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Toxicity to soil microorganisms

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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 soil microorganisms.

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No studies on long-term terrestrial toxicity are available for this substance. Due to the high Koc a considerable adsorption to sediment and soil is indicated. However, Fatty acids, C5-10, esters with pentaerythritol (CAS-No. 68424-31-7) has been shown to be readily biodegradable. Furthermore, four terrestrial toxicity studies to earthworms studies are available for four PE group members. Chronic toxicity studies conducted under GLP according to OECD 222 with earthworms exposed to the group members fatty acids, C16-18 and C18-unsaturated, esters with pentaerythritol (CAS 85711-45-1), 2,2-bis(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25151-96-6) and fatty acids, C16-18 and C18-unsatd., tetraesters with pentaerythritol (CAS 68604-44-4) resulted in no effects on mortality and reproduction up to a concentration of 1000 mg/kg dw soil in all three chronic toxicity studies. Additionally, in an acute test according to OECD 207 with decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS No. 71010-76-9) no mortality occurred in both the control and treatment group resulting in a NOEC (14 d) ≥ 1000 mg/kg dw soil. These four substances represent both ends of the group and the results are used to cover other polyol esters by interpolation. The category member decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS 71010-76-9) belongs to the lower end of the category (C5-C10 fatty acid chain length) and is assumed to represent worst case in terms of absorption via pore water as explained above. The long-term studies with fatty acids, C16-18 and C18-unsaturated, esters with pentaerythritol (CAS 85711-45-1), 2,2-bis(hydroxymethyl)-1,3-propanediyl dioleate (CAS 25151-96-6) and fatty acids, C16-18 and C18-unsatd., tetraesters with pentaerythritol (CAS 68604-44-4) strengthen the read-across approach for esters with fatty alcohol chain lengths of C16-18 and C18 unsaturated.

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. (2003). 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.

Therefore as a part of a weight of Evidence (WoE) approach which is in accordance to the REACh Regulation (EC) No 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2, to cover the data requirements of Regulation (EC) No. 1907/2007, one can conclude from all available literature and data that due to a) the observed absence of toxicological effects on aquatic organisms, b) the lack of chronic exposure and c) the, acknowledged metabolisation of fatty acid esters, terrestrial toxicity, and in particular toxicity to soil micororganisms, is not of concern for PE esters.