Emerging contaminants: Evaluation of degradable chelators towards enhancing cadmium phytoextraction efficiency of bioenergy crop grown on polluted soil

Abstract

Exogenous application of chelators towards enhancing heavy metals extraction efficiency of bioenergy crop has received considerable attention in recent time. However, little is known about optimal application rate, comparative evaluation of degradable versus non-degradable chelators and their impact on cadmium (Cd) speciation and uptake, physiological and biochemical activity of sweet sorghum grown under Cd stress. Four chelators namely, Nitrilotriacetic acid (NTA), tetrasodium N,N-diacetate (TDA), Ethylenediamine tetraacetic acid (EDTA), iminodisuccinic acid (IDA) and control (CK) were applied and compared at rates of 2, 5, and 10 mmol kg−1 towards augmenting phytoextraction efficiency of sweet sorghum for Cd remediation in a screen house study. Results showed that sweet sorghum augmented with TDA significantly (P < 0.05) increased biomass, enhanced Cd uptake and accumulation when compared to EDTA at application rate of 2–5 mmol kg−1. TDA influenced Cd speciation via increasing acid-soluble, reducible, oxidizable, and residual fractions of Cd, thus increasing Cd bioavailability. NTA and TDA increased proline concentrations, antioxidant enzymes and net photosynthetic activity rate (Pn) comparably to EDTA in sweet sorghum, thus enhancing stress tolerance and stabilizing photosynthetic activities. Overall, exogenous application of degradable TDA at 2–5 mmol kg−1 could be recommended as replacement for non-degradable EDTA in a chelate assisted approach towards augmenting bioenergy crop for phytoremediation of Cd polluted soil.

Keywords

• Phytoextraction
• Antioxidant enzymes
• Photosynthetic rate
• Stress tolerance
• Cadmium speciation