151. Microplastic pollution : from nanoscale surface interactions to public perceptions
- Author
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Burrows, S., Galloway, Tamara, and Thomas, Kevin
- Abstract
This is an interdisciplinary investigation into microplastic pollution, expanding knowledge of weathering, surface interactions and science communication using a combination of environmental, material and social science. Microplastics are small items of plastic, <5 mm in diameter, that are released into the environment at this size or break down from larger plastic litter items. Their presence in the environment is concerning due to their associated risk to humans and to wildlife. Understanding the interactions of microplastics with the environment around them is key to understanding their fate, degradation and sorption behaviour. Likewise, understanding microplastics within a broader context, including public perception and science communication, is key to more effective approaches towards their mitigation. This thesis is an investigation in two parts: Firstly a laboratory based investigation into microplastic surface interactions; Secondly an investigation into public perceptions of microplastic pollution and the role of science communication. A literature review was conducted critically evaluating three techniques suitable for studying microplastic surfaces: atomic force microscopy, pyrolysis-gas chromatography-mass spectrometry and whispering gallery mode optical nanosensing. Atomic force microscopy, in combination with Fourier-transform infrared spectroscopy, was then used to explore the weathering effects of ultraviolet light on the surface physicochemical properties of test microplastics, measuring surface roughness and carbonyl index of particles exposed to varying UV light spectra. Results found overall that surface oxidation broadly had a negative relationship with surface roughness, causing a surface smoothing effect. Wavelengths <340 nm were found to exert the most significant increases in surface oxidation on high-density and low-density polyethylene, while >340 nm generated the most significant increases in surface oxidation on polystyrene. Study results also highlighted that distribution of photooxidation depended on particle surface topography and additive composition. The study concluded that exposures to difference light spectra are significant to the weathering pathways of microplastic surfaces, as are initial characteristics from surface roughness to additive content. Therefore, these variables must be considered to generate comparable and environmentally relevant material. The impact of weathering on protein sorption was subsequently examined using spectrophotometric methods, to measure the sorption of collagen onto previously photooxidised microplastics. Results showed that heterogeneous surface hydrophobicity, caused by increased surface oxidation, promoted collagen sorption up to a threshold hydrophilicity, beyond which more hydrophilic surface sites are not a limiting factor or become detrimental to collagen sorption. Data collected also indicated that increased surface roughness hinders intermolecular bonding of sorbed collagen. The study concludes that surface oxidation state and roughness impact the sorption behaviour of weathered microplastics. In the context of the previous chapter, without consideration of these variables impacting microplastic weathering (light spectra, additive content, surface roughness), inaccurate conclusions may be drawn regarding sorption behaviour. This is important due to the impact of such sorption behaviours affecting elements of microplastic risk (e.g. particle translocation). Effective communication of actions towards the mitigation of microplastic pollution requires an understanding of the perspectives of public groups. Here a survey of Australian perspectives regarding microplastic pollution is presented. The results revealed insights including that < 25% of Australians knew what microplastics were and that using more biodegradable plastic was perceived as effective as reducing use. This data provides evidence that science communication, relating from microplastic definition to efficacy of solutions have space for improvement. The survey also concludes factors such as media narrative and greenwashing from industry messaging have influenced public perception of microplastic pollution. This study is accompanied by discussion of how and why interdisciplinary working can promote outgroup communication. This is important as if the goal of environmental science communication is to encourage more behavioural change to facilitate sustainable outcomes, then the largest gain lies with perceived outgroups of the science communicator. A review of global plastic labelling follows, including recommendations on potential improvements with sustainability scales, regionally relevant directions for disposal and a list of incorporated additives. This thesis expands knowledge of microplastic surface interactions and public perceptions. Finding that light spectra, surface roughness and additive content can all impact microplastic weathering pathways, and as the weathered characteristics of microplastics impact sorption, these variables may be confounding factors in research towards understanding the risk posed by weathered microplastics. The thesis also found communication regarding what microplastics are to Australian publics has been relatively poor, and messaging from industry and Government influences perceptions of microplastic pollution (including hope it will be addressed). A conceptual model of microplastic degradation is described, informed by thesis data and previous literature. Collating the thesis findings together highlights the value of interdisciplinary work, towards addressing assumptions and oversimplifications common in the field by removing the academic siloing which generates these issues.
- Published
- 2023