Title Page

Contents

요약문 11

Abstract 15

Chapter 1. Introduction 26

1.1. Introduction 26

1.2. Background study 28

1.2.1. Occurrence of environmental microplastics 28

1.2.2. Distribution of microplastics 29

1.2.3. Fates and ecological effects of environmental microplastics 30

1.2.4. Environmental weathering of microplastics 32

1.3. References 34

Chapter 2. Spatial and temporal variation for microplastic distribution in the environment: the H River Estuary & the I Coast and the N Farmland 51

2.1. Microplastics in the H River Estuary & the I Coast 51

2.1.1. Introduction 51

2.1.2. Materials and methods 55

2.1.3. Results and discussion 60

2.1.4. Conclusion 68

2.1.5. References 69

2.2. Microplastics in the N farmland 73

2.2.1. Introduction 73

2.2.2. Materials and methods 79

2.2.3. Results and discussion 87

2.2.4. Conclusion 104

2.2.5. References 106

Chapter 3. Biodegradation of micro-polyethylene particles by bacterial colonization of a mixed microbial consortium isolated from a landfill site 120

3.1. Introduction 120

3.2. Materials and methods 122

3.2.1. Microplastics 122

3.2.2. Isolation and identification of mixed bacterial culture 123

3.2.3. Identification of bacterial strains 125

3.2.4. Screening of bacterial strains for PE degradation 126

3.2.5. Microbial inoculum preparation and assay for PE microplastics degradation 127

3.2.6. Analytical procedures 127

3.3. Results and discussion 130

3.3.1. Isolation and identification of bacterial strains 130

3.3.2. Determination of weight loss of PE and variation on SCOD 134

3.3.3. SEM observation of treated PE microplastics 136

3.3.4. FTIR analysis of microplastic polymers 140

3.3.5. GC-MS analysis of eluted contents from degraded PE microplastics 142

3.3.6. Thermogravimetric analysis of PE microplastics 144

3.4. Conclusion 146

3.5. References 147

Chapter 4. A comprehensive study of the bacterial degradation of PE microplastics by an indigenous bacterial consortium dominated by Paenibacillus spp. 151

4.1. Introduction 151

4.2. Materials and methods 154

4.2.1. Materials: microplastics and bacterial decomposer 154

4.2.2. Bacterial decomposition of PE microplastics 155

4.2.3. Characterization of biologically decomposed microplastics 156

4.2.4. GC-MS analysis for degradation byproducts 158

4.2.5. Biomolecular and biochemical analysis 159

4.2.6. Data analysis 162

4.3. Results and discussion 162

4.3.1. Changes in the biologically decomposed PE microplastics 162

4.3.2. Degradation byproducts 175

4.3.3. Variation on bacterial community and their biochemical properties 177

4.4. Conclusion 181

4.5. References 182

Chapter 5. Conclusive summary 197

5.1. Conclusive summary 197

Chapter 6. Future works 200

6.1. Engineering applications and further study 200

6.2. References 203

Publications 206

Table 2.1. The distribution of microplastics in major domestic rivers and coastal waters. 53

Table 2.2. The spatiotemporal abundance of microplastics. 63

Table 2.3. Correlation matrix for microplastic abundances by season. 67

Table 2.4. Comparative microplastic extraction and analytical procedures from the agricultural soil samples. 77

Table 2.5. The physicochemical characteristics of the agricultural soil samples. Experimental data was expressed as the mean of duplicate ± standard deviation. 89

Table 2.6. The average of microplastic abundance (particles/kg of dry soil) in the tillage (T1 and T2), non-tillage (NT1 and NT2), and near the greenhouses (G1 and G2). All data were expressed as the mean of duplicates ± standard deviation. 98

Table 4.1. The bacterial profile of the consortium which was isolated from a municipal dump site. 164

Table 4.2. The correlation matrix among the various degradation parameters of CBIs, DBIs, and crystallinity. 174

Table 4.3. The relatively intensity of organic matter eluted from PE microplastics compared to the abiotically treated. 176

Table 4.4. Mean values of cell surface hydrophobicity and biofilm formation capacity of bacterial consortium during PE degradation, measured by BATH assay and crystal violet assay, respectively. 180

Figure 2.1. The overview of the microplastic distribution in the domestic river (Eo et al., 2019; T. J. Park et al., 2020b) and marine environments (Chae et al.,... 52

Figure 2.2. Sampling stations within the H River Estuary and the I Coast for microplastic analysis: the downstream of the H River (zone I), G Island (zone... 56

Figure 2.3. The microscopic images of environmental microplastic samples collected in the H River Estuary and the I Coast with various types of polymer... 61

Figure 2.4. Comparison of the spatiotemporal distribution of microplastics (330 μm~5 mm) according to microplastic types. 62

Figure 2.5. Plastic profiles for (a) the different regions (Downstream of the H River, G Island, the I Coast, and D Island), (b) the different sampling times of... 65

Figure 2.6. The study project area of tillage soil (mulched by the agricultural film for vegetation, T1: 37°35.0020'N, 127°13.9690'E; T2: 37°34.9690'N,... 80

Figure 2.7. Schematic diagram of the method used for microplastic extraction from agricultural soil samples. 85

Figure 2.8. Bacterial profiles in the soil samples determined by the next-generation sequencing analysis at the class level. 91

Figure 2.9. FTIR spectra of environmental microplastics in the ATR mode of (a) PE film, (b) PP film, (c) PS fragment, (d) PET fiber cluster, and (e) PVC... 94

Figure 2.10. Microscopic images of microplastics isolated from soil samples taken in (a) tillage, (b) non-tillage, and (c) near greenhouses, respectively. 97

Figure 2.11. Comparison of the abundances of PE, PP, and PET microplastics depending on the agronomic practices. 100

Figure 2.12. (a) The comparison of microplastic abundance according to the arbitrarily assigned particle sizes, (b) the percentages of relative microplastic... 102

Figure 3.1. Locality maps for waste sampling from the landfill site in Incheon, Korea. Sampling was conducted at sites A and B at different depths (2 and 5... 124

Figure 3.2. Phylogenetic dendrogram of the relationships between 16S rDNA gene sequences retrieved from GenBank (NCBI). 133

Figure 3.3. (a) Weight loss of PE microplastics and (b) microbial density of attached and suspended cells observed for 20, 40, and 60 days after the mixed... 135

Figure 3.4. Scanning electron microscopic images of clusters of PE microplastics of (a) control and (b) biologically aged particles. The magnified... 137

Figure 3.5. Fourier transform infrared (FTIR) spectra of (a) control (after incubating for 60 days in the medium without inoculum) and (b) biologically... 141

Figure 3.6. Gas chromatography-mass spectrometry chromatogram of (a) neat PE microplastic and (b) biologically treated PE microplastics incubated for 20... 143

Figure 3.7. Thermogravimetric analysis of PE microplastics before and after biodegradation according to different incubation times. 145

Figure 4.1. A Plausible biodegradation mechanism of PE responsible for the formation of keto-and ester-carbonyl bond at 1,715 cm-1 and 1,740 cm-1 along...[이미지참조] 166

Figure 4.2. (a) The variation of CBIs and DBIs of PE microplastics abiotically treated (w/o inoculum) and microbially decomposed with the different mass... 168

Figure 4.3. Comparison of melting points and the percentages of crystallinity of virgin, abiotic control, and biologically decomposed PE microplastics under... 171

Figure 4.4. Changes in the microbial community according to the length of DNA fragments digested by restriction enzyme Hae III in T-RFLP analysis. 178