Benzene Toxicity and Removal in Laboratory Phytoremediation Studies

Abstract

Hybrid poplar cuttings were shown to impact the fate and transport of subsurface benzene, while toxicity to the poplars was not observed. Laboratory experiments investigated the toxicity response of poplar cuttings to benzene exposure, contaminant distribution in plant tissues, contaminant degradation in the soil profile, and contaminant volatilization from the soil and plant tissues. Two separate studies were conducted to evaluate these parameters. The first study examined the toxicity of benzene to hybrid poplar cuttings in batch reactors. Poplar cuttings were exposed to various concentrations of benzene contaminated water in two different types of soil. Transpiration rates were measured as an indicator of acute toxicity. No acute toxicity was noted for dose concentrations up to 1,000 ppm. The second study evaluated benzene fate and transport. Live poplar cuttings and excised controls were planted in flow-through reactors and supplied with an influent benzene stream to mimic plume conditions. The presence of live poplar cuttings enhanced benzene degradation and decreased the effluent mass of benzene. A small amount of benzene was also volatilized from the plant tissues, providing evidence of plant-enhanced volatilization. Causes for the higher degradation rates appeared to be greater microbial populations of benzene degraders and a more oxygen-rich environment. The higher redox potential observed may be an artifact of the laboratory reactor design. The results obtained in this research combined with previous studies provide evidence that phytoremediation has the potential for effective, efficient, and environmentally friendly application at sites highly contaminated with benzene and potentially for other sites contaminated with biodegradable organics or volatile organic compounds.