On Airborne Tire Wear Particles along Roads, Labeling Microplastics with Fluorescent Dyes, Microplastics in Wastewater Treatment Plant and Beach Sand, and Microplastic-Mercury Affinity

Author

Zhiqiang GaoFollow

Date of Award

1-1-2022

Document Type

Dissertation

Degree Name

Ph.D. in Chemistry

First Advisor

James Cizdziel

Second Advisor

Walter Cleland

Third Advisor

Amal Dass

School

University of Mississippi

Relational Format

dissertation/thesis

Abstract

Microplastics (MPs) with sizes of 1 μm to 5 mm that are intentional manufactured or result from fragmentation of large plastic debris are widely recognized as a global pollutant. The distributions and concentrations of MPs in environmental and biological systems as well as their toxicity are not well understood. This dissertation details five studies providing new insight and methods on (1) the occurrence and characteristics of airborne tire wear particles (TWPs) along roads, (2) manufacturing and labeling of MPs with fluorescent dyes, (3) fate of MPs in a secondary wastewater treatment plant (WWTP) at the University of Mississippi, (4) distribution of MPs in beach sand from Sardis Lake, and (5) affinity of mercuric ions to MPs.

(1) TWP abundances (i.e., deposition rates and mass concentration) increase with proximity to the road and with traffic volume, as well as vehicle braking. Based on single particle SEM-EDX analysis and machine learning, we found particle sources at the high- and moderate-traffic roads were alike: TWPs (~38%) > biogenic (~35%) > minerals (~24%), and metallic (~3%).

(2) The staining efficacies of Nile red and textile dyes (iDye pink dye, iDye blue dye, Rit pink dye, and Rit blue dye) were significantly affected by dye concentration, incubation time, and temperature, with red fluorescent signals stronger than green ones. While Nile Red still remains the optimal choice for MP staining, pink textile dyes represent a cheaper option.

(3) Concentrations of putative MPs in the influent increased with increasing population on campus. However, we observed a higher abundance of MPs in the treated effluent during a low-flow period compared to normal- and high-flow days, which may have resulted from the increased retention time of activated sludge during the low-flow period. The most abundant polymer was polyester in all compartments, including the effluent. Therefore, more attention is needed to reduce polyester fibers entering to WWTPs and natural environment.

(4) The concentration and distribution of MPs on the beach was greatly influenced by the dam’s discharge rates. Concentrations of MPs varied with proximity to the shoreline, with the highest abundance in the wrack zones and the lowest in areas between them. We observed low concentrations of high-density polymers suggesting that they are sinking to the bottom of the lake as opposed to washing up on shore.

(5) Hg showed good affinity to artificially weathered (30% H2O2 + sunlight) MPs, WWTP-based MPs, and sediment, mainly through pore filling and electrostatic interaction. Environmental factors (e.g. pH, salinity) significantly affected Hg adsorption onto MPs. WWTP-based PE released the largest proportion of Hg, followed by w-PA and w-PEST in freshwater and simulated avian digestive conditions. Our study highlights the potential for MPs to act as vectors for increasing uptake of Hg, particularly naturally weathered plastic particles.

Recommended Citation

Gao, Zhiqiang, "On Airborne Tire Wear Particles along Roads, Labeling Microplastics with Fluorescent Dyes, Microplastics in Wastewater Treatment Plant and Beach Sand, and Microplastic-Mercury Affinity" (2022). Electronic Theses and Dissertations. 2503.
https://egrove.olemiss.edu/etd/2503