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Environmental fate & pathways

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Read-across approach

In the assessment of the environmental fate and behaviour of Bi and Bi compounds, a read-across approach is followed based on all information available for inorganic Bi compounds. This grouping of bismuth compounds for estimating their properties is based on the assumption that properties are likely to be similar or follow a similar pattern as a result of the presence of the common bismuth ion. After emission of metal compounds to the environment, it is indeed the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of toxicological concern.

This assumption can be considered valid when, after emission to the environment, the various Bi compounds do not show differences in speciation of bismuth in the environment.

The reliable data selected for the environmental fate and behaviour of bismuth are all based on monitoring data of ambient elemental bismuth concentrations in water, sediment and suspended matter.

Very limited information is available on the chemistry of Bi in the environment. Bismuth can exist under the following oxidation states: 0, +III and +V. No information on measured Bi-speciation in water is available, and it will be assumed that Bi3+ is the dominant species under the prevalent environmental conditions. A Pourbaix diagram, showing the oxidation state and major species of bismuth as a function of pH and reduction potential indeed predicts that trivalent Bi is dominant under conditions commonly found in oxic fresh waters, i.e., pH between 5 and 9; redox potential [Eh] between 0.5 and 1 V. It is assumed that upon dissolution of bismuth substances, the environmental conditions control the (redox) speciation of bismuth in water, soil and sediment, regardless of the Bi compound added. Based on the limited data available, it was concluded that the conditions for read-across are met.

Therefore, all data based on monitoring data are used in a read-across approach for inorganic bismuth compounds and results for environmental fate and behaviour are all expressed based on elemental bismuth concentrations.

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