16:00 〜 16:15
[MIS09-08] 微細プラスチックの質量とサイズの幾何学的関係に関する考察
キーワード：マイクロプラスチック、幾何学的関係、質量推計、河川
Quantification of meso- and microplastic (MMP) concentration in mass is important to grasp the dynamics and ecological impacts of MMPs in aquatic environments (rivers, oceans, and lakes). Currently, several methodologies for evaluating the mass concentration of MMPs exist, and one of the major methodologies is to estimate the mass of each particle from the geometric volume estimated by the shape and two-dimensional size and specific gravity of polymer type identified by a Fourier Transform Infrared (FTIR) Spectroscopy. However, it is not enough to evaluate uncertainty in these mass estimations.
Here we have clarified the geometrical relationship between mass and size of MMP particles collected from the water surface using a 335μm-mesh plankton net at 35 sites of 17 Japanese rivers from May 2019 to October 2022. After sampling in situ, all of the materials were collected into a stainless bottle after washing the net, and then the samples were processed by an oxidative degradation and density separation to efficiently extract MMP particles. After preprocessing, a picture of the MMP particle candidate was taken by a CCD camera-installed stereo microscope (SZX7, OLYMPUS) for subsequent size measurement and shape identification, and then the candidate was measured by an ultramicrobalance (XPR2UV, METTLER TOLEDO). Finally, a polymer type was identified by FTIR (IRAffinity-1S, SHIMADZU) attached to an Attenuated Total Reflection (ATR) device. The MMP particle was categorized into four shape types (Sphere, Fragment, Sheet, Fiber) and nine polymer types (PE, PP, PS, PEPP, PVC, PEs/PET, Acryl, EVA, Others). Also, the major length and projected surface area of each MMP particle were measured by the ImageJ software.
4390 MMP particles were found from 35 sites of 17 sampling rivers. The major shape types were fragmented (70%) and fibrous (28%) particles and the major polymer types were PP (48%), PE (23%), and PEs/PET (18%). The mass of each particle was significantly linearly related to its projected surface area (PSA) on a logarithmic scale. The slope of the mass-PSA relationship was approximately 1.14, which ranged between 1.0 and 1.5 depending on the morphological relation of the idealized particle. Moreover, the intercept of the mass-PSA relationship was dependent on the mean of the estimated third dimension of each shape type assuming the polymer density is approximately 1. These results demonstrate that the mass-PSA relationship was dependent on the shape type rather than the polymer type. Furthermore, the mass concentration at the 35 sites was estimated by the mass-PSA relationship and compared to that estimated based on the geometrical volume assuming four three-dimensional shapes (i.e., sphere, ellipses, cylinder, and flakes) adopted in the previous studies. The former was more accurate than the latter. Consequently, the mass-PSA relationship established in the present study enables us to more accurately evaluate the mass concentration in aquatic environments. Our results guide accurately estimating the mass concentration in aquatic environments as well as insights into the geometrical relation between the mass and size of MMP particles.
Here we have clarified the geometrical relationship between mass and size of MMP particles collected from the water surface using a 335μm-mesh plankton net at 35 sites of 17 Japanese rivers from May 2019 to October 2022. After sampling in situ, all of the materials were collected into a stainless bottle after washing the net, and then the samples were processed by an oxidative degradation and density separation to efficiently extract MMP particles. After preprocessing, a picture of the MMP particle candidate was taken by a CCD camera-installed stereo microscope (SZX7, OLYMPUS) for subsequent size measurement and shape identification, and then the candidate was measured by an ultramicrobalance (XPR2UV, METTLER TOLEDO). Finally, a polymer type was identified by FTIR (IRAffinity-1S, SHIMADZU) attached to an Attenuated Total Reflection (ATR) device. The MMP particle was categorized into four shape types (Sphere, Fragment, Sheet, Fiber) and nine polymer types (PE, PP, PS, PEPP, PVC, PEs/PET, Acryl, EVA, Others). Also, the major length and projected surface area of each MMP particle were measured by the ImageJ software.
4390 MMP particles were found from 35 sites of 17 sampling rivers. The major shape types were fragmented (70%) and fibrous (28%) particles and the major polymer types were PP (48%), PE (23%), and PEs/PET (18%). The mass of each particle was significantly linearly related to its projected surface area (PSA) on a logarithmic scale. The slope of the mass-PSA relationship was approximately 1.14, which ranged between 1.0 and 1.5 depending on the morphological relation of the idealized particle. Moreover, the intercept of the mass-PSA relationship was dependent on the mean of the estimated third dimension of each shape type assuming the polymer density is approximately 1. These results demonstrate that the mass-PSA relationship was dependent on the shape type rather than the polymer type. Furthermore, the mass concentration at the 35 sites was estimated by the mass-PSA relationship and compared to that estimated based on the geometrical volume assuming four three-dimensional shapes (i.e., sphere, ellipses, cylinder, and flakes) adopted in the previous studies. The former was more accurate than the latter. Consequently, the mass-PSA relationship established in the present study enables us to more accurately evaluate the mass concentration in aquatic environments. Our results guide accurately estimating the mass concentration in aquatic environments as well as insights into the geometrical relation between the mass and size of MMP particles.