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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Ecotoxicological information

Ecotoxicological Summary

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Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
17.9 µg/L
Assessment factor:
1
Extrapolation method:
sensitivity distribution

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
9 µg/L
Assessment factor:
1
Extrapolation method:
sensitivity distribution

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
124.5 µg/L
Assessment factor:
1
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
182.8 mg/kg sediment dw
Assessment factor:
1
Extrapolation method:
sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
201.9 mg/kg sediment dw
Assessment factor:
1
Extrapolation method:
sensitivity distribution

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
103.4 mg/kg soil dw
Assessment factor:
1
Extrapolation method:
sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

A basic assumption made in this hazard assessment and throughout this CSR, (in accordance to the same assumption made in the EU RA process) is that the ecotoxicity of zinc and zinc compounds is due to the Zn2+ ion. As a consequence, all aquatic, sediment and terrestrial toxicity data in this report are expressed as “zinc”, not as the test compound as such, because ionic zinc is considered to be the causative factor for toxicity. A further consequence of this is that all ecotoxicity data obtained on different zinc compounds, are mutually relevant for each other. For that reason, the available ecotoxicity databases related to zinc and the different zinc compounds are combined before calculating the PNECs. The only way zinc compounds can differ in this respect is in their capacity to release zinc ions into (environmental) solution. That effect is checked eventually in the transformation/dissolution tests and may result in different classifications.

An elaborated justification for this read-across approach is attached in IUCLID section 13.

General conclusion on relevancy for PNECs and environmental risk assessment for nano ZnO

 

To check the relevancy of the zinc-ion based PNECs for nano-ZnO, a comparative analysis was performed on studies, providing exposures to both the ionic Zn form and the nano ZnO form. By this comparison, it was checked if the ion-based PNECs registered in the ZnO files were protective for the nano-ZnO forms, too. 

 

The available evidence, notably on the chronic data that are considered most relevant for the environmental risk assessment and the PNECs, shows that for all environmental compartments, the ecotoxicity of nano-ZnO is similar or lower than the toxicity of the zinc ion. This is generally explained by the rapid dissolution of ZnO-NP in environmental media. The analysis has revealed that the taxonomic variability is well covered by the present dataset. A few points of attention (e.g. to marine algae) have been mentioned. The relevancy of these observations for risk assessment needs to be confirmed.

When considering relevancy of test data, the test concentrations should be considered. It is at present difficult/impossible to monitor NP in surface waters, due to the difficulties in discriminating between natural NP and artificial NP. Dumontet al.(2015) modelled ZnO-NP concentrations in EU waters using relevant exposure pathways, and using a ZnO-NP input of 1050 T/y into STP. They concluded from their modelling that “half of the river stretches had long-term average concentrations of NP exceeding 1.5 ng/l ZnO-NP, and in 10% of river stretches the concentrations would exceed 150 ng/l” (Dumont et al. 2015). It is clear that these modelled concentrations are far below the levels applied in ecotoxicity testing.

Conclusion on classification

Zinc oxide has a harmonized classification according to Annex VI of the European CLP Regulation ((EC) No 1272/2008) as "Acute 1" (H400: Very toxic to aquatic life) and “Chronic 1” (H410: Very toxic to aquatic life with long lasting effects).

Considering a) the lowest acute aquatic ecotoxicity (EC50) values of 41.4 µg Zn/l and 154 µg Zn/l for the zinc ion at pH 8 and 6 respectively, and b) the molecular weight ratio of zinc oxide versus the Zn2+ ion, resulting in an acute ecotoxicity reference value of 41.4 x MW (ZnO) / MW (Zn) = 51.5 µg substance /l at pH 8 (as worst case), the M-Factor for acute toxicity of zinc oxide is 10.

Considering a) the lowest chronic aquatic ecotoxicity values of 11 µg Zn/l and 99 µg Zn/l for the zinc ion at pH 8 and 6 respectively, and b) the molecular weight ratio of zinc oxide versus the Zn2+ ion, results in a chronic ecotoxicity reference value of 11 x MW (ZnO) / MW (Zn) = 13.7 µg substance /l at pH 8 (as worst case), the M-factor for chronic toxicity of zinc oxide is 1.

In conclusion, zinc oxide is classified for hazards to the aquatic environment under CLP as H400 ("Acute 1"), H410 ("Chronic 1"). The M-factor for acute and chronic aquatic effects is 10 and 1, respectively.

 

Further considerations on the classification based on recent information

Taking into account the lowest chronic ecotoxicity value observed on a wide variety of species of different taxonomic groups (11 µg Zn/l), it can be reconsidered what exactly the level of chronic classification of the substance should be. As was mentioned above the chronic ecotoxicity reference value for the substance is 13.7 µg ZnO/l. This value must be compared with the criteria for chronic classification, also taking into account whether the substance is considered rapidly degradable or not.

The concept of “Degradability” was developed for organic substances and is not applicable as such to inorganic substances like zinc. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” was developed to assess whether or not a given metal ion would remain present in the water column upon addition (and thus be able to excert a chronic effect) or would be rapidly removed from the water column. In this concept, “rapid removal from the water column” (defined as >70% removal within 28 days) is considered as equivalent to “rapidly degradable”. Under IUCLID section 5.6., the rapid removal of zinc from the water column is documented. Consequently, zinc and zinc compounds are considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. 

Considering the chronic ecotoxicity reference value for ZnO of 13.7 µg/l, and considering zinc and its compounds as equivalent to being rapidly degradable, the classification of zinc oxide for chronic aquatic effect should be “Chronic 2” (H411: Toxic to aquatic life with long lasting effects) rather than the "Chronic 1" classification in Annex VI of CLP.

General discussion

A basic assumption made in this hazard assessment and throughout this CSR, (in accordance to the same assumption made in the EU RA process) is that the ecotoxicity of zinc and zinc compounds is due to the Zn2+ ion. As a consequence, all aquatic, sediment and terrestrial toxicity data in this report are expressed as “zinc”, not as the test compound as such, because ionic zinc is considered to be the causative factor for toxicity. A further consequence of this is that all ecotoxicity data obtained on different zinc compounds, are mutually relevant for each other. For that reason, the available ecotoxicity databases related to zinc and the different zinc compounds are combined before calculating the PNECs. The only way zinc compounds can differ in this respect is in their capacity to release zinc ions into (environmental) solution. That effect is checked eventually in the transformation/dissolution tests and may result in different classifications.

The elements brought forward above indicate that the chronic classification of zinc oxide should be “Chronic 2”, rather than the “Chronic 1” classification currently in Annex VI. However, since the substance has been classified under Annex VI of the CLP Regulation, this classification is applied at present.