Benzoic acid, 4-hydroxy-, C18-22-alkyl esters

Bioaccumulation: aquatic / sediment

Description of key information

The bioaccumulation potential is low.

Additional information

No experimental data is available concerning the bioaccumulation potential of Benzoic acid, 4-hydroxy-, C18-22-alkyl esters (CAS No. 201305-16-0).

Bioaccumulation refers to the 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 substance is taken up faster than it can be metabolised and/or excreted.

Benzoic acid, 4-hydroxy-, C18-22-alkyl esters (CAS No. 201305-16-0) exhibits a log Koc value of > 5 and is poorly water soluble (< 0.05 mg/L). The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2012) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, (ECHA, 2012). Thus, discharged concentrations of this substance (if at all) into the aqueous compartment are likely to be low.

If the substance is taken up by ingestion, ingested molecules of the substance is anticipated to undergo ester hydrolysis prior to or following absorption, thus unlikely being available for systemic distribution and accumulation. The available information indicate that the hydrolysis product 4 -hydroxybenzoic acid is rapidly metabolized (conjungated) and excreted mainly in the urine without evidence for accumulation even after chronic exposure. Long-chain fatty alcohols resulting from ester hydrolysis are anticipated to be enzymatically oxidised to the corresponding fatty acids and metabolised accordingly (for details see IUCLID section 7.1).

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 for the 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 L/kg; ECHA, 2008a). This assumption is supported by QSAR calculations using BCFBAF v3.01 performed for benzoic acid, 4-hydroxy-, C18-22-alkyl esters, resulting in BCF/BAF values of 0.98-1.38 L/kg and 16.2-27.1 L/kg (Arnot-Gobas[LPMM1] estimate, including biotransformation, upper trophic). Even though the substance 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 statement 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, 2008).

 

Conclusion

Benzoic acid, 4-hydroxy-, C18-22-alkyl esters is characterized by a low water solubility (< 0.05 mg/L) and high log Kow value (> 10). Based on the physico/chemical properties such as low water solubility and high potential for adsorption a reduced availability in water is expected. Absorbed molecules will be metabolized and the metabolites will be excreted. It can be concluded that the bioaccumulation potential of the substance is low. BCF/BAF values estimated by QSAR (BCFBAF v3.01) also support this assumption (BCF values all well below 2000 L/kg). Taking all these information into account, it can be concluded that bioaccumulation of Benzoic acid, 4-hydroxy-, C18-22-alkyl esters is unlikely to occur.

 

References:

Arnot JA, Gobas FAPC. 2003. A generic QSAR for assessing the bioaccumulation potential of organic chemicals in aquatic food webs. QSAR Comb Sci 22: 337-345

Dimitrov SD, Dimitrova NC, Walker JD, Veith GD, Mekenyan OG. 2002. Predicting bioconcentration factors of highly hydrophobic chemicals. Effects of molecular size. Pure Appl Chem 74 (10): 1823-1830

ECHA. 2012b. Guidance on information requirements and chemical safety assessment – Chapter R. 11: PBT assessment. European Chemicals Agency, Helsinki

Nendza M, Müller M. 2007. Literature study: Effects of molecular size and lipid solubility on bioaccumulation potential. Umweltbundesamt, Dessau

Nendza M, Müller M. 2010. Screening for low aquatic bioaccumulation (1): Lipinski’s “Rule of 5” and molecular size. SAR and QSAR in Environ Res 21(5-6): 495-512.

 [LPMM1]In the EPS you only mention the results according to Arnot-Gobas method. If this is the case, because you assume biotransformation takes place, I would delete the regression based calculations. Otherwise, please include the results in the EPS (they indicate low bioaccumulation anyway)

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