Alcohols, C12-14, ethoxylated, sulfates, sodium salts

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 427 (Skin Absorption: In Vivo Method)

Deviations:

no

GLP compliance:

no

Radiolabelling:

yes

Species:

rat

Strain:

Wistar

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Individual metabolism cages: yes
- Diet: Altromin standard diet; ad libitum
- Water: tap water; ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-22°C

Type of coverage:

semiocclusive

Vehicle:

other: aqueous solution

Duration of exposure:

15 min (Sacrifice after 48h) & 48 h

Doses:

1%

No. of animals per group:

3

Control animals:

no

Details on study design:

TEST SITE
- Preparation of test site: shaving
- Area of exposure: 10 cm2
- Type of cover used: glass capsule

SITE PROTECTION / USE OF RESTRAINERS FOR PREVENTING INGESTION: yes

REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleansing agent: with and without washing with lukewarm water
- Time after start of exposure: 15 min & 48 h

SAMPLE COLLECTION
- Collection of blood: no
- Collection of urine and faeces: yes
- Collection of expired air: no (not possible, because 35S-marked)

ANALYSIS
- Method type for identification: TLC

Signs and symptoms of toxicity:

not examined

Dermal irritation:

not examined

Absorption in different matrices:

The mean amount of sodium laureth sulfate removed from the skin surface (skin wash) ranged from 92.8% to 97.2% of the dose applied when the skin was washed after 15 min exposure and from 91.6% to 98.4% when the skin was not washed until sacrifice. This demonstrates that the test substance has mostly remained on the skin surface.
The amounts in faeces and skin could not always be quantified, since it was below the analytical lower limit of quantification (LLOQ).
The mean absorbed dose in the first experiment, sum of the amounts found in urine, faeces and skin, was about 0.1%; without washing 0.9% in mean was absorbed.
The mean recovery values varied from 98.6% to 103% and 92.6% to 101%, respectively.

Total recovery:

98.6% - 103% (with washing)
92.6% - 101% (without washing)

Key result

Time point:

15 min

Concentrate / Dilution:

dilution

Dose:

1%

Parameter:

percentage

Absorption:

0.1 %

Key result

Time point:

48 h

Concentrate / Dilution:

dilution

Dose:

1%

Parameter:

percentage

Absorption:

0.9 %

Conclusions:

Under the use conditions (rinse off after 15 minutes) only 0.1% of the applied surfactant was absorbed. In another assay the test substance was not rinsed off for 48 h. Here 0.9% of the applied test substance was absorbed through the rat skin. Thus, under these stringent conditions, absorption is considered to be very low.

Reference 2

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25 - 27 Feb 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Species:

human

Strain:

other: not applicable

Sex:

female

Details on test animals or test system and environmental conditions:

Skin region: abdomen
BMI: 22.7-35.5

Type of coverage:

occlusive

Vehicle:

other: HBSS-buffer

Duration of exposure:

24 h

Doses:

10%

No. of animals per group:

3 donors, two fold (n=2)
total: 6

Control animals:

no

Details on study design:

According to Guideline.

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: abdomen of female donors, 31 - 48 years, BMI 22.7 - 35.5
- Ethical approval if human skin: yes
- Type of skin: dermatomed hairless abdominal skin
- Preparative technique: The human skin was cut into 4 cm broad stripes. Subsequently skin sections with a thickness of approximately 500 µm were prepared from the full-thickness skin samples using an Aesculap GA 630 dermatome. The skin surface with intact Stratum corneum is directed towards the dermatome. Prior to use, the thickness of the dermatomized skin was checked with a Heidenhain thickness gage five different
places of each skin sample.
- Thickness of skin (in µm): 500
- Membrane integrity check: yes, via quality control methods using caffeine.
- Storage conditions: -20°C
- Justification of species, anatomical site and preparative technique: female donors were chosen due to lower number of hair follicles.

PRINCIPLES OF ASSAY
- Diffusion cell: Franz diffusion cells with a diffusion area of approximately 3 cm^2 and an acceptor volume of approximately 20 mL were used. The stirring speed and the temperature was set at 400 rotation per minute and 32 °C ± 2 °C, respectively.
- Receptor fluid: Krebs Ringer buffer (KRB)
- Solubility of test substance in receptor fluid: yes
- Occlusion: covered with Parafilm for 24 h
- Reference substance: caffeine

PERMEATION STUDY
The permeation study was performed over a period of 24 hours, after 0.5, 2, 4, 6, 21 ,22, 23 and 24 hours. The samples with a volume of 200 µL were taken from the acceptor compartments and analyzed for the drug content by LC-MS. The taken amount was replaced with a fresh medium preheated to the temperature of 32 °C. In total 8 samples were analysed for each time point (3 donors, n=2).

PENETRATION STUDY
After removing the solution from the skin surface, the skin was partitioned into horizontal segments to determine the distribution profile of NLS in the skin. Two segmenting techniques, Tape stripping and Cryosectioning, were applied to separate different skin layers parallel to the upper surface of the sample and thus provide information on the extent to which the test item has penetrated into the different skin areas. After removing the residual solution, the skin biopsies were transferred into a stripping apparatus. he upper corneous layers (Stratum corneum) of the skin were stripped off using tape film. The stripped skin area was 1.767 cm^2 ± 5 %. In total 20 tape strips were performed per each skin biopsy. The first two strips are always considered separately due to potential contaminations by residual drug on the surface of the skin. The samples for 2 tape strips and 18 tape strips were extracted in 3 mL and 5 mL of the extraction medium, respectively and quantified by LC-MS. Water was used as an extraction medium. After stripping, the skin biopsies were punched out and frozen at –80 °C. The residual skin was cryo-sectioned to determine the amount of test compound, which had penetrated into the deeper skin layers. The skin biopsy was cut into surface parallel sections with a thickness of
25 µm. The surface area of a single cut was approximately 1.327 cm^2. All cuts were collected
into one beaker. All samples were extracted in 3 mL of the extraction medium and quantified by
LC-MS. Water was used as extraction medium.

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Absorption in different matrices:

The mean amount of sodium laureth sulfate (SLS) removed from the skin surface (skin wash) ranged from 87.16% to 94.56% of the dose applied in the mean values of the 3 skin donors. This demonstrates that the SLS has mostly remained on the skin surface. The amounts in the receptor could not be quantified, since it was below the analytical lower limit of quantification (LLOQ). The mean recovery in the two first tape strips was 1.48% during all performed experiments. In the further 18 tape strips a mean recovery of 2.86% was documented. The recovery values for the cryocuts have accounted 0.56% in mean. The mean recovery values have varied from 90.90% to 100.21%, which complies to the acceptance criteria of 100 ± 15%.
The mean absorbed dose of SLS, sum of the amounts found in the viable epidermis, dermis and receptor medium was 0.56%.

Total recovery:

90.90% - 100.21%
Mean of all skins used: 96.38% (SD: 9.65)

Key result

Time point:

24 h

Concentrate / Dilution:

dilution

Dose:

10%

Parameter:

percentage

Absorption:

< 1 %

The permeated amounts of the test substance through three different human skins have presented values in the receptor below the LLOQ (Table 1).

Table 1: Summarized results from the permeation study.

Cumulative amount [µg/cm2] of NLS in the samples
Sample	Skin 336-01-0808		Skin 337-01-0908		Skin 346-01-1108		All skins used
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
dose ap plied	1036.44	11.44	1031.07	11.35	1005.39	40.04	1024.3	24.35
skin wash	904.11	138.13	974.76	32.22	929.26	108.85	936.04	86.14
2 Tape strips	14.1	0.3	15.25	0.68	16.13	0.53	15.16	1
18 Tape strips	24.6	0.34	34.19	1.05	28.85	1.98	29.21	4.42
cryocuts	0.00*	0.00*	8.77	12.4	8.53	12.07	5.77	8.93
receptor	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*

* Values below the LLOQ of the analytical method.

 

 

The mean absorbed dose of the test substance, sum of the amounts found in the viable epidermis, dermis and receptor medium and the mean recovery of the test substance found in the deeper skin layers sum up to 0.56% (Table 2).

Table 2: Mean recovery rate and dose absorbed [%] of NLS in the samples from the three in vitro experiments.

Recovery and dose absorbed [%] of NLS in the samples
Sample	Skin 336-01-0808		Skin 337-01-0908		Skin 346-01-1108		All skins used
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
skin surface	87.16	12.37	94.56	4.17	92.72	14.52	91.48	9.39
2 Tape strips	1.36	0.01	1.48	0.08	1.61	0.12	1.48	0.13
18 Tape strips	2.37	0.06	3.32	0.07	2.88	0.31	2.86	0.45
cryocuts	0.00*	0.00*	0.86	1.21	0.83	1.17	0.56	0.87
receptor	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*	0.00*
Dose absorbed	0.00*	0.00*	0.86	1.21	0.83	1.17	0.56	0.87
Total recovery	90.9	12.32	100.21	5.39	98.03	13.78	96.38	9.65

* Values below the LLOQ of the analytical method.

Conclusions:

In the present in vitro/ex vivo dermal absorption study compliant with GLP and OECD test guideline 428, the test substance was tested for its capacities to penetrate human skin. The permeated amounts of the test substance through three different human skins have presented values in the receptor below the LLOQ. The mean absorbed dose of the test substance, sum of the amounts found in the viable epidermis, dermis and receptor medium and the mean recovery of the test substance found in the deeper skin layers sum up to 0.56%.

Description of key information

Absorption: Oral absorption 100%; dermal absorption 0.9%

Distribution/Metabolism: Once absorbed, AES substances are extensively metabolized by - or ω-oxidation. Tissue accumulation can be excluded.

Excretion: AES substances are excreted predominantly via the urine. However, Alkyl Ether Sulfates with longer ethoxylate chains (> 7-9 EO groups) are excreted at a higher proportion in the faeces. There is no evidence of hydrolysis of the sulfate group.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

0.9

Additional information

ADME considerations based on physico-chemical properties

AES substances are salts consisting of a non-polar aliphatic hydrocarbon chain, which is coupled to a polar moiety containing 1 - 2.5 ethoxy groups via ether bonds, and a sulfate group, neutralized with a counter-ion. The alkyl chain length in the AES category varies from C8 to C18. This structural feature (non-polar chain bound to a polar terminal group) confers the surfactant properties of the AES substances. The surfactant properties of the AES substances in turn represent the predominant attribute in causing effects on human health.

Substances in the AES category are marketed in products, containing varying amounts of water. The tests examining their physico-chemical properties were conducted on pure dried substances after removing the aqueous phase. Importantly, the AES category member substances are not mono-constituent substances but substances with variable and/or unknown composition, i.e. substances of UVCB . Therefore, several physico-chemical properties are not defined or not applicable.

The physico-chemical properties of the AES category members that can be determined are similar over the category. Measured values are often in predictable narrow ranges (e.g. surface tension). The differences are related to the length of the alkyl chain, the ethoxylation degree of the material tested, or are due to different counter ions. However, most of the physico-chemical properties can only be estimated for surface active substances. The AES category members are pasty or waxy solids under ambient conditions, with broad melting ranges. They tend to decompose before boiling. Their molecular weight is mostly < 500 g/mol. They are non-volatile (vapour pressure << 100 Pa) and they do not partition into the air. AES substances are surfactants and the measured values for surface tension clearly identify the AES substances as surface-active. The accurate determination of a log Pow value is very difficult for surface-active substances. Surfactants tend to concentrate at hydrophilic/hydrophobic boundaries rather than to equilibrate between phases. Therefore, this parameter is of limited significance for AES member substances. However, all obtained values are low, i.e. log Pow < 3. Similarly, the determination of water solubility is difficult for surface-active substances. The AES substances are fully dissociating in water and miscible in any proportion with water. Estimated values for water solubility are in a range of several hundreds g/L.

Based on the relatively low molecular weight, the high water solubility and the log Pow value, absorption from the gastro-intestinal tract after oral exposure is expected for ionised AES substances, considering, however, that irritation is the leading health effect. Inhalation exposure to neat AES substances is considered negligible due to the low vapour pressure of the substances. However, inhalation in the form of droplets, dusts or other aerosols can occur. In case of inhalation, it is assumed that a certain proportion may well be absorbed. But again, the irritant properties are considered the leading health effect. Similarly, in case of dermal exposure, the irritant properties of AES substances are considered the leading health effect. Based on the physico-chemical properties, uptake to the stratum corneum is expected for AES substances. However, penetration from the stratum corneum to the epidermis and subsequent absorption to the circulation are expected to be very low. If absorbed and systemically available, it is assumed that the AES substances are supplied to the fatty acid metabolism and degraded via oxidation processes (e.g. β-oxidation). Subsequently, excretion via the kidneys and urine is the most likely route of excretion.

 

Experimental data on dermal absorption

There are two reliable and relevant studies available assessing the dermal absorption rate of the AES category member alcohols, C12-14, ethoxylated, sulfates, sodium salts (CAS No. 68891-38-3, EC No. 500-234-8). An ex vivo dermal absorption study was performed according to OECD guideline 428, and in compliance with GLP requirements, with human skin of the abdomen region (3 donors, n = 2). The test substance was applied at a concentration of 10% for 24 h (BASF, 2009). The mean amount removed from the skin surface (skin wash) ranged from 87.16% to 94.56% of the dose applied. The test substance amount in the receptor medium could not be quantified since it was below the analytical limit of quantification (LOQ). The mean recovery in the two first tape strips was 1.48% during all performed experiments. In the further 18 tape strips a mean recovery of 2.86% was documented. The mean absorbed dose of the test substance, i.e. sum of test substance amount found in the viable epidermis, dermis and receptor medium sum up to 0.56% of the applied dose. The mean recovery values have varied from 90.90% to 100.21%, which complies with the acceptance criteria (100 ± 15%). Under the conditions of the study, dermal absorption was found to be very low.

An in vivo study similar to OECD guideline 427, non-GLP compliant, was conducted with alcohols, C12-14, ethoxylated, sulfates, sodium salts (CAS No. 68891-38-3, EC No. 500-234-8; BASF, 1996a). Wistar rats were exposed to 1% aqueous solution of the test item for 15 min and 48 h under semi-occlusive conditions. The mean amount of alcohols, C12-14, ethoxylated, sulfates, sodium salts (CAS No. 68891-38-3, EC No. 500-234-8) rinsed off the skin surface after a 15 min exposure period ranged from 92.8% to 97.2% of the dose and from 91.6% to 98.4% after 48 h exposure, when the skin was not washed until sacrifice. The amounts in faeces and skin could not always be quantified since it was below the analytical LOQ. The mean absorbed dose of the test substance, i.e. sum of test substance amount found in urine, faeces and skin was about 0.1% and 0.9% of the applied dose in the experiment with washing (15 min exposure) and without washing (48 h exposure), respectively. The mean recovery values varied from 98.6% to 103%. Under the conditions of the study, dermal absorption was found to be very low.

 

Data on toxicokinetics described in HERA report

The following studies were conducted in the course of a voluntary industry programme carrying out Human and Environmental Risk Assessments (HERA, 2003, and references therein). The programme investigated the toxicokinetic behaviour of AES substances with various C-chain lengths (alkyl moieties) and ethoxylation degrees (number of ethoxy (EO) groups). The studies compiled in the HERA report were performed mainly with AES substances carrying 0 - 8 EO groups. However, the information derived in those studies is considered appropriate to assess the toxicokinetic behaviour of the members of the AES category.

The nomenclature used in this section follows the one applied in the HERA report. This nomenclature is generally accepted throughout the surfactant industry and thus widely used. The short names of AES substances contain the description of the alkyl moiety (the C-chain length), followed by ‘AE’ (alkyl ether) and the number of the ethoxy groups. Examples are C8AE4S, C12AE3S and C16AE8S representing tetraethylene glycol monooctyl ether sulfate, triethylene glycol mono dodecyl ether sulfate and octaethylene glycol monohexadecyl ether sulfate, respectively.

 

Absorption and excretion

McDermott et al. (1975) studied the absorption of C16AE3S and C16AE9S, labelled with ¹⁴C in the 1-position of the alkyl chain, after oral exposure in man and rats. Seventy-two hours after administration of C16AE3S, radioactive material was mainly excreted via urine (man: 80%; rat: 50%) and to a lesser extent via faeces (man: 9%; rat: 26%) and air (man: 7%; rat: 12%). For C16AE9S however, the radioactivity was mainly excreted via faeces (man: 75%; rat: 82%) and to a lesser extend via urine (man: 4%; rat: 0.6%) and air (man: 6%; rat: 4%). The length of the ethoxylate portion of an AES molecule appears to determine the toxicokinetic behaviour of the compound following oral administration in both man and rat. There was no evidence of hydrolysis of the sulfate group or of metabolism of the ethoxylate portion of the molecule. The major metabolite found in urine had the following structure: -OOCCH2(OCH2CH2)_xOSO3^- where x equals either 3 or 9, respectively.

In a similar investigation, Taylor et al. (1978) studied the metabolic fate of orally, intraperitoneally, or intravenously administered ¹⁴C-C11AE3S and ¹⁴C-C12AE3S in the rat. The authors observed that both compounds were extensively metabolized (β-, ꞷ-oxidation) with the proportion of radioactivity appearing in urine and respired air generally independent of the route of administration. Some sex differences in the proportions of radioactivity excreted in urine and respired air was seen, but total recoveries for both compounds were comparable. By the oral route, 67% of the administered radioactivity with C11AE3S appeared in the urine of male rats compared to 45% in females; expired air contained 19% and 35% of administered radioactivity respectively; 4 - 5% was present in faeces for both sexes. The major urinary metabolite of C12AE3S was identified as 2-(triethoxy sulfate) acetic acid, with C11AE3S, the major urinary metabolite was tentatively identified as 3-(triethoxy sulfate) propionic acid.

Taylor et al. (1978) also measured the percutaneous absorption of ¹⁴C-labelled NaC12AE3S. The NaC12AE3S was applied to rats as 150 µL of a 1% v/v solution. The ¹⁴C-levels were measured in urine collected over 48 h. Penetration of NaC12AE3S was 0.39 ± 0.12 µg/cm². In experiments in which application was continued for up to 20 min, skin penetration was proportional to the duration of the contact. It was also proportional to the number of applications.

 

Summary of toxicokinetics from HERA report

Following oral exposure, AES substances are readily absorbed in the gastrointestinal tract in man and rat and excreted mainly via the urine. The length of the ethoxylate portion, i.e. the number of ethoxy (EO) groups, in an AES molecule seems to have an important impact on the toxicokinetic behaviour of AES substances in humans and in the rat. AES substances with longer ethoxy chains (> 7 - 9 EO groups) are excreted at a higher proportion in the faeces. Once absorbed, AES substances are extensively metabolized by β- or ꞷ-oxidation.

The dermal absorption of AES substances is relatively poor as can be expected from an ionic molecule. The percutaneous absorption of C12AE3S was measured in a rat in vivo study. The study determined a dermal flux of the tested compound of 0.0163 µg/cm²/h.

 

Conclusion on toxicokinetic behaviour

Following exposure, the irritating properties of the AES category member substances are considered as the leading health effect at the site of first contact. Following oral exposure, AES substances are readily absorbed in the gastrointestinal tract in human and rat and excreted mainly via the urine or faeces depending on the length of the ethoxy (EO) chain but independently of the route of administration. Following dermal exposure, dermal absorption of AES substances is very low (< 1%). Available ex vivo and in vivo data demonstrate that the AES test substance remains on the skin surface. Once absorbed, AES substances are extensively metabolized by β- or ꞷ-oxidation. The alkyl chain appears to be oxidized to CO₂, which is expired. The EO-chain seems to be resistant to metabolism. The length of the ethoxy chain, i.e. the number of ethoxy (EO) groups, in an AES molecule seems to have an important impact on the toxicokinetics of AES substances in humans and in the rat. AES substances with ethoxy chains > 7 - 9 EO groups are excreted at a higher proportion in the faeces. This is however not of relevance for the present AES category members as their mean ethoxylation degree is < 2.5.