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Environmental fate & pathways

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The available reliable studies on the ready biodegradability of TCP and the inherent biodegradability of the closely related substance 1,2-dichloropropane show that no biodegradation under aerobic conditions is to be expected for the substance in water. Preliminary studies on the co-oxidative degradation of 1,2,3-trichloropropane by ammonia-oxidising bacteria showed resulted in a relevant degradation of the substance. No standard tests on the biodegradation of the substance in sediments under aerobic conditions are available. Simulation tests with sediments under anaerobic conditions performed over a period of 14 days resulted in a primary degradation half-life of approximately 7 days. However, based on the physicochemical properties of the substance it is predicted that no significant adsorption to the sediment will occur. No biodegradation in the aquatic environment is thus taken into account in the environmental risk assessment for TCP. In contrast to the aquatic tests, the available simulation test on biodegradation under aerobic conditions in silty and sandy loam soil samples resulted in notable degradation of 1,2,3-trichloropropane with a primary degradation half-life of 2.7 days, which is considered in the environmental risk assessment.

Degradation in water under aerobic conditions

The available reliable screening study on biodegradation of the test substance 1,2,3-trichloropropane in water under aerobic conditions (in accordance with OECD Guideline No. 301C) showed practically no biodegradation of the substance at 25 °C and during the test period of 28 days (MITI 1992). The biodegradation was estimated by determination of the BOD (0 % degradation), the TOC (0 % degradation) and gas chromatographic analysis of the test material content (0 to 22 % degradation, mean 7.7 %). A study on the inherent biodegradability of the closely related substance 1,2-dichloropropane (DOW 2003) using a modification of the Zahn-Wellens/EMPA test (OECD 302B) concluded that the test substance was not biodegradable under the test conditions although it was not inhibitory to the activity of the inoculum.

Degradation in sediment under aerobic/anaerobic conditions

The reductive dechlorination of 1,2,3-trichloropropane was tested under anoxic conditions using anaerobic sediment samples taken from a river in the central Netherlands. The test was carried out for 14 days with a number of sealed, air-tight testing tubes with the lowest chemical concentration possible (10 mmol derived from the zero-order reaction rate constant and the test duration of 14 days). During testing period the reductive degradation was studied by sacrificing at regular intervals testing tubes and analysing the concentration of the test substance by gas chromatography. The degradation followed zero-order kinetics and the reaction rate constant was 0.71 mmol/L per day and the resulting half-life for primary degradation was 7 days.

Degradation in soil under aerobic conditions

The biodegradation in soil under aerobic conditions was studied with two soil samples (silt loam and sandy loam) in a seven day laboratory test using air dried soil samples (Anderson et al. 1991). The toxicity of the substance to soil microorganisms was first tested in a 7-day pre-test. An infrared gas analyser was used to measure CO2 efflux from incubated (20 °C) 50 g soil samples. Every 24 hours a flow of moist CO2-free air was passed through the incubation jars. Toxicity determinations were based on whether microbial respiration in the soil had returned to control levels by the end of the 7-day experiment. Chemical degradation of the substance was then tested with two soils in incubation jars which were fitted with charcoal traps to determine the amount of chemicals lost from soil to the headspace. Chemical solution was added to the soils which were adjusted to 80 % water holding capacity. The soils were afterwards incubated at 20 °C in the dark. Every 24 hours the jars were flushed with a stream of cleaned air to sample the charcoal traps and also to maintain aerobic conditions. The soil was extracted in toto from the jars on days 0, 2, 3, 6 and 7 and the test substances was extracted with methanol to monitor the degradation of 1,2,3-trichloropropane. The chemical was analysed by gas chromatography. The half-life for biodegradation of 1,2,3-trichloropropane under aerobic conditions found in the two loam samples was about 2.7 days.