Plant Uptake and Cycling of Trace Elements on Retorted Oil Shale Disposal Piles

Abstract

AbstractThis study considers some of the environmental hazards posed by high trace element concentrations in plants growing on retorted oil shale disposal piles and the potential for surface accumulation of trace elements via biocycling. Arsenic, B, Cu, F, Mo, and Se concentrations in plants growing on six disposal piles were determined 7 yr following site construction. Disposal treatments consisted of leaving Paraho retorted shale exposed at the surface, leaching exposed retorted shale with 760 mm of water, covering retorted shale with 30, 60, or 90 cm of soil, or a 30‐cm rock capillary barrier and 60 cm of soil. These treatments plus a disturbed soil reference plot (no retorted shale) were seeded in 1977 with three mixtures of native and introduced plant species. In 1983, Mo was present in plants at high enough levels to cause molybdenosis in ruminants. Molybdenum, F, As, and Se concentrations in plants decreased as depth of replaced topsoil increased. Leaching only slightly reduced concentrations in plants. Capillary barrier and 90‐cm treatments were the most effective at reducing plant trace elements concentrations; however, shrubs and legumes from these treatments still occasionally had higher trace element contents than plants growing on disturbed soil reference plots. Legumes had higher concentrations of most trace elements than grasses or shrubs. For this reason species composition had a major effect on total trace element content of stands of vegetation. Rates of movement to the surface via biocycling appear to be relatively slow, although they may continue to increase in the future.