Effect of Redox Potential and pH on the Uptake of Cadmium and Lead by Rice Plants

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Abstract
Redox potential and pH are two of the major factors influencing the mobilization and immobilization of heavy metals in flooded soils and sediments, and their availability to plants. A system developed for growing plants in soil suspensions where redox potential and pH can be controlled was used to study the uptake of cadmium (Cd) and lead (Pb) by rice plants (Oryza sativa L.). Uptake of Cd and Pb by root and shoot tissue, and their translocation from root to shoot, was determined at six different redox potentials (−200, −100, 0, +100, +200, and +400 mV) and four pH values (5, 6, 7, and 8). The effects of redox potential and pH on the levels of water‐soluble Cd and Pb in the soil suspensions were also studied. Almost all Cd entering the rice plants accumulated in the shoots. Total Cd uptake and shoot uptake increased with an increase in suspension redox potential and a decrease in pH. Water‐soluble Cd in the soil suspension was significantly correlated with total plant Cd and Cd uptake by shoot. Total Pb uptake, including Pb associated with the roots, decreased with an increase in suspension redox potential and pH. Uptake of Pb by shoot decreased with an increase in pH. No definite redox potential effect was found on Pb uptake by the shoot. Lead was less mobile than Cd in the rice plants and was primarily associated with the roots. Water‐soluble Pb decreased with an increase in redox potential and pH, and was significantly correlated with total plant Pb uptake and Pb uptake by shoot.

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