1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters

Endpoint summary

Additional information

Exposure of the soil compartment is generally considered to be low. Even if exposed to the soil 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters (CAS 90193-76-3) was shown to be significantly degraded indicating that it will not be persistent in the environment. Indirect exposure via irrigation or atmospheric transport is considered to be negligible based on the physico-chemical properties (water solubility: < 0.05 mg/L at 20 °C, pH = 6.84; vapour pressure: < 0.0001 Pa at 20 °C).

One confirmatory long-term study with the earthworm Eisenia fetida is available. Testing this representative species of the soil fauna evaluates the exposure to the test substance via soil pore water, surface contact as well as by ingestion of soil particles. Due to the high adsorption potential of the substance (log Koc > 5), long-term testing was considered to be relevant to investigate further the effects of the substance on terrestrial organisms. The available study was performed according to OECD 222 (GLP) and did not result in any adverse effects on mortality, behavior, body weight and reproduction. Thus, a NOEC (56 d) ≥ 1000 mg/kg dw was derived for reproduction.

Furthermore, 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters has a high molecular weight of 615 to 671 g/mol. Thus, it is unlikely that it will be readily absorbed, due to the steric hindrance of crossing biological membranes. Following the ‘rule of 5’ (Lipinski et al., 2001), developed to identify drug candidates with poor oral absorption based on criteria regarding partitioning (log Kow >5) and molecular weight (> 500 g/mol), the substance is considered to be poorly absorbed after oral uptake (also see Hsieh & Perkins, 1976).

However, ingested molecules of 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters can undergo a stepwise hydrolysis to the respective alcohol as well as the di- or monoester and the aromatic acid by gastrointestinal enzymes ((Lehninger, 1970; Mattson and Volpenhein, 1972). Further metabolism is expected for that part of the substance that has been absorbed. During the first step of alcohol metabolism, the alcohols are oxidised to the corresponding carboxylic acids, followed by a stepwise elimination of C2-units in the mitochondrial beta-oxidation process (OECD SIDS, 2006). 1,2,4-Benzene tricarboxylic acid might be further metabolized by beta-oxidation, the degradation pathway of fatty acids after cleavage of the aromatic ring. Excretion of the metabolites is expected via urine or via expired air as CO2 after metabolic degradation.

The interaction between lipophilicity, bioavailability and membrane permeability is considered to be the main reason why the relationship between the bioaccumulation potential of a substance and its hydrophobicity is commonly described by a relatively steep Gaussian curve with the bioaccumulation peak approximately at log Kow of 6-7 (e.g. see Dimitrov et al., 2002; Nendza & Müller, 2007; Arnot and Gobas 2003). Substances with log Kow values above 10, which have been calculated 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters, are considered to have a low bioaccumulation potential (e.g. Nendza & Müller, 2007 and 2010). Therefore, the potential for bioaccumulation is low.

Available acute and chronic aquatic toxicity tests to fish, invertebrates, algae and microorganisms showed no adverse effects occurred in the range of the water solubility (< 0.05 mg/L at 20 °C, pH = 6.84). These results further support the low toxicity to terrestrial organisms.

The available data for toxicity to activated sludge microorganisms support the determination of a lack of toxicity to soil microorganisms. No inhibition of respiration rate of a microbial sewage treatment plant community was observed in the available study according to OECD 209. The Guidance Document (ECHA, 2012, page 122) 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. 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). Based on the available information, effects on soil microorganisms are not expected to be of concern, and consequently, no further testing is required.

In conclusion 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters is of low toxicity to terrestrial organisms based on all available data.