Abstract

Microplastics discharged from human daily activities are not decomposed by sewage treatment but are introduced into the oceans through land-water systems, and are accumulated in filter-feeding bivalves. This study aimed to investigate microplastic accumulation in Mytilus galloprovincialis artificially exposed to microplastics. The mussels were exposed to fluorescent microplastics made of polypropylene (diameter of 53-63 μm) for 21 days at concentrations of 50 mg/L, 0.5 μg/L, and 0 μg/L. Microplastic distribution and concentration in mussel tissues were analyzed by histology and image processing, respectively. In our study, the microplastics used were partially decomposed into nano-sized particles during the experiment. Thus, two types of micro-particles were investigated in the present study: microplastics (φ < 5 mm) and nanoplastics (φ < 20 μm). Micro/nano-sized plastics were found only in the mussels exposed to the 50 mg/L concentration; the gill, stomach, stylus sac, secondary duct, and intestine of the mussels were the organs of accumulation. Pathological symptomssuch as hemocyte infiltration and digestive tubule atrophy were found around micro/nano-sized plastics, suggesting that these particles cause physiological disorders in mussels.