Greenhouse evaluation of EDTA effectiveness at enhancing Cd, Cr, and Ni uptake in Helianthus annuus and Thlaspi caerulescens

Background, Aims and Scope. Phytoremediation is a promising means for the treatment of heavy metal contamination. Although several species have been identified as hyperaccumulators, most studies have been conducted with only one metal. Experiments were conducted to investigate the ability of Helianthus annuus and Thlaspi caerulescens to simultaneously uptake Cd, Cr and Ni. Materials and Methods. The efficiency of plants grown in a sandy-loam soil was investigated. The ability of two EDTA concentrations (0.1 and 0.3 g kg(-1)) for enhancing the phytoremediation of Cd, Cr and Ni at two different metal concentrations (24.75 mg kg(-1) and 90 mg kg(-1)) was studied. Results. Thlaspi hyperaccumulated Ni with 0.1 g kg(-1) EDTA. When the EDTA dosage was increased to 0.3 g kg(-1), Thlaspi was able to hyperaccumulate both Ni and Cr. Since Thlaspi is a low-biomass plant, it was considered insufficient for full-scale applications. Helianthus annuus hyperacummulated Cr (with 0.1 g kg(-1) EDTA) and Cd (0.3 g kg(-1) EDTA). Discussion. When the contamination was 8.25 mg kg(-1) per metal, the total metal uptake was 10-25% (1.35 to 2.12 mg) higher and had the same uptake selectivity (Cr >> Cd > Ni) for both EDTA levels. It was hypothesized that complexation with EDTA interfered with Ni translocation. For these experiments, the optimal results were obtained with the H. annuus-0.1-g kg(-1) EDTA combination. Conclusions. Although the use of EDTA did increase the amount of metal that could be extracted, care should be taken during in-situ field applications. Chelators can also increase the amount of metals that are leached past the root zone. Metal leaching and subsequent migration could lead to ground water contamination as well as lead to new soil contamination. Recommendations and Perspectives. Additional research to identify the optimal EDTA dosage for field applications is warranted. This is necessary to ensure that the metals do not leach past the root zone. Identification of a plant that can hyperaccumulate multiple metals is critical for phytoremediation to be a viable remediation alternative. In addition to being able to hyperaccumulate multiple metals, the optimal plant must be fast growing with sufficient biomass to sequester the heavy metals.