Geochronology of anthropogenic radionuclides in Ribeira Bay sediments, Rio de Janeiro, Brazil

Ribeira Bay is located approximately 130 km south of the city of Rio de Janeiro and receives discharges of liquid effluent from the Angra dos Reis nuclear power plant (NPP) site, where two pressurized water reactors are located. To test whether the presence of anthropogenic radionuclides in sediments in Ribeira Bay could be correlated to the NPP operations, we sampled seven sediment cores and determined accumulation rates and chronologies. Only one sediment core did not exhibit a superficial mixing layer; this sample was used for dating purposes. Cesium-137 and 207Bi were observed in this sediment profile, but their presence was associated with atmospheric fall-out rather than the nearby NPP. The exponential decay of 210Pb concentration with sediment layer depth was verified below a superficial mixing layer for all other sediment cores. Calculated accumulation rates ranged from 1.2 mm y−1 in the inner bay to 6.2 mm y−1 close to its entrance.

Figure optionsDownload as PowerPoint slideHighlights
► We have dated seven sediment cores on the region close to the Angra dos Reis nuclear power plant site.
► Cs-137 and Bi-207 were detected and were used as a tool to validate the Pb-210 dating results.
► The spatial variation of the Pb-210 flux indicates two main sources of sediments: the channel between Ilha Grande (Grande Island), and the continental and soil runoff from the adjacent hills.