Accumulation, solid partitioning and remobilisation of 99Tc in subtidal and intertidal sediments in the Irish Sea

Autor: Paul Finegan, Peter I. Mitchell, Peter J. Kershaw, Aurélien Gouzy, L. León Vintró, Julie Lucey, D. Boust
Přispěvatelé: School of Physics, University College Dublin [Dublin] (UCD), Laboratoire de Radioécologie de Cherbourg-Octeville (LRC), Institut de Radioprotection et de Sûreté Nucléaire (IRSN)
Jazyk: angličtina
Rok vydání: 2009
Předmět:
010504 meteorology & atmospheric sciences
[SDV]Life Sciences [q-bio]
dissolution
010501 environmental sciences
mudstone
Sellafield
Oceanography
01 natural sciences
deposition
Deposition (geology)
beach profile
intertidal environment
Atlantic Ocean
Seabed
physical geography
seafloor
Outfall
Geology
Seafloor spreading
Europe
remobilization
speciation (chemistry)
fallout
England
chromatography
geoaccumulation
sequestration (chemistry)
Intertidal zone
Western Europe
Irish Sea
Aquatic Science
Structural basin
Marine pollution
discharge
cesium isotope
subtidal environment
14. Life underwater
reworking
0105 earth and related environmental sciences
sediment pollution
Sediment
surficial sediment
United Kingdom
marine pollution
technetium isotope
homogeneity
Cumbria
fine grained sediment
extraction
Eurasia
time series
volatile element
Zdroj: Continental Shelf Research
Continental Shelf Research, Elsevier, 2009, 29 (16), pp.1995-2010. ⟨10.1016/j.csr.2009.02.005⟩
ISSN: 0278-4343
1873-6955
Popis: Recent studies have shown that accumulation of 99 Tc in seabed sediments labelled by authorised radioactive liquid discharges into the NE Irish Sea from the Sellafield reprocessing complex is greater than previously thought. In this paper, new data on 99 Tc concentration profiles in subtidal and intertidal sediments from the eastern and western Irish Sea are provided with a view to elucidating the processes responsible for the incorporation and retention of 99 Tc in the seabed. The data show that substantial amounts of 99 Tc have accumulated in the fine-grained subtidal sediments off the Cumbrian coast, particularly after increased releases from Sellafield following the commissioning of the Enhanced Actinide Removal Plant (EARP) in 1994. In all the cores taken in this area, 99 Tc has been found to be present to depths in excess of 30 cm. Analysis of 137 Cs and 241 Am profiles, together with other supporting geochemical data, show a high degree of homogenisation of the sediments down to these depths as a result of physical and biological processes, and confirm that incorporation of 99 Tc into the sediment compartment is actually the result of mixing and reworking, rather than active sediment accumulation. In contrast, active deposition of material transported from this mixed pool of sediment appears to be the dominant mechanism controlling 99 Tc profiles in intertidal areas close to the Sellafield discharge outfall. Data obtained from the analysis of subtidal sediment cores from the western Irish Sea mud basin suggest that similar mixing processes to those occurring in the subtidal sediments of the eastern Irish Sea are also active in this area. Time-series data on 99 Tc concentrations in surficial sediments from this basin, gathered in the period 1988–2004, inclusive, show a clear increase in concentrations, by a factor of ∼2, between samples collected pre-EARP and post-EARP. The constancy of 99 Tc concentrations in surface sediments throughout the 1980s and the early-1990s suggests that little redissolution and export of 99 Tc occurred over this extended period. A similar observation applies to the post-EARP period, when concentrations remained relatively constant despite the reported steady decrease in 99 Tc concentrations in the overlying waters. This apparent lack of remobilisation is consistent with data from sequential extraction analyses, which indicate that the bulk of the 99 Tc is strongly bound to non-labile geochemical phases, with only a small proportion associated with exchangeable and acido-soluble phases. Further, these analyses show that 99 Tc is not associated with oxygen-sensitive and highly-reactive acid-volatile sulphides (AVS) to any significant extent.
Databáze: OpenAIRE
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