Biodegradation testing of volatile hydrophobic chemicals in water-sediment systems - Experimental developments and challenges

Degradation data are crucial for the persistence assessment of chemicals and they are generated using standard OECD guidelines. The OECD 308 describes a simulation biodegradation test of chemicals in water-sediment systems. This guideline is not applicable for testing highly volatile chemicals and recommends a closed biometer test setup for testing slightly volatile chemicals. However, proper details on system geometries, construction and monitoring of aerobic conditions are not provided. The choice of system geometry and sediment:water ratio influences the partitioning of test chemicals between different compartments (water, sediment and headspace) and can therefore affect their degradation. The guideline recommends the addition of test chemical via aqueous solutions, which however is not possible for hydrophobic volatile chemicals due to their volatilization losses and low solubility. Thus, the use of a co-solvent is necessary for the application of such chemicals but its effects in a closed setup has not been studied. We recently developed an improved closed test setup for testing volatile chemicals in soil. The objective was to adapt this improved test setup to conduct OECD 308 tests using 14C labelled chemicals with different volatilities. Using the adapted test setup it was possible to obtain a complete mass balance even for n-decane and tetralin having the highest Henry's constants of the tested chemicals. However, the use of co-solvent affected the oxygen levels, which in turn affected microbial activity and likely also the degradation of test chemicals. Therefore, the adapted test setup needs further developments for the testing of volatile hydrophobic chemicals

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

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

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake: Nuclear fuel durability enhancement

Photograph of the exterior of the historic Harn Homestead