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Rising and Settling Propertity of Microplastics in Rivers
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This study investigates the vertical distribution and rising/settling velocities of microplastics in river water through field observations at the Edo River and laboratory experiments, finding that settling velocity (average 13.5 mm/s) exceeds rising velocity (average 2.68 mm/s) and that denser microplastics accumulate near the riverbed.
本研究では，河川水中の5mm以下の微細なプラスチック片（microplastics，MP）の輸送特性を明らかにするために，平常時に江戸川野田橋で現地観測を行い，MP濃度鉛直分布を調べるとともに，採取されたMPを用いた室内実験を行うことでMPの上昇（沈降）速度を調べた．河川におけるMP濃度の鉛直分布には，水表面と底面付近にピークがあり，水表面（底面）には比重が1以下（1以上）のMPが比較的多く分布していた．また，MPの沈降速度（平均: 13.5 mm/s）は，上昇速度（平均: 2.68mm/s）よりも大きく，サイズと共に増加していた．従って，河川水中の鉛直混合下であっても，比重の大きなMPが底層に沈降していることが示唆された．
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