Rapid removal of Chernobyl fallout from Mediterranean surface waters by biological activity

• Published in: Nature (London) Vol. 329; no. 6134; pp. 56 - 58
• Main Authors: Fowler, Scott W, Buat-Menard, Patrick, Yokoyama, Yuji, Ballestra, Serge, Holm, Elis, Nguyen, Huu Van
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 03-09-1987; Nature Publishing Group
• Subjects: Accidents; Animals; Chemistry; Continental interfaces, environment; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Euphotic zone; Exact sciences and technology; Feces - analysis; Fission products; Grazing; Humans; Isotope geochemistry; Isotope geochemistry. Geochronology; Marine; Marine biology; Nuclear accidents & safety; Nuclear Reactors; Ocean, Atmosphere; Oceanography; Organic compounds; Particulate organic matter; Plankton - analysis; Radiation; Radioactivity; Radioisotopes; Radioisotopes - analysis; Retention time; Sciences of the Universe; Seawater - analysis; Surface water; Time series; Ukraine; Zooplankton; Ukraine; Chernobyl USSR; Mediterranean Sea; MED; Ukraine, Chernobyl; Pollution; Radioactive isotopes; Biogenic effects; Radioisotope; Mediterranean Sea; Fallout; Zooplankton; Sea water
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/329056a0

The sinking of particulate organic matter from the euphotic zone is an important pathway for the vertical transport of many elements and organic compounds in the sea. Many natural and artificial radionuclides in surface waters are readily adsorbed onto suspended particles and are presumably scavenged and removed to depth on time scales commensurate with both particle sinking rate and retention time of the radionuclide on the particle. Previously, abyssal benthic organisms from the northeast Pacific were found to contain short-lived fission products which entered the sea surface as fallout from nuclear testing. The presence of these radionuclides at great depth could not be explained by Stokesian settling of small fallout particles and it was hypothesized that zooplankton grazing in the surface layers packaged these particle-reactive radionuclides into large, relatively dense faecal pellets which rapidly sank to depth. We report here data from a time-series sediment trap experiment and concomitant zooplankton collections which show conclusively that Chernobyl radioactivity, in particular the rare earth nuclides 141Ce and 144Ce, entering the Mediterranean as a single pulse, was rapidly removed from surface waters and transported to 200 m in a few days primarily by zooplankton grazing.