Civil Engineering ETDs

Publication Date

Spring 3-8-2022

Abstract

This study identified microplastics and heavy metals in fields sites of freshwater systems in New Mexico and evaluated the interactions of arsenic (As) and uranium (U) with commercial microplastics for acidic and neutral pH in laboratory-controlled conditions. The potential interaction of microplastics with other contaminants is not well-established. Microplastics could interact with heavy metals in ecosystems with naturally elevated background concentrations of metals or affected by anthropogenic activities. Previous studies have found heavy metal contamination in freshwater systems in New Mexico near abandoned mine sites. The objective of this study is (1) to identify and characterize microplastics from metal contaminated freshwater systems in New Mexico and (2) to evaluate the interaction of As and U with commercial microplastics in laboratory-controlled conditions. Freshwater samples from Tingley Beach, the Rio Grande, and Laguna Pueblo, NM were collected and treated. Stereomicroscopy and micro- Fourier Transform Infrared (FTIR) spectroscopy were utilized to identify microplastics from the field samples while Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was utilized to quantify heavy metals. The laboratory-controlled experiments were conducted with commercial poly(methyl-methacrylate) (PMMA), polyethylene (PE), and polystyrene (PS) microplastics exposed to 0.02 – 0.2 mM of As and U solutions, separately. Field data indicated microplastics occurrence and elevated heavy metal concentrations in freshwater systems in New Mexico. Laboratory experiments showed no interaction of commercial microplastics with As at pH 3 and pH 7 and U at pH 3. However, U precipitates formed at pH 7 and deposited onto the microplastics surface. These results indicate that microplastics can accumulate and may be acting as nucleation site for U precipitates. Aqueous chemistry analyses indicated that the precipitates formed are potentially sodium-compreignacite and schoepite. The results of this study advance the understanding of the occurrence and interactions of microplastics and heavy metals in freshwater systems in New Mexico, potentially facilitating the transport of metals through the environment and increasing toxicity effects.

Keywords

adsorption, heavy metals, spectroscopy, microscopy, uranium, arsenic, precipitation

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Kerry Howe

Second Committee Member

Jose Cerrato Corrales

Third Committee Member

Jorge Gonzalez Estrella

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