Date of Award

2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Biological and Environmental Sciences

Department

Biological Sciences

First Advisor

Thomas A. Boving

Abstract

Sediments underlay most waterbodies and make up a vital part of aquatic habitats. Due to their physical and chemical properties, sediments can act as a sink for many types of contaminants. Sediments must be routinely assessed for their possible interaction with emerging contaminant classes. But the identification of emerging contaminants in sediments is often hindered by a lack of analytical standards or standardized methods. The research herein develops methods for the detection of two classes of emerging contaminants from sediment, namely microplastics (MPs) and per- and polyfluoroalkyl substances (PFAS). These methods are then used to analyze sediments within the Narragansett Bay watershed, Rhode Island, USA.

The first chapter of this dissertation focuses on microplastics. Microplastics are small (<5 mm) plastic particles which pose a threat to marine ecosystems. Identifying MPs in marine sediments is crucial for understanding their fate and effects. Many MP extraction methods exist, but procedural differences prevent meaningful comparisons across datasets. Chapter one examines the efficiency of five methods for extracting MPs (45–1,000 μm) from marine sediments. Known quantities of MPs were spiked into sediments. The MPs were extracted and enumerated to demonstrate percent recovery. Findings determined that sediment matrix, MP properties, and extraction method affect the percent recovery of MPs from sediments. Average recoveries of spiked microplastics were between 0 % and 87.4% and varied greatly by sediment type, microplastic, and method of extraction. In general, larger particle and lower density MPs were more effectively recovered. Marine sediments low in organic matter and with larger grain size also had higher percent recoveries of MPs. These findings support the need for method optimization and unified procedures.

In chapter two, a hybridized method was developed for the extraction of microplastics (45-1,000 μm) from marine sediments using sodium bromide solution for density separation. Method performance was tested using spiked microplastics as internal standards. The method was then tested by extracting MPs from sediments collected from Narragansett Bay, Rhode Island, USA. Suspect microplastics were analyzed with Raman spectroscopy. Microplastic abundance ranged from 40 particles/100 g sediment to 4.6 million particles/100 g sediment (wet weight). Cellulose acetate fibers were the most abundant microplastic. These results are some of the first data for microplastics in Rhode Island marine sediments.

Chapter three shifts focus to a different class of contaminants: Per- and polyfluoroalkyl substances (PFAS) are a diverse set of synthetic fluorinated chemicals. The use of PFAS in industrial applications predates accessible analytical techniques for their identification in environmental matrices. Therefore, identifying sources of PFAS in environmental matrices can be challenging. Characterizing PFAS from radiometrically dated sediment cores is one mechanism to determine past PFAS deposition and provide a better understanding of the fate of this complex class of contaminants in aquatic environments. In this study, three sediment cores were collected from a dammed section of the Pawtuxet River in West Warwick, Rhode Island, USA. The coring location was chosen for its proximity to former manufacturing facilities suspected to use PFAS. Sediments from the cores were radiometrically dated using 137Cs and 210Pb and analyzed for 24 PFAS compounds using a targeted analytical method. A modified Total Oxidizable Precursor (TOP) assay was performed to identify the presence of PFAS precursors. Suspect and non-targeted analysis was performed to identify additional PFAS missed in targeted analysis. Initial sediment concentrations showed temporal trends of PFAS preserved within the sediment record ranging from <1-50 ng/g sediment. These data identify legacy PFAS compounds previously used in manufacturing processes over several decades, particularly long-chain perfluorinated carboxylic acids (PFCAs). This type of investigation provides a window into the transport behavior and longevity of PFAS once they enter the sedimentary environment.

Available for download on Friday, May 17, 2024

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