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Environmental fate & pathways

Phototransformation in air

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Description of key information

Weight of evidence is used for this endpoint with several studies reporting similar values for half life and rate constants.
TEL compounds have atmospheric half lives from a minimum of several hours to a maximum of a few days. They are transformed primarily to the more stable TriEL and DiEL species through reactions with OH radicals. TEL exists mainly in the gas phase with only a very small percentage bound to aerosol particles. The longest half life figure of 60 hours (Neilsen et al for winter) is used here for CSA purposes. However most studies show half lives of only a few hours particularly in summer conditions. A rate constant in ozone of 10.9x10-18 cm3/molecule/second and 75 x 10-12 cm3/molecule/sec for OH radicals are proposed from Harrison and Laxen (other sources quote rate constants for OH radical in the range 11.6 to 75 x 10-12 cm3/molecule/sec

Key value for chemical safety assessment

Half-life in air:
12.7 h
Degradation rate constant with OH radicals:
10.9 cm³ molecule-1 s-1

Additional information

TEL reacts in the gas phase relatively rapidly to the more stable TriEL and DiEL species and finally to inorganic lead. A small portion of the organic lead compounds in the atmosphere is absorbed to aerosol particles where degradation can also occur. Various studies have been reported investigating the reactions of TEL to direct photolysis, reaction with atomic oxygen in triplet condition, reactions with ozone and reactions with hydroxy radicals. The reaction with OH radicals is the predominant degradation pathway under natural conditions. The reaction with atmospheric oxygen is negligable.

Photolytic degradation is dependent on the intensity of the sun and is thus subject to seasonal fluctuations. TEL has been proven to be relatively stable in the dark. TEL compounds have atmospheric half lives from a minimum of several hours to a maximum of several days. They are transformed primarily to the more stable TriEL and DiEL species through reactions with OH radicals. TEL exists mainly in the gas phase with only a very small percentage bound to aerosol particles. The longest half life figure of 12.7 hours (Harrison et al 1986) is used here for CSA purposes. However most studies show half lives of only a few hours particularly in summer conditions. A rate constant in ozone of 10.9x10-18 cm3/molecule/second and 75 x 10-12 cm3/molecule/sec for OH radicals are proposed from Harrison and Laxen (other sources quote rate constants for OH radical in the range 11.6 to 75 x 10-12 cm3/molecule/sec