Selenium Uptake and Volatilization From Plants Growing in Soil

Selenium volatilization rates from plants and soil confined in a closed transparent chamber varied greatly among five plant species over 3− to 6-day collection periods. Astragalus bisulcatus and broccoli showed the highest rates of volatilization, 1.7 and 1.1 μg Se/kg dry soil/day, respectively. Volatilization rates for soil only, tomato, tall fescue, and alfalfa were 0.7, 0.5, 0.3, and 0.2 μg/kg/day, respectively. Although it was not possible to separate plant and soil microbial volatilization, the large differences between plant species suggest a significant role for plants in Se volatilization from soils. Se(VI) added to soil as sodium selenate was rapidly taken up by all five plant types to the extent that plant uptake dominated Se removal from the soil. Volatilization accounted for only 0.5% (alfalfa) to 6.1% (Astragalus bis.) of the selenium lost from the soil. Although Astragalus had the highest tissue selenium concentration and selenium volatilization rates, it ranked fourth behind broccoli, tomato, and alfalfa in order of selenium removal because of its small biomass at 15 weeks. Alfalfa accumulated 22.1 μg Se/g plant tissue from the Se(VI) amended soil, a concentration exceeded only by Astragalus (80.6) and broccoli (22.3). However, alfalfa had the lowest short-term net volatilization rate of the five plant types.