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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

There is a single biodegradation study for sodium toluene-4-sulphonate as well as six studies for three closely related substances that demonstrate the hydrotropes are readily biodegradable.   
There are 5 additional guideline biodegradation tests for closely related substances discussed below. Three of the four Modified Sturm tests concluded "readily biodegradable". The remaining Modified Sturm test reached 82-87% CO2 in 28 days but did not achieve 60% CO2 until day 16. A Closed Bottle test concluded the test substance was inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

To determine the biodegradation characteristics of sodium toluene-4-sulphonate the following important studies have been conducted on substances in the same hydrotopes category:

- Brunswick-Titze (2004), sodium toluene-4-sulphonate

- Albright and Wilson (1995), sodium cumene sulphonate

- Ruetgers-Nease (1993), sodium cumene sulphonate

- Ruetgers-Nease (1994), calcium xylene sulphonate

- Albright and Wilson (1995), sodium xylene sulphonate

- Bazzon (1993), sodium xylene sulphonate

- Ruetgers-Nease (1993), sodium xylene sulphonate

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 Hydrotropes category, comprising three sub-groups: the methyl, dimethyl and methylethyl benzene sulphonates (or the toluene, xylene and cumene sulphonates). In addition, there are differences in counter ions (i.e. Na+, NH4+ and Ca++) in commercial hydrotropes. The chemical reactivity of the different counter ions is not expected to significantly influence the physical and chemical behaviour of the compounds with regard to environmental fate, ecotoxicity and mammalian toxicity. The presence of one or two methyl groups or a methylethyl group on the benzene ring is not expected to have a significant influence on chemical reactivity. As defined in the ‘Read-Across Justification Document’ section 13, data provided for this category are representative of potassium p-cumene sulphonate and suitable for assessment purposes. Experimental data for the Hydrotrope category has been evaluated and trends in the environmental fate of these hydrotopes were used to meet the requirements for the biodegradation endpoint.

 

Experimental studies on four members of the hydrotrope category of substances confirm ready biodegradability for sodium toluene-4-sulphonate. The key study (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. Two OECD 301D (closed bottle test) guideline studies were undertaken using sodium cumene sulphonate and sodium xylene sulphonate (both by Albright and Wilson, 1995) with each reporting >=50% and >=40% at 28 days, respectively. The substances were biodegradable, although did not achieve ready biodegradability. In studies by Ruetgers-Nease (1993) OECD 301B (CO2 evolution test) guideline tests reported complete biodegradation for sodium cumene sulphonate and between 83 and 85% biodegradation using sodium xylene sulphonate after 28 days. Ruetgers-Nease (1994) and Bazzon (1993) both undertook OECD 301B guideline tests using calcium xylene sulphonate and sodium xylene sulphonate and reported more than 69 to 87% after 29 days and 86 to 88% after 28 days, respectively.

 

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. The key study, supported by a number of biodegradation studies using hydrotropes, confirms that the hydrotrope category substances are 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 hydrotopes are considered to be readily biodegradable according to OECD criteria”. The OECD SIDS Report conclusion supports the experimental evidence provided.