown and variable composition, complex reaction products, and biological materials (UVCBs), because they cannot demonstrate the degradation of all UVCB constituents. The mineralization of the majority of constituents could mask the lack of degradation of persistent constituents. The aim of this study was to develop and apply a new whole UVCB ready biodegradability test, where oxygen depletion is applied to determine whole UVCB mineralization, and solid phase microextraction coupled to gas chromatography-mass spectrometry to determine constituent specific primary degradation. The method development and design optimization addressed oxygen-related and UVCB-related challenges. The designed test system consisted of 100 ml clear injection flasks with oxygen sensor spots mounted inside, closed with crimp caps and butyl/polytetrafluoroethylene septa. The new test was applied to black pepper essential oil (EO) as a model UVCB. The composition of black pepper EO is well defined and contains a balance of monoterpenes and sesquiterpenes permitting validation of the approach across a broad spectrum of naturally occurring components. The EO test concentration was lowered to 10 mg/L to avoid substrate inhibition, and a headspace ratio of 25% ensured aerobic conditions. Mineralization of black pepper EO reached the pass level of 60% within less than 12 days, and primary degradation was rapid and consistent for all measured constituents. The mineralization of the UVCB and the primary degradation of its constituents provide two lines of evidence for black pepper EO being readily biodegradable. The developed approach is a modified rather than an enhanced Organisation for Economic Co-operation and D 301 method, because substance-specific test challenges motivated and justified the test modifications. This approach seems now applicable for improved biodegradation testing and persistence assessment of UVCBs.