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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.

Key value for chemical safety assessment

Additional information

Experimental data on the toxicity of 2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0) to terrestrial microorganisms are not available. Generally, all members of the TMP esters group 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 group members 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 esters group members. Data on a short-term toxicity plant toxicity test according to OECD 208 available for Fatty acids, C14-18 and C16-18 unsatd., triesters with trimethylolpropane (CAS-No. 68002-79-9) indicate no toxicity (NOEC = 300 - 1000 mg/kg soil dw, LOECs = 1000 mg/kg soil dw) to plants.

A chronic exposure of terrestrial organisms is not probable since the members of the TMP esters group 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 members of the TMP esters group 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 group members 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 group members 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.

Based on these results it can be concluded that2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0) will not exhibit effects to soil microflora.

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