Ecological considerations of the behaviour of plutonium in the environment

Radiological considerations of plutonium released to the environment are logically based upon an understanding of ecosystem structure and function. Studies of Pu in the atmosphere, lithosphere, terrestrial ecosystem of the biosphere, and in the hydrosphere are reviewed to evaluate areas for consideration of environmental consequences of nuclear wastes. Soil is the major reservoir of deposited Pu in most terrestrial ecosystems. Resuspension of Pu into the air mass above contaminated soil occurs over a highly variable range of 10−2 to 10−11 m−1, reflecting important effects of several physical and biological variables. Uptake by most natural plant species is of the order of 10−4 (acceptor/precursor). Appreciable external deposition of Pu upon plants through resuspension is a complicating factor in interpretation of field data. Pu concentrations in small terrestrial mammals also emphasize the greater importance of physical processes rather than physiological or chemical processes in the movement of Pu through terrestrial ecosystems. Freshwater and marine investigations indicate that Pu is generally concentrated over ambient levels in water but with decreases of about a factor of ten at each trophic level of a food chain. An apparent change in availability of 238Pu is indicated by several studies and physical processes that may account for this are discussed.