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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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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 (test concentration for TCP was not provided, but was below 2E-05 mol/L). During testing period the reductive degradation was studied by sacrificing testing tubes at regular intervals and analysing the concentration of the test substance by gas chromatography. The primary degradation under anaerobic conditions followed zero-order kinetics and the reaction rate constant was 0.71 mmol/L per day. The resulting half-life for primary degradation was 7 days.

The reductive dehalogenation of TCP under anaerobic conditions is linear. There was no lag phase of degradation in the present study and microbial populations may be able to immediately utilise the contaminant. No increase in degradation velocity was observed over time and constant dehalogenation of TCP occurred. Two explanations for these observations are possible: Either the microbial populations able to utilise 1,2,3-trichloropropane had a limited capacity for dehalogenation, which did not grow in the course of the 14-day testing period meaning that the population size did not significantly change over the testing period. Or the bioavailability of the test substance at the test concentration may be limited and dehalogenation of the substance may require a certain period of time.