Fatty acids, C16-18 (even numbered, C18 unsaturated), 2-ethylhexyl esters, epoxidized

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Remarks:

Performed with metabolic degradation product

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

Critical study for SIDS endpoint

Principles of method if other than guideline:

AME (absorption, metabolism, excretion) following dermal application of [14C]-2-EH. Excretion balance studies were conducted with 2-ethylhexanol (2-EH) in female Fischer 344 rats following single high (500 mg/kg) and low (50 mg/kg) oral doses of [14C]2-El, following repeated oral dosing with unlabelled 2-EH at the low level, following dermal exposure for 6 h with a 1 g/kg applied dose of [14C]2-EH, and following a 1 mg/kg i.v. dose of [14C]2 -EH.

GLP compliance:

yes

Specific details on test material used for the study:

The test item 2-ethylhexan-1-ol is a metabolic degradation product of the substance to be registered.

Radiolabelling:

yes

Species:

rat

Strain:

Fischer 344

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Kingston, NY, USA
- Age at study initiation: 9-11 weeks
- Weight at study initiation: 125-150g.
- Housing: suspended, stainless-steel mesh cages prior to study, and were transferred to the study room to allow acclimatization for at least 1 day prior to dosing.
- Individual metabolism cages: yes/no
- Diet: certified rodent diet (Agway‘” Prolab RMH 3000 or Agway Prolab RMH 3200 meal) adlibitum except for a 4-h period immediately after dosing.
- Water: Domestic tap water was available ad libitum
- Acclimation period: isolation for at least 5 days prior to use

Type of coverage:

other: Pyrex glass cylinders

Vehicle:

unchanged (no vehicle)

Duration of exposure:

96 hours

Doses:

1 g/kg bw

Details on study design:

TEST SITE
- Preparation of test site: shaved dorsal skin
- Area of exposure: 2.27 mm² (inner diameter of the Pyrex glass cylinder)
- Type of cover / wrap if used: adhesive

SITE PROTECTION / USE OF RESTRAINERS FOR PREVENTING INGESTION:
adhesive

REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleaning agent: aspiration of remaining test material, repeated washing with a 40% Hisoderm soap solution
- Time after start of exposure: 6 hrs

SAMPLE COLLECTION
- Collection of blood: from the tail vein; 5 samples within the first 10 min; then at 25, 50, 75, and 95 min.
- Collection of urine and faeces: separately, at intervals 0-8; 8-24; 24-48; 48-96 hrs
- Collection of expired air: (1) in sodium hydroxide traps and (2) in silica gel traps; time intervals as above
- Terminal procedure: no data
- Analysis of organs: no

SAMPLE PREPARATION
- Storage procedure: freezing until use (urine, faeces); blood: heparinised
- Preparation details: combustion (total radiaoactivity in urine and faeces); one-step digestant-scintillant treatment (blood); enzymatic treatment of urine for metabolite identification (ß-glucuronidase, sulfatase, acid) follwoed by filtering

ANALYSIS
- Method type(s) for identification: GC-MS, HPLC-MS-MS, Liquid scintillation counting, TLC

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Absorption in different matrices:

- Non-occlusive cover + enclosure rinse: 11.43%
- Skin wash: 38.95%
- Skin test site: 34.99%
- Urine: 3.32%
- Cage wash: 0.87%
- Faeces: 0.57%
- Expired air: 1.84%

Total recovery:

- Total recovery: 91.97%
- Recovery of applied dose acceptable: yes
- Results adjusted for incomplete recovery of the applied dose: no

Time point:

96 h

Dose:

1 g/kg bw

Parameter:

percentage

Absorption:

ca. 7 %

Time point:

96 h

Dose:

1 g/ kg bw

Parameter:

rate

Absorption:

0.57 mg cm-2 h-1

Table 4. Recovery of radioactivity from a 6-h, 1^.0 g/kg dermal application of neat [¹⁴C]2-ethylhexanol to a 2^.27 cm²area on the clipped backs of female Fischer 344 rat

		Collection period (h)
Sample	0-8	8-24	24-48	48-96	Total
Urine	1.41±0.47	1.66 ±0.25	0.19±0.03	0.07±0.02	3.32±0.72
Faeces	0.03±0^.02	0.39±0.066	0.15±0.06	0.01±0.01	0.57±0.09
Cage wash (water)	0.58±0.13	0.24±0.03	0.04±0.01	0.03±0.01	0.87±0
Silica gel breath traps	0.94±0.83	0.40±0.16	0.04±0.01	0.03±0.01	1.41±0.92
Sodium hydroxide breath traps	0.24±0.04	0.13±0.07	0.03±0.01	0.03± 0.01	0.43±0.06
Dose recovered from the exposure site at 6h					34^.99±16.61
Washing recovery from the exposure site at 6h					38.95±9.78
Dose on cell cover at 6h					11.43±5.17
Total recovery	3.19 ±0.77	2.81±0.38	0.44±0.11	0.17±0.03	91.97±5.75

Values are the mean per cent of dose SSD recovered from four animals.

Table 5. Recovery of radioactivity following a 1 mg/kg i.v. (tail vein) dose of [¹⁴C]2-ethylhexanol (in saline) to female Fischer 344 rats.

		Collection period (h)
Sample	0-8	8-24	24-48	48-96	Total
Urine	35.79±1.89	14.50+2.99	1.59±0.28	1.40±0.26	53.28±3.70
Faeces	0.19±0.30	2.89±0.95	0.55±0.15	0.22±0.05	3.84±1.19
Cage wash (water)	15.94±3.36	3.66±1.74	0.66+0.28	0.92±0.44	21.17±2.92
Silica gel breath	0.22 ± 0.03	0.15±0.04	0.04 ±0.01	0.03 ± 0.01	0.44± 0.07
traps Sodium hydroxide	19.12 ± 1.02	2.15±0.18	0.94±0.11	0.77±0.07	22.97±1.23
breath traps Total recovery	71.24±3.42	23.35+3.01	3.77±0.67	3.33±0.42	101.69±1.11

Values are the mean per cent of dose +/- SD recovered from four animals

Table 6. Quantitation of urinary metabolites of 2-ethylhexanol in female Fischer 344 rats.

				Per cent of dose per peak
	Single low oral dose		Single high oral dose		Repeated low oral dose		Dermal dose
Peak ID	Free	Glucuronide	Free	Glucuronide	Free	Glucuronide	Free	Glucuronide
5-OH-EHA	1.11±0-64	1.28±1.26	3.06±0.88	1.18±0.77	0.73±0.21	2.93±2.27	<0.01	0.30±0.37
2-Ethyladipate + 5-OH-EHA	5.55±2.27	24.12±6.84	4.13+0.95	8.17+4.09	2.37+1.62	25.30±2.19	<0.01	1.61±0.37
6-OH-EHA	1.56±1.10	6.81+1.97	0.80+0.71	6.26±0.55	1.43±0.87	6.89±1.65	<0.01	0.57±0.32
Lactones of 5-OH-EHA	0.44±0.17	0.19±0.25	0.28±0.05	0.01	0.56±0.41	0.82±1.54	<0.01	0.01
2-Ethyl-5-hexenoic acid	<0.01	0.16±0.11	0.01	0.10±0.13	0.06±0.12	0.20±0.11	<0.01	0.01
EHA	0.54±0.68	6.30±1.21	4.77±3.69	20.14±3.25	1.27±1.08	7.45+2.42	<0.01	0.52±0.23
2-Ethylhexanol	0.03+0.05	1.53±0.51	0.01	0.34±0.31	0.22±0.40	1.19±0.15	<0.01	0.06±0.07

Values represent the mean±SD of four animals over the 0-24-h collection period. Quantitation is based on hplc separation and radiochemical detection of metabolites. The structural assignments are based on hplc and glc-mass selective detection analysis of samples and authentic standards both before and after enzymic hydrolysis.

Conclusions:

Bioavailability of 2-EH via the dermal route is low. Metabolism and excretion of absorbed material is fast, with no difference to the oral route.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Remarks:

Performed with metabolic degradation product

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Objective of study:

other: ADME

Principles of method if other than guideline:

Oral rat ADME studies using [14]C-2-EH

GLP compliance:

no

Specific details on test material used for the study:

- Analytical purity: not speciifed
- Specific activity (if radiolabelling): not speciifed
- Locations of the label: 2-ethyl[1-14C]hexan-1-ol
- The test item 2-ethylhexan-1-ol is a metabolic degradation product of the substance to be registered.

Radiolabelling:

yes

Remarks:

[14]C

Species:

rat

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 300 g
- Individual metabolism cages: not speciifed
- Diet: ad libitum
- Water: ad libitum
- Housing: The animals were held in metabolism cages

Route of administration:

oral: gavage

Vehicle:

other: cottonseed oil, 0.4 mL

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Low dose: 1µCi, 8.8 µg of labelled [14C]-2-EH dissolved in 0.4 mL cottonseed oil
High dose: 1µCi, 8.8 µg of labelled [14C]-2-EH dissolved in 0.4 mL cottonseed oil, additionally 0.1 mL (83.3 mg) of unlabeled 2-EH.

VEHICLE
Amount of vehicle (if gavage): 0.4 mL

Duration and frequency of treatment / exposure:

Single dose

Dose / conc.:

29 other: µg/kg bw

Remarks:

labelled 2-EH/ low dose group

Dose / conc.:

278 mg/kg bw/day (actual dose received)

Remarks:

unlabelled 2-EH plus 29 µg/kg bw labelled 2-EH/ high dose group

No. of animals per sex per dose / concentration:

2 male rats per dose level

Control animals:

no

Details on dosing and sampling:

SAMPLING:
CO2 was collected in ethanolamine: cellososolve (1:8). Urine and faeces were collected at hourly intervals. The excreta, an ethanol wash of the cages, the rat hearts, brains, livers, kidneys and the carcass were examined for the radiolabel.

PROCESSING OF URINE:
2 mL of urine were passed through a Dowex 50-H column, 200-400 mesh and eluted with deionised water. Fractions were collected and monitored for radioactivity. Urine fractions from the high dose animals covering the first 18 hours after administration were pooled, made basic and extracted with diethyl ether, then adjusted to pH1 and extracted with diethyl ether. The two extracts were dried and used for characterisation of metabolites.

ANALYSES:
metabolites were separated by GC using FID. Mass spectrometry: chemical ionisation mass spectra and electron impact spectra were taken.

Details on absorption:

2-Ethylhexanol was efficiently absorbed following oral administration to rats. There were no differences between the low dose (27 µg/kg bw) and the high dose ( 278 mg/kg bw) group.

Details on excretion:

- There were no differences between the low dose (27 µg/kg bw) and the high dose ( 278 mg/kg bw) group regarding excretion
- 14C associated with 2-ethyl[1-14C]-hexanol was rapidly excreted in respiratory CO2 (6-7%). The radioactivity reached a peak in less than 2 hours, logarithmic decrease witzh t1/2= 3.5 hrs
- Faeces: nearly complete within 20 hrs; a total of 8.6% of the administered dose eliminated by this route.
- Urine: 25% was excreted within 8 to 10 hrs, approx. 80% after 28 hrs
- Total: 96.1% were excreted after 28 hrs. Cage wash accounted for 2.7%. Only 1.4% was found in the carcasses.

Metabolites identified:

yes

Details on metabolites:

IDENTIFIED METABOLITES:
2- heptanone, 4-heptanone, CO2. 2-ethyl-5-hydroxyhexanoic acid, 2-ethyl-5-keto-hexanoic acid, 2-ethyl-1,6-hexanedioic acid. unchanged 2-ethylhexanol (approx. 3%)

ADDITIONAL INFORMATION ON METABOLISM
- The amount of label recovered in CO2 matched the amount of unlabelled 2-heptanone plus 4-heptanone recovered from urine, suggesting that both types of metabolites may have been derived from the major urinary metabolite, 2-ethylhexanoix acid, by decarboxylation following partial beta-oxidation. The 14CO2 appeared not to be derived from acetate or by reductive decarboxylation.
- There were no differences between the low dose (27 µg/kg bw) and the high dose ( 278 mg/kg bw) group regarding metabolism

OTHER INFORMATION ON METABOLIC PATHWAYS
- Ethylhexanol was a competitive inhibitor of yeast alcohol dehydrogenase, but a good substrate for the mammalian horse alcohol dehydrogenase.
- Metabolic pathways were suggested as follows:
(i) first step: oxidation of 2-ethyl-hexanol via alcohol dehydrogenase and aldehyde dehydrogenase to 2-ethyl-hexanoic acid (2-EHA)
(iia) omega-oxidation of 2-EHA, leading to the di-acid
(iib) omega-1 -oxidation of 2-EHA, leading to 5-hydroxy and 5-keto-2-ethylhexanoic acid
(iic) ß-oxidation, leading to the 2-keto- and 4-keto-pentanones and CO2.

Excretion of [14-C] within 28 hrs after oral administration to rats         (% of dose)
CO2	6-7
Urine	80-82
Faeces	8-9
Total excreted	96.1
Cage wash	2.7
Carcass	1.4

Conclusions:

2-EH was rapidly absorbed, metabolised, and excreted mainly via urine within 28 hours after oral administartion to rats. Accumulation of 2-EH or its metabolites is unlikely to occur.

Executive summary:

2-Ethylhexanol was efficiently absorbed following oral administration to rats. 14C associated with 2-ethyl[1-14C]-hexanol was rapidly excreted in respiratory CO2 (6-7%), faeces (8-9%) and urine (80-82%), with essentially complete elimination by 28 h after administration. There was no difference between the low or high dose (9 µg/kg bw and 278 mg/kg bw, resp.). The major metabolite is 2-ethylhexanoic acid, which appears in urine; alternatively it may also be further metabolised by either ß-oxidation or omega and omega-1 oxidation. Only 3% of the 2-ethylhexanol are excreted unchanged. Overall, 2-EH was rapidly absorbed, metabolised, and excreted mainly via urine within 28 hours following the oral administration to rats. Accumulation of 2-EH or its metabolites is unlikely to occur (Albro, 1975).

Reference 3

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Remarks:

performed with a group of esterified alcohols

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Objective of study:

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

The enzymatic hydrolysis in vitro of the esters of methanol, ethylene glycol, glycerol, erythritol, pentaerythritol, adonitol, sorbitol, and sucrose in which all alcohols groups were esterified with oleic acid was studied. Various preparations of rat pancreatic juice, including pure lipase, were used as the sources of enzymes. To distinguish lipase form non-specific lipase activity, incubations containing sodium taurocholate and pancreatic juice treated with proteolytic enzymes were included.

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report):methanol, ethylene glycol, glycerol, erythritol, pentaerythritol, adonitol, sorbitol, sucrose and oleic acid.
- Analytical purity: Oleic acid - 99% pure by Gas-liquid chromatography.
- Other: The alcohols, except ethylene glycol, were transesterified with an excess of methyl oleate to form the complete esters. Ethylene glycol dioleate was pre- pared by acylation of the alcohol with oleoyl chloride

Details on test animals or test system and environmental conditions:

Preparation of enzymes:
- Combination fluid - The common bile-pancreatic duct was cannulated at a point near its entrance into the duodenum. In the 24 -hr period following the cannulation, the combination of bile and pancreatic fluid was collected at 4°C. The lipolytic enzymes in this preparation retained their activity for at least 48 hr.
- Untreated pancreatic juice solids - Pancreatic juice, free of bile, was obtained by cannulating separately the bile and pancreatic ducts. The pancreatic fluid was collected at 4°C and freezed-dried. On the day of use, the solids were reconstituted, 3 mg/ mL, in 0.01 M histidine, pH 7.0.
- Treated pancreatic juice solids - To inactivate nonspecific lipase in the study, 150 mg of crude pancreatic juice solids and 1 mg of α-chymotrypsin was dissolved in 80 mL of 0.01 M histidine, pH 9.0.
- Purified Lipase - Lipase (EC 3.1.1.3) was isolated from the untreated pancreatic juice solids using the method of Vandermeers, A and Christophe, J (Biochim. Biophy. Acta. 154:110 -129).

Route of administration:

other: In incubation medium

Details on exposure:

- The esters were digested in a cylindrical, flat bottomed glass tube 30 mm (I.D.) x 90 mm. Four 3-mm indentations in the side wall prevented vortexing during stirring.
- Each digest contained 100 mg of substrates, 85 µmoles of CaCl2, 3.5 mg of histidine (final concentration 0.002 M), 152 mg of NaCl (final concentration 0.15 M), and the enzyme in a total volume of 10 mL. For incubations with untreated pancreatic juice, treated pancreatic juice and purified lipase incubations with and without 200 mg of sodium taurocholate (final concentration 37 mM) were included. Prior to the addition of the enzyme, all the components of the digest were stirred for 5 min.
- The digestions were carried out at pH 9.0 and at 27°C. Under these conditions all substrates were liquids.
- The pH was maintained with the aid of a pH stat by the addition of 0.02 N KOH.

Dose / conc.:

100 other: mg

Control animals:

other: sodium taurocholate

Details on dosing and sampling:

The rate of addition of alkali (0.02 N KOH) was linear during the first several minutes of digestion and was reported as the rate of hydrolysis: µmoles of free fatty acid released per minute per milligrams or per millilitre of enzyme preparation.

Metabolites identified:

no

Details on metabolites:

- The combination of bile-pancreatic fluid digested all substrates with the exception of sorbital hexaoleate and sucrose octaoleate. This failure of hydrolysis was obtained in spite of using 400 times as much combination bile-pancreatic fluid as was used when triolein was the substrate.
- When pancreatic juice without bile was used as a source of the enzymes, the esters that were hydrolysed depended on the presence or absence of added sodium taurocholate. In the absence of sodium taurocholate, only those substrates that contained less than four ester groups were hydrolysed. The addition of sodium taurocholate to the digest permitted the hydrolysis also of the substrates containing four and five ester groups. There were marked differences in the rates of hydrolysis of the oleate esters of methanol, ethylene glycol, and glycerol if taurocholate was not present, but these differences disappeared if this bile salt was added to the digest.
- In the absence of sodium taurocholate, the pattern of digestion by treated pancreatic juice was similar to that seen with the untreated pancreateic juice. However, in the presence of added sodium taurocholate, pancreatic juice that had been treated with the proteolytic enzyme could not digest any of the substrates.
- The final set of results was obtained with purified pancreatic lipase. If sodium taurocholate was not present, this enzyme hydrolysed methyl oleate, ethylene glycol dioleate, and triolein, but did not hydrolyse the substrates that contained more than three ester groups. The additions of sodium taurocholate blocked completely the hydrolytic activity of this enzyme.
- The observation that four and five ester groups were hydrolysed by certain preparations of pancreatic juice is attributed to the enzyme nonspecific lipase. This enzyme also hydrolysed esters of primary alcohols.
- Details are provided in 'any other information on results incl. tables'.

The rate of hydrolysis of the esters of the eight different alcohols by the various preparations of rat pancreatic juice is given in the table below. The numbers in parentheses are the volume or weight of enzyme preparation that was used in that particular digest.

Table 1. Relative rates of hydrolysis by rat pancreatic juice enzymes of the complete oleate esters of the listed alcohols.

	Pancreatic-Bile Juice	Untreated Pancreatic Juice		Treated Pancreatic Juice^a		Purified Lipase
	No TC^b	No TC	TC added	No TC	TC Added	No TC	TC added
	µmoles FFA min/ mL	µmoles FFA min/ mg		µmoles FFA min/ mg		µmoles FFA min/ mg
Methanol, 1^c	54    (0.05)^d	2.6 (1.2)	4.0 (1.2)	2.5 (1.2)	0 (1.2)	63 (0.02)	0 (0.3)
Ethylene glycol, 2	160 (0.025)	10  (0.3)	4.3 (0.3)	7.7 (0.3)	0 (0.3)	200 (0.01)	0 (0.1)
Glycerol, 3	2100 (0.005)	73 (0.075)	6.0 (0.15)	70 (0.06)	0 (0.3)	1900 (0.002)	0 (0.02)
Erythritol, 4	1.9   (1)	0   (6)	1.4 (3)	0 (6)	0 (6)	0 (0.1)	0 (0.1)
Pentaerythritol, 4	1.1   (2)	0   (6)	1.1 (3)	0 (6)	0 (6)	0 (0.1)	0 (0.1)
Adonitol, 5	0.53 (2)	0   (6)	0.25 (3)	0 (6)		0 (0.1)	0 (0.1)
Sorbitol, 6	0      (2)	0   (6)	0   (12)	0 (6)	0   (12)	0 (0.1)	0 (0.1)
Sucrose, 8	0      (2)	0   (6)	0   (12)	0 (6)	0   (12)	0 (0.1)	0 (0.1)

^a Nonspecific lipase was inactivated by treatment with α-chymotrypsin.

^b TC, Sodium taurocholate.

^c Number of ester groups.

^d The number in parentheses is the volume or weight of the enzyme preparation that was used.

Description of key information

Hydrolysis (Fully oleic acid esterified methanol,  ethylene glycol,  glycerol, erythritol,  pentaerythritol, adonitol,  sorbitol,  and  sucrose)

In an in vitro metabolism study, the hydrolysis of oleic acid esterified methanol,  ethylene glycol,  glycerol, erythritol,  pentaerythritol, adonitol,  sorbitol,  and  sucrose was studied. The hydrolysis was assessed in incubations with various preparations of rat pancreatic juice, including pure lipase. Incubations with sodium taurocholate were included to distinguish lipase from non-specific lipase activity. Lipase did not catalyse the hydrolysis of substances with more than three ester groups. Compounds with four and five ester groups were hydrolysed by the endogenous enzyme non-specific lipase. Compounds containing six or eight ester groups were not hydrolysed by the pancreatic juice (Mattson and Volpenhain 1972).

ADME study (CAS 104-76-7)

2-Ethylhexanol was efficiently absorbed following oral administration to rats. 14C associated with 2-ethyl[1-14C]-hexanol was rapidly excreted in respiratory CO2 (6-7%), faeces (8-9%) and urine (80-82%), with essentially complete elimination by 28 h after administration. There was no difference between the low or high dose (9 µg/kg bw and 278 mg/kg bw, resp.). The major metabolite is 2-ethylhexanoic acid, which appears in urine; alternatively it may also be further metabolised by either ß-oxidation or omega and omega-1 oxidation. Only 3% of the 2-ethylhexanol are excreted unchanged.

Overall, 2-EH was rapidly absorbed, metabolised, and excreted mainly via urine within 28 hours following the oral administration to rats. Accumulation of 2-EH or its metabolites is unlikely to occur (Albro 1975).

Dermal absorption (CAS 104-76-7)

2-EH was only slowly absorbed following dermal application of 1 g/kg bw. Less than 7% of the dose was absorbed within 6 hours of skin contact. The absorbed dose underwent rapid oxidative metabolism and glucuronidation followed by rapid excretion, predominantly in the urine. The absorption rate was 0.57 mg/cm²/h, which is in the range that was determined for rat skin in vitro (0.22 mg/cm²/h; Barber et al., 1992). The metabolic pattern was similar in all experiments, i.e. there were no differences that could be attributed to the oral or dermal route, the low or high dose level, or to single or repeated treatment. One exception is the marginally delayed excretion at 8 hours after dosing in the group receiving the high oral dose which indicates some saturation of the metabolic capacity (Deisinger, 1994).

Additional information

Toxicokinetic information

Due to the high lipophilicity, an uptake by micellular solubilisation is expected after oral exposure. On the basis of the application profile of the substance and the physico-chemical properties (low vapour pressure), inhalation as a vapour is negligible. The dermal uptake into the stratum corneum is expected to be efficient, but transfer to the epidermis is limited because of the high lipophilicity. Once absorbed, the substance is expected to be efficiently metabolized by esterases and epoxide hydrolases, as the substance has a high structural resemblance to endogenous substrates of these enzymes. The excretion of the degradation products is via exhalation air (carbon dioxide) or urine (water and Phase II-conjugates). A bioaccumulation potential is not expected.

1.    Chemical and physic-chemical description of the substance

The substance to be registered is a reaction product (ester) of fatty acids (C16-18 and C18-unsaturated) with isooctanol, of which the double bond(s) in the fatty acid chain were subsequently epoxidized. It can be described with the CAS no. 97553-05-4 (CAS Fatty acids, C16-18 (even numbered, C18 unsaturated), isooctyl esters, epoxidized).

Description of the physico-chemical properties:

- physical state (20°C): liquid

- vapour pressure (20°C):<0.0037 Pa

- molecular weight: appr. 410 Da (DERMWIN, v1.43)

- log Kow: appr. 10.08 (20° C)

- water solubility: <0.05 mg/L at 20 °C

- Boiling point: substance decomposes at about 387 °C 

The substance is characterized by a lipophilic nature, a low volatility and relatively low water solubility.

2.     Toxicokinetic assessment

No experimental data on absorption, metabolism and distribution are available for the substance. Based on the structure and the physico-chemical properties of the substance, the toxicokinetic behaviour can be evaluated.

2.1 Absorption:

In the gastro-intestinal tract, the highly lipophilic substance (log Kow: appr. 10) with very limited water solubility (<0.05 mg/L) and a relatively high molecular weight (appr. 410 Da) is unlikely to be absorbed by passive diffusion. An uptake due to micellular solubilisation could be expected.

The substance to be registered has a low vapour pressure of <0.0037 Pa and decomposes at about 387°C, indicating that inhalation as a vapour will be negligible. If the substance reaches the respiratory tract, passive diffusion is unlikely due to the high log Kow, the relatively low water solubility the rather high molecular weight. A systemic uptake could take place after micellular solubilisation.

With a molecular weight of >400 Da, the substance is relatively large for the dermal absorption. The high lipophilicity (log Kow: appr. 10) favours the penetration into the stratum corneum, but limits the transfer between stratum corneum and epidermis. Considering the physico-chemical parameters, an accumulation of the substance in the stratum corneum might occur. However, the dermal penetration potential modeled by the QSAR program DERMWIN (kp = 85.3cm/hr, v1.43) suggests that a higher systemic availability might occur than expected in consideration of the physico-chemical data. As worst case assumption, a dermal uptake of 100% is assumed.

2.2 Metabolism and Excretion:

Once absorbed, a metabolic reaction could in principle take place at the epoxide- or the ester site of the substance.

The ester function is likely to be metabolized like dietary fats. As shown by Mattson and Volpenhain, esters of fatty acids and different alcohols (methanol, ethylene glycol, glycerol…) are potential substrates for endogenous lipases in the bile-pancreatic fluid. These enzymes catalyse the hydrolysis to the corresponding alcohol and acid. As cleavage products of the substance to be registered, 2-ethylhexanol as well as epoxidized/non-epoxidized fatty acids are formed.

The fatty acids without epoxy site are further metabolized like any other dietary fatty acid, undergoing an oxidation to carbon dioxide and water.

Epoxidized fatty acids can also be formed endogenously, and some fatty acid epoxides even have a physiological function (e.g. leukotriene A4). Consequently, efficient mechanisms are in place to control the level of epoxides and to further metabolize them. The epoxide function is a typical substrate for epoxide hydrolases, which can be assigned to the Phase I metabolic enzymes. For the conversion of fatty acid epoxides into diol fatty acids, the microsomal epoxide hydrolase mEH_band especially the soluble epoxide hydrolase sEH_TSOplay a major role in the human body (reference: e.g. H. Marquardt/S.G. Schäfer, Lehrbuch der Toxikologie. Spektrum Akademischer Verlag, 1997, chapter “Fremstoffmetabolismus” (author: F. Oesch)). These epoxide hydrolases are present in many human organs. However, the major site of metabolism of the fatty acid epoxides is most likely the liver. The resulting diol fatty acids are further processed by metabolic Phase II enzymes, e.g. by glutathione transferase. The glutathione conjugate has an increased water solubility, which enables the excretion via urine.

The metabolism of 2-ethylhexanol (2-EH) in mammalians is well investigated. As 2-EH is formed during the metabolic degradation of the substance to be registered, absorption plays no role and is therefore not evaluated in this dossier. In the studies of Deisinger (Deisinger et al., 1994) and Albro (Albro, 1975), rapid metabolism and excretion of 2-EH as polar glucuronides predominantly in urine was demonstrated in rats following oral or dermal ingestion. No evidence of metabolic induction was seen following repeated dosing. 2-EH is a good substrate for mammalian dehydrogenases, leading to the formation of 2-ethylhexanoic acid. This metabolite can either be conjugated or further metabolized via partial ß-oxidation, or omega- and omega-1 oxidation, followed by conjugation. Urinary metabolites eliminated following the oral and dermal doses were predominately glucuronides of oxidized metabolites of 2-EH, including glucuronides of 2-ethyladipoic acid, 2-ethylhexanoic acid, 5-hydroxy-2 -ethylhexanoic acid and 6-hydroxy-2-ethylhexanoic acid. Bioaccumulation is unlikely due to virtually complete excretion (>95% within 96 hrs).