Citrate‐mediated increase in the uptake of weathered 2,2‐bis(p‐chlorophenyl)1,1‐dichloroethylene residues by plants

Abstract

AbstractExperiments were conducted to determine the ability of citrate to enhance the plant uptake of weathered 2,2‐bis(p‐chlorophenyl) 1,1‐dichloroethylene (p,pǐ‐DDE) from soil. Plots containing three rows of clover, mustard, hairy vetch, or rye grass were constructed in soils containing p,pǐ‐DDE. On 11 occasions, the rows of each crop received water or sodium citrate (0.005 or 0.05 M). For each crop, there were significant reductions in p,pǐ‐DDE concentration in the soil fractions (near root and rhizosphere) closely associated with the plant versus bulk soil. The roots of each crop accumulated 2 to 5 times more of the weathered contaminant (dry wt) than present in the bulk soil. Citrate (0.05 M) increased the concentration of p,pǐ‐DDE in the roots of clover, mustard, and hairy vetch by 39% compared with vegetation that received water. In batch desorption studies, the release of weathered p,pǐ‐DDE was significantly greater in the presence of 0.05 M citrate than in water. Citrate increased the extracted aqueous concentrations of five metal ions (Al, Fe, Ca, K, Mn) from soil by five‐ to 23‐fold over distilled water. We hypothesize that citrate physically disrupts the soil through chelation of structural metal ions and release of bound humic material, facilitating p,pǐ‐DDE availability and uptake by plants.