Registration Dossier
Registration Dossier
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EC number: 200-813-2 | CAS number: 74-83-9
Phototransformation in water
Administrative data
Link to relevant study record(s)
Description of key information
Results from the studies “Photohydrolysis of Methyl Bromide”, Lee, H., 1993 and “Photohydrolysis of Methyl Bromide and Chloropicrin”, Castro, C. E. and Belser, N. O, 1981, indicated that methyl bromide degradation was enhanced by light (or irradiation) and that the principal degradation products formed were inorganic bromide ions and methanol (CH3OH). Furthermore, the study “Methyl Bromide and Bromide Ion in Drainage Water after Leaching of Glasshouse Soils” Wegman, R. C. C, Greve, P. A., De Heer, H., Hamaker, P. H., calculated the average DT50 for the decline of methyl bromide in surface waters under field conditions to be 6.6h at a temperature of ~11ºC. The major degradants of methyl bromide photohydrolysis are described in the European Commission Guidance Document SANCO/221/2000 – rev. 10 Final (February 25, 2003) which includes inorganic compounds, not containing a heavy metal and organic compounds of aliphatic structure, with a chain length of 4 or less, which consist only of C, H, N, or O atoms and which have no alerting structures as degradation products of no concern. Thus inorganic bromide ions and methanol are considered to be degradation products of no concern and no additional data is required as set out by the aforementioned working document. No identification of photo-hydrolysis products, estimation of DT50 values, determination of quantum yield of direct phototransformation, calculation of a theoretical lifetime in the top layer of aqueous systems, and determination of mass balance is appropriate for metabolites, degradation and reaction products of methyl bromide. Therefore, it is proposed that these points are not relevant to methyl bromide.
Key value for chemical safety assessment
- Half-life in water:
- 10 d
Additional information
Methyl bromide hydrolysis rate can be markedly enhanced by light. Irradiation of aqueous solutions with UV light caused a 6-7 fold increase of the rate constants with respect to samples exposed to natural, diffuse light in the laboratory at the same conditions and temperatures. As a result, the half-life of methyl bromide under test conditions is reduced to a range of 10.0 to 13.0 (days). Bromide ions were the only detected degradant, although the proposed reaction pathways describe methanol.
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