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Dermal absorption

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dermal absorption in vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study
Reason / purpose:
reference to other study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 427 (Skin Absorption: In Vivo Method)
Principles of method if other than guideline:
Other guidances and guidelines taken into account:
European Commission Guidance Document on Dermal Absorption. Sanco/222/2000 rev 7 (2004).
• OECD Guidance Document for the Conduct of Skin Absorption Studies. OECD Environmental Health and Safety Publication Series on Testing
and Assessment No. 28. (2004).
• MAFF Japan, Agricultural Chemicals Laws and Regulations, Japan (II), (59 Nousan Number 4200) (1985).
GLP compliance:

Test material

Details on test material:
- Name of test material (as cited in study report): North American Creosote Composite Test Material P1/P13
- Molecular formula (if other than submission substance): not applicable
- Molecular weight (if other than submission substance): not applicable
- Substance type: organic
- Physical state: liquid
- Analytical purity:not applicable (UVCB)
- Impurities (identity and concentrations):
- Composition of test material, percentage of components:
Target Analyte Conc. in creosote [%, w/w]
Naphthalene 9.0
Biphenyl 1.2
2-Methylnaphthalene 5.1
Anthracene 2.2
Phenanthrene 12.2
Fluoranthene 6.8
Pyrene 6.0
Benzo[a]pyrene 0.5
Sum of marker chemicals in creosote ~43

- Radiochemical purity (if radiolabelling):
spiked with 8 14C-radiolabeled creosote target chemicals (Report p. 9).
The radioactivity of each marker component added to creosote was related to the composition of the creosote
in order to represent compound abundance in the mixture.
• Benzo(a)pyrene–7–14C
• 2-Methynaphthalene – 8 – 14C
• Fluoranthene – 3 – 14C
• Anthracene – 1,2,3,4,4A,9A-14C
• Naphthalene – Benzene – UL – 14C
• Phenanthrene – 9 – 14C
• Biphenyl – UL – 14C
• Pyrene – 4,5,9,10 – 14C

- Specific activity (if radiolabelling):
- Locations of the label (if radiolabelling):
- Expiration date of radiochemical substance (if radiolabelling):
- Stabili
see details on test material

Test animals

Details on test animals and environmental conditions:
- Source: Charles River Lab. NC/USA
- Age at study initiation: 8 - 10 weeks
- Weight at study initiation: 340 +-19 g
- Fasting period before study: not fasted
- Individual metabolism cages: yes
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: quarantine

- Temperature (°C): 18 - 26 °C
- Humidity (%): 30 - 70 %
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Type of coverage:
unchanged (no vehicle)
Duration of exposure:
8 h and 21 d
- Nominal doses: 10 µL/cm2 (10.7 mg/cm2)
- Dose volume: 105 µL on a test site of 10.5 cm2 (= 112.35 mg/test site)
No. of animals per group:
4 in pre-testing (recovery of target chemicals in blood plasma);
8 in the dermal main absorption study (distribution and recovery of radioactivity).
Control animals:
Details on study design:
- spiked creosote aliquote added into an O-ring unit

TEST SITE (main test)
- Preparation of test site: Dorso-lumbar surface, clipped free of hair and washed with an aqueous solution of 2% Ivory Soap 24 h before treatment.
- Glass O-ring appliance glued to the clipped area on the back using Instant Krazy Glue Gel adhesive
- Area of exposure: 10.5 cm2 (internal surface of the O-ring appliance) [radius: ~1.83 cm]
- % coverage: approx. 5 % (estimated from 2/3 of body weight)
- Type of cover / wrap if used: Coban™ body wrap

TEST SITE (supplemental study with t = 496 h post-exposure)
- Procedure as previous main test but using a silicone O-ring not glued to the skin.

After 8 hours (= 0 h post-exposure), the organic trapping contents was removed from the skin site and placed into acetonitrile,
and the application site was then washed using at least 3 cycles of one natural sponge soaked in a 2% Ivory® Soap solution (Report p. 21).
Washings and sponge pieces were collected for LSC.

Urine and faeces: 0-8 hour exposure period, and for surviving rats 8-12, 12-24, and every 24 hours thereafter until sacrifice.

Exhaled air: drawn through a 2N NaOH trap (14CO2) and an ethylene glycol trap (14C-volatiles) in series during the 0-8 hour exposure period,
and for surviving rats 8-12, 12-24, and every 24 h thereafter until radioactivity in sample aliquots was ≤LOD.

Residual feed and cage washings were collected as needed. At the end of the in-life phase, the metabolism cages were rinsed with a dilute
soap solution followed by an acetone rinse. The rinse was placed in a suitable container and retained for analysis.

Blood plasma, organs (lung, liver, kidney, heart), the carcass, and the skin site were collected and preserved at the indicated time intervals
(Report p. 22).

•Aliquots of whole blood were combusted.
• Aliquots of plasma were added directly to Ultima Gold™ XR liquid scintillant.
• Aliquots of red blood cells were combusted.
• Feces were homogenized in water. Aliquots were combusted.
• Residual feed was homogenized in water. Aliquots were combusted.
• Carcasses were homogenized with water. Aliquots were combusted.
• Tissues were minced. Aliquots were combusted.
• Urine, cage wash, sodium hydroxide (14CO2), and ethylene glycol (14C) were not processed further. Aliquots were added directly
to Ultima Gold™ XR liquid scintillant.
• The application skin site and sponge pieces were digested in Soluene®-350. Aliquots were added directly to Hionic-Fluor™ liquid scintillant.

Combustion: Aliquots of whole blood, red blood cells, feces, residual feed, carcass homogenate, and tissues were combusted
using a Packard Tri-Carb Automatic Sample Oxidizer. The resultant 14CO2 generated was collected in a suitable absorbent scintillation system.

- Method type(s) for identification: GC-MS, Liquid scintillation counting
- LSC: All samples were analysed in a Packard liquid scintillation counter for total radioactivity. Samples were counted for 10 min or
until 160,000 disintegrations were accumulated (0.5%, 2σ), whichever came first.
Details on in vitro test system (if applicable):
not applicable

Results and discussion

Signs and symptoms of toxicity:
no effects
Dermal irritation:
not specified
Absorption in different matrices:
see Report, Table 4, p.35, see Attachment
Total recovery:
The mass balances were satisfactory with recoveries of more than 92 % of the applied radioactivity.
Percutaneous absorption
10.7 mg/cm2
>= 7.9 - <= 14.8 %
Remarks on result:
other: 8 hours
low value: minimum without stratum corneum / high value: maximum including label of stratum corneum
Conversion factor human vs. animal skin:
not derivable from this study.

Any other information on results incl. tables

Results of GC analysis in blood (non-labeled target chemicals):

The concentration of the 12 selected chemicals was found to be below the limit of detection (individual LODs see "Any other information.... above) in all serial plasma samples from all collection time points during and following an 8h exposure to a single finite application of the creosote test substance. These results suggest that all 12 target chemicals disappeared very quickly, were metabolised upon first pass through the skin and likely have negligible bioavailability (Report p. 28). See also distribution of radioactivity (below).

Results of LSC analysis in organs and body fluids (Report Tab. 4 / Attachment):

After 8 h (exposure phase), 3.14 % of the applied dose was found in the carcass and >0.2 % in liver and even lower in other organs, while only marginal label was detectable in blood (> 0.05 %). In the post-exposure period over 21 days), radioactivity in the carcass and organs decreased to below quantification limits, while increasing in the urine and feces. This provides evidence that creosote components do not tend to bioaccumulate but are excreted rapidly (see Attachment).

Percutaneous absorption (Report, Tab. 4 / Attachment)

After 8 h (exposure time): absorbed 6.34 % [SD±0.81%] of the applied dose, tape-stripped skin 1.55 ±0.30%, and tape strips of the stratum corneum (SC) 6.89 ±2.74%. SC turnover may reduce absorption, but is considered to be potentially available. hence, the maximum amount that can be absorbed is 14.8 ±3.3.8 %, the sum of the three compartments (= absorbable dose + SC tape strips).

Note: The author considered the dose fraction bound to the upper horny layer of the epidermis (stratum corneum) as being unavailable for absorption. Hence, the absorbable dose is supposed to consist of the fractions of the absorbed dose (6.34%) plus the residual fraction bound to the skin layer after tape stripping (without SC) (1.55%), in total 7.9% as minimum. The real absorption rate is expected to lie in between.

Given this, contrary to specifications in Report, Tab. 4, the total unabsorbable dose after 8 h amounts to about 80 % of the dose applied, with the majority of the remainder accumulated the wash (~59%) and on the O-ring (~18%), while only some 2% was found in the body wrap. Evaporative loss is minimal (see charcoal trap).

The findings after 21 days (496 h post-exposure) are less clear: In the first long-term experiment, the amount absorbed apparently was far too high: The results from the 21d recovery phase could be refuted as artifact due to incomplete removal of unabsorbed material from the skin site directly after the 8h exposure.)

Therefore, a supplemental 21d study was carried out: However, also the second run may have been confounded, in this case by the very high dose fraction that adsorbed to the body wrap: 32% already was removed during the cleaning procedure at termination of exposure period, while only about 22% was left in the skin wash. This conflicts with the findings of the first 8h-experiment (only 2 % in body wrap, but 59 % in wash) and raises the suspicion that a substantial part of the applied dose escaped from potential absorption. Hence, the low absorption rate of 8.85 % [SD±1.57%] of the applied dose may be unreliable.

Irrespective of this deficiency, it is evident that after 21 d practically no radioactivity remained in the treated skin compartments (see Tab. 4. "Dosed skin" and "Tape strips"). The decrease in label in the horny layer (SC) over 21 days may be attributable to physiological SC turnover or to skin permeation into the blood system.

It is assumed that all SC-bound material has been absorbed. The most reliable maximum absorption rate is that one derived from the fractional distribution of radioactivity in the main 8h study, in total 14.8 % of the dose applied.

Note: In the previous assessment, the absorption of 9 % had been adopted as relevant starting point, based on the 21d supplemental study (see KEMI 2010 - Attached Document). However, following the caveats outlined above, this value has been skipped by CCE.

Applicant's summary and conclusion

A maximum of 14.8 % of creosote can be absorbed through rat skin within and after an exposure period of 8 hours, based on the analysis of a representative fraction of creosote. Furthermore, comprehensive analytical data show that creosote is very unlikely to bioaccumulate.