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Toxicity to soil microorganisms

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Description of key information

EC50 > 1000 mg/kg dw soil

Key value for chemical safety assessment

Additional information

Since no experimental data investigating the effects on soil microorganisms are available for fatty acids, C8-10, tetraesters with pentaerythritol (CAS 85586-24-9), in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 a read across to a structurally related group member 2,2-bis(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25151-96-6) was conducted. This read-across is justified in detail in the overall summary (IUCLID chapter 6.1) and within the category justification in IUCLID Section 13. Both substances are esters with pentaerythritol as alcohol and only differ in their carbon chain lengths (the target substance exhibits carbon chain lengths of C and C10 and the read-across substance chain lengths of monounsaturated C18).

In the GLP study the toxicity to soil micro-organisms with 2,2-bis(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25151-96-6) was tested according to OECD 216. The EC50 for the nitrogen transformation was calculated to be > 1000 mg/kg dw soil (the highest concentration tested). This result concludes that there were no long term adverse effects on nitrogen transformation in soils.

As the read-across is based on extrapolation, further studies on effects on terrestrial organisms are also taken into consideration for this assessment.

Since fatty acids, C8-10, tetraesters with pentaerythritol (CAS 85586-24-9)is readily biodegradable, a chronic exposure of terrestrial organisms is not likely. Nevertheless, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances and read-across, a read-across to a structurally related category member was made in order make an assessment of chronic exposure. Further justification is given within the endpoint summary 6.1 and within the category justification section 13. In this case of read-across, the best suited (highest degree of structural similarity, nearest physico-chemical properties) read-across substance within this category was used. The read-across substances are covering the other end of the variability of the group with longer fatty acid chain lengths (≥ C16) and are mono- to tetra-esters. Due to the higher adsorption potential with the longer fatty acid chains, these substances represent a worst case for the uptake via ingestion of soil bounded particles.

Chronic tests with the group members 2,2-bis(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25151-96-6), fatty acids, C16-18 and C18-unsaturated, esters with pentaerythritol (CAS 85711-45-1) and fatty acids, C16-18 and C18-unsatd., tetraesters with pentaerythritol (CAS 68604-44-4) were conducted according to OECD 222 under GLP conditions. No mortality or effects on reproduction of earthworms up to 1000 mg/kg dw soil occurred in any of these three tests.

Moreover, chronic toxicity tests with aquatic invertebrates are conducted with the read-across substances decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS No. 71010-76-9) and fatty acids, C16-18 and C18-unsaturated, esters with pentaerythritol (CAS 85711-45-1). The target as well as the first read-across substance both possess shorter fatty acid chain lengths (≤ C10) and pentaerythritol and are tetra-esters. The second read-across substancecovers the variability of the group with longer fatty acid chain lengths (≥ C16) and is a mono- to tetra-ester.Both read-across substances did not show any chronic effects up to the limit of water solubility on the water flea Daphnia magna in GLP studies according to OECD 211.

Available reliable read-across data for toxicity to aquatic microorganisms for the PE ester group members supports the determination of a lack of toxicity to soil microorganisms. No inhibition of respiration rate of aquatic microorganisms was observed in any of the available studies for the PE ester group members.

Since the substance is readily biodegradable, it will be degraded quickly. Thus, tests with terrestrial organisms from different taxonomic groups in combination with chronic aquatic data and toxicity data on microorganisms indicating no effects up to the limit of water solubility are sufficient to assess that the PE ester group members have a very low toxicity to terrestrial organisms.

This is supported by further evidence from literature data. This data showed that soil microorganism communities are well capable of degrading fatty acid esters (Hita et al., 1996 and Cecutti et al., 2002) and use them as energy source (Banchio & Gramajo, 1997). Hita et al. investigated the degradation of the model molecule tristearin which is a triglyceride containing of glycerin tri-esterified with stearic acid in three different soils for 4 weeks. The amount of stearic acid increased in considerable amounts during the experiment showing the hydrolytic activity of lipases breaking the ester bonds. The investigation of ester fractions moreover showed the generation of new alkanoic acids (methyl stearate, ethyl stearate and propyl stearate) which were not determined in the controls. Nevertheless the amounts were no longer present after 4 weeks, which leads to the assumption that degradation by soil microorganisms had occurred. The same was shown by Cecutti et al. One soil sample was chosen and incubated with methyl oleate (plant oil) for 120 d. Methyl oleate and its metabolites were completely degraded after 60 d. Streptomyces coelicolor, a common gram-positive soil bacterium uses fatty acids (C4-C18) as sole carbon end energy source indicating that fatty acids are not-toxic and can be used for catabolism (Banchio and Gramajo, 1997). The available literature data shows that soil microorganisms are capable to break-up ester bonds and degrade fatty acids in significant amounts. Moreover, the data indicated the non-toxic properties of fatty acids since they can be used as energy source without adverse toxic effects occuring.

Based on these results it can be concluded that fatty acids, C8-10, tetraesters with pentaerythritol (CAS 85586-24-9)will not exhibit effects to soil microflora.

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