Registration Dossier
Registration Dossier
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EC number: 237-057-8 | CAS number: 13597-65-4
Ecotoxicological Summary
Administrative data
Hazard for aquatic organisms
Hazard for air
Hazard for terrestrial organisms
Hazard for predators
Additional information
Conclusion on classification
The standard approach for classifying poorly soluble metals is to use the data generated from T/D tests, and compare this with relevant acute or chronic Ecotoxicity Reference Values (ERV) for the soluble metal compounds (Guidance on the application of the CLP criteria, ECHA, 2017).
Acute or chronic Ecotoxicity Reference Values (ERV) for zinc were derived in the zinc oxide dossier based on a large dataset and these were used as reference values for classification of zinc silicate.
A significant number of short-term aquatic data on zinc are available at both low (6 -<7) and neutral/high (7 -8.5) pH and low/medium (<100mg CaCO3/l) and medium/high (>100 mg CaCO3/l water hardness. At low pH (6-<7), values of 0.413 mg Zn/L (low pH, low hardness) and of >0.530 mg Zn/L (low pH, high hardness) were determined for Ceriodaphnia dubia. The lowest value of 0.413 mg Zn/L observed for Ceriodaphnia dubia was used for the classification at low pH. At neutral/ high pH, the lowest IC50 value of 0.137 mg/L was determined for freshwater algae (Selenastrum capricornutum) and this value was taken as reference value for classification for acute effects at neutral/high pH in the zinc oxide dossier.
In the zinc oxide dossier, the reference values for chronic aquatic toxicity for zinc were determined from the extensive chronic ecotoxicity data available for algae, invertebrates and fish at pH 6 and pH 8. The standard species NOEC values for each taxonomic group for which a bioavailability model is available were taken, and the lowest of the 3 was selected as a reference value at pH 6 and pH 8.
The following reference values for chronic zinc aquatic toxicity were derived in the zinc oxide dossier:
-at pH 6: 0.082 mg Zn/l (Daphnia magna)
-at pH 8: 0.019 mg Zn/l (Pseudokircherniella subcapitata)
The T/D tests with zinc silicate have revealed that zinc is released in test medium at pH 6 to a larger degree than at pH 8, therefore the results at pH 6 are taken into consideration for classification purposes as a worst-case scenario. At pH 6, 0.145 mg/L and 0.162 mg/L of zinc was released after 7 and 28 days, respectively, in the T/D study (Martinez, 2016a). The acute ERV of 0.413 mg Zn/L and chronic ERV of 0.082 mg Zn/L derived at low pH (pH 6 – 7) in the zinc oxide dossier are considered relevant for classification of zinc silicate. Based on comparison of zinc solubility determined in the T/D study with relevant ERV values, zinc silicate is not assigned an acute classification, as the concentration of dissolved zinc released after 7 days in the TD test is lower than the acute ERV. Zinc silicate is classified as Aquatic Chronic 1 since the dissolved zinc concentration released after 28 days in the T/D test at a loading rate of 1 mg/L is greater than the chronic ERV value derived for soluble zinc.
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