5:15 PM - 7:15 PM
[MIS21-P02] Distribution and shape of microplastics in beach sands and river mouth sediments in coastal areas of Japan
Microplastics (MPs) in the marine environment migrate to sediments through a variety of pathways such as discharge from the land to the ocean and transport by ocean currents. Since degradation and fragmentation of MPs progress according to these transported processes, the physical and chemical properties of MPs in the environment are considered to differ. Therefore, this study collected beach sand and river mouth sediments in five regions in Japan (Hokkaido, Yamagata, Yamaguchi, Okinawa, and Lake Suwa in Nagano) and demonstrated the distribution and characteristics of MP above 300 µm.
To extract MPs from large amount sediment, the collected samples were fractionated using tap water filtered through a 10 µm mesh net and a sieve into three fractions; 300-500 µm and over 500 µm. These fractionated samples were collected by density separation with 7.8 mol/L NaI solution and then the collected suspension samples were oxidised with 30% H2O2. The solid particulates were measured shape and color and picked using an automatic measuring microscope system equipped with a manipulator (Itaki et al, 2020). The chemical composition of each solid particulates was determined by using a Fourier-transform infrared spectrometer (FT-IR) coupled with an attenuated total reflectance (ATR) accessory. MPs concentration was calculated as the number of pieces per dry sample weight.
The highest concentration of MPs in beach sand was 254.3 particles/kg in Lake Suwa, Nagano, followed by 166.2 particles/kg around Abu River, Yamaguchi. The MPs concentrations in beach sand around the Kokuba River in Okinawa, the Mogami River and the Gekko River in Yamagata ranged from 30-70 particles/kg. In river mouth sediments, the highest concentration was 1209.1 pcs/kg in Lake Suwa, Nagano, followed by 217.1 pcs/kg in the Abu River, Yamaguchi and 60.4 pcs/kg in the Kokuba River, Okinawa. The chemical composition indicates that polyethylene (PE), polypropylene (PP), and polystyrene (PS) are abundant in the beach sand, while PE, PP, and polyester including polyethylene terephthalate (PET) are abundant in the river mouth sediments, but the trends vary in each site. The measurement results show that beach sand tends to contain more MPs particles with a larger maximum Feret diameter than river mouth sediments. And the aspect ratios of MPs tend to be higher in river mouth sediments, it means that they contain more fiber. The lower concentration and larger Feret diameter of MPs in the beach sand compared to river mouth sediments suggest that finer MPs is less likely to be deposited on the beach sand by waves. The high fiber contains of river mouth sediments indicates that the hydrodynamic influence is smaller than the beach and relatively lighter MPs can be deposited.
In the future, we will analyze MPs in other areas and chemical analysis of the extracted MPs and consider MP transported processes in coastal area with information on the sedimentary environment based on the sediment characteristics and topography.
This research was performed by the Environment Research and Technology Development Fund (PMEERF20221004) of the Environmental Restoration and Conservation Agency provided by Ministry of the Environment of Japan.
Reference: Itaki et al. (2020) Automated collection of single species of microfossils using a deep learning- micromanipulator system. Progress in Earth and Planetary Science, 7, 19.
To extract MPs from large amount sediment, the collected samples were fractionated using tap water filtered through a 10 µm mesh net and a sieve into three fractions; 300-500 µm and over 500 µm. These fractionated samples were collected by density separation with 7.8 mol/L NaI solution and then the collected suspension samples were oxidised with 30% H2O2. The solid particulates were measured shape and color and picked using an automatic measuring microscope system equipped with a manipulator (Itaki et al, 2020). The chemical composition of each solid particulates was determined by using a Fourier-transform infrared spectrometer (FT-IR) coupled with an attenuated total reflectance (ATR) accessory. MPs concentration was calculated as the number of pieces per dry sample weight.
The highest concentration of MPs in beach sand was 254.3 particles/kg in Lake Suwa, Nagano, followed by 166.2 particles/kg around Abu River, Yamaguchi. The MPs concentrations in beach sand around the Kokuba River in Okinawa, the Mogami River and the Gekko River in Yamagata ranged from 30-70 particles/kg. In river mouth sediments, the highest concentration was 1209.1 pcs/kg in Lake Suwa, Nagano, followed by 217.1 pcs/kg in the Abu River, Yamaguchi and 60.4 pcs/kg in the Kokuba River, Okinawa. The chemical composition indicates that polyethylene (PE), polypropylene (PP), and polystyrene (PS) are abundant in the beach sand, while PE, PP, and polyester including polyethylene terephthalate (PET) are abundant in the river mouth sediments, but the trends vary in each site. The measurement results show that beach sand tends to contain more MPs particles with a larger maximum Feret diameter than river mouth sediments. And the aspect ratios of MPs tend to be higher in river mouth sediments, it means that they contain more fiber. The lower concentration and larger Feret diameter of MPs in the beach sand compared to river mouth sediments suggest that finer MPs is less likely to be deposited on the beach sand by waves. The high fiber contains of river mouth sediments indicates that the hydrodynamic influence is smaller than the beach and relatively lighter MPs can be deposited.
In the future, we will analyze MPs in other areas and chemical analysis of the extracted MPs and consider MP transported processes in coastal area with information on the sedimentary environment based on the sediment characteristics and topography.
This research was performed by the Environment Research and Technology Development Fund (PMEERF20221004) of the Environmental Restoration and Conservation Agency provided by Ministry of the Environment of Japan.
Reference: Itaki et al. (2020) Automated collection of single species of microfossils using a deep learning- micromanipulator system. Progress in Earth and Planetary Science, 7, 19.