Investigating the Binding Properties between Strontium and Dissolved Organic Matter under the Influence of pH and Ca 2+ in a Typical Karst Area, China

Due to the unique hydrogeological environment of karst areas, pollutants are more likely to enter the soil and water, showing a special migration and transformation behavior. In this work, the binding behaviors between strontium (Sr 2+ ) and dissolved organic matter (DOM) extracted from soil under the influence of pH and Ca 2+ in a typical karst area were investigated by applying three-dimensional fluorescence spectroscopy combined with parallel factor analysis (EEM–PARAFAC) and two-dimensional correlation analysis (2D-COS) of synchronous fluorescence spectra (SF). The results show that DOM extracted from soil was dominated by tryptophan-like and tyrosine-like materials (77% in total). Two-dimensional COS of SF showed that the tryptophan-like substance in DOM extracted from soil preferentially bound to Sr 2+ . When the pH was 7, the binding coefficient (log K a ) of the four DOM components ranged from 2.69 to 4.04, which was more conducive to the binding of DOM extracted from soil and Sr 2+ than under acidic and alkaline conditions. Ca 2+ in soil weakened the binding of DOM extracted from soil to Sr 2+ by competing for binding sites and changing the molecular surface potential. This research is helpful for acknowledging the migration and transformation of Sr 2+ and offers a reference for groundwater protection in karst areas.