Iron and manganese geochemistry and the distribution of 239,240Pu and 241Am in the sediments of the north east Irish sea

• Published in: The Science of the total environment 1990-06, Vol.95, p.69-87
• Main Authors: Malcolm, S.J., Kershaw, P.J., Cromar, N.J., Botham, L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Exact sciences and technology; Pollution; Soil and sediments pollution
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/0048-9697(90)90054-X

The geochemical cycling of Fe and Mn, within the seabed sediments of the northeast Irish Sea, has been investigated in an attempt to learn more about the factors controlling the distribution and behaviour of plutonium and americium released, under authorisation, from the BNF plc nuclear fuel reprocessing plant at Sellafield, U.K. Enrichment of surface sediment with both Fe and Mn results from active diagenetic redox behaviour which produces characteristic interstitial water concentration profiles at particular sites. The shape of the interstitial water profiles is controlled, in part, by differences in the general bioturbation regime at each site. This factor has been simulated in simple laboratory tank experiments. Evidence from selective chemical leaching suggests that 40% of the Pu and 80% of the Am are associated with the operationally defined Fe/Mn oxide phase. However, in the surface sediment there is no apparent correlation between either Fe or Mn content and either the Pu or Am concentrations determined by strong acid digestion of the samples. Fluxes of Fe [(1.8−29) × 10 −9 μmol cm −2s −1] and Mn [(2.0−2.5) × 10 −8 μmol cm −2 s −1] upward in sediment are similar to those measured at other nearshore sites and indicate a potential for oxide scavenging of trace elements at the sediment/water interface. The behaviour of Pu and Am has probably been dominated by general non-equilibrium conditions resulting from: (i) the recent introduction of the Pu and Am into the environment (Sellafield discharges started in 1952); (ii) the dominating effects of dispersion from the pipeline source, and (iii) the variation with time of the quantities discharged.