Quantification and Characterization of Nanoparticulate Zinc in an Urban Watershed

Shaun Bevers,Thilo Hofmann,Manuel David Montaño,Laya Rybicki,James F Ranville,Frank Von Der Kammer

doi:10.3389/fenvs.2020.00084

Abstract

The recent expansion in the use of nanomaterials in consumer and industrial applications has led to a growing concern over their behavior, fate, and impacts in environmental systems. However, engineered nanoparticles comprise only a small fraction of the total nanoparticle mass in aquatic systems. Human activities, particularly in urban watersheds, are increasing the population of incidental nanoparticles and are likely altering the cycling of more abundant natural nanoparticles. Accurate detection, quantification, characterization, and tracking of these different populations is important for assessing both the ecological risks of anthropogenic particles, and their impact on environmental health. The urban portion of the South Platte watershed in Denver, Colorado (USA) was sampled for zinc to identify and quantify different nanomaterial sources. Single particle ICP-QMS was employed, to provide single elemental (Zn) signals arising from particle detection events. Coupling spICP-QMS to sample pre-fractionation (sedimentation, filtration) provided some insights into Zn association with nanoparticulate, colloidal, and suspended sediment phases. Single particle ICP-TOFMS (spICP-TOFMS) provided quantification across a large atomic mass range, yielding an even more detailed characterization (elemental ratios) on a particle-by-particle basis, providing some delineation of multiple sources of particles. Across the watershed, on average, 21% of zinc mass was present as zinc-only particles with a rather uniform mean size of 40.2 nm. Zinc that was detected with one or more other elements, primarily Al, Fe, and Si, is likely to be present as heteroagglomerates or within mineral colloids. Although spICP-TOFMS provides a substantial amount of information, it is still in its early stages as an analytical technique and currently lacks the requisite sensitivity to study the smallest of nanoparticles. As this technique continues to develop, it is anticipated that this methodology can be broadly applied to study sources, behavior and effects of a disparate variety of nanoparticles from both geogenic and anthropogenic origins.

Highlights

The combination of increasing global human populations, combined with rising urbanization have placed stress on urban watersheds through the direct influx of anthropogenic contaminants and other man-made influences (Baalousha et al, 2016; Zheng et al, 2019)
In addition to intentionally engineered nanoparticles (ENPs), urban centers serve as a source of incidental nanoparticles (INPs) that are unintentionally produced from human-driven processes such as vehicle emissions, (Gonet and Maher, 2019) tire wear, (Sommer et al, 2018) and road dust (Yang et al, 2016)
Total recoverable mass concentrations for those elements that were examined by spICP-MS are given in Table 1, with major cation concentrations provided in ESI

Summary

Introduction

The combination of increasing global human populations, combined with rising urbanization have placed stress on urban watersheds through the direct influx of anthropogenic contaminants and other man-made influences (Baalousha et al, 2016; Zheng et al, 2019). In addition to intentionally ENPs, urban centers serve as a source of incidental nanoparticles (INPs) that are unintentionally produced from human-driven processes such as vehicle emissions, (Gonet and Maher, 2019) tire wear, (Sommer et al, 2018) and road dust (Yang et al, 2016) These man-made particles infiltrate urban streams via storm water, adding to the naturally occurring nanoparticulates (NNP) load present from bio- and geogenic sources (Hochella et al, 2008, Hochella et al, 2019). A likely explanation is that part of the Zn measured in the raw sample is associated (either adsorbed or as a minor component) of larger minerals and hetero-aggregates These larger particles containing low amounts of Zn could avoid detection as a resolvable Zn particle by the spICP-QMS. This approach allows one to use spICP-QMS to gather more indirect evidence on the nature of metal-containing NPs and leads direct to the obvious need for multi-element NP analysis

Methods

Results

Discussion

Conclusion