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

Abstract

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 14C-labelled 4-n-dodecylbenzenesulfonic acid sodium salt (14C-DS−), 4-n-dodecylbenzyltrimethylammonium chloride (14C-DA+) and 4-n-dodecylphenol (14C-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 14C-DS− and 14C-DP which were mainly below 80% of applied radioactivity (AR). Therefore, the suspended sediment test was repeated using 14C-DS−, 14C-DA+ and 14C-DP and whole flasks were harvested at each sampling time resulting in superior recoveries. For 14C-DS− and 14C-DP, mineralisation was the major route of dissipation with 14CO2 evolution of 75.3% and 69.0% AR, respectively, after 62 days. Mineralisation of 14C-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 γ-irradiated sediment and autoclaved water treated with sodium azide. Under sterile conditions, mineralisation of the test compounds as well as NER formation of 14C-DS− and 14C-DP were negligible, whereas small amounts of NER were formed for 14C-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.