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Sodium toluene-4-sulphonate is a member of the Hydrotropes Category, which comprises substances used to solubilise complex formulas in water. It is structurally related to the substances of the OECD SIDS Hydrotopes category, comprising three sub-groups: the methyl, dimethyl and methylethyl benzene sulphonates (or the toluene, xylene and cumene sulphonates). As defined in the ‘Read-Across Justification Document’ section 13, data provided for this category are representative of sodium toluene-4-sulphonate and suitable for assessment purposes. Experimental data for the Hydrotrope category has been evaluated and trends in the environmental fate of these hydrotropes were used to meet the requirements for the biodegradation endpoint.

 

A ready biodegradation study by Brunswick-Titze (2004) using sodium toluene sulphonate (CAS 657-84-1) in OECD 301B guideline test reported almost complete biodegradation by the end of the 28-day test of 99.8% with more than 60% degradation recorded after 7 days. When supporting studies are considered, it is clear that hydrotropes are biodegradable with most studies achieving greater than 69% and higher degradation rates after 28 days. It is concluded that given the similarity between sodium toluene-4 -sulphonate and the hydrotrope substances tested using the OECD biodegradation test guidelines, as well as similar physico-chemical properties and structure, it is fully expected that sodium toluene-4-sulphonate is readily biodegradable. In addition, the OECD SIDS Report (2006) for the hydrotropes category concluded that “studies across the hydrotropes category demonstrate rapid and complete biodegradation under aerobic conditions and the hydrotropes are considered to be readily biodegradable according to OECD criteria”. The OECD SIDS Report conclusion supports the experimental evidence provided.