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Environmental fate & pathways

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Experimental studies for four members of the Hydrotrope Category of substances confirm ready biodegradability of Hydrotropes. Each study was evaluated as Klimisch 1 or 2. The key study (Brunswick-Titze, 2004) using sodium toluenesulphonate in an OECD 301B guideline test reported almost complete biodegradation by the end of the 28-day test of 99.8% and met the 10-day window test with more than 60% degradation recorded after 7 days. Consistent and similar biodegradation was seen in CO2 evolutionary studies (OECD 301B) for sodium cumenesulphonate (>100%), calcium xylenesulphonate (>=69 to <= 87%), sodium xylenesulphonate (>=86 to <= 88% and >=83 to <= 85%). Lower biodegradation rates were observed when using the oxygen consumption test (OECD 301D), although it was still concluded that the test substances, sodium cumenesulphonate and sodium xylenesulphonate, were biodegradable. 

It is concluded that, given the structural and physico-chemical similarities between substances in the Hydrotropes category, that these tests are representative of substances across the whole category. The key study, supported by similar biodegradation studies, confirms that the Hydrotrope category substances are readily biodegradable.

In addition, the OECD SIDS Report (2006) for the Hydrotrope category concluded that “studies across the hydrotrope 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 and demonstrates consistency across the category.

The need for a bioaccumulation study for all the hydrotrope substances under REACH is waived. When the Log Kow is below 3, then in accordance with Annex IX of Regulation (EC) No 1907/2006, testing requirements can be waived as the substance has a low potential for bioaccumulation. The Log Kow is available for most of the category substances and the values range between -3.18 and 0.07.

Additional evidence was provided by two bioaccumulation studies published in the SIDS Dossier for Hydrotropes. Both are experimental studies carried out in 2006 by the Chemicals Evaluation and Research Institute (CERI, Japan) in accordance with OECD Guideline 305 bioconcentration: flow-through fish test methodology. The OECD reviewers considered the two studies to be reliable (Klimisch 2). The same fish species (Cyprinus sp.), duration (42 days) and endpoints were assessed with concentrations confirmed by HPLC analysis. One study assessed sodium xylenesulphonate and the other is its analogue, sodium toluenesulphonate. Both aquatic tests were consistent and determined bioconcentration factors of <2.3 (dimensionless). When the bioconcentration factor (BCF) is below 2000, then testing requirements can be waived in accordance with Annex IX of Regulation (EC) No 1907/2006.

The measured BCFs for sodium xylenesulphonate and sodium toluenesulphonate are very similar (identical) and bioaccumulation is not expected in either case. Both substances are considered not bioaccumulative since measured BCF are < 2000.This conclusion is further evidenced by the measured partition coefficients for Hydrotropes with Log Kow of -3.18 to 0.07. In conclusion, Hydrotrope category substances are not considered to be bioaccumulative.

Further testing to evaluate the hydrolysis, adsorption/desorption and distribution of hydrotropes are waived on the basis of ready biodegradability in the environment.