Novel Methods of Microplastic Identification and Mitigation in Water

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  • Luke Fears

    Research areas

  • Microplastics, Wetland, Identification, Mitigation, Pollution, Environment, Nanoplastic

Abstract

Microplastics present an encroaching danger to the health of global and regional ecosystems, including inland freshwater habitats, the organisms that dwell within them, and potentially human health. As such, the need for identification, monitoring, and mitigation of microplastic pollution in aquatic environments has become ever more pressing. With an increasing need to test water samples for microplastic pollution, previously utilised methods prove slow and labour-intensive. This thesis aims to develop a quicker, efficient methodology of filtering water samples for microplastics, utilising the natural fluorescent properties of plastics to allow for a more accurate analysis. Using a mechanical pump glass filtration system, water samples from a selection of sites across the length of Great Britain and In North Wales (and even Corkscrew Swamp in Florida, USA) were filtered through glass fibre filter papers, dried, and examined via dissection microscopy, using the microscope’s own lighting system, and a separate fluorescence lamp (excitation 440 to 460 nm). A significantly (p <0.05) greater quantity of microplastics L -1 were found utilising fluorescence than using the microscope’s light at 7/ 14 sites: Afon Cegin, Chester Reed Bed, Corkscrew Swamp, Lake Windemere, Llyn Cefni, River Black Water, River Thames and Ullswater. A lack of significant difference (p >0.05) was most likely the result of generally low populations of microplastic pollution (e.g., Loch Lomond) or due to issues with tests for significance (e.g., River Irwell, River Tame). The success of this methodology allows for its inclusion alongside other standard water-monitoring processes and infers microplastic levels could be higher than previously anticipated, as previous methods of environmental microplastic identification rarely use fluorescence. However, it is noted that visual inspection should not be utilised as a replacement for chemospectroscopy methods of identification. There is little to no constant monitoring of microplastic levels across the UK coasts, and no previous studies upon the presence of microplastics around the isle of Anglesey, North Wales. Five sites around the Anglesey coast were selected for a pilot study, at three corners of the island (Porth Dafarch, Penmon Point, Cemaes Bay), and two from opposite sides of the Menai Strait (Bangor and Menai Bridge). A significant difference (p <0.05) was found between each of the surveyed sites and control samples of distilled water, verifying the presence of microplastic pollution along the Anglesey coast. A significantly greater average number of microplastics L-1 were found on the Bangor side (7.958 ± 0.52) of the Menai Strait than the Menai Bridge side (2 ± 0.87). The more-populated tourist beach of Cemaes Bay had a higher average number of microplastics L-1 (1.7 ± 0.29) than the less-populated Porth Dafarch (1.1 ± 0.13), but less than the less-populated Penmon Point (1.95 ± 0.27). Causation was 8 speculated to result from human population, distance from shoreline, distance from human habitation, weather, and tidal current speed. The presence of nanoplastics within the Bangor samples was confirmed with high-end fluorescence microscopy. Significantly more fragment-type microplastics than other types were found at every site barring Cemaes Bay. These results demonstrate the need for further sampling for microplastics across not only Anglesey, but across the UK and worldwide. Efforts must be taken to investigate methods to reduce the proliferance of microplastics in the natural environment as potential mitigation strategies to hamper the consequences of MP pollution in a world where single use plastics are pandemic. One such method could be the utilisation of CTWs (Constructed Treatment Wetlands); a cheap, effective, and durable system already successfully being utilised to treat wastewater from industry, and commercial and residential areas. Previous studies have already shown promise, with high microplastic retention rates of CTWs being observed. This study aims to use small-scale CTWs to further bolster these results, prove that treatment works on a smaller scale, and distinguish the effectiveness between wetland habitats and their substrata at retaining microplastics. Four small wetland microcosms had two to four litres of custom microplasticpolluted water added to them daily (with ~500 microplastic particles per litre, initially starting with four litres/ ~2000 microplastics), and two litres of sample water were taken daily, which were then filtered and examined to determine the loss of microplastics. Control microcosms consisting of four empty microcosms and two microcosms consisting of the wetland pebble substrate underwent the same procedure. Significantly more microplastics (p <0.05) were found to be retained by the wetland treatments over the 15-day sampling period than the control and pebbles treatments, with the pebbles treatment having a higher retention rate than the plain water treatment. Though there was a significant difference (p <0.05) found between the wetland and water treatments on each day, no significant difference was found between the water and pebbles treatments on any day, and on many days (1-4, 13-15) there was no significant difference between the wetland and pebble treatments. These findings give credence to CTWs being effective at retaining microplastics, with the wetland plants/ habitat as a whole being the driving force behind microplastic retention.

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Original languageEnglish
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Award date12 Oct 2021