A significant portion of microplastics < 1mm are "missing", since the assumed inputs from land-based sources do not reflect the quantities reported on the ocean surface , This discrepancy suggests that sedimentation of microplastics occurs readily in the marine environment. Sediment microplastic concentrations were found to be an order of magnitude higher than surface water. This is consistent with data reported for Hiroshima Bay and Tokyo Bay , which are the only other known studies within Japan as well as coastal areas of Guangdong, South China 42 and river mouths of Manila Bay . The higher concentrations of microplastics found in sediment highlight the sinking of microplastic particles in the coastal ocean. The exact processes involved in the vertical transfer of microplastics from surface water to sediment are still widely unknown .