Dodecyl nonan-1-oate

Endpoint summary

Additional information

There is only limited data available for the environmental fate of lauryl nonanoate (CAS 17671-26-0). Therefore, QSAR predictions were considered for the estimation of the adsorption/desorption endpoint in order to fulfill the standard information requirements laid down in REACH Regulation (EC) No 1907/2006.

 

The target substance lauryl nonanoate (CAS 17671-26-0) is characterized by low water solubility (2.43 µg/L at 20 °C), a low estimated vapour pressure (3.4E-5 Pa, SPARC v4.6), a high log Kow (9.21, QSAR, EPISuite v4.11) and a high log Koc (5.20, MCI method, KOCWIN v2.00), indicating a high adsorption potential to soil and sediment particles. Moreover, experimental results from a standard biodegradation study showed that the target substance is readily biodegradable (85.5% after 28 d, OECD 301 B). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs) (ECHA, 2017). Furthermore, the Guidance also 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 come into 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, 2017) and whatever remains will be extensively biodegraded (due to ready biodegradability).

Therefore, only negligible concentrations of the substance are likely to be released into the environment through conventional STPs, if at all, and whatever fraction is released will preferentially distribute into the sediment compartment where the bioavailability of the substance is presumably very low based on the physico-chemical properties of the substance (i.e. strong binding properties). Thus, abiotic degradation via hydrolysis and evaporation into the atmospheric compartment are presumably not relevant removal pathways. No abiotic degradation was observed in the apparatus blanks of the biodegradation study.

 

Bioaccumulation

Experimental data for bioaccumulation are not available for lauryl nonanoate (CAS 17671-26-0) and the estimated log Kow is high (9.21), which may be indicative of a potential for bioaccumulation. However, the information gathered on environmental behaviour and metabolism, in combination with QSAR calculations (in accordance with Regulation (EC) No 1907/2006, Annex XI General rules for adaptation of the standard test regime set out in Annexes VII to X 1.2) provide sufficient information to cover the data requirements of Regulation (EC) No 1907/2006, Annex VIII. On this basis it is concluded that the potential for bioaccumulation of both the substance and its metabolites is in all likelihood negligible.

Environmental behaviour

Due to ready biodegradability and high potential of adsorption, the substance can be effectively removed in conventional STPs by biodegradation and by sorption to biomass. The low water solubility (2.43 µg/L, 20 °C) and high estimated log Kow (9.21, KOWWIN v.1.68) indicate that the substance is highly lipophilic. If released into the aquatic environment, the substance undergoes extensive biodegradation and sorption to organic matter. Thus, the bioavailability of the substance in the water column is rapidly reduced and the relevant route of uptake in aquatic organisms is therefore expected to predominantly occur via ingestion of particle bound substance.

Metabolism of aliphatic esters

In case of uptake by fish, aliphatic esters such as lauryl nonanoate (CAS 17671-26-0) are expected to be initially metabolized via enzymatic hydrolysis to the corresponding free fatty acid (here: nonanoic acid) and free fatty alcohol (here: dodecanol) during the process of digestion and absorption in the intestine. Hydrolysis is catalyzed by classes of enzymes known as carboxylesterases or esterases (Heymann, 1980). The most important of which are the B-esterases in the hepatocytes of mammals (Heymann, 1980; Anders, 1989). Carboxylesterase activity has been reported in a wide variety of tissue in invertebrates as well as in fish (Leinweber, 1987; Soldano et al., 1992; Barron et al., 1999; Wheelock et al., 2008). The catalytic activity of this enzyme family leads to a rapid biotransformation/metabolism of xenobiotics, which reduces the bioaccumulation or bioconcentration potential (Lech & Bend, 1980). Esters are known to be readily metabolized in fish (Barron et al., 1999) and literature clearly shows that esters do not readily bioaccumulate in fish (Rodger & Stalling, 1972; Murphy & Lutenske, 1990; Barron et al., 1990). In fish species, this might be explained by the wide distribution of carboxylesterase, high tissue content, rapid substrate turnover and limited substrate specificity (Lech & Melancon, 1980; Heymann, E., 1980). The metabolism of the enzymatic hydrolysis products is presented in the section below.

Metabolism of enzymatic hydrolysis products

Fatty alcohols

The metabolism of alcohols is well known. The free alcohols can either be esterified to form wax esters which are similar to triglycerides or they can be metabolized to fatty acids in a two-step enzymatic process by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) using NAD+ as coenzyme as shown in the fish gourami (Trichogaster cosby) (Sand et al., 1973). The responsible enzymes ADH and ALDH are present in a large number of animals, plants and microorganisms (Sund & Theorell, 1963; Yoshida et al., 1997). They were found among others in the zebrafish (Reimers et al., 2004; Lassen et al., 2005), carp and rainbow trout (Nilsson, 1988; Nilsson, 1990). The metabolism of alcohols was also investigated in the zebrafish Danio rerio, which is a standard organism in aquatic ecotoxicology. Two cDNAs encoding zebrafish ADHs were isolated and characterized. A specific metabolic activity was shown in in-vitro assays with various alcohol components ranging from C4 to C8. The corresponding aldehyde can be further oxidized to the fatty acid catalyzed by an ALDH. Among ALDHs, the ALDH2 located in the mitochondria is the most efficient. The ALDH2 cDNA of the zebrafish was cloned and a similarity of 75% to mammalian ALDH2 enzymes was found. Moreover, ALDH2 from zebra fish exhibits a similar catalytic activity for the oxidation of acetaldehyde to acetic acid compared to the human ALDH2 protein (Reimers at al., 2004). The same metabolic pathway was shown for longer chain alcohols like stearyl- and oleyl alcohol which were enzymatically converted to its corresponding acid in the intestines (Calbert et al., 1951; Sand et al., 1973; Sieber et al., 1974). Branched alcohols show a high degree of similarity in biotransformation compared to linear alcohols. They will be oxidized to the corresponding carboxylic acid followed by the ß-oxidation as well. The presence of a side chain does not terminate the ß-oxidation process (OECD, 2006).

The influence of biotransformation on bioaccumulation of alcohols was confirmed in GLP studies with the rainbow trout (according to OECD 305) with commercial branched alcohols with chain lengths of C10, C12 and C13 (de Wolf & Parkerton, 1999). This study resulted in an experimental BCF of 16, 29 and 30, respectively for the three alcohols tested. The 2-fold increase of BCF for C12 and C13 alcohol was explained with a possible saturation of the enzyme system leading to a decreased elimination.

Fatty acids

The metabolism of fatty acids in mammals is well known and has been investigated intensively in the past (Stryer, 1994). The free fatty acids can either be stored as triglycerides or oxidized via mitochondrial ß-oxidation removing C2-units to provide energy in the form of ATP (Masoro, 1977). Acetyl-CoA, the product of the ß-oxidation, can further be oxidized in the tricarboxylic acid cycle to produce energy in the form of ATP. As fatty acids are naturally stored as triglycerides in fat tissue and re-mobilized for energy production it can be concluded that even if they bioaccumulate, bioaccumulation will not pose a risk to living organisms. Fatty acids (typically C14 to C24 chain lengths) are also a major component of biological membranes as part of the phospholipid bilayer and therefore part of an essential biological component for the integrity of cells in every living organism (Stryer, 1994). Saturated fatty acids (SFA; C12 - C24) as well as mono-unsaturated (MUFA; C14 - C24) and poly-unsaturated fatty acids (PUFA; C18 - C22) are naturally present in muscle tissue of the rainbow trout (Danabas, 2011) and in the liver (SFA: C14 - C20; MUFA: C16 - C20; PUFA: C18 - C22) of the rainbow trout (Dernekbasi, 2012).

Conclusion

The biochemical process metabolizing aliphatic esters is ubiquitous in the animal kingdom. Based on the enzymatic hydrolysis of aliphatic esters and the subsequent metabolism of the corresponding carboxylic acid and alcohol, it can be concluded that the high log Kow, which indicates a potential for bioaccumulation, overestimates the true bioaccumulation potential of lauryl nonanoate (CAS 17671-26-0) since it does not reflect the metabolism of substances in living organisms. Taking all this information into account, it can be concluded that the bioaccumulation potential of lauryl nonanoate (CAS 17671-26-0) is low.

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