Dibutyl adipate

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well documented publication which meets basic scientific principles

Qualifier:

no guideline followed

Principles of method if other than guideline:

The activity of carboxylesterase (CaE), a class of nonspecific serine hydrolases, was evaluated in vitro in tissues and microsomes of rainbow trout. In the assays the formation of 4-nitrophenol from 4-nitrophenyl acetate was measured spectrophotometrically.

GLP compliance:

no

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: rainbow trout
- Source: Trouts were obtained as eyed embryos from Mt. Lassen Trout Farms, Mt. Lassen CA, USA
- Age at study initiation: < 1 year
- Length at study initiation (lenght definition, mean, range and SD):
- Weight at study initiation: 1.64 ± 0.07 g wet weight
- Weight at termination (mean and range, SD):
- Method of holding: Trout were held in flow-through aerated raceways at 12 ± 1 °C. The laboratory water was softened Lake Huron water that had been sand-filtered, pH adjusted with CO 2, carbon-filtered, and ultraviolet irradiated. Laboratory water was monitored weekly for pH, alkalinity, conductivity, and hardness; and quarterly for selected inorganics, pesticides, and poly-chlorinated biphenyls. Typical water quality values were pH of 7.5, alkalinity of 43 mg/L, hardness of 70 mg/L (as CaCO3 ), and conductivity of 140 mhos/cm. Fish were killed by a blow to the head and placed immediately on ice before tissue preparation.

Route of exposure:

other: In vitro exposure

Test type:

other: In vitro study

Water / sediment media type:

natural water: freshwater

The results of this study demonstrated that rainbow trout had high esterase activity over a broad range of temperatures, that carboxylesterase (CaE) activity significantly increased between the yolk-sac and juvenile life stages, and that variation between the CaE activity in trout and three other families of freshwater fish was limited.

Reference 2

Endpoint:

bioaccumulation in aquatic species, other

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Validated QSAR model

Justification for type of information:

QSAR prediction: migrated from IUCLID 5.6

Principles of method if other than guideline:

Calculation based on BCFBAF v3.01, Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10. US EPA, United States Environmental Protection Agency, Washington, DC, USA.

GLP compliance:

no

Test organisms (species):

other: Fish

Route of exposure:

aqueous

Test type:

other: calculation

Water / sediment media type:

natural water: freshwater

Details on estimation of bioconcentration:

BASIS FOR CALCULATION OF BCF
- Estimation software: BCFBAF v3.01
- Result based on calculated log Pow of: 4.33 (KOWWIN v1.68)

Type:

BCF

Value:

11.1 L/kg

Basis:

whole body w.w.

Remarks on result:

other: Regression based estimate

Details on results:

For detailed description on the model and its applicability, see "Any other information on materials and methods incl. tables".

Reference 3

Endpoint:

bioaccumulation in aquatic species, other

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Validated QSAR model

Justification for type of information:

QSAR prediction: migrated from IUCLID 5.6

Principles of method if other than guideline:

Calculation based on BCFBAF v3.01, Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10. US EPA, United States Environmental Protection Agency, Washington, DC, USA.

GLP compliance:

no

Test organisms (species):

other: Fish

Route of exposure:

aqueous

Test type:

other: calculation

Water / sediment media type:

natural water: freshwater

Details on estimation of bioconcentration:

BASIS FOR CALCULATION OF BCF
- Estimation software: BCFBAF v3.01
- Result based on measured log Pow of: 4.17

Type:

BCF

Value:

12.55 L/kg

Basis:

whole body w.w.

Remarks on result:

other: Arnot Gobas (including biotransformation rate estimates, upper trophic)

Type:

BAF

Value:

12.55 L/kg

Basis:

whole body w.w.

Remarks on result:

other: Arnot Gobas (including biotransformation rate estimates, upper trophic)

Details on results:

For detailed description on the model and its applicability, see "Any other information on materials and methods incl. tables".

Arnot-Gobas BCF & BAF

Estimated Log BCF (mid trophic) = 1.23 (BCF = 16.82 L/kg wet-wt)

Estimated Log BAF (mid trophic) = 1.23 (BAF = 16.82 L/kg wet-wt)

Estimated Log BCF (lower trophic) = 1.26 (BCF = 18.38 L/kg wet-wt)

Estimated Log BAF (lower trophic) = 1.27 (BAF = 18.51 L/kg wet-wt)

 

Arnot-Gobas BCF & BAF Methods (assuming a biotransformation rate of zero):

Estimated Log BCF (upper trophic) = 3.18 (BCF = 1505 L/kg wet-wt)

Estimated Log BAF (upper trophic) = 3.64 (BAF = 4349 L/kg wet-w)

 

Biotransformation Rate Constant:

kM (Rate Constant): 25 /day (10 gram fish)*

kM (Rate Constant): 14.06 /day (100 gram fish)*

kM (Rate Constant): 7.906 /day (1 kg fish)*

kM (Rate Constant): 4.446 /day (10 kg fish)*

Bio Half-Life Normalized to 10 g fish at 15 deg C: 0.0229 days

 

* Predicted value exceeds theoretical whole body maximum value.

Reference 4

Endpoint:

bioaccumulation: aquatic / sediment

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Data from review article.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Review article, describing biotransformation reactions and their effect on toxicity and bioaccumulation of certain chemicals in fish.

GLP compliance:

no

Test organisms (species):

other: not applicable

Route of exposure:

other: not applicable

Test type:

other: not applicable

The catalytic activity of the carboxylesterase family leads to a rapid biotransformation/metabolism of xenobiotics which reduces the bioaccumulation or bioconcentration potential. Several in-vivo and in-vitro experiments showed the biotransformation of xenobiotics in fish. The biotransformation reactions have been shown to occur in fish at rates which have siginificant effects on toxicity and residue dynamics of selected chemicals. Inhibition of these reactions can lead to increased toxicity and bioaccumulation factors. Thus, it was shown that the carboxylesterase activity has an influence on the bioaccumulation of xenobiotics.

Reference 5

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

1979

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

see Category justification document attached to chapter 13.

Reason / purpose for cross-reference:

read-across source

Key result

Type:

BCF

Value:

27 dimensionless

Basis:

whole body w.w.

Time of plateau:

7 d

Calculation basis:

steady state

Remarks on result:

other: Conc.in environment / dose:0.25 mg/L

Key result

Elimination:

yes

Parameter:

DT50

Depuration time (DT):

1 d

Description of key information

PFAE linear category members are not expected to bioaccumulate in aquatic or sediment organisms and consequently secondary poisoning does not pose a risk.

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.