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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

If aquatic exposure occurs, neopentyl glycol (NPG) esters will be mainly taken up by ingestion and digested through common metabolic pathways, providing a valuable energy source for the organism, as dietary fats. These substances are thus not expected to bioaccumulate in aquatic or sediment organisms.  

Key value for chemical safety assessment

Additional information

No experimental data is available on the bioaccumulation potential of the NPG polyol esters. 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 (ECHA, 2012).

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 of NPG esters, uptake of dissolved substance via water is expected to be low. Since the NPG esters are poorly water soluble (< 0.05 mg/L - 0.1 mg/L), have high adsorption potential based on calculated adsorption coefficients (log Koc 3.2 - 9.4, MCI method, KOCWIN v2.00) and are readily biodegradable (60.4 - 95.6% after 28 d), they will be eliminated in sewage treatment plants to a high extent. Release to surface waters and sediment is thus expected to be minimal. In the unlikely event of release into the aquatic environment, the aqueous concentration will be rapidly decreased by biodegradation and adsorption to suspended particles and sediment. Due to low exposure concentrations through water, no significant uptake from the water phase is expected.

Food ingestion is likely to be the main uptake route for NPG esters in fish, since the substances will be adsorbed to solid particles potentially ingested by fish based on the high potential for adsorption (log Koc > 3). Also for sediment-dwelling organisms the main uptake route will be ingestion of contaminated sediment. In the case of ingestion, NPG esters are predicted to undergo metabolism. Esters are known to be enzymatically hydrolyzed into carboxylic acids and alcohols by esterases (Fukami and Yokoi, 2012). Indeed, the result of the pancreatic digestion study of the NPG group member 2,3-dimethyl-1,3 –propandiolheptanoate (CAS No. 68855-18-5) shows a degradation of the ester of almost 90% within 4 hours (Oßberger, 2012; IUCLID section 7.1.1). Carboxylesterase activity has been noted in a wide variety of tissues in invertebrates as well as in fish (Leinweber, 1987; Soldano et al, 1992; Barron et al., 1999, Wheelock et al., 2008). Therefore, it is expected that under physiological conditions, NPG esters will hydrolyse to neopentyl glycol and the respective fatty acids. Neopentyl glycol, undergoes conjugation with glucuronic acid and is excreted in the urine (Gessner, 1960). The free 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). 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 a crucial role as source of metabolic energy in fish, 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 0.9 - 33.8 were obtained (BCFBAF v3.01) for the NPG esters. Although, the larger group members are outside the log Kow range of the training set, the results can be taken as an indication of low bioaccumulation potential. In any case, the BCF values are far below 2000 L/kg, which is the trigger value for bioaccumulation for the PBT assessment.

In conclusion, NPG esters will be mainly taken up by ingestion and are digested through common metabolic pathways, providing a valuable energy source for the organism, as dietary fats. These substances are thus not expected to bioaccumulate in aquatic or sediment organisms.

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