Utilization of boron as a critical parameter in water quality evaluation: implications for thermal and mineral water resources in SW Germany and N Switzerland

In order to investigate the application of the elemental abundance of boron and its stable isotopes, B-10 and B-11, for tracing anthropogenic contamination of variably mineralized thermal and mineral waters, B concentrations and isotopic compositions (delta B-11) were determined for sample pairs collected during surveys in 1984-1986 and 1995 from representative wells discharging water from deep crustal reservoirs within the central European crystalline basement and sedimentary cover (SW Germany and N Switzerland). The data presented show that natural temporal variations in the total B contents of thermal and mineral waters are a common feature, which makes it difficult to recognize admixture of extraneous (anthropogenic) components from B concentrations alone. Delineation of the natural versus anthropogenic origin of solutes and quantification of the relative mixing proportions may thus benefit considerably from the utilization of boron isotypes as an additional parameter. Hypothetical mixing scenarios involving various thermal waters and municipal wastewater effluents form the study area, with the latter being characterized by conspicuously light boron isotopic compositions, reveal that, in certain cases, delta B-11 values provide a superior diagnostic tool for detection of objectionable substances derived from the discharge of man-made boron products.