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Water solubility

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A water solubility study acc. to guideline OECD 105 was conducted and the following conclusion derived: The concept of “equilibrium solubility” is not applicable to metals or metalloids like boron. Instead, it is reasonable to assume that a very thin oxide layer exists on the surface of boron powder particles, and that it is this oxide layer which initially dissolves in water, leading to low but measurable concentrations of dissolved boron in this test (loading of 100 mg boron powder per litre; slow stirring for 72h at 20°C). Based on the measured concentrations of dissolved boron after filtration, approx. 0.155 % (mass) of the boron powder loading were detected as dissolved boron.

These findings are supported by the outcome of the screening (24h) and 7 day Transformation/Dissolution tests that were conducted at a loading of 100 mg/L. At t=0 (immediately after addition of the test item to the test solution), and initial release of approx. 100 µg/L was observed, corresponding to 0.1% of the total loading, but no further increase of dissolved B was noted after 24 hours (pH 6,7,8) or 7 days (pH 6). A full 28d-T/Dp test at a loading of 1 mg/L further confirmed the very low solubility of B (<5 µg/L)

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