Uptake and Exudation Behavior of Perchlorate in Smartweed

Perchlorate uptake has been reported in a variety of vascular plants, but the mechanisms affecting the uptake, translocation, and exudation of ClO - 4 in plants are not well known. The uptake and transport behavior of ClO - 4 was studied in smartweed (Polygonum spp.) grown in aerated hydroponic ClO - 4 solutions with or without other common anions. Uptake followed first-order kinetics (0.017 ± 0.003 day -1 ) and there was no apparent competitive effect on ClO - 4 uptake for up to 500 mg L -1 of NO - 3 –N, SO 2- 4 , PO 3- 4 , or Cl-. The net ClO - 4 mass uptake was proportional to transpiration but with some exclusion of ClO - 4 from the transpiration stream. Up to 4% of the ClO - 4 in plants after a 30-d exposure to a 10-mg/L solution of ClO - 4 was exuded from the roots within 15 d after the exposure was ended. Perchlorate exudation followed first-order kinetics with a rate coefficient of 0.0018±0.0006 (day -1 ). Results obtained in this study indicate that evapotranspiration may be the critical variable to predict accumulation potential in plants and that phytoremediation strategies should take into account the re-release potential of ClO - 4 via exudation.