- Title
- Environmentally relevant risk assessment of microplastics and complex chemical mixtures in the marine environment: implications for trophic transfer and human health
- Creator
- Carbery, Maddison
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Plastic waste generation is a global problem, affecting all life on Earth. Marine plastics are particularly problematic, due to the role of the marine environment as a sink for plastic pollution. Globally, just 9% of plastic waste is recycled, 12% incinerated and 79% sent to landfill or lost to the environment. Best estimates suggest that between 4 – 12 million tonnes of plastic waste enter the oceans every year, where ageing and weathering processes transform plastic debris into an infinite number of small plastic particles, known as microplastics (MPs, < 5 mm in size). Microplastics are problematic due to their small size, chemical vector potential and resemblance to natural prey items, providing a pathway for MPs to enter into marine food webs. A major concern surrounding microplastic ingestion by marine organisms is the capacity for chemical additives and sorbed contaminants to desorb from ingested MPs in the gut, where they may bioaccumulate in organs and tissues. Weathering is anticipated to enhance the release of hazardous additives and monomers, and adsorption-desorption of potentially toxic chemicals in the environment and biota. However, little information currently exists on the long-term behaviour and fate of marine MPs to support this hypothesis. Consequently, we highlight a significant knowledge gap regarding the natural ageing and weathering progression of marine microplastics and the role of weathered MPs as a vector of toxic chemical contaminants to marine food webs. Much of the plastics literature focuses on the impacts of pristine primary MPs which have little relevance to real environments, leading to a significant knowledge gap in the behaviour, fate and effects of environmentally relevant plastic particles. In order to understand the full impact of plastic particle toxicity, we must move past virgin plastic studies and begin to consider the effects of ageing and weathering. Furthermore, Australia has the largest ocean territory in the world, yet limited information exists on the occurrence and distribution of microplastics within Australian marine environments. Therefore, the primary aim of this thesis was to investigate the effects of ageing and weathering processes on the behaviour and fate of microplastics in Australian marine environments, to better understand the role of microplastics as vectors for toxic contaminants and their subsequent risks to marine organisms, food webs and environmental health. A series of sequential investigations were used to generate environmentally relevant data on the physicochemical properties of long-term weathered microplastics. The methodical approach consisted of desktop-based research, field surveys and controlled field experiments incorporating marine fieldwork, analytical chemistry, statistical analysis and modelling. Chapter 2 summarises existing information on the occurrence, distribution, physicochemical characteristics and environmental behaviour and fate of MPs in marine environments and highlights the need for research into the potential for weathered microplastics to transport toxic chemical mixtures to marine organisms and food webs. Chapter 3 reports the occurrence and characteristics of MPs on Australian shorelines and reveals that plastic particles associated with industrial locations contained elevated levels of toxic metal(loid)s compared with those from other land uses, confirming the role of microplastics as a vector for toxic chemical compounds in marine environments. Chapter 4 employs an advanced analytical approach to generate valuable time-series data on the long-term ageing and weathering of microplastics in marine surface water environments. Experimental findings demonstrate that long-term marine ageing and weathering processes modify the physical and chemical properties of the surface and bulk phase of marine microplastics, leading to slow environmental degradation and the release of small plastic particles (<1 μm) to marine surface waters in-situ. Chapter 5 explores the influence of long-term ageing and weathering on the adsorption-desorption kinetics of (in)organic chemical contaminants by environmental MPs, to determine the role of weathered plastic particles as a vector for complex chemical mixtures. The findings indicate that long-term ageing and weathering processes facilitate the adsorption and desorption of organic and inorganic contaminants to microplastics in marine environments, rendering plastics as both a source and sink of complex chemical mixtures. Mean levels of target metal(loid)s, polyaromatic hydrocarbon and phthalates on aged MPs varied by polymer type and/or time, suggesting that the adsorption of inorganic and organic compounds to aged plastics were governed by different mechanisms. Furthermore, some chemicals (e.g. metals) did not reach equilibrium on aged plastics by 12 months, indicating plastics may continue to accumulate toxic chemical mixtures the longer they reside in marine environments. Finally, the significance and limitations of the key findings are discussed in Chapter 6, in terms of their contribution to the current state of microplastics research and the future research priorities. This thesis demonstrates that long-term aged MPs serve as a source and sink for potentially toxic chemical contaminants and plastic degradation products to marine surface water environments, posing a significant risk to marine wildlife. The time-series data generated through this research contributes valuable information on the long-term degradation of marine microplastics and (de)sorption of complex chemical mixtures in-situ and will serve as a baseline for future monitoring of the occurrence, characteristics, behaviour and fate of weathered MPs in marine environments. The outcomes of this research are expected to inform a detailed risk assessment of long-term weathered MPs and guide future policy and management with regards to marine plastic pollution. The findings of this research will inform environmentally relevant exposure studies seeking to address the real risks associated with the uptake and retention of environmental plastic particles by marine biota. Future research into the role of microplastics as a vector for toxic chemical mixtures to marine organisms and food webs is urgently needed to preserve marine biodiversity and safeguard valuable food resources.
- Subject
- ageing; adsorption; chemical contaminants; desorption; food webs; marine; microplastic; weathering; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1513223
- Identifier
- uon:56699
- Rights
- Copyright 2022 Maddison Carbery
- Language
- eng
- Full Text
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