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EC number: 222-477-6 | CAS number: 3486-35-9
Acute oral toxicity: key study carried out according to OECD guideline no 401 indicating for zinc oxide LD50 > 5000 mg/kg bw (read across to zinc carbonateAcute inhalation toxicity: key study carried out according to OECD guideline no 403 indicating for zinc oxide LC50 > 5.7 mg/L/4hrs (read-across to zinc carbonate
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.
With LD50values consistently exceeding 2,000 mg/kg bw, slightly soluble or insoluble zinc compounds such as zinc oxide (LD50ranges between 5,000 and 15,000mg/kg bw), zinc phosphate (LD50is >5,000mg/kg bw), zinc metal (LD50 >2,000mg/kg bw) or zinc sulphide (LD50is >15,000mg/kg bw), show very low level of acute oral toxicity. Moreover, zinc oxide and zinc metal were further shown to be of low acute inhalation toxicity (i.e., LC50 values of > 5.7 and 5.41 mg/L/4hrs). Given the common characteristics shared via their solubility characteristics, the remaining slightly soluble zinc compounds are also considered to be of low acute inhalation toxicity. There are no available data on which to evaluate acute dermal toxicity for slightly soluble or insoluble zinc compounds, however, acute dermal toxicity can be considered to be low in view of the poor absorption by this route.
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).
The slightly soluble and insoluble zinc compounds (i.e., zinc oxide, zinc hydroxide, zinc phosphate, zinc carbonate, zinc metal and zinc sulphide)
are of low acute, dermal and inhalation toxicity not requiring a classification for acute toxicity according to the EC criteria.
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