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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Key value for chemical safety assessment

Additional information

Experimental data investigating the bioaccumulation potential of Fatty acids, C18-unsatd., dimers, reaction products with fatty acids, C14-18 and C16-18-unsatd. and propylidynemethanol (CAS 162353-70-0) are not available. The high log Kow (> 10), as an intrinsic chemical property of the substance, indicates a potential for bioaccumulation. However, the information gathered on environmental behaviour and metabolism, in combination with QSAR-estimated values, provide enough evidence (in accordance to the 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 1907/2006, Annex IX and to state that the substance is likely to show negligible bioaccumulation potential.

Environmental behaviour

Due to the high adsorption potential an effective removal of the substance in conventional sewage treatment plants (STPs) by sorption to biomass is likely. The low water solubility (< 25 µg/L at 20 °C, pH = 6.3) and high estimated log Kow (>10) indicate that the substance is highly lipophilic. If released into the aquatic environment, the substance will extensively adsorb to organic matter. Thus, the bioavailability in the water column will be rapidly reduced. The relevant uptake route in aquatic organisms is expected to be predominantly by ingestion of particle bound substance. 

Uptake/Absorption

If the substance is taken up by ingestion, absorption is expected to be low based on the molecular weight, size and structural complexity of the substance. For these large and complex structures a high degree of conformational flexibility is assumed. Dimitrov et al. (2002) revealed a tendency of decreasing log BCF in combination with an increase in conformational flexibility of molecules. The authors assume that this effect is related to an enhancement of the entropy factor on membrane permeability of chemicals. Thus, there is a high probability that the substance exists in a conformation which does not allow permeation. Furthermore, the substance has a high molecular weight >600 g/mol. Thus, it is unlikely that it is 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).

This 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 has been calculated for the test substance, are considered to have a low bioaccumulation potential (e.g., Nendza & Müller, 2007; 2010). Furthermore, for those substances with a log Kow value > 10 it is unlikely that they reach the pass level of being bioaccumulative according to OECD criteria for the PBT assessment (BCF > 2000; ECHA, 2014).

This assumption is supported by QSAR calculations using BCFBAF v3.01 performed for main components of Fatty acids, C18-unsatd., dimers, reaction products with fatty acids, C14-18 and C16-18-unsatd. and propylidynemethanol. The BCF and BAF values calculated for the main substance components were 0.89 L/kg (Arnot-Gobas estimate, including biotransformation, upper trophic). Even though Fatty acids, C18-unsatd., dimers, reaction products with fatty acids, C14-18 and C16-18-unsatd. and propylidynemethanol is outside the applicability domain of the model, the estimation can be used as supporting indication of low bioaccumulation potential. The model training set is only consisting of substances with log Kow values of 0.31 - 8.70. But it supports the tendency that substances with high log Kow values (> 10) have a lower potential for bioconcentration as summarized in the ECHA Guidance R.11 and they are not expected to meet the B/vB criterion (ECHA, 2014).

Conclusion

Fatty acids, C18-unsatd., dimers, reaction products with fatty acids, C14-18 and C16-18-unsatd. and propylidynemethanol is characterized by a low water solubility (< 25 µg/L at 20 °C, pH = 6.3), high log Kow (> 10) and high molecular weight (>600 g/mol). Based on the physico/chemical properties such as low water solubility and high potential for adsorption a reduced availability in water is expected. The high molecular weight of the substance significantly reduces the absorption due to steric hindrance to cross biological membranes. It can be concluded that the bioaccumulation potential of Fatty acids, C18-unsatd., dimers, reaction products with fatty acids, C14-18 and C16-18-unsatd. and propylidynemethanol is negligible. BCF/BAF values estimated by QSAR (BCFBAF v3.01) also support this assumption (BCF values all well below 2000 L/kg).

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