Dizinc orthosilicate

Endpoint summary

Description of key information

Acute oral and acute inhalation toxicity data are read across from zinc and soluble zinc compounds.

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.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

5 700 mg/m³ air

Additional information

There are no data available on acute toxicity by oral or inhalation routes for zinc silicate. However, the analysis of the dissolution and bioaccessibility of zinc silicate demonstrated that significant quantities of ionic zinc are released in physiological test media (2.45 - 94.0%) (Martinez 2016a), therefore it is justified to read across the acute toxicity data from zinc oxide and soluble zinc compounds to zinc silicate. See attached justification in IUCLID section 13 for further details.

Acute oral and acute inhalation toxicity data are read across from zinc oxide dossier.

- With Oral LD₅₀values consistently exceeding 2,000 mg/kg bw, zinc oxide (LD₅₀ranges between 5,000 and 15,000mg/kg bw), both micro- and nano- zinc oxide shows a very low level of acute oral toxicity.
- With Inhalation LC50 value > 5.7 mg/L/4hrs, zinc oxide is shown to be of low acute inhalation toxicity. 

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. The 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 nano-material) is of low acute oral and inhalation toxicity, not requiring a classification for acute toxicity according to the EC criteria.