title: Evaluating a 'biotic ligand model' applied to chloride-enhanced Cd uptake by Brassica juncea from nutrient solution at constant Cd2+ activity.
abstract: Evidence of chloride-enhanced cadmium uptake by plants in soil experiments has been reported. However, it is still unclear whether this finding is due to increased rates of Cd2+ diffusion to plant roots or the direct uptake of complexes such as CdC1+. A controlled hydroponic experiment was undertaken to distinguish and quantify the uptake rates of free and inorganic-complexed cadmium and to model the uptake of cadmium by Indian mustard plants with a 'biotic ligand model'. Plants were treated with NaCl (0 to 200 mM) including equivalent Na2SO4 treatments. Cadmium speciation in solution was calculated using the WHAM-VI model. Results of the current trials showed that higher Cl-concentrations in solution generally resulted in greater cadmium accumulation by plants than predicted by the Cd2+ activity. Activities of Cd-chloro complexes showed the best correlations with the cadmium concentrations in the plants compared with the activity of Cd2+. The biotic ligand model showed a reasonable good fit for the plants when assuming competition by Cd2+ and CdCl+ for sorption sites at root level. The relative values of the two reaction constants suggest that root affinity for Cd2+ is 3.4 times greater than for CdCl+. Nevertheless this clearly indicates a substantial role for chloro-complexed cadmium accumulation.
authors.affiliation: Division of Agricultural & Environmental Sciences, The University ofNottingham, Loughborough, UK. ulrico.lopezch@uanl.mx
authors.forename: Ulrico J
authors.initials: UJ
authors.lastname: López-Chuken
authors.forename: Scott D
authors.initials: SD
authors.lastname: Young
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Guzmán-Mar
mesh_terms: D018533:Biomass; D002104:Cadmium / Q000737:chemistry*; D019256:Cadmium Chloride / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry; D007477:Ions; D008024:Ligands; D009149:Mustard Plant / Q000378:metabolism*; D010944:Plants / Q000378:metabolism; D012492:Salts / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D012987:Soil; D014874:Water Pollutants, Chemical / Q000302:isolation & purification; D018508:Water Purification / Q000379:methods
chemical_list: D002712:Chlorides; D007477:Ions; D008024:Ligands; D012492:Salts; D012987:Soil; D014874:Water Pollutants, Chemical; D002104:Cadmium; D012965:Sodium Chloride; D002713:Chlorine; D019256:Cadmium Chloride