Literature Review: Phytoaccumulation of Chromium, Uranium, and Plutonium in Plant Systems (ANRCP-1998-3)

expressed herein are those of the author(s) and do not necessarily reflect the views of DOE. Phytoremediation is an integrated multidisciplinary approach to the cleanup of contaminated soils, which combines the disciplines of plant physiology, soil chemistry, and soil microbiology. Metal hyperaccumulator plants are attracting increasing attention because of their potential application in decontamination of metal-polluted soils. Traditional engineering technologies may be too expensive for the remediation of most sites. Removal of metals from these soils using accumulator plants is the goal of phytoremediation (Baker et al. emphasis of this review has been placed on chromium (Cr), plutonium (Pu), and uranium (U). With the exception of Cr, these metals and their decay products exhibit two problems, specifically, radiation dose hazards and their chemical toxicity. The radiation hazard introduces the need for special precautions in reclamation beyond that associated with non-radioactive metals. The uptake of beneficial metals by plants occurs predominantly by way of channels, pores, and transporters in the root plasma membrane. Plants characteristically exhibit a remarkable capacity to absorb what they need and exclude what they don't need. But most vascular plants absorb toxic and heavy metals through their roots to some extent, though to varying degrees, from negligible to substantial. Sometimes absorption occurs because of the 2 chemical similarity between beneficial and toxic metals. Some plants utilize exclusion mechanisms, where there is a reduced uptake by the roots or a restricted transport of the metal from root to shoot. At the other extreme, hyperaccumulator plants absorb and concentrate metals in both roots and shoots (Baker, 1981). Some plant species endemic to metalliferrous soils accumulate metals in percent concentrations in the leaf dry matter (Brooks et al., 1977). The term 'hyperaccumulator' was introduced by Brooks et al. (1977) for plants growing on serpentine sites that are capable of concentrating nickel (Ni) to more than 1000 µg g-1 (0.1 percent) in their leaves on a dry matter basis. A concentration of 1000 µg g-1 has also been used to delineate exceptional uptake of copper (Cu), cobalt (Co), and lead (Pb). The delineation level is raised to 10,000 µg g-1 (1.0 percent) for zinc (Zn) and manganese (Mn) because of greater background concentrations of these metals in soil.