The distribution and effects of microplastics in freshwater ecosystems

Muller, Gemma 2024. The distribution and effects of microplastics in freshwater ecosystems. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Plastic is essential in modern society, yet over-use and improper disposal have increased microplastic pollution dramatically over the past century. Microplastics pose unique physical, chemical, and biological threats to the environment, with particular concern for freshwater ecosystems due to their proximity to microplastic sources, importance for biodiversity, and role in human well-being. Despite growing research on microplastic distribution, load, and ecological effects in freshwater systems, substantial gaps remain. Major challenges include: (i) both the dynamic nature of freshwater ecosystems and complex behaviour of microplastic particles; (ii) poorly resolved interactions between microplastics and organisms over space and time; and (iii) inconsistencies in research methodologies. This thesis empirically assesses some ecological risks of freshwater microplastic pollution at the global, catchment, and reach scale in four steps. First, published studies are reviewed to identify trends in microplastic distribution in freshwater ecosystems across a hierarchy of spatial and temporal scales. Next, methodologies to sample, extract, quantify and characterise microplastic are evaluated to determine how varying protocols might influence estimated loads and trends. Third, recommended protocols are used to sample microplastic comprehensively across the whole River Taff catchment, Wales, as a model river system with varying land use. Lastly, ecological interactions and impacts of microplastic from point sources are assessed experimentally in field stream mesocosms. Globally, the results reveal that freshwater microplastic pollution is associated with urban sources and poor waste management, though variations amongst sources and hydrodynamics lead to site-specific exceptions. The review of methods reinforces the need for harmonised protocols. In the model catchment, sampling shows the widespread but patchy distribution of microplastic in freshwater sediment and invertebrates. At the reach-scale, microplastic addition can have limited ecological effects either reflecting limited interaction with organisms or limited immobilisation of microplastic under natural stream conditions. These novel findings contribute toward improved risk assessment.

Item Type:	Thesis (PhD)
Date Type:	Acceptance
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Funders:	EPSRC
Date of First Compliant Deposit:	11 July 2025
Date of Acceptance:	11 August 2024
Last Modified:	11 Jul 2025 14:50
URI:	https://orca.cardiff.ac.uk/id/eprint/179752

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