Aggregation and Aggregate Strength of Microscale Plastic Particles in the Presence of Natural Organic Matter: Effects of Ionic Valence

Considering the recent plastic loads in water bodies we studied the aggregation, charging, and aggregate strength of polyethylene microsphere (PEM) particles in the presence of natural organic matter (NOM) as a function of KCl and CaCl 2 concentrations. We used the Suwannee river humic acid (SRHA) as NOM and PEM as microplastics. The aggregation was triggered in the presence of CaCl 2 solutions more effectively than KCl due to the divalent bridging and strong electrostatic attraction between Ca 2+ and SRHA as well as between PEM particles. We found that the maximum aggregate strength around 1.87 nN in the presence of 100 mg/L SRHA at 0.5 M CaCl 2 solution. The aggregate strength of PEM particles in the KCl solution was lower than that of CaCl 2 solution, manifesting the more effective bridging flocculation and divalent bridging due to the Ca 2+ ions. Graphic Abstract