UPTAKE AND ACCUMULATION OF SELENIUM BY TERRESTRIAL PLANTS GROWING ON A COAL FLY-ASH LANDFILL .3. FORBS AND GRASSES

Plants grown on coal fly ash landfills can accumulate relatively high concentrations of selenium (Se), which may be ameliorated with gypsum application to the soil. In 1988 and 1989, experiments were conducted to measure the accumulation of Se in forbs and grasses growing on a coal fly ash landfill. In 1990, a dose-response study was conducted to determine whether forbs and grasses growing on a fly ash landfill would respond to gypsum applications with reduced tissue levels of Se and increased levels of S. Higher concentrations of Se were found in plants grown on the landfill than on nonlandfill control plots, and leguminous species tended to accumulate more Se than nonlegumes. Two of the four studied species - bird's-foot trefoil (Lotus corniculatus L.) and bitterweed (Picris hieracioides L.) - had higher concentrations of S when grown with gypsum. However, only bird's-foot trefoil showed significantly reduced Se. The difference in tissue levels of Se and S was a presence/absence response, not a monotonic response to the rate of applied gypsum. Although it is clear that gypsum applications have the potential for mitigating Se uptake by some plants, the response is quite variable on a fly ash landfill, probably due to variability in concentration and availability of Se in the soil cap.