Anthropogenic Osmium in Macroalgae from Tokyo Bay Reveals Widespread Contamination from Municipal Solid Waste.

Human activity is influencing the global osmium cycle, driving the Os isotopic composition (187Os/188Os) of the hydrosphere and associated sedimentary material to lower values. Here, we present the Re and Os abundance and isotope systematics of macroalgae, a proxy for seawater, from Tokyo Bay to elucidate the potential sources of anthropogenic Os to the Pacific Ocean. Macroalgae from the Uraga Channel, which connects Tokyo Bay to the Pacific Ocean, record relatively low Os abundances (∼10.1 pg/g) and an 187Os/188Os of ∼0.9, indicative of surface ocean seawater. Contrastingly, macroalgae within the bay closest to central Tokyo record the highest Os abundances (∼22.8 pg/g) and lowest 187Os/188Os values (∼0.47), suggesting contamination from human activity. To determine the source of anthropogenic Os, we have developed the first Os emission inventory, based on the East Asian Air Pollutant Emission Grid database (EAGrid2010). The close relationship (R2 = 0.67 and p-value = <0.05) between Os inventories and macroalgal data suggests that municipal solid waste incinerators (MSWIs) are the dominant source of Os to Tokyo Bay. Projections for Japan estimate that 26-18+38 ng Os/m2/yr is released from MSWI smokestacks, leading to a concentration in precipitation of 26-18+38 fg/g, identifying MSWIs as a major contributor of anthropogenic Os to the hydrological cycle.