title: Temporal record of Pu isotopes in inter-tidal sediments from the northeastern Irish Sea.
abstract: A depth profile of (239)Pu and (240)Pu specific activities and isotope ratios was determined in an inter-tidal sediment core from the Esk Estuary in the northeastern Irish Sea. The study site has been impacted with plutonium through routine radionuclide discharges from the Sellafield nuclear reprocessing plant in Cumbria, NW England. A pronounced sub-surface maximum of ~10 k Bq kg(-1) was observed for (239+240)Pu, corresponding to the peak in Pu discharge from Sellafield in 1973, with a decreasing trend with depth down to ~0.04 k Bq kg(-1) in the deeper layers. The depth profile of (239+240)Pu specific activities together with results from gamma-ray spectrometry for (137)Cs and (241)Am was compared with reported releases from the Sellafield plant in order to estimate a reliable sediment chronology. The upper layers (1992 onwards) showed higher (239+240)Pu specific activities than would be expected from the direct input of annual Sellafield discharges, indicating that the main input of Pu is from the time-integrated contaminated mud patch of the northeastern Irish Sea. The (240)Pu/(239)Pu atom ratios ranged from ~0.03 in the deepest layers to >0.20 in the sub-surface layers with an activity-weighted average of 0.181. The decreasing (240)Pu/(239)Pu atom ratio with depth reflects the changing nature of operations at the Sellafield plant from weapons-grade Pu production to reprocessing spent nuclear fuel with higher burn-up times in the late 1950s. In addition, recent annual (240)Pu/(239)Pu atom ratios in winkles collected during 2003-2008 from three stations along the Cumbrian coastline showed no significant spatial or temporal differences with an overall average of 0.204, which supports the hypothesis of diluted Pu input from the contaminated mud patch.
authors.affiliation: School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom. patriclindahl@yahoo.com
authors.forename: Patric
authors.initials: P
authors.lastname: Lindahl
authors.forename: Paul
authors.initials: P
authors.lastname: Worsfold
authors.forename: Miranda
authors.initials: M
authors.lastname: Keith-Roach
authors.forename: Morten B
authors.initials: MB
authors.lastname: Andersen
authors.forename: Peter
authors.initials: P
authors.lastname: Kershaw
authors.forename: Kins
authors.initials: K
authors.lastname: Leonard
authors.forename: Min-Seok
authors.initials: MS
authors.lastname: Choi
authors.forename: Dominique
authors.initials: D
authors.lastname: Boust
authors.forename: Patrick
authors.initials: P
authors.lastname: Lesueur
mesh_terms: D000576:Americium / Q000032:analysis; D001267:Atlantic Ocean; D002586:Cesium / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods / Q000706:statistics & numerical data*; D004785:Environmental Pollutants / Q000032:analysis*; D019015:Geologic Sediments / Q000737:chemistry*; D007494:Ireland; D055848:Nuclear Power Plants; D011005:Plutonium / Q000032:analysis*; D011868:Radioisotopes / Q000032:analysis; D013051:Spectrometry, Gamma; D013997:Time Factors
chemical_list: D004785:Environmental Pollutants; D011868:Radioisotopes; D002586:Cesium; D011005:Plutonium; D000576:Americium