The impact of EDTA on the rate of accumulation and root/shoot partitioning of cadmium in mature dwarf sunflowers

In addition to increasing the mobility of metal ions in the soil solution, chelating agents such as EDTA have been reported to alter both the total metal accumulated by plants and its distribution within the plant structures. Here, mature Mini-Sun Hybrid dwarf sunflowers exposed to 300 μM Cd2+ in hydroponic solution had initial translocation rates of at least 0.12 mmol kg−1 h−1 and reached leaf saturation levels within a day when a 3-fold molar excess of EDTA was used. EDTA also promoted cadmium transfer from roots to the shoots. A threefold excess of EDTA increased the translocation factor (TF) 100-fold, resulting in cadmium levels in the leaves of 580 μg g−1 and extracting 1400 μg plant−1. When plants were exposed to dissolved cadmium without EDTA, the vast majority of the metal remained bound to the exterior of the root. The initial accumulation could be successfully modeled with a standard biosorption pseudo second-order kinetic equation. Initial accumulation rates ranged from 0.0359 to 0.262 mg g−1 min−1. The cadmium binding could be cycled, and did not show evidence of saturation under the experimental conditions employed, suggesting it might be a viable biosorbant for aqueous cadmium.

Research highlights
► EDTA-chelated Cd reaches saturation levels in sunflower leaves within 24 h.
► Passive uptake of EDTA-chelated Cd by sunflowers likely.
► EDTA-chelation of Cd increases translocation factor 100-fold.
► Binding of Cd to plant roots fits pseudo-2nd-order mechanism.
► Sunflower roots can cyclically absorb and release Cd; may be viable biosorbant.