Comparison of different versions of simulation studies following OECD 309 using 14C-labelled ionic compounds - Does it make a difference?

Simulation studies following OECD guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test) are performed to determine the biodegradation of chemicals in surface water. The aim of our study was to perform different versions of this test to identify possible shortcomings. In order to investigate the influence of a chemical charge on the degradation, we used C-14-labelled 4-n-dodecylbenzenesulfonic acid sodium salt (C-14-DS-), 4-n-dodecylbenzyltrimethylammonium chloride (C-14-DA(+)) and 4-n-dodecylphenol (C-14-DP) Additionally, abiotic degradation of these compounds and the effectiveness of different sterilization methods was assessed. The sampling technique of withdrawing sub-samples provided insufficient recoveries for C-14-DS and C-14-DP which were mainly below 80% of applied radioactivity (AR). Therefore, the suspended sediment test was repeated using C-14-DS-, C-14-DA(+) and C-14-DP and whole flasks were harvested at each sampling time resulting in superior recoveries. For C-14-DS- and C-14-DP, mineralisation was the major route of dissipation with (CO2)-C-14 evolution of 75.3% and 69.0% AR, respectively, after 62 days. Mineralisation of C-14-DA(+) accounted for only 6.7% AR. Non-extractable residues (NER) of all compounds were similar after 62 days (7.3% - 9.2% AR). Sterile test conditions were best achieved using gamma-irradiated sediment and autoclaved water treated with sodium azide. Under sterile conditions, mineralisation of the test compounds as well as NER formation of C-14-DS- and C-14-DP were negligible, whereas small amounts of NER were formed for C-14-DA(+) (5.5% AR). We showed that OECD guideline 309 provides too much scope for the experimental setup which affects the outcome of the test and thus, needs further refinement. (C) 2020 Elsevier B.V. All rights reserved.