Phytoremediation of Soils with Mixed Contamination

Phytoremediation has the potential to be a green and sustainable approach to decontaminate and restore contaminated sites, while maintaining the biological activity and physical structure of the soils. However, its effectiveness to address the problems of mixed contaminants is not well understood since the interaction of co-contaminants can result in different phytoremediation responses. This study presents a series of laboratory experiments that probe the applicability of phytoremediation to soils co-contaminated with naphthalene, phenanthrene, lead, cadmium, and chromium; five contaminants that are commonly found at industrial sites. The specific research objectives are to investigate which plant species can best survive and remediate these typical mixed industrial contaminants in soils; examine the synergistic effects of mixed contaminants; consider the effect of the initial contaminant levels on the phytoremediation of mixed contaminants in soils; weigh strategies to enhance that phytoremediation process, including the use of biomass, chemical and electrokinetic amendments; and, finally, to study the effects of enhanced phytoremediation on historically contaminated soil that is polluted with mixed contamination. Five plant species (oat plant, sunflower, rye grass, tall fescue, and green gram) were identified as plants that can survive in the typical mixed contaminated soil considered. Although the sunflower produced the least biomass in mixed contaminated soil, it achieved the best heavy metal dissipation. Rye grass, tall fescue, and green gram did not effectively reduce the heavy metal concentrations from the soil. However, they enhanced the microbial degradation of organic contaminants. Cr alone in the soil produced the most phytotoxic soil in which no plants survived to the end of test period. Heavy metal phytoextraction by the plants reduced in presence of organic contaminants. The chemical amendments used in the study increased the phytotoxicity symptoms and reduced phytoextraction efficiency. Biomass growth and phytoextraction efficiency improved with the application of compost as a soil amendment. Experiments on the aged industrial soil confirmed this finding. The study showed that for the mixed contaminated soil considered here, compost amendment in combination with phytoremediation using the sunflower plant is a promising approach for remediation.