Zirconium propionate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.79 mg/L

Assessment factor:

1 000

PNEC freshwater (intermittent releases):

7.9

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.079 mg/L

Assessment factor:

10 000

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

7.9 mg/L

Assessment factor:

100

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

2.95 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.3 mg/kg sediment dw

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:

0.2 mg/kg soil dw

Assessment factor:

1 000

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read-across approach

There are no ecotoxicological data available for zirconium propionate (CAS: 84057-80-7) and in the assessment of the ecotoxicity of this substance, a read-across approach from data for the metal cation and the organic anion is followed. This read-across strategy is based upon the assumption that upon release to the environment and dissolution in aqueous media, zirconium propionate will dissociate and only be present in their dissociated form, i.e. as zirconium and propionate ions.

Upon dissolution in water, it is indeed predicted that metal carboxylates dissociate completely into the metal cation and the organic anion at environmentally relevant conditions. Information on the stability constant of zirconium propionate predicts that in a standard ISO 6341 medium (2 mM CaCl₂, 0.5 mM MgSO₄, 0.77 mM NaHCO₃ and 0.077 mM KCl, pH 6 and 8) propionic acid has no potential for complexing zirconium ions in solution (<1% of total metal concentration complexed at 0.001 mM Zr; Visual minteq. Version 3.0, update of 18 October 2012. http://www2.lwr.kth.se/English/OurSoftware/vminteq/index.html).

The fate and behaviour (e.g. partitioning) in the environment for zirconium and the propionate anion are predicted to be significantly different from each other, resulting in a different distribution over the environmental compartments (water, air, sediment and soil). Because the relative exposure to both constituent ions is hence predicted to be different from the original composition of zirconium propionate, data for the ecotoxicological properties of this substance tested as such are considered less relevant for its environmental effects and risk assessment and a read-across approach to separate data for both zirconium and the propionate anion is preferred.

For most metal-containing compounds, it is the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of ecotoxicological concern. In water, liberated zirconium ions however precipitate as ZrO₂ or Zr(OH)₄ at environmentally relevant pH values, resulting in extremely low dissolved zirconium concentrations. This precipitation is controlled by the environmental conditions, irrespective of the original zirconium compound dissolved. Therefore, ecotoxicity data for ZrO₂ can be directly used in a read-across approach for assessing the effects of zirconium from zirconium propionate. As a conservative approach also the ecotoxicological properties of the carboxylic acid are considered in the effects assessment.

According to the REACH Guidance on information requirements and chemical safety assessment, chapter B.8 Scope of exposure assessment, an environmental exposure and risk assessment is mandatory for a substance if it is classified as hazardous to the aquatic environment or if it has another classification and an aquatic PNEC can be derived. The threshold for PNEC derivation is not reported in the guidance, and was set at the limit test concentration for acute toxicity tests with fish, daphnids and algae, i.e. 100 mg/L. Therefore if a substance is not classified as dangerous for the aquatic environment, but meets the criteria for at least one of the other hazard classes or categories and has L(E)C50 values <100 mg/L, it was still considered for the environmental exposure assessment.

According these rules, both the zirconium and propionate moieties of zirconium propionate do not require an environmental exposure and risk assessment. Zirconium does not have any classification under CLP while propionic acid has an official Annex VI classification (Skin Corr. 1B) but has no key L(E)C50 values for effects on aquatic organisms <100 mg/L (Table 1).

Table 1: Acute toxicity data for the constituent ions of zirconium propionate to aquatic organisms (only most sensitive species per trophic level).

Trophic level	Endpoint	Propionic acid (CAS: 79-09-4)	Zirconium dioxide (CAS : 1314-23-4)
Fish	96-h LC50	>10,000 mg/L (Leuciscus idus)	>100 mg ZrO2/L (Brachydanio rerio)
Aquatic invertebrates	48-h EC50	>500 mg/L (Daphnia magna)	>100 mg ZrO2/L (Daphnia magna)
Algae	72-h ErC50	>500 mg/L (Desmodesmus subspicatus)	>100 mg ZrO2/L (Desmodesmus subspicatus)

Conclusion on classification

The substance zirconium propionate will completely dissociate into zirconium and propionate ions after dissolution in water and hence can be regarded as a mixture of both constituent ions. In the absence of toxicity data for zirconium propionate itself, its classification for environmental hazards is based on the classification of its moieties (zirconium and propionic acid). Both zirconium and propionic acid are not classified as hazardous to the aquatic environment, and therefore, it is concluded that zirconium propionate is not classified as hazardous to the aquatic environment.