Registration Dossier
Registration Dossier
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EC number: 202-905-8 | CAS number: 100-97-0
Endpoint summary
Administrative data
Description of key information
In the atmosphere, methenamine is expected to be degraded by photochemical processes with a half life of < 1 hour.
The conversion rate of methenamine to formaldehyde at a constant ionic strength was found to be pH dependent, with a reaction half-life decreasing from 13.8 h at pH 5.8 to 1.6 h at pH 2.0.Thevalue below is given forpH 5.8.
Additional information
In the atmosphere, methenamine is expected to be degraded by photochemical processes with a half life of < 1 hour.
In aqueous systems, methenamine is susceptible to hydrolysis. The process is strongly pH depending. At acidic pH-levels the substance is degraded in a few hours, at neutral and basic pH-levels the half life increases to several days.
After the release of the remaining substance from the waste water treatment plant into surface water, methenamine is expected to be further degraded hydrolytically to ammonia and formaldehyde. This needs to be considered especially for acidic receiving waters. Formaldehyde is classified as readily biodegradable (OECD 2002), and hence expected to be degraded by microbial activity. Ammonia is natural widely occurring, e.g. as excretion product of aquatic organisms. Ammonia is expected to volatilise from water to a certain degree. Under aerobic conditions it is transformed by nitrifying bacteria to nitrite and nitrate. As a realistic worst case for the degradation of methenamine a hydrolytical half-life of ~ 10 days is assumed. The half-life for the biodegradation of the hydrolysis products is estimated to be 15 days (according to the TGD, 2003). Hence, as realistic worst-case a half-life of 15 days, corresponding degradation rate constant of 0.046 d-1 is used for the exposure estimation.
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