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Short-term toxicity data for each type of organism indicate the Hydrotropes are of low toxicity to aquatic organisms. The two available fish studies for sodium xylenesulphonate and calcium xylenesulphonate report similar acute toxicity values of > 1,000 and 1,580 mg/L. 

A range of short-term data is available for aquatic invertebrates from 40.3 to > 1,020 mg/L corresponding to four Hydrotrope category substances. Two studies report similar values at the upper end of the range (>1,000 and >1,020 mg/L) and three studies report similar results with values of >40.3, >40.3 and 54 mg/L at the lower end of the range. The test design and concentration gradients used in the studies influence the reported toxicity values. Toxicity was not observed in the studies where the results are reported as “>” or “>=”. The measured value of 54 mg/L is considered to be an outlier and it is concluded that toxicity to aquatic invertebrates is >1,000 mg/L (key study).

Short-term toxicity to algae was reported in three studies corresponding to three different Hydrotrope category substances. The EC50based on growth rates ranged from 150 mg/L to >758 mg/L. The consistent trend is for low toxicity to algae across the Hydrotrope category.

Two activated sludge respiration inhibition studies were available for sodium toluenesulphonate and sodium cumenesulphonate. Both reported no toxicity at the limit test concentration, which was 1,000 mg/L for both substances. These studies indicate Hydrotropes are of comparable and low toxicities to microorganisms involved in sewage treatment processes.

From the available short-term toxicity data it can be concluded that aquatic organisms are of low sensitivity to Hydrotrope category substances. Most studies across the three trophic levels report no toxicity at the highest concentration tested. The Hydrotrope category substance with the lowest toxicity values for invertebrates and algae appears to be sodium toluenesulphonate. In addition, the studies relating to microbial activity (respiration) indicate low potential for toxicity at similar concentrations to fish, invertebrates and algae. As a combined body of evidence the toxicity data for these test substances can be considered to be representative of the Hydrotropes category. Long-term toxicity data for Hydrotropes were not available to compare sensitivities between the category of substances, however long-term toxicity studies are not required based on the low acute toxicity and ready biodegradability of the Hydrotropes. On this basis, the reliable aquatic toxicity data can be used to fill the data gaps in aquatic toxicity across the category in accordance with guidance set out in Chapter R.6 (ECHA, 2008).