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Basic Study for Surveying Method and Distribution of Microplastics in Japanese Rivers
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A Japanese study developed and standardized microplastic sampling methods for rivers and applied them across 18 Japanese river sites, finding microplastic number densities of 0.0064 to 2.5 particles/m3 — roughly one order of magnitude lower than concentrations in nearby Japanese coastal waters. The work establishes a baseline for freshwater microplastic monitoring in Japan.
近年，直径5mm以下の微細プラスチック片（microplastics，以下MP）による環境影響が懸念されている．海洋では多くの調査・研究が行われているが，河川での調査例は少なく，調査手法も統一されていない．現地観測を行う際，プラスチック製用具の使用や周辺環境中のプラスチックとの接触による予期せぬプラスチック混入はMP採取量の誤差要因となるため，プラスチック混入への十分な配慮が必要となる．そこでまずMP調査手法に関して基礎的検討を行った．検討結果を踏まえ，これまで国内18河川で実施したMP調査の結果を整理した．得られたMP数密度（0.0064~2.5 個/m3）は日本近海（0.6~4.2 個/m3）13)より1オーダー小さく，地点毎に材質構成に違いが見られた．サイズは2mm以下がほとんどであった．
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