| Author: | Leung, Ming Lok |
| Title: | Method improvement for determination of microplastics in seafood |
| Advisors: | Fang, Kar-hei James (ABCT) |
| Degree: | M.Phil. |
| Year: | 2022 |
| Subject: | Microplastics Seafood -- Contamination Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | xvi, 78 pages : color illustrations |
| Language: | English |
| Abstract: | Microplastics are commonly known as plastic particles < 5 mm in size. There is growing evidence showing that microplastics are increasingly abundant and associated with negative ecological consequences in marine environments. Microplastics can be easily ingested by diverse marine organisms and transferred along food chains into higher-trophic animals. Many of these animals are seafood species, raising the concern about the human health risk of microplastics through seafood consumption. There have been worldwide research efforts into the development of monitoring techniques for microplastics, but the diverse methods adopted by different researchers have made data comparison difficult among studies. Each of these approaches has its own pros and cons, which were evaluated in the present study aiming to develop an improved protocol for assessing microplastics in seafood samples. The first part of this thesis was a literature review on recent monitoring studies of microplastics in marine mussels and fishes, two major groups of seafood. Here we summarised the findings from 50 scientific papers on this topic, from which the most common practice to extract microplastics was tissue digestion using alkaline chemicals (43%), followed by oxidative chemicals (25%), among others. About a third to a half of the tissue digestion treatments were followed by a density separation step to isolate microplastics from undigested higher-density residue such as bone fragments and sand. Almost all of these studies relied on visual inspection to manually sort microplastics (98%), which were then usually identified using Fourier-transform infrared spectroscopy (72%) or Raman spectroscopy (14%). According to the advantages and limitations of these procedures, the second part of our work was to establish an improved protocol for assessing microplastics, using the green-lipped mussel, Perna viridis and the Japanese jack mackerel, Trachurus japonicus as the test models. A combined chemical treatment using potassium hydroxide, hydrogen peroxide and ethylenediaminetetraacetic acid disodium salt dihydrate was developed to extract microplastics from the mussel and fish samples, which achieved 99–100% digestion efficiency for both organic and inorganic biomass, and 90–100% recovery rates for seven common types of microplastics. The chemical treatment imposed only minimal effects on the particles' surface features and accuracy of polymer identification, which showed 94-99% similarity to untreated microplastics based on Raman spectra. Another highlight was the use of an automated Raman mapping technique to minimise human handling errors in the analysis of microplastics. The third part was about field application, in which the developed protocol was used to assess microplastics in the mariculture areas of Hong Kong. We focused on P. viridis, a filter-feeding mussel which can accumulate and concentrate microplastics from the ambient water. The mussel samples were collected from five sites, where the mean numbers of microplastics were determined to be 1.60-14.7 particles per individual, or 0.21-1.83 particles per g wet weight. The peak abundance of particle sizes occurred at 90-110 μm. The shapes of microplastics were dominated by fragments (89%) and fibres (9.7%). The polymer types were identified to be polypropylene (56%), polyethylene (25%), polystyrene (9.0%) and polyethylene terephthalate (10%). Through consumption of P. viridis, the estimated human ingestion rates of microplastics could be as high as 10,380 pieces per person per year. These findings suggest the potential human health risk of microplastics in Hong Kong and other areas in the southern China. Overall, this thesis presented an effective digestion method for mussel and fish biomass to extract microplastics, which can be coupled with an automated Raman mapping approach to streamline the workflow of microplastic identification. Our protocol is applicable to other seafood and biological samples, providing an improved alternative for routine monitoring of microplastics in marine environments. |
| Rights: | All rights reserved |
| Access: | open access |
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