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Environmental fate & pathways

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Read across approach:

In the assessment of the environmental fate and behaviour of barium substances, a read-across approach is applied based on all information available for inorganic barium compounds. This is based on the common assumption that after emission of metal compounds into the environment, the moiety of toxicological concern is the potentially bioavailable metal ion (i.e., Ba2+). Thedissolution of barium substances in the environment and corresponding dissolved Ba levels are controlled by the solubility of barite (BaSO4) and witherite (BaCO3), two naturally occurring barium minerals (Ball and Nordstrom 1991; Menzie et al, 2008), and the concentration of dissolved Ba cations in freshwater is rather low. However, in the dissolved state, the divalent barium cation, is the predominant form in soil, sediments and water. The solubility of barium compounds increases as solution pH decreases (US EPA, 1985a). Nevertheless, the speciation of barium in the environment is considered to be rather simple (USEPA 2005):

-         Barium cations are not readily oxidized or reduced

-         Barium cations do not bind strongly to most inorganic ligands or organic matter

 

Barium  in soils  is not  expected  to  be  very mobile  because of the formation  of water-insoluble salts (sulphate and carbonate) and its inability to form soluble complexes with humic and fulvic materials.  Under acid conditions, however, some of the  water-insoluble  barium compounds  may become soluble and move into ground water (US EPA, 1984).

 

In sum, transport, fate, and toxicity of barium in the environment are largely controlled by the solubility of barium minerals. The barium cation is the moiety of toxicological concern, and thus the hazard assessment is based on Ba2+.

 

US EPA (1985a) Health advisory — barium. Washington, DC, US Environmental Protection Agency, Office of Drinking Water.

 

US EPA (1984) Health effects assessment for barium,Cincinnati, Ohio, US Environmental Protection Agency, Office of Health and Environmental

Assessment, Environmental Criteria and Assessment Office (Prepared for the Office of Emergency and Remedial Responsible, Washington, DC) (EPA 540/1-86-021).

 

Abiotic degradation

The endpoints "Phototransformation of an element in water, soil or air" are not relevant for substances that are assessed using a read-across approach on an elemental basis, i.e., based on the exposure and effects of barium, expressed as elemental barium.

 

The term ‘Hydrolysis’ refers to the “Decomposition or degradation of a chemical by reaction with water”, and this as a function of pH (i. e., abiotic degradation). The need for testing may be waived in accordance with Regulation (EC) 1907/2006, Annex VIII, column 2, if “The substance is highly insoluble in water”, or if “The substance is readily biodegradable”. The latter property of a substance assumes a rapid mineralization of the substance and therefore hydrolysis tests will provide little information.

In the case of barium dichloride the chemical safety assessment is based on elemental metal concentration, i.e., the assessment of barium is conducted regardless of the (pH-dependent) speciation in the environment. Hence, as the assessment is based on the element concentration, physicochemical processes like decomposition and degradation by reaction with water are not relevant. This elemental-based assessment (pooling together of all speciation forms) can be considered as a worst-case assumption for the chemical assessment.

 

In general, (abiotic) degradation is an irrelevant process for inorganic substances that are assessed on an elemental basis.

Biotic degradation

For inorganic substance like barium salts 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, regardless of the environmental compartment that is under consideration: biotic processes may alter the speciation form of an element, but it will not eliminate the element from the aquatic 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.