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 ClO₄^- was studied in smartweed (Polygonum spp.) grown in aerated hydroponic ClO₄^- 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 ClO₄^- uptake for up to 500 mg L^-1 of NO ₃^--N, SO₄^2-, PO₄ ^3-, or Cl^-. The net ClO₄^- 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 ClO₄^- 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 ClO₄^- via exudation.