A critical evaluation of the available measurements for the stable isotopes of boron

The reported measurements for the stable isotopes of B (¹¹B and ¹⁰B) in natural materials are compiled, critically reviewed and evaluated. The selected values along with a discussion of the error, indicate the potential exists for using B isotopes in interpreting geochemical environments. The isotopic values for δ¹¹B range from -31%₀ for terrestrial rocks to +40%₀ for sea water, relative to NBS SRM-951 which has a reported ¹¹B/¹⁰B ratio of 4.04362 ± 0.00137 (2σ). Furtherm the isotope ratios generally form a narrow cluster of values for specific rock types. In some instances the reported δ¹¹B may be shifted substantially from the mean of “unaltered” rock as a result of weathering or reaction such as the progressive enrichment of δ¹¹B in marine sediments over time due to reaction with sea water.An application of widespread interest is the use of B isotopes in environmental studies. Boron is a contaminant derived from numerous sources such as municipal and industrial waste. The δ¹¹B in these wastes or processed waters is often significantly different from the δ¹¹B of the local ground-water, which will likely reflect the δ¹¹B values of the nearby rocks. This modification by contaminated water can be >20%₀ different from the δ¹¹B of the unaffected water, providing a useful tool in delineating the source of contamination and the direction of migration.