Quaternary ammonium compounds, C12-14-alkyl[(ethylphenyl)methyl]dimethyl, chlorides

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

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

Adequacy of study:

weight of evidence

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

KL2 due to RA

Reason / purpose for cross-reference:

read-across source

Objective of study:

other: Absorption, distribution, metabolism and excretion

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

14C-labelled test substance

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Test animals:
- Source: Charles River
- Age at study initiation: 6 weeks
- Weight at study initiation: Average body weight: 268.6 g (male) and 167.0 g (female)

Details on exposure:

Preparation of dosing solutions:
Preliminary experiments: Oral gavage – single low dose
Experiment 1: Oral gavage – single low dose
Experiment 2: Dietary – repeated low dose
Experiment 3: Oral gavage – single high dose
Experiment 4: Intravenous


Vehicle:
Distilled water (Preliminary experiments and Experiments 1, 3 and 4)
Rodent diet/distilled water (Experiment 2)

Concentration in vehicle:
Preliminary experiments and Experiment 1: 1.0 mg/mL
Experiment 2: 100 ppm in diet for 14 d/1 mg/mL in water single oral dose
Experiment 3: 5.0 mg/mL
Experiment 4: 4 mg/mL


Homogeneicity and stability of the test material: Stable

Duration and frequency of treatment / exposure:

Preliminary experiments: Oral gavage – single low dose
Experiment 1: Oral gavage – single low dose
Experiment 2: Dietary – repeated low dose for 14 d
Experiment 3: Oral gavage – single high dose
Experiment 4: Intravenous

Dose / conc.:

10 other:

Remarks:

Doses / Concentrations:
Preliminary experiments and Experiment 1: 10 mg/kg
Experiment 2: 100 ppm non-radiolabelled substance for 14 d, followed by 10 mg/kg radiolabelled.
Experiment 3: 50 mg/kg
Experiment 4: 10 mg/kg

No. of animals per sex per dose / concentration:

Preliminary experiments: 2 per sex per group (Total 8 animals)
Main experiments:5 per sex per group (Total 40 animals)

Control animals:

no

Details on dosing and sampling:

Pharmacokinetic study (Absorption, distribution, excretion):
- Tissues and body fluids sampled: urine, faeces, blood, plasma, cage washes
- Time and frequency of sampling: Urine, faeces and urine/feces separator washing samples were collected at the following time intervals: 0-4, 4-8, 8-12, 12-24, 24-36, 36-48, 48-72, 72-96, 96-120, 120-144 and 144-168 h.

Metabolite characterisation studies:
- Tissues, urine and faeces were collected and analysed for radioactivity and faeces were analysed by TLC, HPLC and MS for metabolites and parent compound.

Preliminary studies:

A preliminary study had indicated that insignificant 14CO2 was generated.

Details on absorption:

Percent Recovery:

Experiment 1:
Males: 5.77% urine; 98.61% faeces
Female: 6.88% urine; 91.20% faeces
Total Recovery: 104.54 ± 5.29% - males; 98.11 ± 3.25% females

Experiment 2:
Males: 4.76% urine; 95.12% faeces
Female: 5.80% urine; 97.22% faeces
Total Recovery: 100.19 ± 4.94% - males; 103.1 ± 5.18% females

Experiment 3:
Males: 7.75 % urine; 90.03% faeces
Female: 6.95% urine; 87.48% faeces
Total Recovery: 98.36 ± 2.42% - males; 94.58 ± 7.57% females

Experiment 4:
Males: 30.63% urine; 44.44% faeces
Female: 20.58% urine; 55.09% faeces
Total Recovery: 108.43 ± 5.56% - males; 111.45 ± 3.96% females

Less than 1% in tissues in all oral dosing experiments. Approximately 30-35% of the administered dose in tissues following i.v. dosing.

Details on distribution in tissues:

Residual 14C in tissues was negligible after administration of radiolabelled test substance by gavage both after single and repeated dosing, indicating low potential for bioaccumulation. After i.v. administration a higher amount of radioactivity (30−35%) was found as residue in the tissues.

Details on excretion:

About 6−8% of orally administered test substance is excreted in the urine whereas, 87−98% was found in the faeces. Since no data on bile duct-cannulated rats are available, it is not possible to conclude if this radioactivity accounts exclusively for unabsorbed test substance or not. However, the i.v. experiment showed that 20−30% was excreted in the urine and 44-55% in the faeces, suggesting that both the kidney and liver are capable of excreting test substance once absorbed and that absorption is higher than the % found in the urine after oral administration.

Metabolites identified:

yes

Details on metabolites:

Over 50% of the faecal radioactivity was unchanged parent compound. Four major metabolites were identified, as oxidation products of the two decyl side chains to hydroxy and hydroxyketo derivatives. The only metabolism which occurred involved oxidation of the two decyl side chains to hydroxy and hydroxyketo derivatives. All were more polar and presumed less toxic than the parent compound. It is predicted that there is no major metabolite greater than 10% of the dosed radioactivity.

Conclusions:

Based on the results of the read across substance study, following the single doses or the last dietary dose, urine and faeces were collected for 7 d. Tissues, urine and faeces were collected and analysed for radioactivity and faeces were analysed by TLC, HPLC and MS for metabolites and parent compound. Following oral administration, radiolabelled test substance was rapidly absorbed, although in very limited amounts, consistent with its highly ionic nature. Residual 14C in tissues was negligible after administration of by gavage both after single and repeated dosing, indicating low potential for bioaccumulation. After i.v. administration a higher amount of radioactivity (30−35%) was found as residue in the tissues. About 6−8% of orally administered test substance is excreted in the urine whereas, 87−98% was found in the faeces. Since no data on bile duct-cannulated rats are available, it is not possible to conclude if this radioactivity accounts exclusively for unabsorbed test substance or not. However, the i.v. experiment showed that 20−30% was excreted in the urine and 44-55% in the faeces, suggesting that both the kidney and liver are capable of excreting test substance once absorbed and that absorption is higher than the % found in the urine after oral administration. Less than 50% of the orally administered test substance is metabolised to side-chain oxidation products. In view of the limited absorption of the test substance, the four major metabolites identified may be at least partially formed in the gut of rats, apparently by microflora. No significant difference in metabolism between male and female rats or among the dosing regimens was observed. Repeated dosing did not alter the uptake, distribution or metabolism of test substance.

Executive summary:

A study was conducted to determine the basic toxicokinetics of the read across substance, C12-16 ADBAC (active ingredient: 81.09% aqueous solutions), according to EPA OPP 85-1, in compliance with GLP. Sprague-Dawley rats (10 animals per sex per group) were treated with radiolabelled test substance. The study was conducted in four experiments: a single low dose (10 mg/kg); a single high dose (50 mg/kg); a 14 d repeated dietary exposure with non-radiolabelled test substance (100 ppm) and single low dose of radiolabelled (14C) test substance (10 mg/kg); and single intravenous dose (10 mg/kg). Based on the results of the read-across substance study, following the single doses or the last dietary dose, urine and faeces were collected for 7 d. Tissues, urine and faeces were collected and analysed for radioactivity and faeces were analysed by TLC, HPLC and MS for metabolites and parent compound. Following oral administration, radiolabelled test substance was rapidly absorbed, although in very limited amounts, consistent with its highly ionic nature. Residual 14C in tissues was negligible after administration of by gavage both after single and repeated dosing, indicating low potential for bioaccumulation. After i.v. administration a higher amount of radioactivity (30−35%) was found as residue in the tissues. About 6−8% of orally administered test substance is excreted in the urine whereas, 87−98% was found in the faeces. Since no data on bile duct-cannulated rats are available, it is not possible to conclude if this radioactivity accounts exclusively for unabsorbed test substance or not. However, the i.v. experiment showed that 20−30% was excreted in the urine and 44-55% in the faeces, suggesting that both the kidney and liver are capable of excreting test substance once absorbed and that absorption is higher than the % found in the urine after oral administration. Less than 50% of the orally administered test substance is metabolised to side-chain oxidation products. In view of the limited absorption of the test substance, the four major metabolites identified may be at least partially formed in the gut of rats, apparently by microflora. No significant difference in metabolism between male and female rats or among the dosing regimens was observed. Repeated dosing did not alter the uptake, distribution or metabolism of test substance (Selim, 1987). Based on the results of the read across study, the test substance, C12 -14 ADEBAC, can also be considered to have a similar ADME profile.

Reference 2

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

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

Adequacy of study:

weight of evidence

Study period:

From August 18, 2005 to August 17, 2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

KL2 due to RA

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Species:

human

Details on test animals or test system and environmental conditions:

Human skin membranes, in vitro

Type of coverage:

other: Automated flow-through diffusion cell system

Vehicle:

water

Doses:

0.03% (w/w) and 0.3% (w/w), in water

Details on in vitro test system (if applicable):

Skin preparation:
- Source of skin: Eight samples from Plastic Surgery unit, St. Johns Hospital, West Lothian NHS Trust, Livingston, UK
- Ethical approval if human skin: Yes
- Type of skin: Full-thickness human skin (1 upper arm, 2 abdomen and 5 breast)
- Preparative technique: Skin was transferred to Charles River Laboratories on ice and cleaned of subcutaneous fat and connective tissue using scalpel. Skin was washed in cold running tap water and dried using tissue paper. Each sample was then cut into smaller pieces, wrapped in aluminium foil, put into self sealing plastic bags and stored at -20°C until required. Split-thickness membranes were prepared by pinning the full thickness skin, stratum corneum uppermost, onto a raised cork board and cutting at a setting equivalent to 200-400 µm depth using a Zimmer electric dermatome.
Principles of assay:
- Diffusion cell: Automated flow-through diffusion cell system (Scott/Dick, University of Newcastle-upon-Tyne, UK)
- Receptor fluid: Tissue culture medium containing approximately 5% (w/v) bovine serum albumin, 1% (w/v) streptomycin (approximately 0.1 mg/mL), and penicillin G (approximately 100 units/mL)
- Solubility of test substance in receptor fluid:
- Flow-through system: Automated
- Test temperature: The mean temperature 19°C (SD=0.8°C)
- Humidity: The mean relative humidity 35% (SD=0.6%)

Total recovery:

Refer to Table-1

Key result

Dose:

0.03%

Parameter:

percentage

Absorption:

0.05 %

Remarks on result:

other: 24 h

Remarks:

96.80% was not absorbed

Key result

Dose:

0.3%

Parameter:

percentage

Absorption:

0.03 %

Remarks on result:

other: 24 h

Remarks:

94.68% was not absorbed

- Low dose (0.030%):

The mean mass balance was 99.03% of the applied dose (3.09 μg equiv./cm²). The mean dislodgeable dose was 60.53% of the applied dose (1.89 μg equiv./cm²). The mean total unabsorbed dose was 96.80% of the applied dose (3.02 μg equiv./cm²). This consisted of the dislodgeable dose, unexposed skin (0.02%) and the radioactivity associated with the stratum corneum (36.25%). The stratum corneum acted as a good barrier to the test substance as the bulk of the radioactivity (30.26%) was recovered in the outermost 5 tape strips (tape strips 1-5). Considerably less radioactivity was recovered with each of the subsequent 3 groups of tape strips (3.20%, 1.82% and 0.97% in tape strips 6-10, 11-15 and 16-20 respectively), suggesting that the test substance would be sloughed off with the skin in the future. The absorbed dose (0.05%, or <0.01 μg equiv./cm²) was the sum of the receptor fluid (0.05%) and the receptor rinse (<0.01%). Dermal delivery (2.22%, or 0.07 μg equiv./cm²) was the sum of the absorbed dose and the exposed skin (2.18%). There was no apparent lag time and the fluxes ranges from 0.03 to 0.12 ng equiv./cm²/h over the 1 to 24-h exposure period.

 

- High dose (0.300%):

The mean mass balance was 96.84% of the applied dose (29.91 μg equiv./cm²). The dislodgeable dose was 77.87% of the applied dose (24.05 μg equiv./cm²). The mean total unabsorbed dose was 94.68% of the applied dose (29.24 μg equiv./cm²). This consisted of the dislodgeable dose, unexposed skin (0.17%) and the radioactivity associated with the stratum corneum (16.64%). The stratum corneum acted as a good barrier to the test item as the bulk of the radioactivity (10.86%) was recovered in the outermost 5 tape strips (tape strips 1-5). Considerably less radioactivity was recovered with each of the subsequent 3 groups of tape strips (3.11%, 1.71% and 0.96% in tape strips 6-10, 11-15 and 16-20, respectively), again suggesting that the test item would be sloughed off with the skin in the future. The absorbed dose (0.03%, or 0.01 μg equiv./cm²) was the sum of the receptor fluid (0.03%) and the receptor rinse (<0.01%). Dermal delivery (2.16%, or 0.67 μg equiv./cm²) was the sum of the absorbed dose and the exposed skin (2.13%). There was no apparent lag time. There was no apparent lag time and the fluxes ranges from 0.22 to 0.74 ng equiv./cm²/h over the 1 to 24-h exposure period.

Table 1. Summary of recoveries after 24h

Test Preparation	Low Concentration	High Concentration
Target test substance concentration (%, w/w)	0.03	0.30
Test substance concentration by Radioactivity (%, w/w)	0.031	0.306
Test preparation application rate (mg/cm^2)^a	10.01	10.09
Test substance application Rate (μg equiv./cm^2)	3.12	30.87
Dislodgeable Dose (% Applied Dose)	60.53	77.87
Unabsorbed Dose (% Applied Dose)	96.80	94.68
Absorbed Dose (% Applied Dose)	0.05	0.03
Dermal Delivery (% Applied Dose)	2.22	2.16
Mass Balance (% Applied Dose)	99.03	96.84
Dislodgeable Dose (μg equiv./cm^2)	1.89	24.05
Unabsorbed Dose (μg equiv./cm^2)	3.02	29.24
Absorbed Dose (μg equiv./cm^2)	<0.01	0.01
Dermal Delivery (μg equiv./cm^2)	0.07	0.67
Mass Balance (μg equiv./cm^2)	3.09	29.91

^a mg of test preparation per cm of skin

 

Conclusions:

Based on the results of the read across substance study, following topical application of 14C-radiolabelled test substance in low (0.03%, w/w) and high (0.3%, w/w) concentration, the mean absorbed dose and mean dermal delivery of 14C-radiolabelled test substance were 0.05% (<0.01 μg equiv./cm2) and 2.22% (0.07 μg equiv./cm2) of the applied dose for the low concentration test preparation, respectively, and 0.03% (0.01 μg equiv./cm2) and 2.16% (0.67 μg equiv./cm2) of the applied dose for the high concentration test preparation, respectively. The maximum fluxes for the low and high doses were 0.12 ng equiv./cm2/h and 0.74 ng equiv./cm2/h, respectively, at 2 h.

Executive summary:

A study was conducted to determine the dermal absorption of the test substance, C12-16 ADBAC (active ingredient: 80.5%), according to OECD Guideline 428, in compliance with GLP. In an in vitro study, split-thickness human skin membranes were mounted into flow-through diffusion cells. Receptor fluid was pumped underneath the skin at a flow rate of 1.5 mL/hour. The skin surface temperature was maintained at approximately 32°C. A barrier integrity test using tritiated water was performed and any skin sample exhibiting a permeability coefficient (kp) greater than 2.5 x 10-3 cm/h was excluded from subsequent absorption measurements. Two test preparations containing 14C- radiolabelled test substance (i.e. 0.03% and 0.3%), were applied at an application rate of 10 mg/cm2. Absorption was assessed by collecting receptor fluid in hourly intervals from 0-6 hours post dose and then in 2-hourly intervals from 6-24 h post dose. At 24 h post dose, the exposure was terminated by washing and drying the skin. The stratum corneum was then removed from the skin by 20 successive tape strips. All samples were analysed by liquid scintillation counting. Based on the results of the study, following topical application of 14C- radiolabelled test substance in low (0.03%, w/w) and high (0.3%, w/w) concentration test preparations to human skin in vitro, the mean absorbed dose and mean dermal deliveries were 0.05% (0.01 ηg equiv. /cm2) and 2.22% (0.07 ηg equivalent/cm2) of the applied dose for the low concentration test preparation, respectively, and 0.03% (0.01 ηg equivalent /cm2) and 2.16% (0.67 ηg equivalent/cm2) of the applied dose for the high concentration test preparation, respectively. The stratum corneum acted as a barrier to absorption, with the mean total unabsorbed doses (recovered in skin wash, tissue swabs, pipette tips, cell wash, stratum corneum and unexposed skin) of 96.80 and 94.68% of the applied dose for the low and high concentration test preparations, respectively. The maximum fluxes for the low and high doses were 0.12 ηg equivalent /cm2/h and 0.74 ηg equivalent /cm2/h, respectively, at 2 h (Roper, 2006). Based on the results of the read across study, the test substance, C12 -14 ADEBAC can also be considered to have low dermal absorption, with mean dermal absorbed dose ranging between 0.03-2.16% of the applied doses.

Description of key information

Based on the available weight of evidence experimental studies, the test substance, C12-14 ADEBAC, is expected to be have a poor absorption potential through oral and dermal routes and primarily excreted via faeces. Based on QSAR predictions, it is likely to undergo aliphatic hydroxylation as the first metabolic reaction. Further, based on the MW and key physico-chemical properties it is likely to have low bioaccumulation potential.​

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

10

Absorption rate - dermal (%):

10

Absorption rate - inhalation (%):

100

Additional information

ABSORPTION:

Oral absorption

Based on physicochemical properties:

According to REACH guidance document R7.C (May 2014), oral absorption is maximal for substances with molecular weight (MW) below 500. Water-soluble substances will readily dissolve into the gastrointestinal fluids; however, absorption of hydrophilic substances via passive diffusion may be limited by the rate at which the substance partitions out of the gastrointestinal fluid. Further, absorption by passive diffusion is higher at moderate log Kow values (between -1 and 4). If signs of systemic toxicity are seen after oral administration (other than those indicative of discomfort or lack of palatability of the test substance), then absorption has occurred.

The test substance, C12-14 ADEBAC is a multi-constituent substance, which is an alkyl ethyl benzyl dimethyl ammonium chloride (ADEBAC) type of surfactant with alkyl chains comprising majorly C12 and C14 carbon atoms. Its MW ranges from 368.05 to 396.11 g/mol (average 377 g/mol). The purified form of the substance is a white solid, with moderate water solubility of 294-312 mg/L at 20°C (based on CMC) and a low log Kow of 2.48 (calculated based on solubility in octanol and water/CMC).

Based on the R7.C indicative criteria, and considering that the test substance is highly ionic therefore, it is expected not to be readily absorbed from the gastrointestinal tract.

Based on experimental data on read across substances:

A study was conducted to determine the basic toxicokinetics of the read across substance, C12-16 ADBAC (active: 30%), according to EPA OPP 85-1, in compliance with GLP. Sprague-Dawley rats (10 animals per sex per group) were treated with radiolabelled read across substance. The study was conducted in four experiments: a single high dose (50 mg/kg); a 14 d repeated dietary exposure with non-radiolabelled test substance (100 ppm) and single low dose of radiolabelled (14C) test substance (10 mg/kg); and single intravenous dose (10 mg/kg). Following the single doses or the last dietary dose, urine and faeces were collected for 7 d. Tissues, urine and faeces were collected and analysed for radioactivity and faeces were analysed by TLC, HPLC and MS for metabolites and parent compound. Following oral administration, radiolabelled test substance was rapidly absorbed, although in very limited amounts, consistent with its highly ionic nature. Residual 14C in tissues was negligible after administration of by gavage both after single and repeated dosing, indicating low potential for bioaccumulation. After i.v. administration a higher amount of radioactivity (30−35%) was found as residue in the tissues. About 6−8% of orally administered test substance is excreted in the urine whereas, 87−98% was found in the faeces. Since no data on bile duct-cannulated rats are available, it is not possible to conclude if this radioactivity accounts exclusively for unabsorbed test substance or not. However, the i.v. experiment showed that 20−30% was excreted in the urine and 44-55% in the faeces, suggesting that both the kidney and liver are capable of excreting test substance once absorbed and that absorption is higher than the % found in the urine after oral administration. Less than 50% of the orally administered test substance is metabolised to side-chain oxidation products. In view of the limited absorption of the test substance, the four major metabolites identified may be at least partially formed in the gut of rats, apparently by microflora. No significant difference in metabolism between male and female rats or among the dosing regimens was observed. Repeated dosing did not alter the uptake, distribution or metabolism of the test substance (Selim, 1987). Based on the results of the read across study, the test substance, C12-14 ADEBAC, can also be considered to have a similar ADME profile.

Conclusion:Overall, based on the available weight of evidence information, the test substance can be expected to overall have low absorption potential through the oral route. Therefore, as a conservative approach a value of 10% has been considered for the risk assessment.

Dermal absorption

Based on physicochemical properties:

According to REACH guidance document R7.C (ECHA, 2017), dermal absorption is maximal for substances having MW below 100 together with log Kow values ranging between 2 and 3 and water solubility in the range of 100-10,000 mg/L. Substances with MW above 500 are considered to be too large to penetrate skin. Further, dermal uptake is likely to be low for substances with log P values <0 or <-1, as they are not likely to be sufficiently lipophilic to cross the stratum corneum (SC). Similarly, substances with water solubility below 1 mg/L are also likely to have low dermal uptake, as the substances must be sufficiently soluble in water to partition from the SC into the epidermis.

The test substance is a white solid, with an MW exceeding 100 g/mol, moderate water solubility and a calculated log Kow between 2 and 3. This together with the fact that the test substance is highly ionic suggests that the test substance is likely to have a low penetration potential through the skin.

Based on QSAR prediction:

The two well-known parameters often used to characterise percutaneous penetration potential of substances are the dermal permeability coefficient (Kp[1][1]) and maximum flux (Jmax). Kp reflects the speed with which a chemical penetrates across SC and Jmax represents the rate of penetration at steady state of an amount of permeant after application over a given area of SC. Out of the two, although Kp is more widely used in percutaneous absorption studies as a measure of solute penetration into the skin. However, it is not a practical parameter because for a given solute, the value of Kp depends on the vehicle used to deliver the solute. Hence, Jmax i.e., the flux attained at the solubility of the solute in the vehicle is considered as the more useful parameter to assess dermal penetration potential as it is vehicle independent (Robert and Walters, 2007).

In the absence of experimental data, Jmax can be calculated by multiplying the estimated water solubility with the Kp values from DERMWIN v2.01 application of EPI Suite v4.1. The calculated Jmax of the constituents were found to range from 2.2 E-08 to 7.78E-08 μg/cm2/h leading to a weighted average value of 6.09E-08 μg/cm2/h. As per Shenet al.2014, the default dermal absorption for substances with Jmax is ≤0.1 μg/cm2/h can be considered to be less than 10%. Based on this, the test substance can be predicted to have low absorption potential through the dermal route.

Based on experimental data on read across substances:

Anin vitrostudy was conducted to determine the dermal absorption of the test substance, C12-16 ADBAC (active: 80.5%), according to OECD Guideline 428, in compliance with GLP. In anin vitrostudy, split-thickness human skin membranes were mounted into flow-through diffusion cells. Receptor fluid was pumped underneath the skin at a flow rate of 1.5 mL/hour. The skin surface temperature was maintained at approximately 32°C. A barrier integrity test using tritiated water was performed and any skin sample exhibiting a permeability coefficient (kp) greater than 2.5 x 10-3 cm/h was excluded from subsequent absorption measurements. Two test preparations containing 14C- radiolabelled test substance (i.e. 0.03% and 0.3%), were applied at an application rate of 10 mg/cm2. Absorption was assessed by collecting receptor fluid in hourly intervals from 0-6 hours post dose and then in 2-hourly intervals from 6-24 h post dose. At 24 h post dose, the exposure was terminated by washing and drying the skin. The stratum corneum was then removed from the skin by 20 successive tape strips. All samples were analysed by liquid scintillation counting. Based on the results of the study, following topical application of 14C- radiolabelled test substance in low (0.03%, w/w) and high (0.3%, w/w) concentration test preparations to human skinin vitro, the mean absorbed dose and mean dermal deliveries were 0.05% (0.01 ηg equiv. /cm2) and 2.22% (0.07 ηg equivalent/cm2) of the applied dose for the low concentration test preparation, respectively, and 0.03% (0.01 ηg equivalent /cm2) and 2.16% (0.67 ηg equivalent/cm2) of the applied dose for the high concentration test preparation, respectively. The stratum corneum acted as a barrier to absorption, with the mean total unabsorbed doses (recovered in skin wash, tissue swabs, pipette tips, cell wash, stratum corneum and unexposed skin) of 96.80 and 94.68% of the applied dose for the low and high concentration test preparations, respectively. The maximum fluxes for the low and high doses were 0.12 ηg equivalent /cm2/h and 0.74 ηg equivalent /cm2/h, respectively, at 2 h. Under the conditions of the study, the dermal absorption of the test substance was determined to be 8.3% obtained by summing up the radioactivity in the receptor fluid (0.05%), at the application site (after 20 consecutive tape stripping procedures) and the one present in tape strips (no. 6-20). The two different concentrations tested (0.03% and 0.3%) showed no significant differences in the absorption values (Roper, 2006). Based on the results of the read across study, the dermal absorption of the test substance, C12-14 ADEBAC can also be considered to be maximum 8.3% (rounded to 10%).

Conclusion: Overall, based on all the available weight of evidence information, the test substance can be expected to have a low absorption potential absorption through the dermal route. Therefore, as a conservative approach a default value of 10% has been considered for the risk assessment.

Inhalation absorption

Based on physicochemical properties:

According to REACH guidance document R7.C (ECHA, 2017), inhalation absorption is maximal for substances with VP >25 KPa, particle size (<100 μm), low water solubility and moderate log Kow values (between -1 and 4). Very hydrophilic substances may be retained within the mucus and not available for absorption.

The test substance, because of its relatively low vapour pressure of 4.4E-5 Pa at 25°C, will not be available as vapours for inhalation under ambient conditions. Therefore, the substance will neither be available for inhalation as vapours nor as aerosols. Further, if at all there is any inhalation exposure, considering the moderate water solubility of the substance, it is expected to be retained in the mucus and only very little may reach the lower respiratory tract. The absorption fate of the deposited material thereafter is expected to be similar to the oral route/gastrointestinal tract.

Conclusion: Based on all the available weight of evidence information, the test substance can be expected to have moderate to high absorption through the inhalation route. Therefore, as a conservative approach, a default value of 100% has been considered for the risk assessment.

METABOLISM:

Based on identified literature:

As discussed in the Selim, 1987 study, less than 50% of the orally administered test substance is metabolised to side-chain oxidation products (including hydroxyl- and hydroxyjeto- derivatives of the dodecyl, tetradecyl and hexadecyl chains). No metabolite accounted for more than 10% of the total administered dose. In view of the limited absorption of the test substance, the four major metabolites identified may be at least partially formed in the gut of rats, apparently by microflora. No significant difference in metabolism between male and female rats or among the dosing regimens was observed. Repeated dosing did not alter the uptake, distribution or metabolism of the test substance (Selim, 1987).

Based on QSAR modelling:

The OECD Toolbox was used to predict the first metabolic reaction, since the rat liver S9 metabolism simulator performs predictions for salts, while SMARTCyp and MetaPrint2D are not powered enough for this type of substances. The second simulator of the OECD Toolbox (in vivorat metabolism simulator) was not used as it does not consistently perform predictions for salts. As per the rat liver S9 metabolism simulator, all the major constituents (present at >5%) are primarily predicted to undergo ω or ω-1 aliphatic hydroxylation reactions. See table in the CSR for the reaction sites. For further details, refer to the read across justification.

Similar reactive sites were predicted for structurally similar ADBACs.

BIOACCUMULATION:

Based on the ionic nature of substance together with estimated BCF and MW, the bioaccumulation potential of the substance is expected to be low.

EXCRETION:

Based on the evidence from the available oral study (Selim, 1987), the test substance is primarily expected in faeces (>90%) and less via urine (<10%). 

[1]Log Kp = -2.80 + 0.66 log kow – 0.0056 MW