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Description of key information

Phototransformation in water is not expected to be a significant removal process.

Key value for chemical safety assessment

Additional information

There is no information available for phototransformation in water of TOPP as a whole substance. Phototransformation in water is not expected to be a significant removal process for the substance due to low light absorption and low light intensity in most natural waters.

Kieber et al 1996 exposed solutions of dimethyl sulfide in natural water to sunlight for a fixed solar flux of 0.3 W.h.cm-2 (3-5 h of exposure depending on the cloud cover). The solutions were also exposed in laboratory experiments using a lamp.

The photolytic turnover rate for dimethyl sulfide ranged from 0.05 to 0.15 day-1. The photolysis of dimethyl sulfide followed pseudo-first order kinetics at concentrations less than 50 ± 15 nM. In laboratory experiments, the photolysis of 20 nM dimethyl sulfide was followed to 75% completion. No loss was observed in dark controls.

This data gives insufficient information to draw any conclusions on rates of phototransformation in water.Therefore, no adjustment is made to the predicted half-life of 1 x 106 days (EUSES 2.1.2) for photolysis of dimethyl sulfide in surface water for TOPP Block 5.

 

Reference:

Kieber D J, Jiao J, Kiene R P and Bates T S (1996). Impact of dimethylsulfide photochemistry on methyl sulfur cycling in the equatorial Pacific Ocean. Journal of Geophysical Research, Vol. 101, No. C2, Pages 3715 -3722, February 15, 1996.