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. © 1990.