Biodegradation of Volatile Chemicals in Soil: Separating Volatilization and Degradation in an Improved Test Setup (OECD 307)

Abstract

During environmental risk assessments of chemicals, higher-tier biodegradation tests in soil, sediment, and surface-water systems are required using OECD standards 307, 308, and 309 guidelines, respectively. These guidelines are not suitable for testing highly volatile chemicals, and a biometer closed-incubation setup is recommended for testing slightly volatile chemicals. In this setup, the degradation kinetics of highly volatile chemicals can largely be influenced by volatilization. Additionally, guidelines lack sufficient information on test-system geometry and guidance on how to measure and maintain aerobic conditions during the test. Our objectives were (1) to design a closed test setup for biodegradation tests in soil in which the maintaining and measuring of aerobic conditions was possible without the loss of volatile test chemicals and (2) to suggest data-treatment measures for evaluating the degradation kinetics of volatile test chemicals. With the new setup, full-scale OECD 307 tests were performed using the volatile 14C-labeled chemicals decane and tetralin. For both test chemicals, reproducible complete mass balances were observed, and the new setup ensured that the volatilization losses were kept below the mineralized fraction. Based on the obtained data, an extended model was developed that enabled consideration of the volatilization in the modeling of degradation kinetics.

Can a chemical be both readily biodegradable AND very persistent (vP)? Weight-of-evidence determination demonstrates that phenanthrene is not persistent in the environment

“…In other non-standard studies where phenanthrene degradation has been measured in freshly spiked soils, halflives are generally in agreement with Shrestha et al [32] (Additional file 1: Table S1). In total, thirteen such studies were found in the literature, with phenanthrene being dosed to soils using varying approaches, including direct addition or solvent spiking of phenanthrene individually, as a composed PAH mixture, or as a constituent of materials such as crude oil [77][78][79][80][81][82][83][84][85][86][87][88][89].…”

“…Current European Chemicals Agency (ECHA) guidance places heavy emphasis on Organisation of Economic Co-operation and Development (OECD) guideline biodegradation tests. However, even with these standard tests, technical challenges remain that introduce variability and reliability issues, particularly where substance properties require modification to the standard test setups [28,[29][30][31][32].…”

“…Higher-tier simulation tests were performed using the standard OECD 307 aerobic flow-through setup (Additional file 1: Section S4) [32,46]. In this study, degradation of the 14 C-labelled phenanthrene was investigated in four reference soils using acetone as an application solvent.…”

Linking biodegradation kinetics, microbial composition and test temperature – Testing 40 petroleum hydrocarbons using inocula collected in winter and summer

“…"difficult to test chemicals") such as many petroleum hydrocarbons, which then necessitate signicant methodological adjustments. [4][5][6][7] While such adjustments should improve the technical and scientic quality of the tests and their degradation results, they can also lead to regulatory rejection of data. A very recent example of this is the persistency assessment of three ringed alkylated PAHs, where all 18 different biodegradation data sets identied were rejected and this hydrocarbon group was then assessed to be persistent without using the experimental degradation data.…”

Improving our understanding of the environmental persistence of chemicals

“…The next presentation, based on research undertaken by the Fraunhofer IME for both Concawe and Cefic, identified the limitations and potential enhancements of the OECD 307 and OECD 309 tests. Some of the issues and recommendations for improvement for these tests have subsequently been published (Shrestha et al, 2019(Shrestha et al, , 2020. For example, both tests are considered to be poorly suited for the assessment of volatile substances.…”