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Bioaccumulation: aquatic / sediment

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Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification
Remarks:
Validated QSAR model. However, the components are outside of the domain of the training set (log Kow of the training set: 0.31-8.70). Nevertheless, the value of the prediction will be used in a weight of evidence approach for risk assessment purposes, in accordance with 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., since a) there is currently no universally accepted definition of model domain, and b) since further measurements/testing would not result in additional knowledge for this substance.
Qualifier:
according to
Guideline:
other: REACH Guidance on QSARs R.6
Principles of method if other than guideline:
- Software tool(s) used including version: EPI Suite v4.11
- Model(s) used: BCFBAF v3.01
Full reference and details of the used formulas can be found in:
1. Arnot JA, Gobas FAPC. 2003. A generic QSAR for assessing the bioaccumulation potential of organic chemicals in aquatic food webs. QSAR and Combinatorial Science 22: 337-345.
- Model description: see field 'Justification for non-standard information', 'Attached justification' and 'any other information on material and methods'
- Justification of QSAR prediction: see field 'Justific ation for type of information', 'Attached justification' and/or 'overall remarks'
GLP compliance:
no
Vehicle:
no
Test organisms (species):
other: Fish
Route of exposure:
other: aqueous and dietary
Test type:
other: calculation
Water / sediment media type:
natural water: freshwater
Details on test conditions:
For further detailed description on the model and its applicability, see "Any other information on materials and methods incl. tables" and attached model background information in "Overall remarks, attachments".
Details on estimation of bioconcentration:
BASIS FOR CALCULATION OF BCF
- Estimation software: BCFBAF v3.01
- Result based on calculated log Pow of: 22.85 - 35.96 (KOWWIN v.1.68)
Type:
BCF
Value:
0.893 L/kg
Basis:
whole body w.w.
Remarks on result:
other: Arnot-Gobas including biotransformation, upper trophic
Type:
BAF
Value:
0.893 L/kg
Basis:
whole body w.w.
Remarks on result:
other: Arnot-Gobas including biotransformation, upper trophic
Details on results:
For detailed description on the model and its applicability, see "Any other information on materials and methods incl. tables".

Biotransformation Rate Constant:

 kM (Rate Constant): 3.406e-00 - 0.0001498 /day (10 gram fish)

 kM (Rate Constant): 1.915e-00 - 8.426e-005 /day (100 gram fish)

 kM (Rate Constant): 1.077e-006- 4.738e-005 /day (1 kg fish)

 kM (Rate Constant): 6.056e-007 - 2.665e-005 /day (10 kg fish)

 

Arnot-Gobas BCF & BAF Methods (including biotransformation rate estimates):

  Estimated Log BCF (upper trophic) = -0.049 (BCF = 0.893 L/kg wet-wt)

  Estimated Log BAF (upper trophic) = -0.049 (BAF = 0.893 L/kg wet-wt)

  Estimated Log BCF (mid trophic)  = -0.031 (BCF = 0.9315 L/kg wet-wt)

  Estimated Log BAF (mid trophic)  = -0.031 (BAF = 0.9315 L/kg wet-wt)

  Estimated Log BCF (lower trophic) = -0.027 (BCF = 0.9402 L/kg wet-wt)

  Estimated Log BAF (lower trophic) = -0.027 (BAF = 0.9402 L/kg wet-wt)

 

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

  Estimated Log BCF (upper trophic) = -0.049 (BCF = 0.893 L/kg wet-wt)

  Estimated Log BAF (upper trophic) = -0.049 (BAF = 0.893 L/kg wet-wt)

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
weight of evidence
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
Remarks on result:
not measured/tested

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.

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: Acceptable publication which meets basic scientific principles.
Qualifier:
according to
Guideline:
OECD Guideline 305 (Bioconcentration: Flow-through Fish Test)
GLP compliance:
yes
Radiolabelling:
not specified
Vehicle:
not specified
Test organisms (species):
Oncorhynchus sp.
Details on test organisms:
TEST ORGANISM
- Common name: rainbow trout
- Weight at study initiation: 0.2 - 0.9 g with 3.5 - 5.8% lipid
Route of exposure:
aqueous
Test type:
flow-through
Water / sediment media type:
natural water: freshwater
Reference substance (positive control):
not specified
Type:
BCF
Value:
16 dimensionless
Basis:
not specified
Calculation basis:
steady state
Remarks on result:
other: C10 alcohol
Type:
BCF
Value:
29 dimensionless
Basis:
not specified
Calculation basis:
steady state
Remarks on result:
other: C12 alcohol
Type:
BCF
Value:
30 dimensionless
Basis:
not specified
Calculation basis:
steady state
Remarks on result:
other: C13 alcohol

Water analysis (n = 6 - 7) showed that exposure concentrations were maintained constant during uptake phase. The test species attained rapidly a steady-state concentration of the alcohol. Rapid elimination occurred after transfer to clean water. The BCF values were dependent on water concentration with a two-fold increase observed for the C12 and C13-alcohol.

Endpoint:
bioaccumulation in sediment species, other
Remarks:
aquatic / sediment
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Data from review article/book chapter.
Qualifier:
no guideline followed
Principles of method if other than guideline:
no data
GLP compliance:
no
Test organisms (species):
other: not applicable
Route of exposure:
other: not applicable
Remarks on result:
not measured/tested

Carboxylesterases are a class of enzymes responsible for the ester cleavage of carboxylic esters. Liver B-carboxylesterases are the most prominent group of all “nonspecific” ester-cleaving enzymes. The preferred substrates of B-esterases are aliphatic esters. B-type esterases have been characterized in human muscle, kidney, brain, liver and serum of mammals. The activity of B-esterase from pig and rat liver was shown for several carboxylesters (e.g. methyl octanoate, heptyl acetate).

Endpoint:
bioaccumulation in sediment species, other
Remarks:
aquatic / sediment
Type of information:
experimental study
Adequacy of study:
weight of evidence
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
Remarks on result:
not measured/tested

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.

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Qualifier:
no guideline followed
Principles of method if other than guideline:
The study was conducted to examine the effects and fate of a number of chemicals, including hydrocarbons and chlorinated hydrocarbons. The interactions between these chemicals in fish were studied using several approaches: examination of the uptake, metabolism and elimination of selected chemicals by fish; assessment of the effects of selected inducing agents on hepatic xenobiotic metabolizing enzymes (assayed in vitro); and studies of the effects of inducing agents on the metabolism and disposition of other chemicals in vitro.
GLP compliance:
no
Test organisms (species):
other: Salmo gairdneri, Lepomis macrochirus, Cyprinus carpio and Archosargus probatocephalus
Route of exposure:
other: intraperitoneal injection
Remarks on result:
not measured/tested

Esters do not readily bioaccumulate in fish. This might be caused by the wide carboxyesterase distribution, high tissue content, rapid substrate turnover and limited substrate specificity.

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
28-days uptake/4-days depuration study with Lepomis macrochirus under flow-through conditions.
GLP compliance:
no
Radiolabelling:
yes
Details on sampling:
- Sampling intervals/frequency for test organisms: Fish were sampled at 0.5, 1, 2, 4, 8, 14, 21 and 28 days during the exposure phase (5 fish per time point) and at 1, 2 and 4 days during the clearance phase (5 fish per time point).
- Sampling intervals/frequency for test medium samples: Water samples were taken daily. For analysis of parent compound and metabolites water samples from exposure aquarium were analysed at least once a week.
- Sample storage conditions before analysis: immediate analysis
- Details on sampling and analysis of test organisms and test media samples: Water samples were analysed using Liquid Scintillation (LS) counting method. Fish tissue samples were analyzed for radioactivity after combustion.
Vehicle:
yes
Details on preparation of test solutions, spiked fish food or sediment:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Chemical name of vehicle: acetone
- Concentration of vehicle in test medium: 0.095 mL/L in the vehicle control
Test organisms (species):
Lepomis macrochirus
Details on test organisms:
TEST ORGANISM
- Common name: bluegill
- Source: Fish were purchased from Osage Catfisheries of Osage Beach MO, USA.
- Length at study initiation: 3.0 - 4.5 cm
- Weight at study initiation: 0.5 - 0.7 g

ACCLIMATION
- Acclimation period: > 21 days
- Type and amount of food: synthetic diet
- Feeding frequency: ad libitum
Route of exposure:
aqueous
Test type:
flow-through
Water / sediment media type:
natural water: freshwater
Total exposure / uptake duration:
28 d
Total depuration duration:
4 d
Hardness:
73 - 76 mg/L CaCO3
Test temperature:
16.3 - 17.9 °C
pH:
7.7 - 8.1
Dissolved oxygen:
8.1 - 9.6 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: aquarium
- Type: covered with plexiglas lids
- Material, size: glass, 40 L
- Aeration: Aquaria were equipped with magnetic stirring bars.
- Type of flow-through: A three-way valve was located between the peristaltic pump and the mixing chambers so that the flow could be measured daily and adjusted.
- Renewal rate of test solution : 6 volume changes every 24 h
- No. of organisms per vessel: 85
- No. of vessels per concentration (replicates): 1 for exposure, 1 for depuration
- No. of vessels per control / vehicle control (replicates): 1

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Dilution water used was from the upper Saginaw Bay of Lake Huron and was sand filtered, pH adjusted with CO2 to pH 8, carbon filtered and UV-radiated before use.
- Alkalinity: 46 - 52 mg/L as CaCO3
- Conductance: 140 - 150 µmhos/cm
- Intervals of water quality measurement: Temperature, pH and oxygen were measured periodically.
Nominal and measured concentrations:
Nominal: 0 (vehicle control), 0.33 µg/L
Measured: < LOD, 0.29 µg/L (average)
Reference substance (positive control):
no
Details on estimation of bioconcentration:
BASIS FOR CALCULATION OF BCF
- Estimation: Two compartment model is used to describe the uptake and elimination of xenobiotics by fish.
Type:
BCF
Value:
< 17 dimensionless
Basis:
not specified
Remarks on result:
other: Conc.in environment / dose:0.29 µg/L (measured average)
Metabolites:
Haloxyfop, polar metabolites 1 and 2.

Bluegill exposed to 14C haloxyfop-methyl for 28 days were found to rapidly absorb the ester from water which was then biotransformed at an extremely fast rate within the fish such that essentially no haloxyfop-methyl was detected in the fish. The estimated bioconcentration factor for the haloxyfop-methyl in whole fish was < 17, based upon the detection limit for ester in fish and the average concentration of haloxyfop-methyl in exposure water. The total 14C residue level within whole fish averaged about 0.27 µg/g equivalents over the course of the uptake phase. The principal component of the 14C residue was haloxyfop, which accounted for an average of about 60% of the radioactivity. Two other polar metabolites were detected in the fish which accounted for an average of about 14% of the radioactivity and an average of about 25% of the radioactivity. Once the fish were transferred to clean water, all metabolites cleared quickly with similar clearance rates. A simulation model estimated the uptake rate constant of haloxyfop-methyl from water to be about 720 mL/g*day. The rate constants for biotransformation of haloxyfop-methyl and the clearance of metabolites formed were estimated to be 200/day (DT50 = 5 min) and 0.82/day (DT50 = 0.8 days), respectively. The high rate of biotransformation of the parent compound within the fish demonstrates the importance of basing the bioconcentration factor upon the actual concentration of parent material within the organisms rather than the total radioactive residue levels for radiolabeled bioconcentration studies.

Endpoint:
bioaccumulation in aquatic species: fish
Type of information:
experimental study
Adequacy of study:
weight of evidence
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:
In vitro enzyme study with liver microsomal and cytosolic fractions from different fish species recommended as test species in OECD guidelines.
GLP compliance:
no
Test organisms (species):
other: Poecilia reticulata, Cyprinus carpio, Danio rerio, Leuciscus idus, Salmo gairdneri
Details on test organisms:
TEST ORGANISM
- Common name: Guppy, common carp, zebra fish, golden orfe, rainbow trout
- Source: Guppy, common carp and zebra fish were purchased from Euraquarium, Bologna, Italy. Rainbow trout was kindly supplied by Istituto Ittiogenico, Rome, Italy.
- Length at study initiation: see Tab. 1
- Weight at study initiation: see Tab. 1
- Method of breeding: The guppy stocks were made up of adult females only, whereas all other fish stocks included individuals of both sexes. Fish sizes and rearing conditions were chosen to meet EEC test guidelines as closely as possible.

ACCLIMATION
- Acclimation period: Fish were acclimatised for at least one week.
- Type and amount of food: Fish were fed a semisynthetic diet purchased from Piccioni, Brescia, Italy.
- Health during acclimation (any mortality observed): Less than 2% mortality per week was observed in all the stocks used.
Route of exposure:
other: not applicable, in vitro study
Test type:
other: in vitro
Water / sediment media type:
natural water: freshwater
Remarks on result:
not measured/tested

The metabolic efficiency of the liver in the enzymatic hydrolysis of exogenous substrates is dependent on both the substrate type and the fish species. Indeed, the fish studied metabolise much more readily phenyl acetate, the typical substrate of A-esterases, and the phosphate monoester, than the B-esterase substrates. The inter-species differences in activities (referred to unit body weight) vary within a factor of 7 – 17 for esterases (with p-nitrophenyl phosphate, phenyl acetate or ethyl-butyrate as substrate), while reaching a factor of variation of even 60 for acetanilide amidase.

In line with previous evidence on hepatic mono-oxygenase and glutathione S-transferases, guppy is the most active fish species, also with reference to non-specific hydrolases. At variance with results on the other enzyme families, carp also is endowed with the highest levels of hydrolases.

Description of key information

Based on all the available data, it is concluded that the potential for bioaccumulation of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) is low.

Key value for chemical safety assessment

Additional information

Experimental data for bioaccumulation are not available. However, all the available information on environmental behavior and metabolism, in combination with QSAR calculations, provide sound evidence suggesting that the effective potential for bioaccumulation is negligible.

Environmental behavior

The low water solubility (1.39 µg/L, 20 °C, pH 6.3) and high estimated log Kow (> 10, KOWWIN v1.68) indicate that the substance is highly lipophilic. If released into the aquatic environment, the substance is expected to undergo extensive biodegradation and sorption to organic matter leading to an effective reduction of its bioavailability in water. However, only low concentrations of the substance are expected to be released into the environment, if at all. Due to the ready biodegradability and high potential for adsorption, the substance is effectively removed from conventional sewage treatment plants (STPs) by biodegradation and sorption to biomass. Thus, the overall bioavailability of the substance in surface water is presumable low and the most relevant route of uptake by aquatic organisms is expected to occur via ingestion of particle bound substance.

However, based on the intrinsic physico-chemical properties of the substance, its bioavailability in the sediment environment is presumably very low, which reduces the probability of chronic exposure of sediment organisms in general.

 

Metabolization of aliphatic esters

Should the substance be taken up by fish, aliphatic esters are expected to be initially metabolized via enzymatic hydrolysis during the process of digestion and absorption in the intestinal tissue, resulting in the corresponding free fatty acids and the free fatty alcohols. 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 noted in a wide variety of tissues 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/metabolization of xenobiotics, which reduces the bioaccumulation or bioconcentration potential (Lech & Bend, 1980). It is known for esters that they are 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 caused by the wide distribution of carboxylesterase, high tissue content, rapid substrate turnover and limited substrate specificity (Lech & Melancon, 1980; Heymann, 1980). The metabolization of the enzymatic hydrolysis products is presented in the next section below.

Metabolization of enzymatic hydrolysis products

Fatty alcohols

Fatty alcohols, including unsaturated and branched alcohols, are the products of the enzymatic reaction of long chain aliphatic esters catalyzed by carboxylesterases. The metabolization 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 zebrafish (Reimers et al., 2004; Lassen et al., 2005), carp and rainbow trout (Nilsson, 1988; Nilsson, 1990).

The alcohol metabolism 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 the 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 their corresponding acids in the intestines (Calbert et al., 1951; Sand et al., 1973; Sieber, et al., 1974). Branched alcohols like 2-hexyldecanol or 2-octyldodecanol show a high degree of similarity in biotransformation compared to the linear alcohols. They will be oxidized to the corresponding carboxylic acid followed by the ß-oxidation as well. A 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 as reported in 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 which lead to a decreased elimination.

Fatty acids

The metabolism of fatty acids in mammals is well known and has been investigated intensively (Stryer, 1994). 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) were naturally found 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).

Data from QSAR calculations

Additional information on bioaccumulation could be generated by (Q)SAR calculations using the BCFBAF v3.01 model integrated in EPISuite v4.11. The estimated values forIsohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) are a BCF of 0.893 L/kg and a BAF of 0.893 L/kg whole body w. w. (Arnot-Gobas, including biotransformation, upper trophic),indicating negligible bioaccumulation in organisms. However, the substance only partially falls within the applicability domain. Nonetheless, the (Q)SAR calculations can be used as a supporting indication of a low potential for bioaccumulation. The model training set only consists of substances with log Kow values in the range of 0.31 - 8.70 but correctly models the trend of decreasing bioconcentration potentials with increasingly high log Kow values (> 10).Based on current knowledge, a calculated log Kow of 10 or above is taken as an indicator of reduced bioconcentration, as stated in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7c (Endpoint specific guidance, Version 3.0. ECHA, 2017), and Chapter R. 11 (PBT/vPvB assessment, Version 3.0, ECHA, 2017). Together with other information, this information can be used in a weight-of-evidence approach to conclude that the substance is not B/vB, according to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment v3.0 (ECHA, 2017). This reasoning is in line with the estimated BCF of 0.893 L/kg (BCF/BAF, Arnot-Gobas, including biotransformation, upper trophic) for this substance. Thus, the substance is notexpected to meet the B/vB criterion.

Conclusion

Based on the enzymatic hydrolysis of aliphatic esters and the subsequent metabolization of the corresponding carboxylic acid and alcohol, it can be concluded that the high log Kow overestimates the true bioaccumulation potential of the substance since it does not take into account the metabolization of substances in living organisms. Current knowledge suggests that log Kow values of 10 or above are indicators of reduced bioconcentration, as stated in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7c: Endpoint specific guidance (ECHA, 2017) as well as in Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment v3.0 (ECHA, 2017). In addition no chronic mammalian toxicity was recorded in the available studies indicating that the substance is chronically not toxic to mammals or not taken up to a significant extent. This conclusion is supported by QSAR results for BCF values clearly showing negligible potential for bioaccumulation.

Furthermore, the biochemical processes for the metabolization of aliphatic esters and its metabolites is ubiquitous in the animal kingdom. In consideration of all the available information, it can be concluded that the potential for bioaccumulation of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) is low.

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

References are provided in Annex 1 of the Chemical Safety Report.