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Sediment toxicity

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Description of key information

Key value for chemical safety assessment

Additional information

No experimental data evaluating the toxicity to sediment organisms is available for 3,5,5-trimethylhexyl 3,5,5 trimethylhexanoate  (CAS 59219-71-5). The substance is not toxic to aquatic organisms up to the limit of water solubility and in addition, available data indicate that 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate is not bioaccumulative. Based on the available information, toxicity to sediment organisms is not expected to be of concern.

 

Intrinsic properties, fate and bioaccumulation

3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate (CAS 59219-71-5) exhibits a log Koc value ≥ 3.9 and is poorly water soluble (1.5-4.4 µg/L at 20 °C). The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2014) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, based on the results of the ready biodegradation test, it is expected that activated sludge will rapidly mineralize the substance. Thus, discharged concentrations of this substance (if at all) into the aqueous/sediment compartments are likely to be low.

Moreover the quick metabolism of aliphatic esters and their enzymatic hydrolysis products demonstrated in the literature in numerous organisms, as well as the estimated BCF/BAF values obtained with the Arnot-Gobas model (BCF and BAF values were calculated to be 152.9/703.9 L/kg, respectively), both indicate that 3,5,5-trimethylhexyl 3,5,5 trimethylhexanoate will not be bioaccumulative.

Considering this, one can assume that the 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate exposure in the sediment environment is generally low, which reduces the probability of chronic exposure of sediment organisms.

 

Aquatic ecotoxicity data

Aquatic toxicity tests of the substance to fish, invertebrates and microorganisms showed no adverse effects in the range of the water solubility (1.5-4.4 µg/L at 20 °C). The obtained results indicate that the test substance is likely to show no toxicity to sediment organisms as well.

 

Conclusion

Taking into account the intrinsic properties of 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate, significant adsorption and biodegradation will take place in conventional STPs, and consequently only low concentrations are expected to be released (if at all) into the aquatic environment. So the exposure of the aquatic and sediment compartments are considered to be negligible. Moreover since the substance is not bioaccumulable, it will not reach levels of concern into the organisms. So the chronic exposure of sediment organisms can be considered of no concern.  

Furthermore, chronic toxicity to aquatic organisms showed that no effects occur up to the limit of water solubility. Therefore 3,5,5-trimethylhexyl 3,5,5-trimethylhexanoate is unlikely to pose a risk for sediment organisms and testing is thus omitted.

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within the CSR.

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