Microplastic loads in fish and invertebrates in Malaysian rivers

Ng, Yong Sin (2023) Microplastic loads in fish and invertebrates in Malaysian rivers. MRes thesis, University of Nottingham.

PDF (Thesis - as examined) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
Available under Licence Creative Commons Attribution.
Download (5MB) | Preview


Microplastic pollution is a global problem, but little is known about the degree of microplastic contamination in tropical rivers, and even less is known of contamination levels in the animals in these systems. Additionally, there is a gap in knowledge regarding the extent of microplastic pollution in rapidly developing regions, where environmental infrastructure (e.g., sewage systems) and waste management are often inadequate. This study assessed the microplastic loads in invertebrates and fish in the Semenyih River, Malaysia. The Semenyih is a rapidly urbanising catchment on edge of Kuala Lumpur, Malaysia’s capital city. Microplastic contamination levels in river sediment and water were assessed at 8 sites along the river to develop a better understanding of the relations between environmental contamination levels and body loads of fish and invertebrates. Relations between body sizes and feeding preferences of animals were also examined. Microplastic loads in animals were assessed using two methods, one capable of detecting material in the 0.1-5 mm size range (low-resolution, manual microscopy), and the other down to 0.004 mm (semi-automated high-resolution, counterstaining dye method). Thus, microplastics including nanoparticles were assessed as part of this research.

Using the widely used low-resolution method, 94.7% of fish, 44.2% of insect larvae, and 58.3% of mussels were found to contain microplastic. For the four insect families studied, this low-resolution method detected an average of 1.1 pieces of microplastic per individual. When expressed per body weight, individuals of these families contained an average of 11.06 pieces of microplastic per mg of dry tissue. Numbers increased markedly when the high-resolution method was used, with an average of 128.8. pieces per individual and 704.3 per mg dry weight for the four insect families. The overall ratio between microplastic detected using high- and low-resolution methods was around 120:1.

Microplastic loads in aquatic animals varied between major taxonomic groups (i.e., between fish, mussels, and insects) but not between all four of the insect families studied; Hydropsychidae contained more pieces per individual than Simuliidae, but Baetidae and Chironomidae did not differ significantly from each other or the other insect taxa. Microplastic contamination of water and sediment differed significantly between sites. However, there was no simple direct relationship between bed contamination levels and body loads in invertebrates at the site. Analysing all the taxonomic groups together, there was a significant relationship between body size and contamination levels; the same positive relation was found for insects and mussels but not fish.

Fibre was the most abundant microplastic in water and sediments in the Semenyih River, though fragments were present in greater abundance on the bed than in the water column. There was a much greater prevalence of fragments in the bodies of animals than either in the water column or in the sediment. Microplastic loads differed significantly between functional feeding groups when expressed as microplastic concentration per mg of dry tissue, with filterers containing less microplastics in their tissue per unit weight than gatherers. Invertebrates and fish ingested microplastic of all four different shapes (beads, fibres, fragments, and films).

The work shows widespread contamination by microplastic in the Semenyih River and its aquatic biota. Organisms appear to ingest microplastics in ways that do not simply reflect their gross abundance in the environment but reflect their mode of feeding. Contamination loads also reflect body size, although differences between taxa depend on whether the load is expressed simply as pieces of microplastic per individual or unit body weight. The work also indicates that body loads may be much higher than suggested using conventional low-resolution enumeration methods, averaging 120 times greater across the four insect families when the high-resolution method was used. The high-resolution method applied in this study is more time-consuming than low-resolution ones, so may not always be practical. However, the 120:1 ratio could potentially be applied to data generated using the low-resolution method, to provide an estimate of the likely true load in the body of aquatic organisms.

Item Type: Thesis (University of Nottingham only) (MRes)
Supervisors: Gibbins, Christopher
Selvam, Sivathass Bannir
Ting, Kang Nee
Keywords: microplastic; aquatic animals; Malaysia; environmental pollution; freshwater
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Science > School of Environmental and Geographical Sciences
Item ID: 74036
Depositing User: Ng, Yong
Date Deposited: 22 Jul 2023 04:40
Last Modified: 24 Jul 2023 02:01
URI: https://eprints.nottingham.ac.uk/id/eprint/74036

Actions (Archive Staff Only)

Edit View Edit View