UPTAKE OF PHOSPHORUS AND LEAD BY BRASSICA JUNCEA AND MEDICAGO SATIVA FROM CHLOROPYROMORPHITE

Abstract

In situ remediation of lead (Pb)-contaminated soils via phosphate amendments has been extensively used to immobilize Pb as pyromorphite. However, in phosphorus (P) deficient soils, plants may develop extensive root systems to access P in any P-containing minerals, thereby affecting the stability of Pb₅(PO4)₃Cl (Chloropyromorphite; CP). We grew Brassica juncea and Medicago sativa in sand culture to evaluate the stability of CP in the presence or absence of hydroxyapatite (HA) as P source. Treatments (per kilogram of sand) watered with P-nutrient solution were control [PC₀, (without CP)], 1, and 5 g Pb as CP [PC₁, and PC₅] and 0.45 g P as HA (PA), and those of watered with P-free nutrient solution were 1 and 5 g Pb as CP [NC₁ and NC₅], 5 g Pb as CP plus 0.45 g P as HA [NAC₅], and 0.45 g P as HA [NA]. Plants in NC₁ and NC₅ treatments showed stunted growth and reductions in shoot elongation and leaf size. Among CP treated pots, the highest shoot Pb uptake was observed in NAC₅ treatment. The results suggested that Pb accumulation and translocation in the plants was markedly higher in P-sufficient conditions than in P-deficient conditions.

KEY WORDS:

• phytoremediation
• immobilization
• sand culture

ACKNOWLEDGMENTS

The authors are greatly thankful to Fikre Debela, Abbas Shafiee Banej, and Shawn Botton at University of Northern British Columbia, Prince George, B.C. Canada for their kind help in the chemical analyses of the plant samples.