Boron Isotope Application for Tracing Sources of Contamination in Groundwater

Boron isotope composition and concentration of sewage effluent and pristine and contaminated groundwater from the Coastal Plain aquifer of Israel have been determined. The application of boron compounds, especially sodium perborate as a bleaching agent in detergents, leads to an enrichment of boron in wastewaters. Anthropogenic boron in wastewater is isotopically distinct from natural boron in groundwater and thus can be utilized to identify the source of contamination. It is shown that δ¹¹B (where δ¹¹B = [((¹¹B/¹⁰B)_sample/(¹¹B/¹⁰B)_{NBS 951}) - 1] × 1000) values of raw and treated sewage effluents from the Dan Region Sewage Reclamation Project (δ¹¹B = 5.3-12.9%₀) overlap those of natural nonmarine sodium borate minerals (-0.9%₀ to +10.2%₀) but differ significantly from those of regional uncontaminated groundwater (~30%0) and seawater (39%₀). Groundwater contaminated by recharge of treated sewage yields a high B/Cl ratio with a distinctive anthropogenic isotopic signature (7-25%₀). Elemental B and δ¹¹B variations reflect both mixing with regional groundwater and boron isotopic fractionation associated with boron removal by adsorption onto clay minerals. The distinctive isotopic signature of anthropogenic boron can be recognized, however, in most samples and differs significantly from those of natural sources of contamination in the Coastal Plain aquifer of Israel, such as marine-derived saline groundwater (35-60%₀). This enables utilization of the boron isotope composition of groundwater as a tracer for identification and quantification of contaminants in groundwater.