Interactive effects of Cd and PAHs on contaminants removal from co-contaminated soil planted with hyperaccumulator plant Sedum alfredii

Purpose Soil contamination by multiple organic and inorganic contaminants is common but its remediation by hyperaccumulator plants is rarely reported. The growth of a cadmium (Cd) hyperaccumulator Sedum alfredii and removal of contaminants from Cd and polycyclic aromatic hydrocarbons (PAHs) co-contaminated soil were reported in this study. Materials and methods Soil slightly contaminated by Cd (0.92 mg kg DW) was collected from a vegetable field in Hangzhou and was spiked with two levels (0 and 6 mg kg DW) of Cd and three levels (0, 25, and 150 mg kg DW) of phenanthrene (PHE) or pyrene (PYR). A pot experiment was conducted in a greenhouse using S. alfredii with unplanted controls for 60 days. Shoot and root biomass of plants, dehydrogenase activity (DHA), and microbial biomass carbon in the soil were measured. Concentrations of Cd and PAHs in the plant and soil were determined. Results and discussion Elevated Cd level (6.38 mg kg DW) increased S. alfredii growth. The presence of PAHs decreased the stimulatory effects of Cd on plant biomass and Cd concentrations in shoots in Cd spiked soil, thus decreasing Cd phytoextraction efficiency. Cadmium removal by S. alfredii after 60 days of growth varied from 5.8% to 6.7% and from 5.7% to 9.6%, in Cd unspiked and spiked soils, respectively. Removal rate of PAHs in the soil was similar with or without the plants. Removal rate of PYR decreased at the elevated Cd level in the soil. This appears to be due to a decrease in soil microbial activity. This is confirmed by a decrease in DHA, which is a good indicator of soil microbial activity. Conclusions Our results demonstrate that S. alfredii could effectively extract Cd from Cd-contaminated soils in the presence of PHE or PYR; however, both PAHs exhibited negative effects on phytoextraction of Cd from Cd spiked soil (6.38 mg kg DW). S. alfredii is not suitable for remediation of PAHs. The effects of Cd and PAHs concentrations on the removal rate of PAHs appear to be attributed to the changes in microbial activities in the soil.