Zinc sulphate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

35.6 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

17.8 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

246.9 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

362.7 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

400.5 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:

205.2 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.

Conclusion on classification

Zinc sulphate 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 sulphate versus the Zn²⁺ ion, resulting in an acute ecotoxicity reference value of 41.4 x MW (ZnSO₄/ MW (Zn) = 102.2 µg substance /l at pH 8 (as worst case), the M-Factor for acute toxicity of zinc sulphate is 1.

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 sulphate versus the Zn²⁺ ion, results in a chronic ecotoxicity reference value of 11 x MW (ZnSO₄/ MW (Zn) = 27.2 µg substance /l at pH 8 (as worst case), the M-factor for chronic toxicity of zinc sulphate is 1.

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

 

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 27.2 µg ZnSO₄/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 ZnSO₄of 27.2 µg/l, and considering zinc and its compounds as equivalent to being rapidly degradable, the classification of zinc sulphate 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 sulphate 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.