Soil Cd availability to Indian mustard and environmental risk following EDTA addition to Cd-contaminated soil

A pot experiment was conducted to investigate the influence of EDTA on the extractability of Cd in the soil and uptake of Cd by Indian mustard (Brassica juncea). Twenty levels of soil Cd concentration ranging from 10 to 200 mg kg^-1 were produced by spiking aliquots of a clay loam paddy soil with Cd(NO₃)₂. One week before the plants were harvested EDTA was applied to pots in which the soil had been spiked with 20, 40, 60 ... 200 mg Cdkg^-1. The EDTA was added at the rate calculated to complex with all of the Cd added at the 200 mg kg^-1 level. Control pots spiked with 10, 30, 50 ... 190 mg Cdkg^-1 received no EDTA. The plants were harvested after 42 days' growth. Soil water- and NH₄NO₃-extractable Cd fractions increased rapidly following EDTA application. Root Cd concentrations decreased after EDTA application, but shoot concentrations increased when the soil Cd levels were > 130 mg kg^-1 and Cd toxicity symptoms were observed. The increases in soil solution Cd induced by EDTA did not increase plant total Cd uptake but appeared to stimulate the translocation of the metal from roots to shoots when the plants appeared to be under Cd toxicity stress. The results are discussed in relation to the possible mechanisms by which EDTA may change the solubility and bioavailability of Cd in the soil and the potential for plant uptake and environmental risk due to leaching losses to groundwater.