Fatty acids, C8-10, C12-18-alkyl esters

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:

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 CO2, 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:

other: calculation of BCF value not in focus of this study

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: fish

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Qualifier:

according to guideline

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

Key result

Type:

BCF

Value:

16 dimensionless

Basis:

not specified

Calculation basis:

steady state

Remarks on result:

other: C10 alcohol

Key result

Type:

BCF

Value:

29 dimensionless

Basis:

not specified

Calculation basis:

steady state

Remarks on result:

other: C12 alcohol

Key result

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.

Reference 3

Endpoint:

bioaccumulation: 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:

other: determine a BCF value is not the focus of this study

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).

Reference 4

Endpoint:

bioaccumulation: 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:

other: determine a BCF value is not the focus of this study

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:

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.

Reference 6

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:

results derived from a (Q)SAR model, with limited documentation / justification, but validity of model and reliability of prediction considered adequate based on a generally acknowledged source

Remarks:

the component is outside of the domain of the training set (log Kow of the training set: 0.31-8.70; log Kow of the component: 9.70). Nevertheless, the value of the prediction will be used for risk assessment purposes, 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.

Justification for type of information:

see QMRF and QPRF attached

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: 9.7 (estimated, KOWWIN v.1.68)

Type:

BAF

Value:

206.2 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Type:

BCF

Value:

3.505 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Estimated Log BCF (mid trophic) = 0.656 (BCF = 4.527 L/kg wet-wt)

Estimated Log BAF (mid trophic) = 2.769 (BAF = 587 L/kg wet-wt)

Estimated Log BCF (lower trophic) = 0.691 (BCF = 4.906 L/kg wet-wt)

Estimated Log BAF (lower trophic) = 3.039 (BAF = 1095 L/kg wet-wt)

 

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

Estimated Log BCF (upper trophic) = 2.212 (BCF = 163 L/kg wet-wt)

Estimated Log BAF (upper trophic) = 5.913 (BAF = 8.177e+005 L/kg wet-wt)

 

Biotransformation Rate Constant:

kM (Rate Constant): 0.1027 /day (10 gram fish)

kM (Rate Constant): 0.05772 /day (100 gram fish)

kM (Rate Constant): 0.03246 /day (1 kg fish)

kM (Rate Constant): 0.01825 /day (10 kg fish)

Bio Half-Life Normalized to 10 g fish at 15 deg C: 6.753 days

 

Reference 7

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:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Remarks:

the component is outside of the domain of the training set (log Kow of the training set: 0.31-8.70; log Kow of the component: 12.65). Nevertheless, the value of the prediction will be used for risk assessment purposes, 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.

Justification for type of information:

see QMRF and QPRF attached

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: 12.65 (estimated, KOWWIN v.1.68)

Type:

BAF

Value:

23.72 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Type:

BCF

Value:

0.911 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Estimated Log BCF (mid trophic) = -0.019 (BCF = 0.9572 L/kg wet-wt)

Estimated Log BAF (mid trophic) = 1.261 (BAF = 18.23 L/kg wet-wt)

Estimated Log BCF (lower trophic) = -0.014 (BCF = 0.9687 L/kg wet-wt)

Estimated Log BAF (lower trophic) = 1.186 (BAF = 15.36 L/kg wet-wt)

 

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

Estimated Log BCF (upper trophic) = 0.035 (BCF = 1.083 L/kg wet-wt)

Estimated Log BAF (upper trophic) = 2.986 (BAF = 968 L/kg wet-wt)

 

Biotransformation Rate Constant:

kM (Rate Constant): 0.01501 /day (10 gram fish)

kM (Rate Constant): 0.008442 /day (100 gram fish)

kM (Rate Constant): 0.004747 /day (1 kg fish)

kM (Rate Constant): 0.00267 /day (10 kg fish)

Bio Half-Life Normalized to 10 g fish at 15 deg C: 46.17 days

 

Reference 8

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 and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

see QMRF and QPRF attached

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: 8.72 (estimated, KOWWIN v.1.68)

Type:

BAF

Value:

314 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Type:

BCF

Value:

14.07 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Estimated Log BCF (mid trophic) = 1.280 (BCF = 19.06 L/kg wet-wt)

Estimated Log BAF (mid trophic) = 3.191 (BAF = 1551 L/kg wet-wt)

Estimated Log BCF (lower trophic) = 1.321 (BCF = 20.93 L/kg wet-wt)

Estimated Log BAF (lower trophic) = 3.594 (BAF = 3926 L/kg wet-wt)

 

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

Estimated Log BCF (upper trophic) = 3.081 (BCF = 1204 L/kg wet-wt)

Estimated Log BAF (upper trophic) = 6.755 (BAF = 5.686e+006 L/kg wet-wt)

 

Biotransformation Rate Constant:

kM (Rate Constant): 0.1948 /day (10 gram fish)

kM (Rate Constant): 0.1096 /day (100 gram fish)

kM (Rate Constant): 0.06161 /day (1 kg fish)

kM (Rate Constant): 0.03465 /day (10 kg fish)

Bio Half-Life Normalized to 10 g fish at 15 deg C: 3.558 days

 

Reference 9

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:

results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification

Remarks:

the component is outside of the domain of the training set (log Kow of the training set: 0.31-8.70; log Kow of the component: 11.67). Nevertheless, the value of the prediction will be used for risk assessment purposes, 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.

Justification for type of information:

see QMRF and QPRF attached

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: 11.67 (estimated, KOWWIN v.1.68)

Type:

BAF

Value:

58.01 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Type:

BCF

Value:

0.991 L/kg

Basis:

whole body w.w.

Remarks on result:

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

Estimated Log BCF (mid trophic) = 0.028 (BCF = 1.067 L/kg wet-wt)

Estimated Log BAF (mid trophic) = 1.797 (BAF = 62.72 L/kg wet-wt)

Estimated Log BCF (lower trophic) = 0.038 (BCF = 1.09 L/kg wet-wt)

Estimated Log BAF (lower trophic) = 1.821 (BAF = 66.16 L/kg wet-wt)

 

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

Estimated Log BCF (upper trophic) = 0.434 (BCF = 2.718 L/kg wet-wt)

Estimated Log BAF (upper trophic) = 3.968 (BAF = 9279 L/kg wet-wt)

 

Biotransformation Rate Constant:

kM (Rate Constant): 0.02849 /day (10 gram fish)

kM (Rate Constant): 0.01602 /day (100 gram fish)

kM (Rate Constant): 0.009011 /day (1 kg fish)

kM (Rate Constant): 0.005067 /day (10 kg fish)

Bio Half-Life Normalized to 10 g fish at 15 deg C: 24.33 days

 

Reference 10

Endpoint:

bioaccumulation: aquatic / sediment

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:

other: determine a BCF value is not the focus of this study

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.

Reference 11

Endpoint:

bioaccumulation: aquatic / sediment

Type of information:

other: review article

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:

Review article describing the metabolism and functions of lipids and fatty acids in fish. Both play major roles as source of metabolic energy in processes as growth and reproduction.

GLP compliance:

no

Test organisms (species):

other: Fish

Route of exposure:

other: not applicable, review article

Test type:

other: not applicable, review article

Remarks on result:

other: determine a BCF value is not the focus of this study

- Fatty acid catabolism is the predominant source of energy in many species of fish. The catabolism of fatty acids occurs in the cellular organelles, mitochondria (and peroxisomes). The process is termed beta-oxidation and involves the sequential cleavage of two-carbon units, released as acetyl-CoA, through a cyclic series of reactions catalyzed by several distinct enzyme activities. Activated fatty acids are transported to the mitochondrion in the form of fatty acyltransferase, converted back into fatty acyl-CoA derivatives, and then undergo a round of dehydrogenation, hydration, second hydrogenation, and cleavage steps to produce acetyl-CoA and NADH. Then, the acetyl-CoA can be metabolized via the tricarboxylic cycle to produce more NADH. The NADH will eventually lead to the release of ATP through the process of oxidative phosphorilation, available to be used as energy source.

- Fatty acid oxidation is an important source of energy in several tissues in fish (heart, red muscles, etc). Furthermore, fatty acids are the major source of metabolic energy in the development from egg to adult fish and also during reproduction and lipid depletion processes, such as migrations. They are also involved in the maintainance of the structure and function of cellular biomembranes (as part of phosphoglycerides).

Description of key information

The potential for bioaccumulation of the LCAE category members is low.

Additional information

Aquatic bioaccumulation of Long Chain Aliphatic Esters

Experimental bioaccumulation data are not available for the members of the Long Chain Aliphatic Esters (LCAE) category. The high log Kow (> 7) as an intrinsic chemical property of the category members indicates a potential for bioaccumulation. However, the information gathered on environmental behaviour and metabolism, in combination with QSAR-estimated values, provide enough evidence (in accordance to the 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 1907/2006, Annex IX to state that these substances are likely to show negligible bioaccumulation potential.

Environmental behavior

Due to ready biodegradability and high potential of adsorption, the category members can be effectively removed in conventional sewage treatment plants (STPs) by biodegradation and by sorption to biomass. The low water solubility (< 0.05 mg/L) and high estimated log Kow values indicate that the members of the LCAE category are highly lipophilic. If released into the aquatic environment, the category members undergo extensive biodegradation and sorption on organic matter. Thus, the bioavailability of these substances in the water column is reduced rapidly. The relevant route of uptake of LCAE in aquatic organisms is considered predominatly by ingestion of particle bound substance. 

Metabolism of aliphatic esters

Should category members be taken up by fish during the process of digestion and absorption in the intestinal tissue, aliphatic esters like LCAE are expected to be initially metabolized via enzymatic hydrolysis to the corresponding free fatty acids and the free fatty alcohols such as oleic acid and tetradecan-1-ol, for example. The 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/metabolism of xenobiotics which reduces the bioaccumulation or bioconcentration potential (Lech & Bend, 1980). It is known for esters that they are readily susceptible to metabolism in fish (Barron et al., 1999) and literature data have clearly shown 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, E., 1980). The metabolism of the enzymatic hydrolysis products is presented in the following chapter.

Metabolism of enzymatic hydrolysis products

Fatty alcohols

Fatty alcohols ranging from C8 (octan-1-ol) to C22 (docosan-1-ol), including unsaturated and branched alcohols, are the products from the enzymatic reaction of the LCAE catalyzed by carboxylesterases. 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 alcohol metabolism was also investigated in the zebrafish Danio rerio, which is a standard organisms 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 its corresponding acid, 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 and thus 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 trigylcerides in fat tissue and re-mobilized for energy production is 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 calculation

Additional information on bioaccumulation could be gathered through BCF/BAF calculations using BCFBAF v3.01. The estimated BCF values for the LCAE indicate negligible bioaccumulation in organisms (BCF: 42.84 L/kg, regression based). When including biotransformation, BCF and BAF values of0.89 - 14.07 and 0.90 - 314 L/kg, respectively were obtained (Arnot-Gobas estimate, including biotransformation, upper trophic). Even though the members of the LCAE category are outside the applicability domain of the model they can be used as supporting indication that the potential of bioaccumulation is low. The model training set is only consisting of substances with log Kow values of 0.31 - 8.70. But it supports the tendency that substances with high log Kow values (> 7) 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

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 the LCAE category members since it does not reflect the metabolism of substances in living organisms. BCF/BAF values estimated with the BCFBAF v3.01 program also indicate that the members of the LCAE category will not be bioaccumulative (all well below 2000 L/kg). Taking all these information into account, it can be concluded that the bioaccumulation potential of the LCAE category members is low.

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