Effect of chloride application and low soil pH on cadmium uptake from soil by plants

Abstract

Although phytoremediation is a promising method for the removal of cadmium (Cd) from contaminated soil, plants remove Cd from soil slowly. To increase Cd uptake by plants, the effects of the application of chloride ions (Cl−) and a decrease in soil pH on the amount of Cd taken up by plants were investigated in a pot experiment using soil collected from paddy fields contaminated with Cd from mining wastewater. Three treatments were applied (all quantities were expressed on a 350 g soil basis): control (0.6 g (NH4)2SO4 as N fertilizer), Cl− application (0.5 g NH4Cl as N fertilizer and 0.15 g CaCl2) and low pH (0.8 g powdered sulfur plus NH4Cl and CaCl2). Sunflower (Helianthus annuus), kenaf (Hibiscus cannabinus) and sorghum (Sorghum vulgare) plants were grown in the treated soil for 33 days in a growth chamber under a 26°C/24°C day/night (16 h/8 h) regime. At harvest, the plants were separated into roots, stems and leaves, and the Cd concentration was determined. The application of Cl− approximately doubled the amount of Cd taken up by sunflower and kenaf leaves compared with the control. The effect of soil acidification on Cd uptake differed among the plant species owing to differences in tolerance to low pH. Soil pH after harvesting in the low pH treatment was approximately 3.5, which led to an increase in Cd uptake by kenaf plants, but markedly decreased Cd uptake by sorghum plants because of root damage. The results showed that the application of Cl− increased Cd uptake in all the plant species studied, and that it could be a promising method for phytoremediation of Cd in combination with soil pH adjustment, depending on the tolerance of the plant species to low pH.