An investigation on the presence and characteristics of microplastics in freshwater sediment in the Vaal River

Simple item page
dc.contributor.authorNdlovu, Michelle
dc.date.accessioned2023-11-17T06:48:13Z
dc.date.available2023-11-17T06:48:13Z
dc.date.issued2022
dc.descriptionA dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, University of the Witwatersrand, Johannesburg, 2022
dc.description.abstractMicroplastics (MPs) have become a bane on the environment for decades, and their impact on freshwater systems is still understudied. With the advancement in research techniques, MPs have been detected in the air, tap water, underground water, food, soil, and human stool. Their potential harmful impacts have drawn significant attention in recent years in the context of environmental protection. In comparison to marine waters, studies of MPs in freshwater sediment are limited. A thorough review of the literature on MPs in freshwater sediment also revealed a lack of standardisation in MP studies, ranging from the true definition of MPs to sampling and analytical methods. In addition to the unavoidable and potentially irreversible ecosystem imbalances caused by MP pollution, the establishment of environmental standard benchmarks and coordinated responses is also hampered by a lack of knowledge on their abundance, distribution, and fate. As such, this study aimed at generating scientific evidence to provide evidence-based recommendations and risk-informed standards to influence and guide policymaking. This project was designed to generate new data on the presence and characteristics of MPs pollution in South African freshwaters, as well as assessing the contribution of land-based activities to MPs pollution in freshwater bodies using the Vaal River as a study case. The main objectives were to determine the presence, abundance, and physical and chemical characteristics (size, shape, colour, and polymer composition) of MPs in sediment samples from the Vaal River. Twenty-five sediment samples were collected from the Vaal River over 3 days using a 500 mL Van Veen grab sampler. Prior to analysis, samples were pretreated for effective MPs extraction and identification. Sample preparation and extraction were performed using modified National Oceanic and Atmospheric Administration (NOAA) laboratory methods for the analysis of the MPs. Samples were first oven-dried to remove moisture, digested using 10% potassium hydroxide (KOH) to remove organic and inorganic matters which may hamper MPs identification, after which, MP particles were separated based on their density. Density separation was conducted using saturated sodium iodide solution (NaI). For MPs analysis, optical microscopy (stereomicroscope) was used to detect and identify MPs in terms of size, shape, and colour. Scanning electron microscopy (SEM) was used to study the surface morphology of the MP particles. The polymer composition was determined by Raman Spectroscopy to identify polymer type. MPs were detected in all samples with varying abundances from 30 to 1096 particles/kg_dry weight (dw) and a mean abundance of 463 ± 284 particles/kg_dw. The examination of the physical properties of MPs revealed a predominance on fragments (63%) and fibers (35%), small-sized particles of less than 0.5 mm (32%), as well as the prevalence of coloured MPs (60%), mostly blue, white, and green. Detected MPs were identified as Polyethylene (PE) “both high and low density”, polypropylene (PP), and polyethylene co-vinyl acetate (PEVA), polyester (PES), polyurethane foam (PU), and polyethylene/hexene-1-copolymer (PEH), according to Raman Spectroscopy analysis. These findings reveal elevated levels of MP contamination within the Vaal, with the prevalence of fragments and fibers (98%) over pellets (2%) indicating that MPs pollution is from secondary sources. Fragments are formed by the breakdown of larger plastic pieces; fibers, on the other hand, are mostly attributed to domestic sewage, and, in this case, it is likely the protracted sewage input around the Vaal triangle. The prevalence of PE, PP, and PEVA is consistent with MPs from secondary sources as they are commonly used in single-use plastic, packing bags, textiles, and containers. These findings provide a benchmark for guiding future monitoring studies and identifying research gaps. In general, anthropogenic activities, including heavy industrial and tourism activities in the area, agriculture, fishing, and wastewater discharge, were identified as potential sources of MPs in this study. The pollution profile, in terms of the physical and chemical properties of the detected MPs, indicates serious threats and health risks. For instance, small-sized MPs that were found to be predominantly abundant in the sediment samples, are considered to be more harmful to aquatic organisms due to their bioavailability (size similarity to natural preys). The large surface area of small MPs also increases the possibility of adsorbing and desorbing other pollutants from the surrounding environment. Coloured MPs may pose additional harm due to the toxicity of most colorant agents. Thus, the high prevalence of small-sized and coloured MPs within the Vaal River is therefore of a particular concern.
dc.description.librarianPC(2023)
dc.facultyFaculty of Science
dc.identifier.urihttps://hdl.handle.net/10539/37022
dc.language.isoen
dc.schoolChemistry
dc.subjectMicroplastics
dc.subjectFreshwater sediment
dc.titleAn investigation on the presence and characteristics of microplastics in freshwater sediment in the Vaal River
dc.typeDissertation
Files
Original bundle
Now showing 1 - 1 of 1
No Thumbnail Available
Name:
MSc Final Submission_Michelle Ndlovu_2511968.pdf
Size:
2.64 MB
Format:
Adobe Portable Document Format
Download
License bundle
Now showing 1 - 1 of 1
No Thumbnail Available
Name:
license.txt
Size:
2.43 KB
Format:
Item-specific license agreed upon to submission
Description:
Download
Collections
ETD Collection