Investigating the Binding Properties between Strontium and Dissolved Organic Matter under the Influence of pH and Ca2+ 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 (Sr2+) and dissolved organic matter (DOM) extracted from soil under the influence of pH and Ca2+ 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 Sr2+. When the pH was 7, the binding coefficient (logKa) 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 Sr2+ than under acidic and alkaline conditions. Ca2+ in soil weakened the binding of DOM extracted from soil to Sr2+ by competing for binding sites and changing the molecular surface potential. This research is helpful for acknowledging the migration and transformation of Sr2+ and offers a reference for groundwater protection in karst areas.