Cadmium speciation and biouptake-influence of sodium competition and ligand type

Dave, Keron
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University of Guelph

Soil solution speciation of Cd can be modified by presence of complexing inorganic and organic ligands. Hydroponically grown durum wheat was used as a model organism to study Cd accumulation under various experimental conditions. The potential for Na+ as a competitive cation for Cd accumulation was explored when {Na+}={Cd2+}, and 2.0 x 10 -3 - 2.0 x 10-5, supplied as the counterion for nitrate (NO3-), chloride (Cl-) or acetate (CH3 COO-), with a range of Cd concentrations ({Cd 2+} = 1.8 x 10-4- 1.8 x 10-7 M). When {Na+} = 0, the counterion for the anionic ligands was K +. The effect of ligand type was evaluated using nitrate and chloride (widely studied inorganic anions) and acetate (a scantly studied organic anion). The {Na+} had a significant effect on root Cd accumulation. When plants were exposed to Cd2+ and NO3 -, Cl-, or CH3COO- with K + as counterion, root Cd accumulation was similar. This was also the case when K+ was replaced with Na+ as a counterion at {Na+) " {Cd2+}. Root Cd accumulation was reduced (P<0.05) in plants exposed to Cd2+ and Na + at (Na+} = {Cd2+} in both Cl - and CH3COO- buffered exposures. For NO 3- buffered exposures, even with an excess of Na + (~ 30 mM), root Cd was still lower than that observed for plants exposed to Cl- and CH3COO-buffered Cd in same solution matrix. These results revealed a striking contrast in mechanism of counter ion activity in enhancing Cd2+ uptake in presence of a competitive cation (Na+) which was further affirmed by observations from toxicity assays.

soil solution, speciation, cadmium, inorganic ligands, organic ligands, durum wheat, cadium accumulation|sodium, competition, biouptake-influence