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Environmental fate & pathways

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Description of key information

Although the test item was not readily biodegradable in an OECD 301F test, simulation studies in natural freshwater-sediment systems show that the test item is not persistent. DT50 values of 25.6 to 30.8 days have been reported for rivers and lakes in China, and a DT50 of 33 days was reported for a groundwater aquifer in Australia under aerobic conditions.

Additional information

The biodegradability of the test substance was tested according to OECD Guideline 301F (1994). A nominal concentration of 100 mg/L test substance was incubated with activated sludge for 28 days under aerobic conditions, alongside an inoculum blank and a toxicity control. Oxygen consumption was measured electrolytically daily. The test substance is not readily biodegradable, as no degradation was observed after 28 days. This result may be due to the physical state (solid) and low water solubility of the test substance. This study is considered to be reliable without restriction (Klimisch 1).

The combined sorption and degradation of the test material in a natural water-sediment system was determined according to OECD Guideline 308 under aerobic conditions. Water and sediment were collected from Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, in China. The experiments were conducted in 30-mL amber glass tubes, containing 5 grams (dry weight) of sediment (2.5 cm sediment layer) and overlying water to achieve a water/sediment ratio of 3/1 (w/w). The study included an abiotic control and an inoculum control. The combined sorption and degradation tests were conducted in duplicate for 80 days. Sediment and water samples were analysed by UPLC with MS-ESI and concentrations were corrected based on the recovery data. The DT50 values were determined to be 13.4 ± 1.4, 4.1 ± 0.6, 7.1 and 6.5 days for water from the Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, respectively, and the DT50 values for the whole system (water + sediment) were 29.0 ± 1.7, 30.8 ± 1.5, 28.8 ± 2.4 and 25.6 ± 1.8 days, respectively. In the whole system, the disappearance rate was lower than that observed in the water phase. All the experiments in this study were performed in the absence of light, which ensured that photolysis was not a possible cause for the dissipation of target compounds in the total system. In addition, the result of the control experiment showed that the loss of test item in autoclaved deionised water was negligible (<10 %) within 80 days, indicating that degradation mechanisms such as hydrolysis or oxidation-reduction reactions could be eliminated. Thus, it appears that biotransformation is the most plausible cause for the disappearance of the test item. This study is reliable with restrictions (Klimisch 2) as it was conducted according to guideline, however there were minor limitations in experimental design (i.e. smaller scale than recommended) and reporting (e.g. test item concentration, number of replicates, experimental conditions).

In a supporting simulation study, the degradation of 3-(4-methylbenzylidene) camphor under various redox conditions was tested using water and sediment collected from a groundwater aquifer in South Australia. Samples containing 5 g of aquifer materials (97.1% sand / 0.8% silt / 1.7% clay, 0.4% organic carbon) and 5 mL of groundwater, amended with 1 μg/g test item, were prepared under aerobic, anaerobic-nitrate reducing, sulfate reducing and Fe(III) reducing conditions and degradation was monitored over 77 days. Triplicate samples were prepared for each treatment, alongside sterile controls. Samples were incubated at 20 °C under continuous darkness, and test item concentrations were analysed on Days 0, 7, 14, 21, 28, 35, 49, 63, and 77 using GC-MS. Degradation half-lives of the test item under different redox conditions had the following order: aerobic (33 d) > anaerobic control (75 d) > Fe(III) reducing (77 d) > nitrate reducing (80 d) > sulfate reducing (85 d). No hydrolysis of the test item was observed in the sterile control. This study is reliable with restrictions (Klimisch 2) as it was not conducted according to guideline, however the study design is scientifically acceptable, with minor limitations in experimental design (e.g. small test volume, mixture conditions).