| 1. |
Zijiang Yang, Çelik Murat, Haruka Nakano, Hisayuki Arakawa, Accessing the intrinsic factors of carbonyl index of microplastics: Physical and spectral properties, baseline correction, calculation methods, and their interdependence., Marine pollution bulletin, 10.1016/j.marpolbul.2023.115700, 197, 115700-115700, 2023.10, Carbonyl index (CI) is a measure of the degradation status of microplastics. While many studies address environmental factors of microplastic degradation, intrinsic factors like physical properties, spectral properties, baseline correction, and CI calculation methods are less explored. This research focused on these aspects using surface seawater samples. We found that color and shape have limited dependence on particle size or signal-to-noise ratio (SNR). Baseline correction can significantly alter CI values, with the direction of the shift depending on the methods used. Additionally, most CI values before and after baseline correction and those calculated using different methods tend to be strongly correlated. Using the selected CI calculation methods, we found that CI values varied significantly by shape and color. CI's relation to the similarity between the sample and its pristine form suggests an alternative degradation measure. Our findings emphasize the need for standardized CI calculation methods.. |
| 2. |
María B Alfonso, Dhugal J Lindsay, Andrés H Arias, Haruka Nakano, Suppakarn Jandang, Atsuhiko Isobe, Zooplankton as a suitable tool for microplastic research., The Science of the total environment, 10.1016/j.scitotenv.2023.167329, 905, 167329-167329, 2023.09, In recent years, significant efforts have been dedicated to measuring and comprehending the impact of microplastics (MPs) in the ocean. Despite harmonization guidelines for MPs research, discrepancies persist in the applied methodologies and future challenges, mostly for the smaller fractions ( |
| 3. |
Hiraku Tanoiri, Eduardo Estevan Barrientos, Haruka Nakano, Hisayuki Arakawa, Masashi Yokota, The pretreatment method in marine organisms and sediment for microplastics analysis by FTIR using “Cylindrical Microplastics Fractionator”, MethodsX, 10.1016/j.mex.2023.102396, 11, 102396-102396, 2023.09, For the detection of microplastics (MPs) in aquatic biota using Fourier transform infrared spectroscopy (FTIR), the ability to remove organic matter (OM) in pretreatment steps is essential to increase the time efficiency of MPs measurement and method uniformity. In principle, decreasing OM can be achieved by increasing the number of pretreatment steps. However, MPs are lost in proportion to the number of transfers between each step. Therefore, we have created a "Cylindrical MPs Fractionator" composed of commercially available materials. This container allows for a six-step pretreatment process that is designed to increase the removal capacity of OM with only one transfer to prevent the loss of MPs.•Biological or sediment samples are placed in the extractor and subjected to chemical treatment and density separation.•Residues containing MPs are obtained on filters by vacuum filtration.•After additional chemical treatment of the obtained residue, the components of the residue are identified by microscopic FTIR.This method removed 99.3% of OM and recovered 88.5% of MPs. The presenting method confirmed that this can be used with the same process for 11 organisms and sediments from estuarine ecosystem in Japan as models.. |
| 4. |
Shaikh Tareq Arafat, Hiraku Tanoiri, Masashi Yokota, Haruka Nakano, Hisayuki Arakawa, Takeshi Terahara, Takeshi Kobayashi, Microplastic pollution in the gastrointestinal tract of giant river catfish Sperata seenghala (Sykes, 1839) from the Meghna River, Bangladesh., Environmental science and pollution research international, 10.1007/s11356-023-28750-z, 30, 38, 89627-89637, 2023.07, Freshwater rivers are considered the major route for microplastics (MPs), yet limited studies have been reported on MPs in freshwater river fish, especially in Bangladesh. This research reveals the intake of MPs by the giant river catfish Sperata seenghala, collected from the Meghna River, which is the only outlet of the Ganges-Brahmaputra River. Three locations, namely, Chandpur Sadar, Bhola Sadar, and Char Fasson, along the Meghna River, were selected in order to investigate the gastrointestinal tracts (GIT) of the fish. Ninety percent (n=27) of fish (n=30) were contaminated, with fragment-shaped MPs (65%) as the most abundant among the four types. A total of 179 MP particles were detected using micro-Fourier transformed infrared spectroscopy (μ-FTIR), with an average of 5.96 ± 1.32 MP particles per fish. Among the four size groups, the highest proportion of MPs (54%) occurred in the 45-100 μm group; the dominant color among the seven color groups was white (30%). The highest quantity of MPs was found in the relatively densely populated Chandpur Sadar region. Polypropylene-polyethylene copolymer (PP-PE, 23%) was proportionally dominant among the 15 types. No significant relationship was found between the total number of observed MPs and the GIT weight. This study will help us to understand MP pollution in S. seenghala that may transmit to the human body through the food chain.. |
| 5. |
Yipeng Cheng, Jiaqi Zhang, Haruka Nakano, Naofumi Ueyama, Hisayuki Arakawa, Coumarin 6 staining method to detect microplastics., Marine pollution bulletin, 10.1016/j.marpolbul.2023.115167, 193, 115167-115167, 2023.06, Microplastics have contaminated the ocean in large quantities and are widely distributed throughout the world. Thus, our understanding of the concentration of microplastics in various environments should be increased. However, current methods to detect microplastics require considerable effort and expensive equipment. In this study, we developed a fluorescence staining technique using coumarin 6 and examined its effectiveness. A mixture of acetone and ethanol was used as the solvent, and 10 different types of plastics were able to be stained with coumarin 6. The fluorescence peak for coumarin 6 staining was approximately 500 nm for each plastic type. The optimal immersion time and coumarin 6 concentration for staining were determined to be 60 min and 1 mg L-1, respectively. Using this technique, we were able to stain all of the microplastics obtained from samples collected in Tokyo Bay seawater.. |
| 6. |
Haodong Xu, Haruka Nakano, Tadashi Tokai, Tadashi Miyazaki, Hiroaki Hamada, Hisayuki Arakawa, Contamination of sea surface water offshore the Tokai region and Tokyo Bay in Japan by small microplastics., Marine pollution bulletin, 10.1016/j.marpolbul.2022.114245, 185, Pt A, 114245-114245, 2022.10, A nested double neuston net was prepared and used to collect samples from the surface of coastal waters around Japan to obtain information about the properties of both small microplastics (SMPs; 350 μm). The SMP concentrations ranged from 1000 to 5900 pieces m-3 in the open ocean and averaged approximately 3000 pieces m-3 in the inner part of Tokyo Bay. The SMP concentrations were around 20-60 times greater than the LMP concentrations. By analyzing the seawater, we obtained a microplastic size distribution that spanned 50-5000 μm. The LMPs mainly comprised packaging-related plastics, such as polyethylene (PE) and polypropylene, while the SMPs were dominated by paint-related plastics. SMPs derived from packaging materials (e.g., PE) may have gradually sank down from the sea surface when they were smaller than 600 μm.. |
| 7. |
Scales and non-dimensional numbers characterizing ocean turbulence and their practical application for estimating eddy diffusivities. |
| 8. |
Yehao Wang, Haruka Nakano, Haodong Xu, Hisayuki Arakawa, Contamination of seabed sediments in Tokyo Bay by small microplastic particles, ESTUARINE COASTAL AND SHELF SCIENCE, 10.1016/j.ecss.2021.107552, 261, 2021.10, This study investigated small microplastic particle (SMP, |
| 9. |
Hiraku Tanoiri, Haruka Nakano, Hisayuki Arakawa, Ricardo Shohei Hattori, Masashi Yokota, Inclusion of shape parameters increases the accuracy of 3D models for microplastics mass quantification., Marine pollution bulletin, 10.1016/j.marpolbul.2021.112749, 171, 112749-112749, 2021.10, As microplastics may bring about adverse effects on living organisms, it is important to establish more precise quantification approaches to better understand their dynamics. One method to determine the concentration of microplastics is to estimate their mass using three-dimensional (3D) models, but its accuracy is not well known. In this study, we evaluated the shape of the particles and verified the accuracy of a 3D model-based mass estimation using samples from a tidal flat facing Tokyo Bay. The particle shape evaluation suggested that the microplastics were flat and irregular in shape; based on these data, we created two types of models to estimate their mass. As a result, an accuracy of mass estimation by our model was higher than other models that consider the slenderness and flatness of particles. The optimization of mass estimation methods based on 3D models may improve the reliability of microplastic evaluation in monitoring studies.. |
| 10. |
Haruka Nakano, Keiichi Uchida, Tetsutaro Aikawa, Toshifumi Hayashi, Hisayuki Arakawa, Reevaluation of microplastics identification based on Neuston net survey data., Marine pollution bulletin, 10.1016/j.marpolbul.2021.112799, 171, 112799-112799, 2021.10, To verify data accuracy regarding microplastics (MPs), the effects of chemical preprocessing and optical identification with Fourier transform infrared spectroscopy (FTIR) were examined using survey data. We aimed to clarify the cause of overestimation of the number concentration of MPs without FTIR by focusing on shape types. The proportion of fragments (foam) decreased (increased) after FTIR analysis. Although significant difference was found in terms of the size distribution of fragments (after FTIR > before FTIR), no such difference was found with regard to foam. These findings indicate that impurities categorized as fragments via visual confirmation, especially those measuring 1000 μm, this threshold should be applied only to fragments and not to foam.. |
| 11. |
Haruka Nakano, Hisayuki Arakawa, Tadashi Tokai, Microplastics on the sea surface of the semi-closed Tokyo Bay., Marine pollution bulletin, 10.1016/j.marpolbul.2020.111887, 162, 111887-111887, 2021.01, Microplastics (MPs) pollution surveys were conducted in Tokyo Bay using neuston nets (May 2019 and January 2020). Although the pollution level in Tokyo Bay was high (3.98 pcs/m3, May), it was lower than reported in other semi-closed bays because of differences in the Enclosed Index. It was found that polyethylene fragments dominated the retrieved MPs; the mode of MPs size was 800 μm. As MPs abundance in rivers had the same seasonality as found in the inner bay, rivers were considered the main source of MPs. The seawater residence time is shorter than the time required for the density of MPs to become greater than that of seawater; therefore, it was considered that MPs are transported out of the bay instead of sinking. MPs were aggregated into a convergence zone by residual currents (the thermohaline front) in May (January). These findings will improve understanding of MPs pollution in other bays.. |
| 12. |
Statistical Analysis of Surface Circulation in Sagami Bay Using High-Frequency (HF) Radar. |
| 13. |
Haruka Nakano, Jiro Yoshida, A note on estimating eddy diffusivity for oceanic double-diffusive convection, Journal of Oceanography, 10.1007/s10872-019-00514-9, 75, 5, 375-393, 2019.10, In this note, we provide an overview of the theoretical, numerical, and observational studies focused on oceanic eddy diffusivity, with an emphasis on double-diffusive convection (DDC). DDC, when calculated using the turbulent kinetic energy (TKE) equation, produces a negative diffusion of density. A second-moment closure model shows that DDC is effective within a narrow range. Other parameterizations can use in the actual sea, but improvements are still needed. Mixing coefficients referring to mixing efficiency are key factors when distinguishing DDC from conventional turbulence. Here, we show that measurements involving the gradient Richardson number, the buoyancy Reynolds number, and density ratio play a crucial role in determining eddy diffusivity in the presence of DDC. Therefore, deployment of a microstructure profiler together with either an acoustic Doppler current profiler (ADCP), lowered ADCP, or electromagnetic current meter is essential when measuring eddy diffusivity in the ocean's interior.. |
| 14. |
Nakano H, Kuroki K, Sato Y, Koshita S, Maeda M, Matsuura K, Ship Speed Loss Estimation Using Wave Spectrum of Encounter, OCEANS - MTS/IEEE Kobe Techno-Ocean (OTO), 10.1109/OCEANSKOBE.2018.8559122, 2018.06, An accurate estimation of ship speed loss is required to verify ship propulsion performance in actual sea conditions. In this study, ship speed loss was estimated using a neural network. Firstly, the directional spectra were extracted from the ocean wave hindcast database of Japan Weather Association. Then, the spectra were converted into wave spectra of encounter. Secondly, ship speed through water was modeled using ship monitoring data and spectra with a neural network. Thirdly, speed-power curves were estimated using the model. Effects of the wind and waves on ship speed were checked by considering the sensitivity of the model's outputs. Finally, ship speed loss was calculated using this model. The estimated ship speed loss was consistent with the ship speed loss obtained using ship monitoring data.. |
| 15. |
The relationship between the behavior of fish school, Jack mackerel Trachurus japonicus and oceanic conditions in Tateyama Bay, Chiba Prefecture, Japan. |
| 16. |
Statistical analysis of the variation of the Kuroshio path. |
