Fluvial Transport of Chernobyl Plutonium (Pu) to the Black Sea: Evidence from 240Pu/239Pu Atom Ratios in Danube Delta Sediments

Abstract

Sector field ICP-MS has been used to determine 239+240 Pu activity and 240 Pu/ 239 Pu atom ratio profiles in a sediment core obtained in 1997 from the Danube Delta region of the Black Sea. The 239+240 Pu activity profile reveals the presence of a 1963 stratospheric fallout peak, along with two more recent peaks stemming from fluvial transport of Chernobyl Pu through the Danube watershed into the Black Sea. The two recent peaks occur in the early 1990's and are associated with 240 Pu/ 239 Pu atom ratios as high as 0.307, significantly exceeding the established range of stratospheric fallout ( 240 Pu/ 239 Pu = 0.180 ± 0.014). The Chernobyl-derived 240 Pu/ 239 Pu features in the core are also associated with elevated 238 Pu activities (determined by alpha spectrometry), and 238 Pu/ 239+240 Pu activity ratios of 0.08-0.10 in excess of the stratospheric fallout signature ( 238 Pu/ 239+240 Pu = 0.04).