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Environmental fate & pathways

Biodegradation in water: screening tests

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The biodegradation in water of the test substance TCP was studied under aerobic conditions in a standard screening test (MITI 1992a) performed in three parallel series in accordance with OECD Guideline No. 301C. To this end 100 mg/L test substance and 30 mg/L activated sludge were added to a total test volume of 300 mL. The test was performed at 25 °C for 28 days. 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 %). In conclusion, the study found that TCP is not readily biodegradable in water under aerobic conditions. The inherent biodegradability of the closely related 1,2-dichloropropane was assessed using a modification of the Zahn-Wellens/EMPA test (DOW 2003). The test was in accordance with OECD Guideline No. 302B. Reaction mixtures were prepared by dispersing activated sludge from a municipal wastewater treatment plant in a standard mineral medium. Reaction mixtures were amended with 150 mg/L 1,2 -dichloropropane and incubated in closed vessels to minimize the loss of test material due to volatilization. Oxygen concentrations in the headspace of the vessels were monitored and oxygen gas was added as necessary to ensure that aerobic conditions were maintained. The reaction mixtures were continuously mixed and incubated at 22 ± 1 °C for 28 days. Compound specific analyses of 1,2 -dichloropropane in the liquid phase of the reaction mixtures by gas chromatography with flame ionization detection (GC-FID) showed little difference in test material concentrations over time between viable and abiotic control mixtures (biologically inhibited with mercuric chloride). Thus, 1,2 -dichloropropane did not biodegrade under the conditions of this test. Measurement of dissolved organic carbon (DOC) concentrations in the reaction mixtures confirmed the results of the GC-FID analyses. The studies indicate that a biodegradation of TCP in the aquatic environment is unlikely under aerobic conditions. The CICAD 56 document for TCP (WHO) discusses a preliminary study on the co-oxidative transformation of the substance by the ammonia-oxidising bacterium Nitrosomonas europaea (Vannelli et al. 1990). In the experiment, the chlorinated substrate at a concentration of about 6.8 mmol/L was reduced to a residual amount of 91 % in the absence of the energy source ammonia and to 77 % in the presence of ammonia after 24 hours of incubation.