A water-sediment screening tool for measuring biodegradation of organic chemicals

A water-sediment screening tool (WSST) was developed based on OECD guideline 301 C (MITI I; Ministry of International Trade and Industry, Japan) to generate biodegradation data. The WSST and experimental procedures were tested and validated using aniline (CAS No. 62-53-3) and benzoic acid (CAS No. 65-85-0) as reference substances. In the presence of sediment components a higher endogenous respiration rate in the control vessels without test substance was measured compared to the water-only MITI test system, particularly due to organic constituents. However, it could be demonstrated that a distinct biodegradation in the presence of sediment can be determined and that there is no influence of the sediment pre-treatment on the biological oxygen demand in the WSST. Experiments resulted in biodegradation rates >60% after approximately six days for both compounds. However, degradation of benzoic acid resulted in a shorter lag-phase and a higher degree of degradation compared to aniline. Differences in results between the MITI test system and the WSST observed for aniline can be explained by adsorption to constituents of the sediment and assimilation by activated sludge. In comparison with literature data the results obtained for aniline in the MITI test system and the WSST showed reproducibility and were within the expected range. In conclusion, the WSST is a suitable screening tool to determine kinetic biodegradation data required to predict the biodegradation behaviour of organic chemicals in water-sediment systems and the data might be used to improve quantitative structure-property relationships (QSPRs).