Zinc sulphate

Endpoint summary

Description of key information

Zinc sulphate (ZnSO₄•7 H₂O) was tested in a mouse local lymph node assay (Ikarashiet al., 1992), according to the testing methods developed by Kimberet al.(1989 and 1990). After gentle dermal abrasion, 25ml of a 5% zinc sulphate solution in 20% ethanol was applied for three consecutive days at the dorsal side of both ears of 3 Balb/c mice. On the fourth day the animals were sacrificed and the ear-draining lymph nodes were collected. Lymph node lymphocyte proliferation was determined by tritiated thymidin incorporation. The results were compared to those of vehicle-treated controls. Zinc sulphate did not induce proliferative activity, whereas for potassium bichromate, nickel sulphate and cobalt chloride (known dermal sensitizers) positive results were obtained.

The skin sensitising potential of zinc sulphate (ZnSO₄•7 H₂O) was also investigated in guinea pigs. A well-performed maximisation test, conducted according to Directive 96/54/EC B.6 and OECD guideline 406, was carried out in female Dunkin Hartley guinea pigs. Based on the results of a preliminary study, in the main study 10 experimental animals were intradermally injected with a 0.1% concentration and epidermally exposed to a 50% concentration. Five control animals were similarly treated, but with vehicle (water) alone. Approximately 24 hours before the epidermal induction exposure all animals were treated with 10% SDS. Two weeks after the epidermal application all animals were challenged with a 50% test substance concentration and the vehicle. A second challenge followed one week after the first. In response to the 50% test substance concentration, in some experimental animals and controls skin reactions of grade 1 were observed 48 hours after the first (5/10 and 2/5, respectively) and the second challenge (4/10 and 2/5, respectively). As the skin reactions were comparable among the experimental and control animals, and as there was poor consistency of the skin reactions among individual experimental animals after the first and second challenge, the observed skin reactions can be considered to be non-specific signs of irritation. Hence, it can be concluded that zinc sulphate did not induce hypersensitivity in experimental animals (Van Huygevoort, 1999).

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not applicable

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Qualifier:

no guideline followed

Principles of method if other than guideline:

The basic principle underlying the LLNA method used is to induce a primary proliferation of lymphocytes in the lymph node draining the site of test material application. An ear abrasion technique is employed which enhances penetration of the metal ion by removing the horny layer of the epidermis. It enables the detection of ear-swelling responses of weak contact allergens by increasing their LNC proliferation. This proliferation is proportional to the dose applied (and to the potency of the allergen) and provides a simple means of obtaining an objective and quantitative measurement of sensitisation. The LLNA assesses this proliferation, wherein the proliferation in test groups is compared to that in vehicle treated controls. The ratio of the proliferation in treated groups to that in vehicle controls (Stimulation Index), is determined, and must be at least three. The methods described here are based on the use of radioactive labelling to measure the proliferation of the lymph node cells.

GLP compliance:

not specified

Type of study:

mouse local lymph node assay (LLNA)

Species:

mouse

Strain:

Balb/c

Sex:

female

Details on test animals and environmental conditions:

TEST ANIMALS
- Age at study initiation: 6-8 wk

Vehicle:

other: 20 % ethanol

Concentration:

10 % test material in 20 % ethanol solution

No. of animals per dose:

Three

Details on study design:

MAIN STUDY
ANIMAL ASSIGNMENT AND TREATMENT
- Name of test method: Local Lymph Node Assay
- Criteria used to consider a positive response: Stimulation index ≥ 3


TREATMENT PREPARATION AND ADMINISTRATION: 25 µL of test material was applied to the dorsum of both ears for three consecutive days. Prior to the test material treatment, the ears of each mouse were gently abraded using a 19 g needle. Four days following the initial application, draining lymph nodes were excised.

Preparation of cell suspension: A single cell suspension of LNC was prepared by mechanical disaggregation through sterile 200 mesh steel gauge. The cells were washed twice with an excess phosphate-buffered saline (PBS) and resuspended in RPMI-1640 culture medium supplemented with 10 % fetal calf serum (FCS), 25 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (Hepes), 100 µg/mL penicillin and 100 U/mL streptomycin. The cell concentration was adjusted to give 5 x 10E6 cells/mL.
Lymphocyte suspensions were seeded into 96 well microtiter plates at a concentration of 1 x 10E6 cells/well (5 wells per animal), and cultured with 0.5 µCi [3H] methyl thymidine ([3H]TdR) for 18 h at 37 °C in a humidified atmosphere of 5 % CO2 in air.
The incorporation of [3H]TdR was measured using a liquid scintillation counter and expressed as mean counts per min (cpm) ± standard deviation per node of three animals for each test group.

Other: Compound solubility - Completely dissolved in 20 % ethanol solution

Positive control substance(s):

not specified

Statistics:

Not reported

Positive control results:

Not reported

Parameter:

SI

Value:

1.41

Variability:

na

Test group / Remarks:

3 animals per dose

Remarks on result:

other: 10 % zinc sulfate = 1.41

Parameter:

SI

Remarks on result:

other: not tested <10% zinc sulfate

Parameter:

SI

Remarks on result:

other: not tested >10% zinc sulfate

Parameter:

other: disintegrations per minute (DPM)

Value:

2.14

Variability:

0.77

Test group / Remarks:

3 animals per dose

Remarks on result:

other: Mean value cpm ± SD ( x 10-3) = 2.14 ± 0.77

Validity of ear abrasion technique: It does not affect the LNC response in the vehicle treated group.

Interpretation of results:

not sensitising

Conclusions:

Under the conditions of the test, the test material was determined to be non-sensitising to mice.

Executive summary:

A study was conducted to evaluate the skin sensitisation potential of the test material in mouse using a modified Local Lymph Node Assay. No guideline or GLP compliance was documented in the study report.

Groups of BALB/c mice (n=3) were treated with 10% concentration of test material or vehicle (20% ethanol solution) by applying 25 µL to the dorsum of both abraded ears for three consecutive days. Four days following the initial application, draining lymph nodes were excised. A single cell suspension of LNC was prepared and the incorporation of [3H]TdR was measured using a liquid scintillation counter.

[3H]TdR incorporation (expressed as mean counts per min (cpm) ± standard deviation per node x 10^-3) was 2.14 ± 0.77 and the ratio of the proliferation in treated group to that in vehicle control (stimulation index) was 1.41.

Hence, under the conditions of the test, the test material was determined to be non-sensitising to mice.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

While there is no particular study addressing respiratory sensitisation in experimental animals, there is no information suggesting zinc compounds to cause such effects in animals.Taking into account the complete absence of skin sensitization potential of zinc compounds, respiratory sensitisation is not expected to be of concern for the zinc and zinc compounds.

Considering the absence of evidence of respiratory sensitization responses in humans, this endpoint is not expected to be of concern for zinc and zinc compounds.

Justification for classification or non-classification

The data on soluble zinc sulphate indicates no skin sensitisation potential and therefore no classification is required according to EC criteria.