MEASURING THE ADHERENCE OF CARBOXYLATED AND NON-FUNCTIONALIZED POLYSTYRENE MICROSPHERES ONTO A KARST SEDIMENT

Particle movement and processing in karst aquifers has received comparatively less attention than solute and aqueous transport. Since sediment can act as a sorption site for some contaminants and move them through the aquifer, it is important to understand how particles are transported in karst aquifers. Microspheres (laboratory engineered particles ranging from <1 um – 1,000 um with a variety of surface charges and fluorescent tags) offer an opportunity to study particle movement in karst aquifers via laboratory batch experiments and multitracer field tests. Several researchers have used microspheres in multitracer field experiments to better understand particle movement in karst aquifers with respect to bacterial motility. Many of these experiments resulted in low recovery of microspheres which was attributed to sorption of the spheres onto aquifer sediments or mineral surfaces, yet few researchers carried out sorption trials to quantify the adherence. Here, we measure the adherence of 1-um, yellow-green, fluorescent carboxylated and non-carboxylated microspheres on a karst sediment collected from a limestone cave in Monroe County, WV. Initial concentrations and supernatant concentrations of microspheres were measured using an LSR Fortessa Analyzer. Preliminary results indicate that sorption of non-functionalized microspheres in a deionized water-sphere based solution was between 53% - 97% with K_D = 33 and in a CaCO₃-sphere based solution was 55% - 75% with K_D = 52. The adherence of carboxylated microspheres in deionized water-sphere based solution ranged from 37% - 62% with K_D = 22 and in a CaCO₃-sphere based solution, adherence ranged from 93% - 98% with K_D = 231. The pKa of various carboxylic acid groups lies between pH 4-5 thus the increase in adherence of carboxylated microspheres may indicate that the pH of karst waters, generally being higher than pKa of the carboxylated groups, results in the dissociation of an H+ ion from the carboxyl group (COOH) and increased sorption of microspheres.