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Estimation of Microplastic Generation from Plastic Debris Littered on River Basin Based on UV Exposure Experiments
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UV irradiation experiments on plastic beverage bottle caps examined changes in molecular structure, surface morphology, and mass loss to estimate microplastic generation rates from littered plastic debris. Annual microplastic generation from bottle caps scattered across Japan's river basins was estimated at 22.6 kg, representing less than 0.01% of annual river plastic waste flux but highlighting the need for further research.
本研究では新品の飲料用ボトルキャップ試料片に紫外線を照射し，分子構造・表面形状・質量変化に着目して劣化度を評価した．UV照射によってキャップ試料片の質量減少が見られ，表面に亀裂等が生じていることが確認された．また表面粗さの指標である算術平均粗さが質量比（初期質量に対する劣化質量の比率）と有意な相関があることから，粗くなった表面からnmサイズレベルの微細プラスチックが発生している可能性が示唆された．そこで，紫外線照射量を説明変数に，質量減少率を目的変数にした一般化線形モデルを構築し，全国各地の年間紫外線量を代入することで，全国に散乱する飲料用ボトルキャップからの年間微細プラスチック発生量を推計したところ，年間22.6kgであった．これは，国内河川からの年間プラごみフラックスの0.01%未満であったが，河川流域における散乱プラごみの微細化について更なる研究の進展が求められる.
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