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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The ready biodegradability of the registered substance was determined via read-across to the results of biodegradation testing on a structurally similar substance (tosyl salt). The substance was found to be readily biodegradable but without meeting the 10 day window criteria.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window

Additional information

The biodegradation potential of the registered substance was determined via read-across to testing on the structurally similar substance tosyl salt. The tosyl salt was tested in accordance with the OECD Guideline for Testing of Chemicals 301B using activated sludge of a sewage treatment plant receiving predominantly domestic sewage. The test was conducted over a period of 28 days. After 28 days the biodegradation of the test substance was recorded as 76.84% (based on CO2 evolution) and 72.03% (based on DOC). Based on measuring the test substance concentration by HPLC, the test substance was < 0.1 mg/L at the 14th day of the test. The test item is regarded as readily biodegradable without meeting the 10 day window criteria.

In addition, the ready biodegradation of a formulated product containing tosyl salt was determined in accordance with OECD Testing Guideline 302B. The test material was found to be ultimately, but not inherently, biodegradable in this study. Read-across between the registered substance and tosyl salt is considered justified owing to the structural similarity of the two substances. Both are salts of a carboxylic acid and triethanolamine. The acid components are structural isomers and differ only in the position of a single methyl group in the N-methyl salt. This is not expected to change the behavior or properties of the substances, and both substances have shown similarity in the results of other physical endpoints such as water solubility.

Read-across between the tosyl salt carboxylic acid (6-[(p-tosyl)amino]hexanoic acid) and the registered substance is considered justified as the registered substance is manufactured directly from 6-[methyl(phenylsulphonyl)amino]hexanoic acid by simple neutralisation with triethanolamine (TEA). 6-[methyl(phenylsulphonyl)amino]hexanoic acid and 6-[(p-tosyl)amino]hexanoic acid are structural isomers. They are the same molecular weight and differ only in the position of a single methyl group. In the former, the methyl group is bound to the nitrogen atom of the sulphonamide linkage whereas in the latter, it resides on the aromatic ring. Other than ionization of the carboxylic acid group, the 6-[methyl(phenylsulphonyl)amino]hexanoic acid remains chemically unchanged upon salt formation. In water, the acid and amine components of 6-[methyl(phenylsulphonyl)amino]hexanoic acid, compound with 2,2’,2’’-nitrilotriethanol (1:1) dissociate completely and behave essentially as independent substances. Since TEA can be considered non-hazardous, it is the acid component of the salt that will have a more significant impact on the outcome of any (eco)toxicological or environmental tests.