ASSESSING TRACE ELEMENT UPTAKE BY VEGETATION ON A COAL FLY ASH LANDFILL

摘要

Improved methods are required to assess the risks posed by the uptake of potentially toxic elements such as selenium (Se), boron (B). and molybdenum (Mo) by vegetation on contaminated sites. In order to develop such methods and assess risk. vegetation was collected from two sites on a soil--capped coal fly ash landrill near Dunkirk, New York, during June of l99l and June and August of l992. The mean concentrations (μg g~-l dry weight) of Se and Mo in the shoots did not exceed, respectively, 0. l2 and l8.7 in bird's--foot trefoil , 0.06 and l2. l in red clover 0.07 and 5.3 in timothy , and 0.09 and 2.2 in a mixture of grasses. These concentrations were greater than those in the same species harvested concurrently from a non--landfill site. The mean concentrations of B at the landrill ranged from 29 to 53 μg g~-1 in the legumes and from 2 to l μg g~-1 in the grasses, less than those at one non--landril1 site but greater than those at another. Within tbe landrill, the concentration of Se in grasses was not correlated with the concentration of Se in soi1 and fly ash. The concentration of Se in grasses on both landfill sites was double that of grasses on the non--landrill site despite higher mean concentrations of Se in the upper soil (0--l5 cm) on the non--landfill site. Therefore grass roots seem to be accessing Se from the ash by means of mass flow or other mechanisms. Based on our findings of significant variation in trace element uptake among species, harvests, and locations within sites, we recommend that contemporaneous transect sampling of at least two species be used to assess uptake of potentially toxic trace elements on landrills or other sites where contamination may occur.