Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Some experimental data evaluating the bioaccumulation potential of the PFAE linear category members are available. 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, 2012c).

Intrinsic properties and fate

All substances included in the PFAE linear category are readily biodegradable. 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, 2012b). Therefore, after passing through conventional STPs, only low concentrations of these substances are likely to be (if at all) released into the environment.

Once available in the water phase, the estimated log Koc values (<3, KOCWIN v2.00) of Diisopropyl adipate (CAS 6938-94-9), Dibutyl adipate (CAS 105-99-7) and Diisopropyl sebacate (CAS 7491-02-3) indicate low adsorption potential of these substances to sediment and organic particles, and therefore, they will be available for uptake by aquatic organisms such as fish mainly via water.

The other substances in the PFAE linear category have log Koc values >3. The Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2012b) 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, 2012a) and the rest will be extensively biodegraded (due to ready biodegradability). Thus, discharged concentrations of these substances into the aqueous compartment are likely to be very low. Should the substances be released into the water phase, due to their hydrophobicity and expected high adsorption potential, they will tend to bind to sediment and other particulate organic matter, and therefore, the actual dissolved fraction available to fish via water will be reduced. Thus, the main route of exposure for aquatic organisms such as fish will be via food ingestion or contact with suspended solids.

Experimental data

The potential for accumulation of the poorly soluble, highly lipophilic, read across substance Bis(2-ethylhexyl) adipate (DEHA) (CAS 103-23-1) in aquatic organisms was examined in a bioconcentration test with bluegill sunfish (Lepomis macrochirus) using 14C-labelled DEHA (Felder et al., 1986). The test was carried out for 42 days. Concentrations of DEHA in water, whole fish, viscera, and fillet were analyzed at intervals during the test. After the first 35 days of exposure, the remaining fish were exposed to clean water for an additional 14 days and concentrations of DEHA were measured in the fish at intervals. A whole fish bioconcentration factor (BCF) of 27 was reported at day 35. Following exposure to clean water, a depuration rate for DEHA of 0.26/day (t 1/2 = 2.7 days) was determined.

The results imply that the accumulation of DEHA is low despite a high log Pow (log Pow = 8.94), most likely due to rapid metabolization. Furthermore, when transferred to freshwater, the substance is apparently rapidly and extensively excreted from the fish.

QSAR data

Additional information on the bioaccumulation of PFAE linear in fish species is available. Estimated bioconcentration (BCF) and bioaccumulation (BAF) values were calculated for all substances using the BCFBAF v3.01 program (Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA), including biotransformation rates (Arnot-Gobas method). In the case of the UVCB substances, the calculations were performed on the main alcohol components, as representative structures for each UVCB. With the exception of Bis(2-ethylhexyl) azelate, Bis(2-octyldodecyl) azelate and Bis(2-ethylhexyl) sebacate (CAS 103-24-2, CAS 897626-46-9 and CAS 122-62-3, log Pow ≥ 9.6 ), all PFAE linear substances (or at least their main components) are within the applicability domain of the QSAR model (log Pow 0.31-8.70) and therefore, provide valid supporting information to be considered in the overall bioaccumulation assessment of these substances.

Within the category, BCF and BAF values ranging from <1 to 29 L/kg are calculated. BCF calculations reflect the bioaccumulation potential after uptake via water, whereas the BAF gives an indication of the bioaccumulation when all exposure routes (water, food, etc.) are taken into account.

The obtained results indicate that the members of the PFAE linear category are likely to show no bioaccumulation potential. According to Regulation (EC) No. 1907/2006, Annex XIII, 1.1.2, a substance only fulfills the bioaccumulation criterion (B) when BCF values are >2000. Even though this condition is preferred to be confirmed with experimental data, in this case of rapidly metabolized esters, the estimated QSAR-based BCFs provide sufficient reliable evidence which suggests that the PFAE linear category members will not be bioaccumulative.

In general, for substances with a log Pow value >10 it is recognized by the relevant authorities that it is unlikely that they accomplish the pass level of being bioaccumulative according to OECD criteria for the PBT assessment (BCF = 2000; ECHA, 2012d). Therefore, the bioaccumulation potential of the two PFAE linear members that are outside of the applicability domain of the BCFBAF v3.01, Bis(2-ethylhexyl) azelate, Bis(2-octyldodecyl) azelate and Bis(2-ethylhexyl) sebacate (CAS 103-24-2, CAS 897626-46-9 and CAS 122-62-3), can be considered as low. Furthermore, even though these substances are outside of the applicability domain of the used model, the calculations (especially the low BCF values calculated using the Arnot-Gobas method) reflect the rapid biotransformation assumed for the category members.

Metabolism of aliphatic esters and metabolites

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. 

If any of the PFAE linear category members are taken up by living organisms, aliphatic esters such as the members of the category will be initially metabolized via enzymatic hydrolysis to the respective dicarboxylic acid and alcohol components as would dietary fats (e.g., Linfield, 1984). The hydrolysis is catalyzed by carboxylesterases and esterases, with B-esterases located in hepatocytes of mammals being the most important (Heymann, 1980; Anders, 1989). However, carboxylesterase activity has also been reported from a wide variety of tissues in invertebrates and fishes (e.g., Suldano et al., 1992; Barron et al., 1999; Wheelock et al., 2008). In fish, the high catalytic activity, low substrate specificity and wide distribution of the enzymes in conjunction with a high tissue content lead to a rapid biotransformation of aliphatic esters, which significantly reduces its bioaccumulation potential (Lech & Melancon, 1980; Lech & Bend, 1980).

Alcohols ranging from C3 (Iso-propanol) to C20 (2-octyl 1-dodecanol) and linear dicarboxylic acids (C6, C9, C10) are the expected hydrolysis products from the enzymatic reaction catalyzed by carboxylesterase. The metabolism of alcohols has been extensively reviewed in the literature (e.g., see Rizzo et al., 1987; Hargrove et al., 2004). The free alcohols can either be esterified to form wax esters (which are similar to triglycerides) or they can be transformed to fatty acids in a two-step enzymatic process catalyzed by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). The responsible enzymes ADH and ALDH are present in a large number of animals including plants, microorganisms and fish (e.g., Sund & Theorell, 1963; Nilsson, 1990; Yoshida et al., 1997; Reimers et al., 2004; Lassen et al., 2005). 

The metabolism of alcohols in fish was extensively studied by Reimers et al. (2004). They isolated and characterized two cDNAs from the zebra fish, Danio rerio, encoding ADHs, which showed specific metabolic activity in in-vitro assays with various alcohol components ranging from C4 to C8. The emerging aldehydes were shown to be further oxidized to the corresponding fatty acid by ALDH enzymes. The most effective ALDH2, which is mainly located in the mitochondria of liver cells showed a sequence similarity of 75% to mammalian ALDH2 enzymes and a similar catalytic activity (also see Nilsson, 1988). The same metabolic pathway was shown for longer chain alcohols, such as stearyl and oleyl alcohol in the intestines of rats (Sieber et al., 1974).

Furthermore, cleavage products with high water solubility like adipic acid do not have the potential to accumulate in adipose tissue due to their low log Pow and are thus widely distributed within the body and rapidly eliminated via renal excretion. To a smaller extent the dicarboxylic acids are also metabolised via peroxisomal beta-oxidation.

Conclusion

The substances included in the PFAE linear category are not expected to be bioaccumulative. Due to their readily biodegradable nature, extensive degradation of these substances in conventional STPs will take place and only low concentrations are expected to be released (if at all) into the environment. Once present in the aquatic compartment, further biodegradation will occur and, depending on their log Pow, water solubility and adsorption potential, the PFAE linear will be bioavailable to aquatic organisms such as fish mainly via water or on the other hand via feed and contact with suspended organic particles. After uptake by fish species, extensive and fast biotransformation of the PFAE linear(s) by carboxylesterases into dicarboxylic acids and the corresponding alcohol is expected. Alcohols will be further oxidized to fatty acids and used by these organisms as their main source of energy throughout all the different life stages (early development, growth, reproduction, etc.). The dicarboxylic acids do not have the potential to accumulate in adipose tissue due to their low log Pow. An in vivo fish test reporting a BCF value of 27 for a similar ester substance, supports the conclusion that rapid metabolism takes place, even when log Pow values are above the trigger value of 3. The supporting BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that these substances will not be bioaccumulative (all well below 2000).

The information above provides strong evidence supporting the statement that rapid metabolism and low bioaccumulation potential can be expected for the members of the PFAE linear category.

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