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EC number: 215-222-5 | CAS number: 1314-13-2
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 bwAcute 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.
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.
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.
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.
- 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 alsovery 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 wasthe 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).
Zinc oxide (micro- and nanomaterial) isof low acute, dermal and inhalation toxicity not requiring a classification for acute toxicity according to the EC criteria.
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