Phytoextraction of metals and rhizoremediation of PAHs in co-contaminated soil by co-planting of Sedum alfredii with ryegrass (Lolium perenne) or castor (Ricinus communis).

A pot experiment was conducted to investigate the potential for phytoextraction of heavy metals and rhizoremediation of polycyclic aromatic hydrocarbons (PAHs) in co-contaminated soil by co-planting a cadmium/zinc (Cd/Zn) hyperaccumulator and lead (Pb) accumulator Sedum alfredii with ryegrass (Lolium perenne) or castor (Ricinus communis). Co-planting with castor decreased the shoot biomass of S. alfredii as compared to that in monoculture. Cadmium concentration in S. alfredii shoot significantly decreased when grown with ryegrass or castor as compared to that in monoculture. However, no reduction of Zn or Pb concentration in S. alfredii shoot was detected in co-planting treatments. Total removal of either Cd, Zn, or Pb by plants was similar across S. alfredii monoculture or co-planting with ryegrass or castor, except enhanced Pb removal in S. alfredii and ryegrass co-planting treatment. Co-planting of S. alfredii with ryegrass or castor significantly enhanced the pyrene and anthracene dissipation as compared to that in the bare soil or S. alfredii monoculture. This appears to be due to the increased soil microbial population and activities in both co-planting treatments. Co-planting of S. alfredii with ryegrass or castor provides a promising strategy to mitigate both metal and PAH contaminants from co-contaminated soils.