Boron isotopic composition of freshwater lakes from central Europe and possible contamination sources

The boron isotopic compositions of common synthetic boron products, municip al wastewaters from Switzerland, and three Swiss freshwater lakes were inve stigated. The delta(11)B values (delta(11)B values are normalized to the st andard NIST SRM-951) of synthetic Na-borates (-0.4 to 7.6 parts per thousan d) and Ca-Na-borates (-13.4 to -4.9 parts per thousand) overlap with those of natural berate minerals and hence suggest that the isotopic signal of an thropogenic boron is not modified during the manufacturing process. As a re sult it is possible to predict the isotopic composition of synthetic boron products and their potential impact upon contamination of water resources. The delta(11)B values of municipal wastewaters from two locations in northe rn Switzerland (-7.7 to -4.5 parts per thousand) reflect utilization of Na/ Ca- and/or Ca-borates depleted in B-11. Freshwater lakes from Switzerland ( Lake Zurich, Greifensee, Lake Lugano) yielded a delta(11)B range of -1.7 to 7.1 parts per thousand and boron concentrations of 17 to 102 mg L-1. The b oron isotopic ratios decrease with increasing boron concentrations, indicat ing mixing between anthropogenic boron with a low delta(11)B signature and meteoric boron with a heavier isotopic signal. We suggest that the isotopic composition of meteoric boron over central Europe has delta(11)B values in the range of ca. 10 to 20 parts per thousand, whereas in coastal areas the marine component is larger with a higher B-11/B-10 ratio (delta(11)B appro ximate to 30 parts per thousand).