Diisooctyl adipate

Toxicity to terrestrial plants

Description of key information

The chemical safety assessment according to Annex I of Regulation (EC) No. 1907/2006 does not indicate the need to investigate further the toxicity to terrestrial plants. 

Additional information

No experimental data on toxicity to terrestrial plants are available for the category PFAE linear. However, for the assessment of terrestrial toxicity three studies investigating the acute toxicity to earthworm are available for the category PFAE linear. The results of all tests show LC50 values well above 100 mg/kg soil dw for Eisenia fetida. No further experimental data evaluating the toxicity to soil organisms is available for any other member of the PFAE linear. However, the members of the PFAE linear are not expected to pose a risk to terrestrial organisms (see below). Therefore, in accordance with Regulation (EC) No. 1907/2006, Annex X, Column 2, 9.4 further studies on the effects on terrestrial organisms does not have to be conducted since the chemical safety assessment indicates that there is no need.

Intrinsic properties and fate/ exposure

All members of the PFAE linear category are readily biodegradable. According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs) (ECHA, 2012b). If direct/indirect application of these substances occurs (indirect via sludge application) the substances will again be rapidly degraded until ultimate biodegradation. In addition, for some category member direct and indirect exposure to soil can be excluded (see table above).

Aquatic and terrestrial ecotoxicity data

The PFAE linear is a robust category with sufficient experimental data for the aquatic toxicity covering acid carbon numbers from C6 to C10 and total carbon numbers ranging from C10 to C38. Short-term aquatic toxicity data is available for all trophic levels within the PFAE linear category. Long-term data is available for aquatic invertebrates and algae. Based on the experimental data, the majority of category members exhibit no acute and chronic toxicity to aquatic organisms. Only two ester with Adipic acid (C6) as dicarboxylic acid component and short chain alcohols, are supposed exhibit toxicological effects (CAS 105-99-7, Dibutyl adipate and CAS 6938-94-9, Diisopropyl adipate) to aquatic organisms. Nevertheless, the absence of chronic or long-term toxicological effects in aquatic organisms up to the substance solubility limit, can, as ECHAs Guidance R.7c states, can be used as part of a Weight of Evidence argument to modify/waive the data requirements of Annex IX and X. There are three chronic tests on aquatic invertebrates available for insoluble category members (i.e. CAS 103-23-1 Bis(2-ethylhexyl) adipate; CAS 33703-08-1 Diisononyl adipate and CAS 103-24-2 Bis(2-ethylhexyl) azelate. These substances exhibit log Kow values > 5 and a water solubility < 0.05 mg/L. In none of these tests effects on Daphnia were observed in nominal concentrations well above the limit of water solubility. This result is also supported by algal toxicity data where either all NOEC´s are above 1mg/L or where no toxicity was observed within the water solubility. Therefore, it is assumed that due to the lack of chronic aquatic toxicity, long term tests on terrestrial organisms will not result in a different outcome. Therefore no chronic tests for terrestrial organisms are either provided, or deemed as necessary for the chemical safety assessment.

For the assessment of terrestrial toxicity three studies investigating the acute toxicity to earthworm are available for the category PFAE linear, covering “poorly or insoluble” members (i.e Bis(2-ethylhexyl) adipate CAS 103-23-1 and Bis(tridecyl) adipate CAS 16958-92-2) to “water soluble” members (i.e. Dibutyl adipate CAS 105-99-7). The results of all tests show LC50 values well above 100 mg/kg soil dw for Eisenia fetida.

Available reliable data for toxicity to aquatic microorganisms for the PFAE linear category members support the assumption of a lack of toxicity to soil organisms, including soil microorganisms. No inhibition of respiration rate of aquatic microorganisms was observed in any of the available studies for the PFAE linear members. The Guidance Document (ECHA, 2012) states that a test on soil microbial activity will only be additionally necessary for a valid PNEC derivation if inhibition of sewage sludge microbial activity has occurred and this is clearly not the case.

Metabolisms/Bioaccumulation

After absorption, members of the PFAE linear category are expected to be enzymatically hydrolysed in vivo by the ubiquitary enzyme carboxylesterase, yielding the corresponding alcohols and acid. QSAR estimations using BCFBAF v3.0 support the expected rapid biotransformation of this substance with BCF/BAF values of < 29 L/kg, respectively (Arnot-Gobas estimation including biotransformation, upper trophic level).

The metabolism of the hydrolysis products: alcohol (e.g. Isopropanol) and dicarboxylic acid (e.g. Adipic acid) is well established and not of concern in terms of bioaccumulation (for further information see chapter 5.3 of the technical dossier).

Conclusion

All members of the category PFAE linear are unlikely to pose a risk for terrestrial organisms based on a) the lack of chronic exposure due the ready biodegradation, b) the absence of bioaccumulation potential and c) the low toxicity as expected for this substance for terrestrial organisms based on metabolism considerations and available short term tests to earthworm. Taking all the available information into account toxicological effects on soil organisms are thus not expected to be of concern, and consequently, in accordance with Regulation (EC) No. 1907/2006, Annex X, Column 2, 9.4 further studies on the effects on terrestrial organisms do not have to be conducted since the chemical safety assessment indicates that there is no need.

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