Effect of mixed cadmium,copper, nickel and zinc at different pHs upon alfalfa growth and heavy metal uptake

Alfalfa plants were grown in soil-pots contaminated with a mixture of Cd(II), Cu(II), Ni(II), and Zn(II), (at 50 mg/kg each) at pHs of 4.5, 5.8, and 7.1. The plants were fertilized using a nutrient solution, which was adjusted appropriately to the same pH. Plants in the control treatment were grown in the absence of the heavy metals mixture. The growth of the control plants was the same at the three pHs studied and the heavy metal stressed plants also showed similar behavior at each pHs. There were statistically significant differences (P<0.05) between the shoot length of the control treatment plants and the length of plants grown in the presence of the heavy metal mixture. Under the effects of the heavy metal mixture, nickel was the most accumulated element in the shoot tissue, with 437, 333, and 308 ppm at pH 7.1, 5.8, and 4.5, respectively. Cadmium was found to be second in accumulated concentrations with 202 ppm, 124 ppm, and 132 ppm at pH 7.1, 5.8, and 4.5, respectively, while zinc was third, followed by copper. The maximum relative uptakes (element in plant/element in soil-water-solution) were found to be 26 times for nickel, 23 times for cadmium, 12 times for zinc. and 6 times for copper. We considered these relations as indicative of the ability of alfalfa plants to take up elements from a soil matrix contaminated with a mixture of cadmium, copper, nickel, and zinc.