Zinc oxide

Endpoint summary

Description of key information

Acute oral toxicity: key studies carried out according to OECD guideline no 401 or 423 indicating for both micro- and nanomaterial zinc oxide LD50 > 2000 mg/kg bw
Acute inhalation toxicity: key study carried out according to OECD guideline no 403 indicating for micro zinc oxide LC50 > 5.7 mg/L/4hrs.
Acute dermal toxicity: key study carried out according to OECD guideline no 402 indicating for nano zinc oxide LD50 >2000 mg/kg bw.

 

 

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 423 (Acute Oral toxicity - Acute Toxic Class Method)

Deviations:

no

GLP compliance:

not specified

Remarks:

the publication does not specify GLP compliance

Test type:

other: limit test

Limit test:

yes

Species:

mouse

Strain:

not specified

Sex:

male/female

Details on test animals or test system and environmental conditions:

No data

Route of administration:

oral: gavage

Vehicle:

DMSO

Details on oral exposure:

- Rationale for the selection of the starting dose: Based on the result of another study (Yamaki & Yoshino 2009).

Doses:

5,000 mg/kg bw for both ZnO nanoparticle and microparticle

No. of animals per sex per dose:

5/sex/dose

Control animals:

yes

Details on study design:

Thirty mice were divided into three groups (five males and five females per group). Mice were fed with vehicle (control group), 5,000 mg/kg bw ZnO-nanoparticle suspension or 5,000 mg/kg bw ZnO-microparticles suspension. Dosed mice were conditioned for 14 d. The mortality and clinical behaviour were observed daily. Body weights were recorded twice weekly. At the end of the study (on Day 14), the mice were anaesthetised with isoflurane and blood (for serum biochemistry analysis) was collected from the orbital sinus, followed by gross necropsy. Tissue samples (for histopathologic examination) were taken and fixed in 10% neutral buffered formalin

Statistics:

All data were expressed as the mean ± SD from at least three independent experiments (N ‡ 3). The significance of the difference between the control and each experimental test condition was analysed by Student’s t-test. Statistically significant differences among groups were determined using one-way analysis of variance (ANOVA). A value of p < 0.05 was taken as statistically significant.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 5 000 mg/kg bw

Based on:

test mat.

Mortality:

Not observed

Clinical signs:

other: Not observed

Body weight:

other body weight observations

Remarks:

In comparison with vehicle control group, ZnO microparticles treated group showed a body weight reduction in both males (Days 5 and 10) and females (Days 5, 10, and 14); the body weight changes were unobvious in ZnO nanoparticle treated groups.

Gross pathology:

Decreased wet weights of the spleen, kidney, and liver were observed in ZnO microparticles treated females but not in ZnO nanoparticle treated males. However, no obvious gross pathological signs were found in the study.

Other findings:

All serum biochemistry measures were without any significant alternation except for marginal variations in certain parameters.

Interpretation of results:

GHS criteria not met

Conclusions:

Based on the study details, the LD50 value of both the ZnO nanoparticles and ZnO microparticles can be established at >5,000 mg/kg bw in mice.

Executive summary:

The study was conducted to examine the acute toxicity of both ZnO nanoparticles and ZnO microparticles in mice.

Thirty mice were divided into three groups (five males and five females per group). Mice were fed with vehicle (control group), 5,000 mg/kg bw ZnO-nanoparticle suspension or 5,000 mg/kg bw ZnO-microparticles suspension. Dosed mice were conditioned for 14 d.

All the mice survived throughout the testing period without exhibiting any abnormalities related to the test substances. In comparison with the vehicle control group, ZnO-microparticles treated group showed a body weight reduction in both males (Days 5 and 10) and females (Days 5, 10, and 14); the body weight changes were not obvious in ZnO-nanoparticle treated groups. All serum biochemistry measures were without any significant alterations except for marginal variations in certain parameters.

Based on the study details, the LD50 value of both the ZnO nanoparticles and ZnO microparticles can be established at >5,000 mg/kg bw in mice.

Reference 2

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study is conducted according to OECD TG 423 with some modifications in terms of different dose levels, usage of sexes, animal number, and inclusion of hematology, biochemical parameters and histopathology evaluation.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 423 (Acute Oral toxicity - Acute Toxic Class Method)

Deviations:

yes

Remarks:

there were modifications in terms of different dose levels, usage of sexes, animal number, and inclusion of hematology, biochemical parameters and histopathology evaluation.

GLP compliance:

not specified

Remarks:

the publication does not specify GLP compliance

Test type:

acute toxic class method

Limit test:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Animals and housing conditions:
- Experimental animals were obtained from in-house animal facility. All procedures using animals were reviewed and approved by the institutional animal ethics committee.
- The healthy Sprague Dawley rats of both sex, aged between 8 and 9 weeks and body weights of 180–220 g were used. Females were nulliparous and nonpregnant.
- Animals were housed in polypropylene cages with stainless steel grills and gamma-irradiated corn cobs were used as bedding. Bedding material, cages, grills and water bottles were changed on alternate days.
- Animals were housed individually sex wise and group wise.
- Animals were acclimated for a minimum period of 5 d in the controlled environment (temperature: 22 + 3C; relative humidity: 50 + 20% and light: 12-h light/dark cycle) and ad libitum supply of reverse osmosis water and a standard rodent pellet feed. Feed alone was withdrawn overnight prior to the dosing and following dosing, for a period of 3 h.

Route of administration:

oral: gavage

Vehicle:

water

Remarks:

distilled

Details on oral exposure:

- The test substance was suspended in distilled water and administered through oral gavage once at dose levels of 5, 50, 300, 1,000 and 2,000 mg/kg bw.
- The test solution was prepared shortly prior to the administration. The dose volume maintained for all the groups was maximum (10 mL/kg bw).
Similarly, control group of animals (5 males and 5 females) were dosed with distilled water alone.

Doses:

0, 5, 50, 300, 1,000 and 2,000 mg/kg bw

No. of animals per sex per dose:

Five/sex/dose

Control animals:

yes

Details on study design:

- Animals were observed for mortality/morbidity, clinical signs of toxicity, weekly body weight and weekly food consumption during the experimental period.
- At the end of 14 d of administration, the animals were killed and the blood was obtained through ophthalmic vein. The organs such as esophagus,
stomach, small and large intestines, liver, spleen, thymus, mandibular and mesenteric lymphnodes, kidney, urinary bladder, heart, pancreas, brain, lungs ovaries and testes were collected, and all the organs were kept in 10% buffered formalin and the testes in modified Davidson fluid.


METHOD DETAILS
- Clinical biochemistry: The serum obtained after centrifuging was analyzed for biochemical parameters such as creatinine, albumin, alkaline phosphatase (ALP), alanine aminotransferase (ALT), amylase, aspartate aminotransferase (AST), blood urea nitrogen (BUN), calcium, cholinesterase, total cholesterol, glucose, HDL cholesterol, iron, phosphorus, total protein, triglycerides, urea and zinc using Humastar 300 fully automated biochemistry analyzer (Human GmbH., Germany), and sodium, potassium and chlorides in serum were analyzed on Day 14 by means of a humalyte electrolyte analyzer (Human GmbH., Germany).
- Hematology: Blood treated with EDTA was used for analyzing hematology parameters such as erythrocyte count (red blood cell [RBC]), hemoglobin, hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), platelet (PLT) count, total leucocyte count (white blood cell [WBC]) and differential count (five parameters namely neutrophils, eosinophils, basophils, lymphocytes and monocytes)were determined on Day 14 using Bayer ADVIA 120, fully automated hematology analyzer. Clotting time of blood was determined by capillary tube method.
- Necropsy: Gross pathology was performed at the end of experimental period (Day 14).
- Histopathology: Histopathology of organs (liver, spleen, kidneys, heart, adrenals, lungs, pancreas, stomach, esophagus, small and large intestine) was evaluated. Tissues were collected and preserved in 10% buffered formalin. All tissues required for histopathology evaluation were subjected to dehydration procedure and processed in tissue processor, embedded in paraffin wax and prepared sections of 5–8 mm thickness and stained with hematoxylin-eosin stain.

Statistics:

- The data was expressed as mean +/- standard deviation for statistical analysis. A comparison of treated rats with control groups was done using Newman–Keuls multiple comparison test. The data found to be heterogeneous were subjected to nonparametric-Kruskal–Wallis multiple comparison Z value test.
- The alpha level at which all tests were conducted is 0.05, and the NCSS 2007 software was used for analysis.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Remarks on result:

other: Not reported in the article, but can be inferred based on the available study description.

Mortality:

No details available.

Clinical signs:

other: No details available

Body weight:

other body weight observations

Remarks:

No details available

Gross pathology:

No gross pathological lesions were observed in any of the treatment groups.

Other findings:

Clinical biochemistry (see Table 1 for details):
- The results indicated that the plasma ALT and AST were significantly higher than the controls in both the sexes.
- There is an inverse dose-dependent increase in the AST and ALT serum levels in animals treated with nano-size ZnO.
- Calcium levels in the serum were also significantly high from control. However, there are no significant differences in rest of the parameters analyzed.

Hematology:
- There were no statistically significant changes in the hematologic parameters when compared to control.

Histopathology:
Animals treated with nano-size ZnO showed lesions in liver and pancreas. In addition to this, animals treated with nano-size ZnO at 2,000, 1,000, 300, 50 and 5 mg/kg bw showed lesions in stomach and heart as well.

Table1: Clinical biochemistry parameters (males and females)

Groups	ALT	AST	Ca
Males
G1 (N-5)	747.0 ± 120.6*	687.4 ± 83.1*	10.1 ± 0.1*
G2 (N-50)	514 ± 88.0*	553.6 ± 55.5*	10.3 ± 0.2*
G3(N-300)	428.6 ± 111.5*	509.6 ± 41.5*	10.6 ± 0.4*
G4 (N-1000)	395.2 ± 57.8*	411.8 ± 66.6*	10.2 ± 0.2*
G5(N-2000)	298.4 ± 119.1*	357.4 ± 69.3*	10.1 ± 0.1*
Females
G1 (N-5)	712.2 ± 169.5*	501.6 ± 49.3*	10.0 ± 0.3
G2 (N-50)	521.4 ± 39.8*	404.8 ± 86.7*	9.6 ± 0.8
G3(N-300)	464.2 ± 61.2*	345.8 ± 50.1	9.6 ± 0.7
G4 (N-1000)	355.6 ± 106.6*	276.6 ± 47.6*	10.2 ± 0.8
G5(N-2000)	248.6 ± 126.4*	226.8 ± 18.8*	10.0 ± 0.4

ALP: alkaline phosphatase, ALT: alanine transaminase, AST: aspartate transaminase, Ca: calcium.

*Statistically different from control; p <0.005 (n=5)

Interpretation of results:

GHS criteria not met

Conclusions:

Although an LD50 value has not been reported in the study report, but based on the study description, the LD50 value can be established at >2,000 mg/kg bw.

Executive summary:

An acute oral toxicity study was performed with ZnO nanoparticles using Sprague Dawley rats according to OECD guideline 423. A group of 10 fasted animals (five males and five females) were administered with 5, 50, 300, 1,000 and 2,000 mg/kg bw of ZnO nanoparticles suspended in distilled water once through oral gavage. The animals were observed for mortality/morbidity, clinical signs of toxicity, weekly body weight and weekly food consumption during the experimental period. The study focused on the effects of the test substance on biochemical and hematological parameters which were analyzed on Day 14 of administration. At the end of 14 days the animals were sacrificed and subjected to gross pathological examination along with histopathology or organs.

An inverse dose-dependent increase was noted in AST, ALT serum levels when compared with control. Calcium levels in the serum were also significantly high from control. However, there are no significant differences in rest of the parameters analyzed. There were also no statistically significant changes in the hematologic parameters. No gross pathological lesions were observed in any of the treatment groups. Histopathological evaluation showed incidences of microscopic lesions in liver, pancreas, heart and stomach which were higher at lower doses compared to higher dose.

Although an LD50 value was not reported in the study report, based on the study description and considering that no mortality occurred at any of the tested dose levels, the LD50 value can be established at >2,000 mg/kg bw.

Overall the authors concluded that the high toxicity at low doses which were evident in the present study may be due to the fewer number of nanoparticles in that mass, which may result in less agglomeration thereby making them penetrate into the cells.

Reference 3

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

According to the OECD guideline, but mice used

Qualifier:

according to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

GLP compliance:

not specified

Test type:

standard acute method

Limit test:

no

Species:

mouse

Strain:

other: CD-ICR

Sex:

male/female

Details on test animals or test system and environmental conditions:

Age: 8 weeks
Weight: 20-22 g

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Doses:

1000, 2000, 3000, 4000, 5000 mg/kg

No. of animals per sex per dose:

5

Control animals:

yes

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing:before begin of study, after 2 and 14 days
- Necropsy of survivors performed: yes
- Other examinations performed: clinical signs, body weight, histopathology, blood analysis

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 5 000 mg/kg bw

Remarks on result:

other: 20 nm ZnO

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 - < 5 000 mg/kg bw

Remarks on result:

other: 120 nm ZnO

Mortality:

One female death occurred in the nano-scale 2000 mg group and one male death in the nano-scale 5000 mg group.
As for 120-nm ZnO treated mice, one and three female mice died in the sub-micro 2000 mg and 5000 mg group.

Body weight:

other body weight observations

Remarks:

In the second day after administration, the body weight (BW) of female mice in N4 (4000 mg/kg bw 20- nm ZnO) and male mice in N1 (1000 mg/kg bw 20-nm ZnO) , N5 (5000 mg/kg bw 20-nm ZnO) , SM2 (2000 mg/kg bw 120-nm ZnO) , SM4 (4000 mg/kg bw 120-nm ZnO) and SM5 (5000 mg/kg bw 120-nm ZnO) groups significantly decreased (P < 0.05), whereas, on day 14, the body weight regained gradually and no significant difference was found between the control and the exposed group mice except it of the female mice in SM2 (2000 mg/kg bw 120-nm ZnO) group notably decreased.

Gross pathology:

The pathological observation shows that the lesions of stomach, liver and pancreas were found in 20-nrn ZnO group mice. With the dose increase, 20-nm ZnOinduced severer gastric mucosal damage, but the liver and pancreas lesion was mitigated. In N1 group mice lhe heart and spleen damages were observed.
For the examination or 120-nm ZnO group mice, the pathological damages of stomach, liver, heart, spleen and pancreas were found to aggravate with the dose increase. Moreover, the significantly increased UA level in SM3 and SM4 group mice and the histopathological alteration of cardiovascular cells all indicated that the cardiovascular diseases occurred in 120-nm ZnO treated mice.

Combined with the results of zinc accumulation, pathological examination and the biological indicators assays, according to the authors the target organs for 20- and 120-nm ZnO acute oral administration are demonstrated as liver, heart, spleen, pancreas and bone.

The biochemical and pathological investigation shows that the toxic effects between the 20-nm and 120-nm ZnO particles are a little different. For example, the blood viscosity could be induced by low and median dose of 20-nm ZnO but high dose of fine ZnO after oral administration. The edema and degeneration of hepatocytes, and inflammation of pancreas could be observed in most of the 20-nm ZnO treated mice. The 120-nm ZnO treated mice were found having dose-effect pathological damage in gastric, liver, heart and spleen, however, the 20-nm ZnO treated mice presented lessened liver, spleen and pancreas damage with the increase of treated dose.

Interpretation of results:

GHS criteria not met

Conclusions:

According to the authors nano-scale as well as submicro-scale ZnO are both not classified according to the GHS with a LD50 of greater than 5 g/kg and 2g/mg < LD50 < 5 g/kg, respectively.

Executive summary:

Wang et al. (2008) treated 5 mice per sex and dose orally by gavage with 1000, 2000, 3000, 4000 and 5000 mg/kg bw of nanoscaled ZnO powder (particle size: 20 nm) and submicroscaled ZnO powder (particle size: 120 nm), respectively. The study was performed according to guideline but under non-GLP conditions. After the 14-days observation period the oral LD50 of 20 nm ZnO was estimated to be > 5000 mg/kg bw while the LD50 of 120 nm ZnO was > 2000 and < 5000 mg/kg bw in mice.

As the results, both 20- and 120-nm ZnO belong to non-toxic chemicals according to the Globally Harmonized Classification System (GHS) for the classification of chemicals.

Reference 4

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

GLP compliance:

not specified

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

5 per sex

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

single dose by oral gavage in water and observed for 14 days

Doses:

single dose of 5 gZnO/kg bw

No. of animals per sex per dose:

5 per sex

Control animals:

not specified

Details on study design:

no further information

Statistics:

no data

Preliminary study:

no further information

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 5 000 mg/kg bw

Mortality:

no mortality

Clinical signs:

other: no adverse signs of toxicity

Body weight:

other body weight observations

Remarks:

no adverse signs of toxicity

Gross pathology:

no adverse signs of toxicity

none

Interpretation of results:

GHS criteria not met

Conclusions:

LD50 > 5000 mg ZnO/kg bw was determined.

Executive summary:

In an acute toxicity test Wistar rats (5/sex) were given a single dose of 5 g ZnO/kg bw (in water) by gavage and observed for 14 days. No mortality and signs of toxicity were observed. The LD₅₀for rats is therefore >5 g ZnO/kg bw.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Used in EU risk assessment for zinc oxide

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

GLP compliance:

not specified

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

not specified

Sex:

male/female

Details on test animals or test system and environmental conditions:

no information available

Route of administration:

inhalation

Type of inhalation exposure:

nose/head only

Vehicle:

other: no data

Analytical verification of test atmosphere concentrations:

not specified

Duration of exposure:

ca. 4 h

Concentrations:

Aerosol concentration was 5.7 mg/l

No. of animals per sex per dose:

10 per sex

Control animals:

yes

Details on study design:

10 male and 10 female animals per group were exposed to zinc oxide aerosol (head and nose only) for 4 h. Aerosol concentration was 5.7 mg/l and the particle size distribution had a mass median aerodynamic diameter of 4 µm ± 2.9 (GSD). Only one concentration and a control group were tested. All animals survived up to day 14 post exposure.

Statistics:

no information

Preliminary study:

no information

Sex:

not specified

Dose descriptor:

LC50

Effect level:

> 5 700 mg/m³ air

Exp. duration:

4 h

Mortality:

no mortality

Clinical signs:

other: only a dusty fur on the head, no adverse effects noted

Body weight:

no change in body weights observed

Gross pathology:

no adverse effects observed.

Other findings:

none observed

no information

Interpretation of results:

GHS criteria not met

Conclusions:

LC50 4 hours >5.7 mg ZnO/l

Executive summary:

In an acute inhalation toxicity study, 10 male and 10 female animals per group were exposed to zinc oxide aerosol (head and nose only) for 4 h. Aerosol concentration was 5.7 mg/l and the particle size distribution had a mass median aerodynamic diameter of 4mm ± 2.9 (GSD). Only one concentration and a control group were tested. All animals survived up to day 14 post exposure. Apart from a dusty fur on the head the day after the exposure, no effects were seen. Body weights developed normally. At pathological examination all organs were normal. The LC₅₀was >5.7 mg/l.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

5 700 mg/m³ air

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Common breakdown product(s): This test was done on the hydrophobic coated zinc oxide nanoform which is assumed to be worst case. Zn2+ion determines the toxicity of ZnO and read across between various forms of ZnO (micro-scale, nano, coated or not) is fully supported. 

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source chemical and target chemical are both nanoforms, with the same physical state (solid)
The source nanoform is Z-cote HP; Code: NM111; Surface coating: triethoxycaprylylsilane (2%); Substance type: Inorganic; Physical state: solid powder, nano-form
The target nanoform is Z-cote ®; Code: NM110; Surface coating: none; Substance type: Inorganic; Physical state: solid powder, nano-form

3. ANALOGUE APPROACH JUSTIFICATION
This test was done on the hydrophobic coated zinc oxide nanoform which is assumed to be worst case. Zn2+ion determines the toxicity of ZnO and read across between various forms of ZnO (micro-scale, nano, coated or not) is fully supported. 

4. DATA MATRIX
Source: Bellmann (2010), (KL1), acc. to OECD Guideline 402, rat LD50 > 2000 mg/kg bw
Target: uncoated ZnO nanoform NM110

Qualifier:

according to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, Sulzefeld, Germany
- Age at study initiation: 10 - 11 weeks
- Weight at study initiation: males (mean): 308.92 g, females (mean): 193.28 g
- Housing: 2 rats of same sex per cage, wooden absorbing bedding
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 4 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 22 +/- 2°C
- Humidity: 55 +/- 15%
- Air changes (per hr): fully airconditioning
- Photoperiod (hrs dark / hrs light): 12 h / 12 h

Type of coverage:

semiocclusive

Vehicle:

corn oil

Details on dermal exposure:

TEST SITE
- Area of exposure: back

REMOVAL OF TEST SUBSTANCE
- Washing (if done): water
- Time after start of exposure: 24 h

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 2000mg/kg bw
- Concentration (if solution): 0.5mg test item in 400µl corn oil
- Constant volume or concentration used: no
- For solids, paste formed: yes

Duration of exposure:

24 h

Doses:

2000 mg/kg bw

No. of animals per sex per dose:

5/sex

Control animals:

other: untreated skin of same animal

Details on study design:

- Duration of observation period following administration: 14 d
- Frequency of observations and weighing: Twice a day, once on weekends
- Necropsy of survivors performed: Yes
- Other examinations performed: Clinical signs, body weight, gross pathology

Statistics:

Means and standard deviation were calculated using standard statistical tests.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Remarks on result:

other: No mortality occured

Mortality:

Not observed

Clinical signs:

other: Slight signs of general discomfort as often seen in dermal toxicity studies, the general health status was good throughout the study

Body weight:

other body weight observations

Remarks:

Treatment related effects were not observed

Gross pathology:

No abnormalties detected

Interpretation of results:

GHS criteria not met

Conclusions:

Under the test conditions, the LD50 of nanoscaled ZnO is estimated to be > 2000mg/kg bw.

Executive summary:

The study was conducted to determine the acute dermal toxicity of nanoscaled ZnO according to the OECD Guideline 402 in compliance with GLP.

 

2000 mg/kg bw of the test substance were semiocclusively administered for 24 h as pasty formulation in corn oil to the shaved and defaffed back of 5 female and 5 male rats. After the end of the exposure period, the test substance paste was recovered as effectively as possible using water and the animals were observed for 14 d. During the present study no mortality occurred and there were no indications of systemic toxicity, no effects regarding the body weight and neither clinical signs nor pathological findings observed.

 

The LD50 of the test substance is therefore estimated to be > 2000 mg/kg bw.

 

This test was done on the hydrophobic coated zinc oxide nanoform which is assumed to be worst case. In conclusion  Zn²⁺ion determines the toxicity of ZnO and read across between various forms of ZnO (micro-scale, nano, coated or not) is fully supported. 

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

2 000 mg/kg bw

Additional information

Zinc oxide micro:

- With LD₅₀values consistently exceeding 2,000 mg/kg bw, zinc oxide (LD₅₀ranges between 5,000 and 15,000mg/kg bw), shows very low level of acute oral toxicity.
- With LC50 value > 5.7 mg/L/4hrs, zinc oxide is shown to be of low acute inhalation toxicity. 
- There are no available data on which to evaluate acute dermal toxicity for ZnO micromaterial. However, acute dermal toxicity can be considered to be low in view of the poor absorption by this route.

Zinc oxide nanomaterial:

 

Tests performed specifically on nano-ZnO demonstrate also very low acute oral toxicity (i.e. LD50 values consistently exceeding 2,000 mg/kg bw). The only available inhalation data on nano-ZnO indicates an LC50 value of > 1.79 mg/L. However, only this one single dose of 1.79 mg/L was tested which was the maximum attainable exposure concentration for achieving respirable particle size. Data on nano-ZnO confirms low acute dermal toxicity with LD50>2000 mg/kg bw.

 

In conclusion, for nano-ZnO no nano-specific acute toxicity could be identified. Zn²⁺ion determines the toxicity of ZnO and read across between various forms of ZnO (micro-scale, nano, coated or not) is fully supported. 

 

Of significance for humans from an acute toxicity standpoint is the occurrence of metal fume fever following exposure to ultrafine particles of special grades of zinc oxide in context of very specific operations such as cutting or welding of galvanised steel. Metal fume fever is exclusively associated with freshly formed ultrafine particulate zinc oxide (<0.1 µm). As these ultrafine particles (nanoparticles) rapidly agglomerate to bigger particles, which are normally encountered at production and processing sites, at these sites there is no indication for metal fume fever. According to the response from 11 zinc companies to a questionnaire, there have been no observations of zinc metal fume fever over the last decade and in recent occupational practice (EU RAR, 2004a-f). However in light of responsible care and since no studies are available that allow the establishment of a NOAEL for metal fume fever with a reasonable degree of certainty, a LOAEL (5 mg ZnO/m³) for 2 hours (showed the typical metal fume fever symptoms beginning 4 to 8 hours after exposure and disappearing within 24 hours) can be used for metal fume fever based on the study by Gordon et al.(1992).

Justification for classification or non-classification

Zinc oxide (micro- and nanomaterial) is of low acute, dermal and inhalation toxicity not requiring a classification for acute toxicity according to the EC criteria.