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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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Additional information

Experimental data on the toxicity of Fatty acids, C16-18 (even numbered) and C18-unsatd., branched and linear, di- and triesters with trimethylolpropane (former CAS 85005-23-8) to soil microorganisms are not available. Generally, the TMP of the polyol esters category are characterised by a high adsorption potential but also by ready biodegradability. Acute effects to soil microorganisms are not expected since the available data on toxicity of the TMP esters to aquatic microorganisms indicates no detrimental effects. An inhibition of respiration rate of aquatic microorganisms was not observed in the available studies for the TMP ester group members. Data on a short-term toxicity plant toxicity test according to OECD 208 available for fatty acids, C16-18 (even numbered) and C16-18-unsatd. (even numbered), triesters with trimethylolpropane (CAS 68002-79-9) indicate low toxicity (NOEC 300 - 1000 mg/kg soil dw, LOEC 1000 mg/kg soil dw) to plants. Nevertheless this data is insufficient for an accurate assessment as it is not clear if this is related to phytotoxic or any physical effects hence it must be disregarded and the assessment for terrestrial toxicity can be based on the extensive available data for the polyol esters category.

A chronic exposure of terrestrial organisms is not probable since the TMP esters of the polyol esters category are readily biodegradable. Thus, they can be expected to be rapidly and ultimately degraded in the terrestrial environment. When ingested by soil dwelling organisms, the TMP esters are expected to be rapidly metabolised and thus an accumulation and/or chronic effects are not likely. Two earthworm reproduction tests according to OECD 222 are available for the TMP esters 2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0) and 2-ethyl-2-(((1-oxoisooctadecyl)oxy)methyl)-1,3-propanediyl bis (isooctadecanoate) (CAS 68541-50-4). In both studies no chronic toxicity of the substances to Eisenia fetida was determined (Eisner, 2013). The substances caused neither mortality nor a decrease in body weight of adult earthworms. Also the reproduction rates were not affected by the TMP esters and thus a NOECmort/repro ≥ 1000 mg/kg was reported in both studies.

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 toxicity to soil microorganisms is not expected to be of concern.

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 TMP esters 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. (1996) 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. Comparable results were demonstrated by Cecutti et al. (2002). The authors incubated a soil sample 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. 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 microorganisms, is not of concern for TMP esters.