Dimolybdenum trizinc nonaoxide

Ecotoxicological Summary

Conclusion on classification

Acute data is available from three trophic levels (fish, aquatic invertebrates and algae) and chronic data is available for algae. The most sensitive trophic level is algae the results of which are used to consider classification of the substance.

 

As zinc and zinc compounds are generally known to be environmentally toxic, the effect concentrations are based on the measured zinc concentrations. The element molybdenum is not thought to be as ecotoxic and based on the available transformation/dissolution data zinc provides lower solubility values. This would make zinc the most suitable and most conservative for risk assessment purposes.

 

Classification in accordance with the CLP regulation (EC No. 1272/2008, as amended) has been considered with regards to ECHA's Guidance on the Application of the CLP Criteria (Version 5, July 2017). This has a specific section in relation to classification procedures for metals and inorganic metal compounds (Annex IV).

 

The standard aquatic classification procedures are less relevant for such substances as the concept of rapid degradability and bioaccumulation are less appropriate. This is envisaged in the CLP Regulation which states "For inorganic compounds and metals, the concept of degradability as applied to organic compounds has limited or no meaning. Rather, such substances may be transformed by normal environmental processes to either increase or decrease the bioavailability of the toxic species. Equally the use of bioaccumulation data shall be treated with care. Specific guidance has been issued by the European Chemicals Agency on how these data for substance substances may be used in meeting the requirements of the classification criteria".

 

Following the procedure in ECHA guidance:

Aquatic acute classification:

Acute ERV of the compound = Acute ERV of the metal ion; zinc x (MW of the compound/atomic weight of the metal; zinc) = 0.73 mg/L. The metal compound is considered readily soluble as the zinc solubility from the transformation/dissolution study (9.48 - 11.2 mg/L) is greater than the acute ERV value for the dissolved metal ion. As the Acute ERV of the compound is < 1 mg/L, classification as Aquatic Acute.1 is appropriate. An M-factor of 1 is deemed appropriate.

 

Aquatic chronic classification:

Chronic ERV of the compound = Chronic ERV of the metal ion; zinc x (MW of the compound/atomic weight of the metal; zinc) = 0.175 mg/L. As there is insufficient evidence to show rapid environmental transformation, the substance is classified as Aquatic Chronic 2. The chronic ERV of the compound is > 0.1 mg/L and < 1 mg/L.

 

In summary, classification as Aquatic Acute Category 1 (M-Factor 1) and Aquatic Chronic Category 2 are appropriate for this substance.