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Environmental fate & pathways

Biodegradation in soil

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Description of key information

No data are put forward as this endpoint is not relevant for lead , and metals in general. 

Key value for chemical safety assessment

Additional information

Pyrochlore:

The overall chemical and physiological properties of pyrochlore are principally characterised by a degree of inertness because of the specific synthetic process (calcination at high temperatures, approximately 1000°C), rendering the substance to be of a unique, stable crystalline structure in which the majority of atoms are tightly bound and not prone to dissolution in environmental and physiological media. This has been shown in transformation/dissolution testing for antimony, in which dissolved Sb concentrations were below 27 µg/L (after 7 days at a loading of 0.1g/L) and 2 µg/L (after 28 days at a loading of 1 mg/L); thus implying a solubility of < 0.03% of antimony. Hence, Sb can be considered as not bioavailable and is not regarded concerning toxicological and environmental effects.

On the other hand, lead dissolution levels were much higher (>2.9 mg/L at a loading of 100 mg/L after 7 days at pH 6; 105 µg/L at a loading of 1 mg/L after 28 days at pH 6) and therefore have to be regarded concerning toxicological and environmental aspects. No substance-specific data on the toxicity of pyrochlore are available, so that instead read-across to lead oxide and sparingly soluble lead compounds was conducted

Annex VIII states that "Further degradation testing shall be considered if the chemical safety assessment according to Annex I indicates the need to investigate further the degradation of the substance. The choice of the appropriate test(s) will depend on the results of the chemical safety assessment."

Waiving of the need for data for this endpoint in the terrestrial compartment may be considered if “The substance is highly insoluble in water), or if “The substance is readily biodegradable” (ECHA 2008, Chapter R.7B – Endpoint Specific Guidance).

However, for an inorganic substance for which the chemical assessment is based on the elemental concentration (i.e., pooling all inorganic speciation forms together), biotic degradation is an irrelevant process: biotic processes may alter the speciation form of an element, but it will not eliminate the element from the terrestrial compartment by degradation or transformation. This elemental-based assessment (pooling all speciation forms together) can be considered as a worst-case assumption for the chemical assessment.