Zinc dipropionate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

66.67 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

19.74 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

323.62 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

381.23 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

182.85 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

115.21 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

Zinc dipropionate is a metal carboxylate. Metal carboxylates are salts consisting of metal cations and carboxylic acid anions. Based on the solubility of zinc dipropionate in water, a complete dissociation resulting in zinc and propionate ions may be assumed under environmental conditions. The respective dissociation is in principle reversible and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH. However, under environmental conditions, a reunion of the dissociated ions is highly unlikely and it may reasonable be assumed that the respective behaviour of the dissociated zinc cations and propionate anions in the environment determine the fate of zinc dipropionate upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning resulting in a different relative distribution in environmental compartments (water, air, sediment and soil) and subsequently its (eco)toxicological potential.

In the assessment of environmental fate and toxicity of zinc dipropionate, read-across to the assessment entities soluble zinc substances and propionate is applied since the individual ions of zinc dipropionate determine its environmental fate and toxicity. Since zinc ions and propionate ions behave differently in the environment, in respect of their fate and toxicity, a separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

In order to evaluate ecotoxicological properties of the substance zinc dipropionate, information on the assessment entities zinc cation and propionate anion were considered. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely "Read-across concept Category approach for zinc dipropionate".

Conclusion on classification

Aquatic toxicity studies with zinc dipropionate are not available. The fate and toxicity of zinc dipropionate in the environment is most accurately evaluated by separately assessing the fate of its moieties zinc and dipropionate. Zinc dipropionate dissolves and dissociates into zinc and propionate ions upon contact with an aqueous medium. Therefore, the aquatic hazard potential is assessed based on the toxicity data available for the assessment entities zinc and propionate ions since the ions of zinc depropionate determine its environmental fate and toxicity.

Existing environmental classification of propionate, respectively propionic acid:

Propionic acid is not classified for environmental hazards.

Existing environmental classification of zinc respectively, zinc oxide:

Zinc oxide was classified N; R50-53 (Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment) according to Annex 1 of Directive 67/548/EEC (ECB 2008).

Accordingly, under CLP, this classification listed in Annex I to Directive 67/548/EEC was translated as H400 - H410 (very toxic to aquatic life with long lasting effects) according to Annex VI of the EU CLP Regulation (EU 2008).

The M-Factor for the acute aquatic effect of zinc oxide is 1, referring to a) the acute aquatic ecotoxicity values of 136 μg Zn/L and 413 μg Zn/L for the zinc ion at pH 8 and 6 respectively, and b) the molecular weight ratio of zinc oxide versus the Zn⁺⁺ ion (136 x MW (ZnO) / MW (Zn) = 136 x 81/65 = 169.5 μg substance/L at pH 8 as worst case).

The M-factor for chronic aquatic effect of zinc oxide is 1, referring to a) the lowest chronic aquatic ecotoxicity value observed for the algae Pseudokircherniella subcapitata (19 μg Zn/L) at neutral pH. The molecular weight ratio of ZnO versus the Zn would lead to a chronic ecotoxicity reference value of 19 μg/L x MW ZnO/MW Zn = 19 x 81/65=23.5 μg substance/L. This reference value is in any case less than factor 10 different from the criterion for chronic 1 classification for aquatic effect (being 10 μg/L or 100 μg/L depending on whether or not the substance is considered rapidly degradable).

In conclusion, zinc oxide is classified under CLP as H400, H410. The M-factor for both acute and chronic aquatic effects is 1.

- Further considerations on the classification of Zinc oxide based on recent information:

Taking into account the lowest chronic ecotoxicity value observed on a wide variety of species of different taxonomic groups (19 μg Zn/L), it can be reconsidered what exactly the level of chronic classification of the substance should be:

As was mentioned above with the reference value for the substance is 23.5 μg Zn/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 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 exert a chronic effect) or would be rapidly removed from the water column. In this concept, "rapid removal" (defined as >70% removal within 28 days) is considered as equivalent to "rapidly degradable". Under section 4.6., the rapid removal of zinc from the water column is documented.

Consequently, zinc is considered as equivalent to being "rapidly degradable" in the context of classification for chronic aquatic effects.

Considering this, in combination with the abovementioned chronic ecotoxicity reference value for zinc oxide of 23.5 μg/L, the classification of the substance for chronic aquatic effect should be "chronic 2", rather than the "chronic 1" classification in Annex VI of the CLP.

Classification of zinc dipropionate:

Zinc dipropionate is classified in acute aquatic hazard category 1 (H400) and chronic aquatic hazard category 2 (H411).

The water solubility of zinc dipropionate is 40.5 g/L at 30°C. Upon dissolution in aqueous media, zinc dipropionate liberates zinc cations and propionate anions. Thus, under environmental relevant conditions, the overall ecotoxicity of the dissociated zinc dipropionate can be interpolated by assessing the ecotoxicity of the individual moieties. As the propionate moiety does not pose a hazard to the environment - propionate respectively propionic acid is rapidly degradable and with a log Pow of 0.33 it is not expected to bioaccumulate. The LC50 value for fisch (> 10.000 mg/L) as well as the EC50 values for crustaceas and algae (both > 500 mg/L) and the EC20 value for algae toxicity which can be taken as a dose descriptor for chronic effects are considerably above the limit doses of the respective guidelines and considerably above the cut values for classification an acute or chronic hazard to the aquatic environment. Thus, it can be concluded that propionate does not pose a hazard to the aquatic environment. The aquatic toxicity of zinc dipropionate is solely driven by the zinc moiety.

The M-Factor for the acute aquatic effect of zinc dipropionate is 1, referring to a) the acute aquatic ecotoxicity values of 136 μg Zn/L and 413 μg Zn/L for the zinc ion at pH 8 and 6 respectively, and b) the molecular weight ratio of zinc dipropionate versus the Zn⁺⁺ion (136 x MW (Zinc dipropionate) / MW (Zn) = 136 x 212/65 = 443,6 μg zinc dipropionate/L at pH 8 as worst case) leading to the acute aquatic hazard category 1 (H400).

The M-factor for chronic aquatic effect of zinc oxide is 1, referring to a) the lowest chronic aquatic ecotoxicity value observed for the algae Pseudokircherniella subcapitata (19 μg Zn/L) at neutral pH. The molecular weight ratio of Zinc dipropionate versus the Zn would lead to a chronic ecotoxicity reference value of 19 μg/L x MW zinc dipropionate/MW Zn = 19 x 212/65=62 μg zinc dipropionate/L. Which leads unter the consideration of the rapid removal of zinc from the water column which is equivalent to being "rapidly degradable" to the chronic aquatic hazard category 2 (H411).