Degradation and Uptake of Benzene in Laboratory Phytoremediation Studies

In whole-plant laboratory studies, hybrid poplar trees were shown to impact a variety of fate and transport mechanisms for benzene. Laboratory experiments investigated the distribution of the contaminant in the plant tissues, degradation in the soil profile, and volatilization from both the soil and leaf tissues. A new testing system was developed that allowed for rapid testing that is more field-representative than earlier studies. Whole plants were utilized in a reactor design that included both a saturated and a vadose zone. The continuous feed reactors were supplied with a steady influent benzene stream to mimic plume conditions. The presence of the poplar trees enhanced the degradation rate of the benzene, and dramatically decreased the effluent mass of benzene. Benzene was also volatilized from the leaf tissues, providing evidence to the extent of plant enhanced volatilization that has not been previously documented. The observed degradation and removal pathways were a result of active/live trees. Reactors with killed controls did not exhibit the removal seen in the live tree replicates. The soil profile maintained higher degradation rates with the trees present. Causes for the higher degradation rates appeared to be larger microbial populations of benzene degraders and preferable redox conditions in the presence of the poplars. These results combined with previous hydroponic and related field scale studies to provide evidence that phytoremediation has potential for effective, efficient, and environmentally friendly application at benzene contaminated sites, and potentially other contaminated sites with biodegradable organics or VOCs.