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Environmental fate & pathways

Phototransformation in air

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Description of key information

A paper published by Chang et all (1977) describes the generation of rate constants of hydroxyl radicals with five halocarbons measured by use of a discharge flow apparatus using resonance fluorescence detection of OH over a temperature range of 250 - 400K. The experimental data from the study indicates that the life of 1,1,1-trichloroethane in the atmosphere is in the range of 3.8 to 6 years. The Arrhenius rate constant for trichloroethane is 1.95 x 10E-12. The findings obtained are compared with those of others workers in this field together and confirm their kinetic significance with regard to stratospheric pollution problems. 

Key value for chemical safety assessment

Half-life in air:
1 388 d

Additional information

Environmental distribution models predict that > 95% of trichloroethane will accumulate in the atmosphere therefore in view of its persistence its inclusion in Montreal Protocol is fully justified. The information provided in the reports indicate that hydroxyl radicals are primarily responsible for its removal but the time period over which removal occurs is extended (3.8 - 6 years). It is worth noting that the information from other studies used to address this endpoint clearly shows that 1,1,1 -trichloroethane represents a much lower risk to the ozone layer than flourinated materials which have a much longer half-life.