Research Doctorate - Doctor of Philosophy (PhD) / Shrimp farming and capture fishery are two of the major industries of Can Gio district, Ho Chi Minh City, southern Vietnam. These industries have recently developed and contributed to the improvement of local economy. However, they have also raised environmental concerns regarding water pollution and fish stock depletion. The negative impacts of shrimp farm effluents on the water quality of mainstream rivers and fish communities have not been studied in Can Gio. Additionally, there is a lack of research on the influence of the current fisheries management on environmental protection and fish conservation in this district. The goal of this study was to address key issues in fisheries management in Can Gio in regard to the impacts of wastewater from shrimp farming on the water quality of mainstream rivers that affect the local fish communities, and the influence of improper fishing practices that lead to the depletion of local fish stocks. This study also aimed to propose strategies to improve the local fisheries management for more environmentally responsible productions. Two mainstream surveys were developed to obtain data, i.e. environmental surveys for the assessment of water quality and pollution impacts on fish communities; and people interviews for the examination of fisheries management related to shrimp farming and fishing practices. The findings were used as a baseline to develop appropriate strategies for improving the management in terms of promoting sustainable productions both in shrimp farming and capture fishery industries and protecting the environment. This study found that shrimp farming, especially intensive farms have contributed to water pollution in mainstream rivers in Can Gio, and in turn the water pollution has adversely affected the local fish communities. The waters adjacent to the intensive farms were contaminated with high concentrations of organic matter. The number of fish species reduced and tolerant species appeared at higher proportions in these areas. Many improper practices in shrimp farming and fishing as well as weaknesses in government management were addressed to be the key issues leading to environmental pollution and fish depletion. The proposed strategies focused on improving the management at both government and community levels. Promoting community-based management was suggested as a key to the success in fisheries management in Can Gio.

Research Doctorate - Doctor of Philosophy (PhD) / Shrimp farming and capture fishery are two of the major industries of Can Gio district, Ho Chi Minh City, southern Vietnam. These industries have recently developed and contributed to the improvement of local economy. However, they have also raised environmental concerns regarding water pollution and fish stock depletion. The negative impacts of shrimp farm effluents on the water quality of mainstream rivers and fish communities have not been studied in Can Gio. Additionally, there is a lack of research on the influence of the current fisheries management on environmental protection and fish conservation in this district. The goal of this study was to address key issues in fisheries management in Can Gio in regard to the impacts of wastewater from shrimp farming on the water quality of mainstream rivers that affect the local fish communities, and the influence of improper fishing practices that lead to the depletion of local fish stocks. This study also aimed to propose strategies to improve the local fisheries management for more environmentally responsible productions. Two mainstream surveys were developed to obtain data, i.e. environmental surveys for the assessment of water quality and pollution impacts on fish communities; and people interviews for the examination of fisheries management related to shrimp farming and fishing practices. The findings were used as a baseline to develop appropriate strategies for improving the management in terms of promoting sustainable productions both in shrimp farming and capture fishery industries and protecting the environment. This study found that shrimp farming, especially intensive farms have contributed to water pollution in mainstream rivers in Can Gio, and in turn the water pollution has adversely affected the local fish communities. The waters adjacent to the intensive farms were contaminated with high concentrations of organic matter. The number of fish species reduced and tolerant species appeared at higher proportions in these areas. Many improper practices in shrimp farming and fishing as well as weaknesses in government management were addressed to be the key issues leading to environmental pollution and fish depletion. The proposed strategies focused on improving the management at both government and community levels. Promoting community-based management was suggested as a key to the success in fisheries management in Can Gio.

Chapter 1 gives a general introduction into plastic polymer and microplastics including concepts, sources and distribution in the environment, microplastic sampling and analytical methods, and sampling area descriptions. Chapter 2 represents all methods and followed equipment used in the thesis. A double-filtration procedure preferable to Raman microscopy technique was developed to collect marine microplastics in brackish water from Can Gio and seawater from the East Sea. Chapter 3 is a comprehensive guideline on IR and Raman spectra interpretation of PE, PP, PVC, PS, PMMA, and polymer textiles, which is especially useful if the automatic library is not available. This chapter represents how to identify polymer type, predict sources and chemical behaviours of microplastics with the smallest size of 15 μm based on microscopic and spectroscopic data. Also, this chapter evaluates the sample handling workflows for salt, water and sand samples. Chapter 4 demonstrates the change in microplastic pollution from 250 MPs/L in Saigon urban canals (the center of Ho Chi Minh City), through UNESCO Can Gio Mangrove Biosphere Reserve (10 – 20 MPs/L), to estuaries of Saigon-Đong Nai River, Soai Rap River, Long Tau River (Ganh Rai Gulf), and eventually to the East Sea (3 – 5 MPs/L). Chapter 5 highlights the correlation of microplastic properties and compositions in beach sand and seawater in the coastal environment, particularly at Can Gio 30 April Tourist Beach. This is a pilot study to identify the differences and similarities in morphologies and compositions of microplastics accumulated in beach sand and distributed in seawater, thereby, concluding sources and transport routes of microplastics in the coastal environment. The results show that microplastics accumulated at concentrations from 0 to 92.56 MPs/kg from the surface to 20-cm sand layers. The seawater at Can Gio Beach and Đong Tranh Cape contained 6.44 and 3.75 MPs/L of microplastics, respectively. White polyethylene fragments predominated, and all the microplastics comprised small secondary microplastics with a minimum size of 25 µm and a maximum size of 260 µm for fragments and a length of 640 µm for fibers. The proportions of PE, PP, PS and PMMA were similar. The differing percentages of other compositions in sand and seawater are attributed to the morphology and density of the microplastics. Chapter 6 deals with the detection and determination of microplastics in Vietnamese sea salts. As a result, there was a higher fluctuation in microplastic amount amongs non-branded salts compared with branded salts. An average of 133.62 MPs/kg salt, corresponding to 487.71 microplastics entering the human body per year via salt consumption. More importantly, this chapter provides a convincing evidence for microplastic contamination in marine salts from the seawater. There are similarities in percentage, shape, size and colour of microplastics, especially PE, PET and PP extracted from sea salt and seawater collected in 3 different regions in Southern Vietnam (Can Gio Reserve and Vung Tau).:Chapter 1. Introduction 1.1. Synthetic polymers and plastic products 1.1.1. Overview of polymers and plastics 1.1.2. Plastic applications and global productions 1.1.2.1. Conventional plastics 1.1.2.2. Bioplastics 1.1.3. The life cycle of plastics and plastic pollution 1.2. Microplastics – definitions, sources and fate 1.2.1. Definition and classification of microplastics 1.2.2. Sources and pathways of microplastics into the environments 1.2.3. Global distribution and behaviours of microplastics in the environment 1.2.3.1. Physical behaviours: temporal and spatial accumulations 1.2.3.2. Chemical behaviours: Degradation and Adsorption 1.2.3.3. Biobehaviours: Ingestion, Translocation and Biodegradation 1.3. Effects and bioavailability of plastics on ecosystems, creatures and humans 1.3.1. Aquatic ecosystem 1.3.2. Terrestrial ecosystem 1.3.3. Food safety and human healths 1.4. Microplastic sampling techniques and analytical methods 1.4.1. Microplastic sampling techniques 1.4.1.1. Water sampling 1.4.1.2. Sediment sampling 1.4.2. Sample preparations for microplastic analysis 1.4.2.1. Matrix removal – oxidation and tissue digestion 1.4.2.2. Microplastic separation – density flotation and filtration 1.4.3. Microplastic qualification and quantification methods 1.4.3.1. Visual identification methods 1.4.3.2. Spectroscopic identification methods 1.4.3.3. Destructive thermal techniques 1.4.3.4. Summarized workflow from samples to the results on microplastics 1.4.3.5. Data expression Chapter 2. Materials and Methods 2.1. Materials 2.2. Microscopy-spectroscopy for microplastic quantification and qualification 2.3. Quality assurances (QA) and quality controls (QC) 2.4. Collected and interviewed data on the study areas 2.5. Water samples 2.6. Sand samples 2.7. Marine salt samples Chapter 3. The comprehensive guideline on micro-spectroscopic interpretation and sample preparations for microplastic analysis 3.1. Abstract 3.2. Visual characterizations of microplastics 3.3. Interpretation of IR and Raman spectra for plastic identification 3.4. The specificity of spectroscopies for identifying polymer type and chemical behaviours of sampled microplastics 3.4.1. Poly-Ethylene (PE) 3.4.2. Poly-Propylene (PP) 3.4.3. Poly-Vinyl Chloride (PVC) 3.4.4. Poly-Styrene (PS) 3.4.5. Poly Methyl Metacrylate (PMMA) 3.4.6. Poly-Ethylene Terephthalate (PET) 3.4.7. Poly-Amides-6, Nylon-6 (PA-6) 3.4.8. Similarity in Raman bands of pure plastics and sampled microplastics 3.5. The evaluation of sample treatment procedures 3.5.1. Salt samples 3.5.2. Sand samples 3.5.3. Water samples Chapter 4. Assessing microplastic prevalence and spatial dispersion from Saigon urban river network to East Sea by µ-Raman spectroscopy 4.1. Abstract 4.2. Microplastic pollution in the freshwater at Saigon urban canals 4.3. Microplastic pollution in the seawater at Can Gio Biosphere Reserve 4.4. Spatial and vertical dispersion of microplastics in the East Sea of Vietnam 4.5. Conclusions Chapter 5. Comparison of Microplastic Pollution in Beach Sediment and Seawater at UNESCO Can Gio Mangrove Biosphere Reserve 5.1. Abstract 5.2. Microplastic pollution in the sand at Can Gio Beach 5.2.1. Spatial variation in the microplastic amounts along the tidal lines 5.2.2. The abundance and composition of microplastics accumulated in sand layers 5.3. Microplastic pollution in seawater at Can Gio Beach and Đong Tranh Cape 5.4. Comparison of microplastic pollution between seawater and beach sand 5.5. Conclusions and recommendations Chapter 6. Microplastic contamination in Vietnamese sea salts 6.1. Abstract 6.2. The microplastics abundance in commercial sea salts 6.3. Microplastic pollution in the seawater taken at salt pans in Vietnam 6.4. Microplastic contamination in the sea salt collected at salt pans in Vietnam 6.5. Comparison of characteristics of microplastics in the seawater and sea salt 6.6. The enhanced toxicity of microplastics-contaminated salt consumption 6.7. Conclusions and recommendations Final Conclusions and Future Recommendations List of references Appendix Statistical data Photos taken on the sampling trips