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Environmental fate & pathways

Phototransformation in air

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Photooxidation of dichloromethane can be estimated using a computer model accepted by the US EPA. The Atmospheric Oxidation Program for Microsoft Windows (AOPWIN) is a programme for estimation of indirect photo-oxidation which estimates the rate constant for the atmospheric, gasphase reaction between photochemically produced hydroxyl radicals and organic chemicals and calculates atmospheric half-lives for organic compounds based upon average atmospheric concentrations of hydroxyl radicals and ozone. Therefore, this model is reliable, adequate and relevant to dichloromethane. Thus, a half life of 79.306 days is estimated for reaction of dichloromethane with hydroxyl radicals in the atmosphere at 25oC [AOPWIN Program, v.1.92].

Overall QSARs estimated half-life for degradation of dichloromethane in air based upon AOPWIN Model is 1808 hours (75.33 days).

Based on the data on photochemical degradation of dichloromethane in the air, it is not considered to rapidly degrade in the atmosphere via photooxidation process.

The following information is taken into account for any hazard / risk / persistency assessment:

AOPWINProgram, v.1.92 estimated data:

Reaction with hydroxyl radicals at 25oC:

Overall OH Rate Constant: =0.1349 x 10-12cm3/molecule-sec

Half Life: =79.306 days (12-hour day; 1.5x106OH/cm3)