Fatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol

Bioaccumulation: aquatic / sediment

Additional information

No experimental data is available on the bioaccumulation potential ofFatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol (CAS 93334-10-2). Therefore, all available related data is combined in a Weight of Evidence (WoE), 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 Annex IX and X.

Bioaccumulation refers to uptake of a substance from all environmental sources including water, food and sediment. However, the accumulation of a substance in an organism is determined, not only by uptake, but also by distribution, metabolism and excretion. Accumulation takes place if the uptake rate is faster than the subsequent metabolism and/or excretion.

In the case ofFatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol, uptake of dissolved substance via water is expected to be low as the water solubility is very low (832 µg/L ± 208 µg/L at 20 °C, pH=6.3). The test substance is readily biodegradable and thus assumed to be eliminated in sewage treatment plants to a high extent. Moreover, high adsorption further promotes rapid removal from waste water. If the substance is to be released in the aquatic environment, the concentration in the water phase will be reduced by rapid biodegradation and adsorption to solid particles and to sediment. Additionally, the substance has an estimated low potential for dermal absorption. QSAR estimations, taking molecular weight, log Pow and water solubility into account, resulted in low dermal absorption of the components of the target substance. Due to low exposure concentrations through water and low dermal absorption potential, no significant uptake through the water phase is expected.

Food ingestion is likely to be the main uptake route for the substance in fish, since it will be adsorbed to solid particles potentially ingested by fish. In the case of ingestion, the substance is predicted to undergo metabolism or excretion. Esters are known to hydrolyse into carboxylic acids and alcohols by esterases (Fukami and Yokoi, 2012). Carboxylesterase activity has been noted in a wide variety of tissues in invertebrates as well as in fish (Leinweber, 1987; Suldano et al, 1992; Barron et al., 1999, Wheelock et al., 2008). Therefore, it is expected that under physiological conditions, the substance will hydrolyse to the respective alcohol (sorbitan, sorbitol and/or1,4:3,6-dianhydro-d-glucitol)and the respective fatty acids. The enzymatic hydrolysis of Sorbitan fatty acid esters occurs within a maximum of 48 h for mono-, di- and tri-ester but decreases with the number of esterified fatty acid so that no hydrolysis of hexa-ester occurs (Croda, 1951; Mattson and Nolen, 1972; Treon, 1967; Wick and Joseph, 1953). The resulting fatty acids are either metabolised via the β-oxidation pathway in order to generate energy for the cell or reconstituted into glyceride esters and stored in the fat depots in the body (Berg, 2002). D-glucitol is primarily metabolised in the liver. The first step of its metabolism involves oxidation by L-iditol dehydrogenase to fructose, which is metabolised by the fructose metabolic pathway (Senti, 1986). D-glucitol is naturally found in several berries and fruits as well as in seaweed and algae (FDA, 1972). Larger Sorbitan fatty acid esters that will not be hydrolysed, such as hexaesters, are unlikely to cross biological membranes due to their high molecular weight. Metabolic pathways in fish are generally similar to those in mammals. Lipids and their constituents, fatty acids, are in particularly a major organic constituent of fish and play major roles as sources of metabolic energy, for growth, reproduction and mobility, including migration (Tocher, 2003).

QSAR calculations support the assumption of rapid metabolism within fish. Using the Arnot-Gobas method, including biotransformation, BCF values of 0.893 - 440.3 L/kg were obtained (BCFBAF v3.01). An exclusion of biotransformation resulted in a BCF of 18860 L/kg clearly indicating biotransformation of the test substance. Although, only the C18 unsaturated fatty acid monoester component of Fatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol and the C18 unsaturated fatty acid monoester component with sorbitan are within the training set defined by the log Pow and/or molecular weight, the results support the assumption of low bioaccumulation potential.

In conclusion, the test substance will be mainly taken up by ingestion and is digested through common metabolic pathways, providing a valuable energy source for the organism, as dietary fats and sugars. Thus, it is not expected to bioaccumulate in aquatic and/or sediment organisms.