Use of metal-tagged environmentally representative micro- and nanoplastic particles to investigate transport and retention through porous media using single particle ICP-MS

Abstract

Microplastics and nanoplastics (collectively, MNPs) are increasingly entering soils, with potential adverse impacts to agriculture and groundwater. Environmental detection, characterization, and quantification of MNPs is difficult and subject to artifacts, often requiring labor-intensive separation from environmental matrices. These analytical challenges make it difficult to conduct experiments investigating specific MNP characteristics influencing their transport and fate, particularly when examining multiple plastic types at low concentrations. By synthesizing a suite of metal-tagged polymers, which are cryomilled to create polydisperse fragmented particle suspensions, single particle ICP-MS (spICP-MS) can be used to quantify MNP particle size and concentration in controlled fate and transport studies. Use of unique metal-polymer pairs enables accurate, simultaneous analysis of multiple MNP types which can be used to track total particle transport and retention within a variety of environmental matrices. This was demonstrated using saturated sand column transport experiments to quantify the movement of two plastics having different properties: tin-tagged polystyrene (Sn-PS) and tantalum-tagged polyvinylpyrrolidone (Ta-PVP). The behavior of these polydisperse, fragmented MNPs was compared to that of fluorescent, carboxylated monodisperse PS spherical microspheres (Fl-PS). Mobility of all MNP types increased with decreasing particle size, and hydrophilic Ta-PVP particles migrated more effectively than the hydrophobic Sn-PS particles. Furthermore, the addition of humic acid (HA) to the carrier solution increased the colloidal stability of both metal-tagged MNP suspensions, resulting in much greater elution from the column than in HA-free deionized water or moderately- hard water (ionic strength = 5mM). This combination of particle synthesis and spICP-MS analysis provides insights into the transport of MNP having physical properties that are representative of environmental MNPs and opens up a broad range of applications for study of MNP environmental fate and transport.