With an increase in consumption, and due to a lack of proper disposal protocol, emerging contaminants such as pharmaceuticals and personal care products (PPCPs) are often detected in natural waters. These organic compounds can interact with the aqueous/polymeric interfaces of particulate natural organic matter (NOM) and man-made microplastics prevalent in the aquatic environment. These surface interactions are likely to impact the fate and transport of organic pollutants. In this project, we explored the effect of colloidal size and surface functional group on the binding affinity and adsorption kinetics of select PPCPs. An interfacial selective spectroscopic technique, second harmonic generation (SHG), and a gravimetric method based on quartz crystal microbalance (QCM) have been used to probe adsorption processes <i>in situ</i>. Our results indicate a negligible effect of size on adsorption of a SHG active dye onto polymeric particles in the size range of 300 nm to 1 um. However, a difference in the binding affinity as a function of surface functional group has been observed. More importantly, the structural parameters (e.g., the number of rotatable bonds or RBN) of the organic molecule appears to play an important role in adsorption. Using amlodipine (AMP) and carbamazepine (CBZ), two commonly detected pharmaceutical contaminants, our QCM findings show that there is a clear surface effect on the uptake and binding strength. For example, AMP which has an RBN of 10 shows proclivity for various surfaces, including but not limited to, carboxyl-, phenyl-, and butyl-, aqueous interfaces. CBZ, with zero RBN, exhibits negligible adsorption on the phenyl surface. Real-time binding kinetic studies of these species also reveal that morphology of the polymeric interface (e.g. closely packed vs. non-rigid hair-like structures) dictate the extent of their uptake. These fundamental studies pave the way to better understand the type of surface interactions PPCPs can have with NOM and microplastics. The applicability and challenges associated with these techniques in probing chemistry at soft environmental interfaces will be discussed.

Interactions of organic dyes and pharmaceutical contaminants with model natural organic matter and microplastic polymeric/aqueous interfaces: Effect of particle size and functional group

ACS Spring 2022

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