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Environmental fate & pathways


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Description of key information

The substance forms reversible equilibria and the proportion of the species present depends on various environmental factors.
There are no proprietary studies investigating the hydrolysis of the substance in aqueous media. The substance is an inorganic element and sufficient information on the speciation of the substance under various environmental conditions is available in the EU RAR for Cr (VI) compounds.

Key value for chemical safety assessment

Additional information

Ionic equilibria for chromium (III)

The predominant forms of chromium (III) present in solution are Cr3+ at very low pH, then with increasing pH, Cr(OH)2+, Cr(OH)2+, Cr(OH)3 and finally Cr(OH)4- at very high pH. The species Cr(OH)2+ is thought to occur only over a very narrow pH range (approximately pH 6.27-6.84).

In solution, the equilibrium between chromium (III) ions and chromium hydroxide lays well over to the side of the relatively insoluble hydroxide at pH>5 according to the following equilibrium:

Cr3++ 3H2O ¿ Cr(OH)3 (s) + 3H+                 Keq = 1.10-12

This means that at pHs >5 chromium (III) can be expected to precipitate out of solution as the insoluble hydroxide, often in conjunction with iron. However, complexation of chromium (III) ions with organic matter (such as citric acid, diethylenetriaminepentaacetic acid (DTPA), fulvic acid) can result in increased solubilisation of chromium (III) at higher pHs.

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