Microplastics Survey in Osaka Bay

Abstract

In September and December 2019, we measured the abundance of microplastics (MPs) with diameters from 0.35 mm to 5 mm suspended in the water surface layer at two locations, the inner part of Osaka Bay and the east central part of the bay. As a result, we found that the density in the inner part of the bay in September was 4.1 particles m^-3, which was the highest in this survey and was higher than those in the surveys conducted by the Ministry of the Environment in 2015 in Osaka Bay (0.75 particles m^-3) and six points in the Seto Inland Sea (average, 0.35 particles m^-3) . The high density of MPs was considered to be due to the following factors: intense rainfall, small tidal range, and stagnation of seawater due to southwestern winds. It was estimated that 49.4% of the MPs collected in the inner part of the bay in September originated from foam beads, artificial turf, and fertilizer shells. In December, no fertilizer shells were detected. The number density of MPs and its origins were considered to show seasonal fluctuations.