concentration of plutonium in tissues of resident biota of these systems is very low. Low concentrations in biota may be related to two factors: 1) solubilization of high-fired oxide is extremely low in natural systems; and 2) apparent trophic transfer factors are expected to be in the range of 10 * to 107°, based primarily on results of mammalian gavage studies Higher .- The objectives of this paper are to: suggest terminology for expressing plutonium concentration in aquatic biota that more clearly reflects the functional relationships that exist between abiotic and biotic components of aquatic ecosystems than the term CF (concentration factor) presently in use. DISTRIBUTION PATTERNS The major repository of transuranic elements entering aquatic systems is the bed sediment. Observed Ky values for plutonium across a wide spectrum of aquatic systems (both freshwater and marine} are surprisingly uniform and on the order of 10° (Table 1). A significant portion of Pu is thought to arrive at the bed sediment surface as a result of association with, and subsequent settling of, suspended particulate matter (Wahlgren et al., 1976). (Pillai and Mathew, 1976). The organic (phytoplankton) :inorganic ratio of suspended particulate matter varies, depending on characteristics of the system. For example, the ratio will be lower in flowing water systems and Qpen oceans than in Takes and estuaries. The plutonium associated with inorganic suspended particulate matter may become incorporated in the bed sediment with very low hydrologic mobility. Conversely, the fraction of plutonjum reaching the bed sediment associated with the organic suspended particulate matter may then be subjected to long-term biologically and/or chemically mediated transformations resulting in its association with components of sediment that exhibit greater hydrologic mobility, (i.e., chelated, associated with organic matter, complexed with inorganic substances, or soluble). However, the biological availability of plutonium from these two components of bed sediment may not differ significantly. The strength of the association between plutonium and mineral and/or organic components of the sediment may be comparable, Distribution Coefficients for Plutonium Isotopes in Freshwater and Marine Systems 2. review the distribution and transport of plutonium in aquatic systems and place the role of primary producers in transport processes in the proper perspective; and : ao q wv om > us os ~ avs * 7 “ « we a a s rd a ao mo “ _ = od a Ss a3 a , io “— wo 2 t- th = iw 3 _t J aw rm: “ . ert it oO mm o ~N wt 42 w 7 2 ~~ or .- “ c co c wv om r on rm = = ta. me oy a = oO n a om m™ “ ° .- a L Qo om = a= u“ oe ~“ . rc oO Qa mn ov & > G 44d p oO wn ~~ ™ ow wo te wn a — ‘a Q * > c wv E c sO m co a i= od t= o” ™ m ™ = 0 3 — Table I. 1. a vO cc o <t oo L = Laboratory n M = Marine ad <+ oO —_ So se — iw Oo og ag Oo — x x a ay on ” — ~ 1 ~ - 478 479 wm <a oO _ * xm . coo = oF wT —_ o “IO x - e om wo Fa F = Freshwater (Weeks et al., 1956; Katz and Weeks, 1954; Buldakov et al. 1967). reported uptake values appear to be related to the presence of gut loading and from surface contamination by sedimentary materials. This explanation seems plausibte when one considers the kinetics of transuranic elements in aquatic systems. .