Zinc

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

14.4 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

7.2 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

100 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

146.9 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

162.2 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:

83.1 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 Zn⁺⁺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

For the classification of zinc metal for aquatic effects, the powder and massive form are considered separately following the criteria of the CLP guidance. A recent survey of the EU market confirms that powders are produced by special processes, and do not result from the normal handling and use of the massive form. Massive zinc is mainly produced in big blocks or plates; the smallest size produced are pellets of cm-size.

• For zinc powders, the classification of Annex VI of CLP applies.


• For zinc in massive form, the critical particle size of particles is determined, based on updated ecotoxicity reference values and transformation/dissolution data. It is shown that for all scenarios (acute and chronic ecotoxicity at low and high pH) the critical particle size of zinc, that would result in reaching the ecotoxicity reference value for the corresponding scenario, is smaller than 1mm. It is thus concluded that zinc in massive form is not classified for aquatic effect.

 

Justification

For the zinc substances including zinc metal, Ecotoxicity Reference Values (ERVs) are based on the soluble ion, Zn²⁺ and are determined from the extensive datasets on acute and chronic ecotoxicity testing of soluble zinc salts.  For details, please refer to IUCLID section 13.2:  “Background document – Environmental Effects Assessment of Zinc in the Aquatic Compartment. The Ecotoxicity Reference Values used for classification for acute and chronic aquatic effect at different pH bands are presented in Table 1 (for a detailed description of the setting of the ERVs, see IUCLID section 13.2, IZA 2021 document: “Ecotoxicity Reference Value for Zinc”).

Table 1. Zinc ERVs at different pH bands

	Acute	Acute	Chronic	Chronic
	pH 6 to < 7	pH 7 to 8	pH 6 to < 7	pH 7 to 8
Zn2+ (µg/l)	154	41.4	99	11

1. Zinc in powder form

 The harmonised classification of CLP Annex VI is applied:

“Zinc powder - zinc dust (stabilised): H400 - H410 (very toxic to aquatic life with long lasting effects)”.

 (NB: The pyrophoric form of zinc powder is not covered in this dossier).

M-factors self-assessment:

• Acute M factor = 10
  Referring to the acute aquatic ERVs of 41.4 µg Zn/L and 154 µg Zn/L defined for the Zn²⁺ ion at pH 8 and 6, respectively, the M-Factor for acute aquatic effect of zinc powder/dust is self-assessed as being 10, using the most conservative value obtained at pH 8.


• Chronic M-factor = 1

Referring to the chronic aquatic ERV values for pH 6 (99 µg Zn /L) and pH 8 (11 µg Zn/L), the M-factor for chronic aquatic effect of zinc powder/dust is self-assessed as being 1. For this last conclusion, zinc is considered equivalent to being ‘rapidly degradable” in a context of chronic classification. For the scientific background documenting this conclusion, please refer to IUCLID section 13.2: “Removal from the Water Column_Nov_2021_IZA”.

1. Zinc in massive form

To check the potential classification, the TD results obtained on zinc in massive form at different pH are compared with the acute and chronic ERVs, set at the corresponding pH. Based on these data, the Critical Particle Size is calculated. Critical Particle Size (CPS) is the size of a particle (massive, powder or alloy) above which an insufficient number of ions is produced in an aqueous medium at the highest loading of the metal (i.e. is 100 mg/L for acute20 and 1 mg/L for chronic) to reach the ecotoxicity reference value (i.e. above which a downgrading in classification or a no classification result is obtained). For standardization it is assumed that the particle size is spherical so that the CPS can be expressed as a diameter. The benefit of this approach is that it allows for comparison on an equal basis between different metals and particle sizes of the same metal. The CPS of massive zinc in presented in Table 2 for the different scenarios.

Table 2. Summary of results on critical particle sizes (diameter in mm) of massive zinc spheric particles in aqueous medium under different conditions of pH and time.

Test condition	Critical Particle Size (CPS in mm)
Acute: 7-d at pH 6	0.12
Acute: 7-d at pH 8	0.09
Chronic: 28-d at pH 6	0.77
Chronic: 28-d at pH 8	0.56

The results show that for all scenarios the CPS is smaller than 1mm. Dissolution of zinc is inversely related to particle size, so at 1mm and bigger size, the ERVs under different conditions are not reached.

• Zinc in massive form is not classified for aquatic effect.

Supporting information:

For a detailed description of the TD tests and results, the CPS concept, and the calculations of the different scenarios, please refer to IUCLID section 13.2, “Classification of Zinc_Nov_2021_IZA”).

The powder and massive form of zinc can and are considered separately for the classification of zinc metal for aquatic effects, since the criteria of the Guidance on the Application of the CLP Criteria (Guidance to Regulation (EC) No 1272/2008 on classification, labelling

and packaging (CLP) of substances and mixtures - Version 5.0 - July 2017, section IV.5.5) are fulfilled:

• A recent survey of the EU market confirms that massive zinc is produced in the EU in big blocks or plates (see for details IUCLID section 13, document: “IZA 2021: Classification of zinc powders and zinc in massive form, Annex 1.”)


• Zinc powder is produced exclusively by the process of atomization, that involves a specific industrial production technique in specially designed apparatus. Zinc powders are not produced by the normal handling and use of the massive form.


• Massive zinc is not polished, ground, machined or handled in any other way that may give rise to small (e.g., <1 mm) particles. Under conditions of normal handling and use, zinc in massive form is melted by the industrial processes of the primary zinc users (e.g., galvanisers, alloyers, manufacturers of semi-finished products such as rolled zinc).


• The evidence on Transformation/Dissolution (TD) on zinc powder and zinc in massive form, obtained according to standard OECD 29 testing and summarized in IUCLID section 4.8., demonstrates the significantly lower potential for Zn²⁺ ion release from the massive form, as compared to the zinc powder.