Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2001
Publication Date: 7/27/2001
Technical Abstract: Phytoextraction of heavy metals by hyperaccumulator plants is a potential method of remediating soils. It has been well documented that soil pH is an important factor affecting absorption of Ni and Co by crop plants. However, to our knowledge, no studies to characterize the effect of altering the pH of contaminated soils on Ni and Co accumulation by Ni/Co- hyperaccumulating Alyssum species have been reported. Two Alyssum Ni- hyperaccumulator species were used in both a greenhouse and a field experiment with farm soils collected near a historic Ni refinery in Ontario, Canada. A muck soil total Ni 1700 mg/kg while a mineral soil had 2550 mg/kg. Soil pH was adjusted using nitric acid and CaCO3 to provide a range of pH before planting; the field study was conducted using similar soils and two pH levels: "as is" and calcareous by limestone addition. An unexpected result of both experiments was that Ni uptake by these Alyssum species was reduced at lower soil pH and increased at higher soil pH, opposite the effect on soil Ni solubility. For A. murale grown on Quarry muck, shoot Ni concentrations of A. murale were 4630 mg/kg at pH 6.32, 4600 mg/kg at pH 6.04, 3140 mg/kg at pH 5.75 and 2180 mg/kg at pH 5.4. In a subsequent field study, limestone treatment significantly increased Ni concentration in Alyssum shoots compared to the control (2500 to 4000 mg/kg). In contrast to the results for Ni, shoot Co, Mn, and Zn showed increased uptake with lower soil pH in agreement with the literature for non-hyperaccumulator plants. These results indicate that pH management will be important factor in commercial phytoextraction, and that natural Ni hyperaccumulator species achieve increased Ni accumulation at higher pH, opposite the effect of pH on Ni solubility.