Effects of Elevated Concentrations of Co-Existing Heavy Metals and PAHs in Soil on Phytoremediation

Abstract

This study presents a series of laboratory experiments conducted to investigate the effects of elevated contaminant concentrations on phytoremediation of soils with mixed contaminants. A silty clay (typical field soil) was spiked with naphthalene and phenanthrene [representative polycyclic aromatic hydrocarbon (PAH) contaminants] and lead, cadmium, and chromium (representative heavy metals) in increased concentrations. Avena sativa (oat plant), and Helianthus annuus (sunflower) were grown in these contaminated soils and in uncontaminated (clean) soil for comparison purposes. The results showed that an increase in contaminant concentrations negatively influenced plant growth and biomass, with the sunflower showing lower germination, survival, growth, and biomass rates under increasing contaminant concentrations. However, the sunflower was relatively more effective than the oat plant for phytoextraction of heavy metals under all of the contaminant concentrations studied. Both plants caused higher chromium reduction than lead and cadmium reduction within the soil for all of the tested conditions. The final PAH concentrations did not indicate a significant decrease in PAH degradation due to the presence of plants. The phenanthrene concentrations in the final planted and unplanted pots were considerably lower than in the initial samples. Overall, plant growth and heavy metal phytoextraction were reduced with an increase in the contaminant concentrations.