Sediment Distribution Coefficients and Concentration Factors for ...

For technetium, the recommended K d(1 × 10 2 ) is based on environmentallyderived values from the Irish Sea [71]. Although they may accuratelyreflect the partitioning between 99 Tc and the sedimentary material in thatarea, the extent to which water and sediments are in equilibrium is notknown. It should not be inferred that the K ds obtained are universally applicable.In particular, the influence of organic material, such as that arising frombenthic algae, has not been determined. Early experimental studies suggestedthat technetium, in either the reduced or oxidized form, generally exhibits aK dof less than 10 [61–66]. In the absence of further particulate data, it istherefore suggested that the recommended value represents an upper boundin oxic systems.Neptunium K ds for suspended sediment in coastal waters of the UK [89,90] and for sediment pore water in the Irish Sea [71] have been reported.Experimental K ds for northeast Atlantic calcareous ooze and clay fall withinthis range [91, 92]. Other reported experimental values, for various substrates,are much lower and are not directly applicable [66, 93, 94].The recommended K dfor plutonium is for a mixture of oxidation states(i.e. Pu III/IV plus V/VI).A relatively large number of environmental K ds havebeen reported from a wide variety of marine, riverine and lacustrine environments,and they consistently fall within the range 1 × 10 4 –1 × 10 6 [47, 71,95–107]. There seems to be little justification in extending the range for sensitivityanalysis. A large number of experimental determinations have also beenmade, and with very few exceptions (e.g. approximately 1 × 10 1 –1 × 10 4 forNorth Pacific red clays [108]) K ds fall within the range 1 × 10 4 –1 × 10 6 [71, 86,92, 109–114]. The latter range also includes values for calcareous sedimentsfrom the northeast Atlantic [71, 92].Environmental K ds for americium and curium are given by Pentreath etal. [101, 102], Lovett (unpublished data) [106],Aarkrog et al. [104] and Noshkin(unpublished data) [107]. Few experimental data are available for curium,although Erickson [108] gives values for abyssal red clays. Far more experimentaldata are available for americium, with most studies reporting values inthe range of the field data [86, 92, 108, 113–116].A default K dof 1 was assigned to non-reactive elements such as hydrogen,the major elements in sea water (Na, Cl and S) and inert gases (Kr and Xe).For some elements (Ru, Te, Pm, Dy and Ir) insufficient data are availableto calculate K ds using the methodology described in Section 2.2.1 or to deriveK ds from published data. The recommended K ds for these elements were chosento be equal to K ds for periodically adjacent elements and appear in parenthesesin Table I.From experimental studies it is assumed that trivalent californiumbehaves like curium and americium [117, 118].16