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Environmental fate & pathways

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Peer reviewed scientific evidence shows that dichloromethane degrading microorganisms ultimately degrade dichloromethane, are wide spread and have a high growth rate. This scientific evidence and the adequate ready biodegradability test result obtained, lead to the conclusion that dichloromethane is readily biodegradable. Peer reviewed scientific evidence is shown for dichloromethane biodegradation both under aerobic and anaerobic conditions.

In the sewage treatment plant, biodegradation will not be a significant sink due to the volatility of dichloromethane. Dichloromethane is reported to completely biodegrade under aerobic conditions with sewage seed or activated sludge between 6 hours to 7 days. 86-92 % conversion to CO2 will occur after a varying acclimation period using anaerobic digestion in wastewater. Dichloromethane was degraded at a concentration of 200 µg/litre in the aqueous phase of natural sediment. Degradation was observed to proceed via methylchloride, although accumulation was not observed , the corresponding half-life is 10.9 d. The aerobic degradation of dichloromethane was observed in a variety of (sub)surface soils (a sand, a sandy loam, a sandy clay loam and a clay soil). Degradation was also observed in the sandy loam soil under anaerobic conditions. Degradation was found to occur over concentrations ranging from appr. 0.1 to 50 ppm. No products other than carbon dioxide were detected in the biologically active microcosms. The time required for 50% disappearance of the parent compound ranged from 1.3 to 191.4 days. The dichloromethane was also observed to be degraded in the sandy loam soil under anaerobic conditions. Dichloromethane degradation was observed under anaerobic conditions in sandy loam soil. The removal of dichloromethane from aerobic soil was significantly increased following exposure to methane.