Effects of Ethylene Diamine Disuccinic Acid (EDDS) on lead (Pb2+) and cadmium (Cd2+) uptake by lettuce (Lactuca sativa L.) seedlings planted in hydroponic solutions

Abstract

This research work was carried out to investigate the effects of ethylene diamine disuccinate (EDDS) on the absorption of cadmium and lead by hydroponically grown lettuce (Lactuca sativa L.). Samples were prepared through digestion (dry ashing) method and the analytes quantitatively analyzed using Atomic Absorption Spectrophotometric (AAS) technique. The effects of EDDS on Pb²⁺ and Cd²⁺ uptake by lettuce (Lactuca sativa L.) seedlings replanted in hydroponic solutions for 72 hr in a greenhouse were investigated. Two months old seedlings were exposed to various doses of Pb²⁺ and Cd²⁺ at constant concentration of EDDS. For unchelated treatments, increase in concentrations of Pb²⁺ and Cd²⁺ in the solution increases the uptake by the plants relative to control.  Pb²⁺ contents in the roots showed more accumulation than in shoots (p<0.05) while Cd²⁺ content in the shoots was higher than in roots.  Addition of 0.0025M EDDS to the solutions of Pb²⁺ and Cd²⁺ inhibits the uptake of the metal ions at the following concentrations (0.0025, 0.005 and 0.0075 mg/L) when compared to unchelated treatments of same concentrations. At 0.025 mg/L of Pb²⁺ and Cd²⁺, chelation substantially enhances their uptakes in both shoot and root of the plant (p<0.05).  Compared to the unchelated treatments, chelation suppresses the translocation of Pb²⁺ and Cd²⁺ to the shoots of the plant (p<0.05), but there was a better translocation of Pb²⁺ (1.257) and Cd²⁺ (0.953) at 0.025 mg/L, thus indicating that, at very high concentration of the metals the plant was hyper-accumulator. For hydroponic solutions containing the combination of both metals; Pb²⁺ + Cd²⁺, Pb²⁺ uptake was more in the roots than in the shoots while Cd²⁺ content in the shoots showed more absorption than the roots for both chelated and unchelated treatments. Also, it was observed that chelation suppresses the uptake of Pb²⁺ and Cd²⁺ in the presence of one another by both root and shoot. Furthermore, increasing the concentrations of Pb²⁺ + Cd²⁺ in chelated treatments of hydroponic solutions results to a better translocation of Pb²⁺ while the translocation of Cd²⁺ to the shoot was enhanced. Generally, addition of EDDS to the hydroponic mixtures affected to a large extent the availability of Pb²⁺ and Cd²⁺ to the growing seedlings.

Keywords: Ethylene diamine disuccinate, greenhouse, hydroponic solution, lettuce, metals.