Phytoremediation using economic crops is an alternative treatment option for contaminated areas that are being utilized by people. In this study, phytoextraction with a local economic crop (corn) that allows simultaneous Cd contamination reduction and corn biomass utilization is proposed. Biosurfactants, rhamnolipid (RL) and saponin (SP), were introduced to enhance Cd phytoextraction. The optimum RL and SP dose was 4 mmol kg-1. Cd uptake and corn biomass were higher with biosurfactant addition than in the control (without biosurfactants addition), by 2.7 and 2.3-fold, respectively, on the 30th day of corn plantation. The optimum biosurfactant doses were applied to phytoextraction experiments with corn at different corn growth stages (7th, 45th, and 80th day). The highest Cd uptake levels were recorded on day 45, and the maximum uptake was achieved with RL addition (39.06 mg Cd kg-1). These results were confirmed by bioaccumulation factors, which indicated that RL enhanced soil Cd uptake by corn plants to the highest extent. However, Cd concentration in corn kernels from RL-assisted phytoextraction exceeded the standards for animal feed. On the other hand, although Cd uptake by corn plants in the presence of SP was lower, Cd content in the resulting corn kernels were within the allowable standard limit for animal feedstock. Moreover, compared to RL and control treatments, SP treatment resulted in higher Cd levels in the shoot than in the root, as confirmed by translocation factors. Meanwhile, SP could significantly promote soil Cd removal efficiency; Cd removal efficiencies on day 80 were in the order of SP (18.80%) > RL (11.33%) > control (4.59%). In addition, Cd leaching after addition of RL and SP was investigated. The two surfactants caused much lower Cd leaching from soil than ethylenediaminetetraacetic acid (EDTA). The results of this study indicate that SP-assisted Cd phytoextraction using corn is applicable for the remediation of Cd-contaminated areas in Mae Sot District.
Keywords: Biosurfactant; Phytoextraction; Phytotoxicity; Rhamnolipid; Saponin.
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