1:45 PM - 3:15 PM
[O11-P95] Distribution of microplastics in the sediments of Obama Bay
Keywords:Sediments, Microplastics, Sea of Japan
Background and Objectives
Plastic products are all around us, and environmental pollution caused by plastic waste is increasing year by year. Microplastics are particularly difficult to collect due to their small size, and many microplastics still exist in the world today. Microplastics exist in the ocean, not only drifting in the sea, but also depositing on the seabed.
For several years, students of our school have been actively conducting research on microplastics in Obama Bay. However, each study used different experimental methods. So it was difficult to compare results. The purpose of this study was to provide an overview of the distribution of microplastics on the seafloor in Obama Bay. We unified the experimental methods and conducted a survey of the entire Obama Bay.
Methods
Three samples of mud from nine locations in Obama Bay were collected at each location using an Ekman barge mud sampler, etc. The mud was dried in an incubator for one week. After weighing the dried mud, it was separated by specific gravity using saturated saline solution, and the supernatant was filtered through a 1000-μm and 100-μm mesh. The entire mesh was then placed in a petri dish and placed in a 30% hydrogen peroxide solution for one week to decompose the organic matter. The remaining material was observed under a microscope and the number of microplastics (hereafter MP) was counted in two categories: 100-1000 μm and 1000 μm and larger.
Results and Discussion
The results of microscopic observations of microplastics (MP) are shown in Table 1. Samples were analyzed for five of the nine sites.
Very little MP was found at any of the sites; the same white thread-like plastic was observed at both sites 1-100 and 2-100 (Table 1). In the 5-1000, about 50 pieces of whitish plastic were found; all 50 pieces were the same type of plastic. Other than the plastics, plants, crustacean legs, shells, and shells were found.
The observed plastics included plants, etc. Those with cell walls were classified as plants, and those without cell walls were classified as MPs (Fig. 1AB). One problem in selecting MPs was that those in the form of shells could be identified as such, but those in the form of fragments were difficult to identify (Fig. 1C).
The results of this study did not reveal a trend in distribution. In the future, we would like to analyze the remaining samples to determine where in Obama Bay MPs are most abundant.
Regarding the analysis method, we thought it necessary to verify how many MPs could be extracted by the method we employed. The first problem is that when the specific gravity separation method is used with saturated brine, what floats up is limited to polypropylene, polyethylene, and polystyrene, which have lower specific gravity than this. Polyethylene terephthalate (PET) and polyvinyl chloride (PVC) sink using this method because of their higher specific gravity. Therefore, they may be underestimated. Secondly, it is difficult to distinguish between the shells and other materials that float in the same way. We believe that this can be solved by using a strong acid and FTIR (Fourier Transform Infrared Spectroscopy) to identify the compounds.
Future Issues
In this study, we investigated the distribution of microplastics on the seafloor of Obama Bay, but we have not yet collected quantitative data, and our experimental methods were not perfect in that we were not able to remove impurities. In the future, we will improve our experimental methods, obtain quantitative data, and analyze the composition of microplastics.
Plastic products are all around us, and environmental pollution caused by plastic waste is increasing year by year. Microplastics are particularly difficult to collect due to their small size, and many microplastics still exist in the world today. Microplastics exist in the ocean, not only drifting in the sea, but also depositing on the seabed.
For several years, students of our school have been actively conducting research on microplastics in Obama Bay. However, each study used different experimental methods. So it was difficult to compare results. The purpose of this study was to provide an overview of the distribution of microplastics on the seafloor in Obama Bay. We unified the experimental methods and conducted a survey of the entire Obama Bay.
Methods
Three samples of mud from nine locations in Obama Bay were collected at each location using an Ekman barge mud sampler, etc. The mud was dried in an incubator for one week. After weighing the dried mud, it was separated by specific gravity using saturated saline solution, and the supernatant was filtered through a 1000-μm and 100-μm mesh. The entire mesh was then placed in a petri dish and placed in a 30% hydrogen peroxide solution for one week to decompose the organic matter. The remaining material was observed under a microscope and the number of microplastics (hereafter MP) was counted in two categories: 100-1000 μm and 1000 μm and larger.
Results and Discussion
The results of microscopic observations of microplastics (MP) are shown in Table 1. Samples were analyzed for five of the nine sites.
Very little MP was found at any of the sites; the same white thread-like plastic was observed at both sites 1-100 and 2-100 (Table 1). In the 5-1000, about 50 pieces of whitish plastic were found; all 50 pieces were the same type of plastic. Other than the plastics, plants, crustacean legs, shells, and shells were found.
The observed plastics included plants, etc. Those with cell walls were classified as plants, and those without cell walls were classified as MPs (Fig. 1AB). One problem in selecting MPs was that those in the form of shells could be identified as such, but those in the form of fragments were difficult to identify (Fig. 1C).
The results of this study did not reveal a trend in distribution. In the future, we would like to analyze the remaining samples to determine where in Obama Bay MPs are most abundant.
Regarding the analysis method, we thought it necessary to verify how many MPs could be extracted by the method we employed. The first problem is that when the specific gravity separation method is used with saturated brine, what floats up is limited to polypropylene, polyethylene, and polystyrene, which have lower specific gravity than this. Polyethylene terephthalate (PET) and polyvinyl chloride (PVC) sink using this method because of their higher specific gravity. Therefore, they may be underestimated. Secondly, it is difficult to distinguish between the shells and other materials that float in the same way. We believe that this can be solved by using a strong acid and FTIR (Fourier Transform Infrared Spectroscopy) to identify the compounds.
Future Issues
In this study, we investigated the distribution of microplastics on the seafloor of Obama Bay, but we have not yet collected quantitative data, and our experimental methods were not perfect in that we were not able to remove impurities. In the future, we will improve our experimental methods, obtain quantitative data, and analyze the composition of microplastics.