Paraquat-dichloride

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 Nov 1999 - 8 Dec 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2000

Report date:

2000

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Version / remarks:

draft OECD guidelines for in vitro percutaneous absorption measurement (OECD, 1996)

GLP compliance:

yes

Test material

Test material information

Test material form:

liquid

Radiolabelling:

yes

Administration / exposure

Type of coverage:

open

Vehicle:

unchanged (no vehicle)

Duration of exposure:

54h

Doses:

- 207 g/L for concentrate formulation
- 2.07 g/L for 1:100 v/v spray strength dilutions and 1:100 v/v spray strength dilutions with wetting agent

Details on study design:

DOSE PREPARATION
- Method for preparation of dose suspensions: Three doses were prepared in total. The concentrate formulation was prepared by adding appropriate quantities of radiolabelled test substance to the formulation concentrate. Two further doses were similarly prepared by adding appropriate quantities radiolabelled test substance to the formulation concentrate and then diluting the mixture with distilled water such that the resultant preparation was equivalent to a nominal 1:100 v/v aqueous spray dilution of the concentrate. One of the preparations also had an amount of wetting agent added equivalent to 0.1 % v/v of the dose.

APPLICATION OF DOSE:
- Amount(s) applied (volume or weight with unit): 10 µL/cm2.

TEST SITE
- Area of exposure: 2.54 cm2
- Time intervals: 2, 4, 6, 8, 10, 12, 18, 24, 30, 36, 42, 48 and 54 h, 0.5 ml samples of the receptor fluid were taken for analysis.

REMOVAL OF TEST SUBSTANCE
- Washing procedures and type of cleansing agent: The epidermal surface of the skin was decontaminated by gently swabbing the application site with natural sponges pre-wetted with 3 % detergent, and with further sponges pre-wetted with water. Decontamination was shown to be complete following assessment of residual radioactivity levels on the skin surface with a Geiger counter. The sponges were combined, digested in a solvent and a sample taken for analysis. The remaining epidermis was carefully removed from the receptor chamber and digested in solvent and the whole digest analysed.
- Time after start of exposure: 54 h.

ANALYSIS
- Method type for identification: Liquid scintillation counting.
- Liquid scintillation counting period: 6 minutes or to a 1 % standard deviation of the count.

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: human whole skin samples obtained post mortem.
- Part of skin: epidermis
- Preparative technique: skin samples were immersed in water at 60 °C for 40-45 seconds and the epidermis teased away from the dermis.
- Membrane integrity check: measurement of their electrical resistance across the skin membrane. Membranes with a measured resistance <10 kQ were regarded as having a lower integrity than normal and not used for exposure to the test material.
- Storage conditions: frozen on aluminium foil.

PRINCIPLES OF ASSAY
- Receptor fluid: distilled water
- Solubility of test substance in receptor fluid: adequate
- Test temperature: 32 ± 1 °C
- Occlusion: unoccluded

Results and discussion

Signs and symptoms of toxicity:

not examined

Dermal irritation:

not examined

Absorption in different matrices:

Detailed absorption rates and percentages are summarised in "Any other information on results incl. tables" section.

Total recovery:

- Total recovery:
- Recovery of applied dose acceptable:
For concentrated formulation - The total mean percent recovery from the mass balance was 103 %. Nearly all the dose was washed off the skin (92.9 %) after 54 hours exposure and a small amount of test substance (0.318 %) remained in the epidermis.

For 1:100 v/v spray dilution - The total mean percent recovery from the mass balance was 99.1 %. Most of the dose was washed off the skin (82.2 %) after 54 hours exposure and a small amount of test substance (1.79 %) remained in the epidermis.

For 1:100 v/v spray dilution with wetter - The total mean percent recovery from the mass balance was 101 %. Most of the dose was washed off the skin (89.7 %) after 54 hours exposure and a small amount of test substance (0.847 %) remained in the epidermis.

Percutaneous absorption

Percutaneous absorption 1

Key result

Time point:

54 h

Dose:

207g/L

Parameter:

rate

Remarks:

µg/cm2/h

Absorption:

0.241

Remarks on result:

other: concentrate formulation

Percutaneous absorption 2

Time point:

54 h

Dose:

2.07g/L

Parameter:

rate

Remarks:

µg/cm2/h

Absorption:

0.004

Remarks on result:

other: 1:100 v/v spray dilution

Percutaneous absorption 3

Time point:

54 h

Dose:

2.07g/L

Parameter:

rate

Remarks:

µg/cm2/h

Absorption:

0.002

Remarks on result:

other: 1:100 v/v spray dilution with wetting agent

Any other information on results incl. tables

Test substance mean absorption rates:

MEAN ABSORPTION RATES
Concentration	Time period (h)	Absorption rate (µg/cm^2/h ± SEM)
concentrate formulation	0-10	0.196	± 0.091
	0-54	0.241	± 0.109
1:100 v/v aqueous spray dilution	0-10	0.004	± 0.001
	0-54	0.004	± 0.001
1:100 v/v aqueous spray dilution with wetting agent	0-10	0.005	± 0.001
	0-54	0.002	± 0.000

Mean amount and percentage of test substance absorbed:

MEAN AMOUNT AND ABSORBED PERCENT OF DOSE
Concentration	Time (h)	Amount (µg/cm^2)	Percent absorbed
concentrate formulation	6	1.11	0.054
	8	1.54	0.074
	10	1.98	0.095
	24 54	5.20 13.24	0.251 0.639
1:100 v/v aqueous spray dilution	6	0.033	0.158
	8	0.039	0.190
	10	0.045	0.218
	24 54	0.093 0.193	0.448 0.929
1:100 v/v aqueous spray dilution with wetting agent	6	0.046	0.220
	8	0.048	0.230
	10	0.054	0.263
	24 54	0.079 0.132	0.380 0.636

Applicant's summary and conclusion

Conclusions:

The amount absorbed at 24 hours was 5.20 µg/cm2 (concentrate; equivalent to 0.251 % of applied dose), 0.093 µg/cm2 (1:100 dilution without wetting agent; equivalent to 0.448 % of applied dose) and 0.079 µg/cm2 (1:100 dilution with wetting agent; equivalent to 0.380 % of applied dose). There was very little difference in the absorption and distribution of paraquat from the 1:100 v/v aqueous spray dilutions with or without wetting agent.
The mass balance and distribution data predict that the majority of test substance which contacts human skin would be washed off the surface during normal washing procedures.

Executive summary:

The absorption of test substance has been measured in vitro through human epidermis.

The formulation was applied as the concentrate formulation (actual content 207 g test substance ion/L) and as a 1:100 v/v spray strength dilution of the formulation in water with and without added wetting agent. The actual test substance ion content of the spray dilutions was 2.07 g/L. The absorption process was followed using¹⁴C-labelled test substance, which was added to the formulations prior to application. The concentrate formulation and the spray strength dilutions were applied to the epidermal membranes at a rate of 10 µL/cm². All applications were left unoccluded for an exposure period of 54 hours. These applications were designed to simulate potential human dermal exposure to the formulation during normal use.

The absorption of test substance from the concentrate formulation through human epidermis was slow during the first 10 hours of exposure, giving a mean absorption rate of 0.196 µg/cm²/h which was slightly higher at 0.241 µg/cm²/h between 0 and 54 hours. The amount of test substance absorbed during working day periods of 6, 8 and 10 hours was 1.11 µg/cm²,1.54 µg/cm²and 1.98 µg/cm², equivalent to less than 0.1 % of the applied dose for each exposure period. The amount absorbed at 24 hours was 5.20 µg/cm²(equivalent to 0.251 % of applied dose).

The total mean percent recovery from the mass balance was 103 %. Nearly all the dose was washed off the skin (92.9 %) after 54 hours exposure and a small amount of test substance (0.318 %) remained in the epidermis.

The absorption of test substance from the 1:100 v/v spray dilution without wetting agent was very slow during the first 10 hours of exposure, giving a mean absorption rate of 0.004 µg/cm²/h which was the same as the 0 to 54 hour period. The amount of test substance absorbed during working day periods of 6, 8 and 10 hours were 0.033 µg/cm², 0.039 µg/cm²and 0.045 µg/cm²,equivalent to 0.158 %, 0.190 % and 0.218 % of the applied dose, respectively. The amount absorbed at 24 hours was 0.093 µg/cm²(equivalent to 0.448 % of applied dose).

The total mean percent recovery from the mass balance was 99.1 %.Most of the dose was washed off the skin (82.2 %) after 54 hours exposure and a small amount of test substance (1.79 %) remained in the epidermis.

The absorption of test substance from the spray dilution with wetting agent was very slow during the first 10 hours of exposure, giving a mean absorption rate of 0.005 µg/cm²/h. The absorption rate during the 0 to 54 hour period was slightly lower at 0.002 µg/cm²/h. The amount of test substance absorbed during working day periods of 6, 8 and 10 hours were 0.046 µg/cm², 0.048 µg/cm²and 0.054 µg/cm²,equivalent to 0.220 %, 0.230 % and 0.263 % of the applied dose, respectively. The amount absorbed at 24 hours was 0.079 µg/cm²(equivalent to 0.380 % of applied dose).

The total mean percent recovery from the mass balance was101 %. Most of the dose was washed off the skin (89.7 %) after 54 hours exposure and a small amount of test substance (0.847 %) remained in the epidermis.

There was very little difference in the absorption and distribution of test substance from the 1:100 v/v aqueous spray dilutions with or without wetting agent.