Calcium and lead cation balance and bioconcentration in hydroponically grown Indian mustard (Brassica juncea)
Mentor:Debra Van Engelen, Professor, Department of Chemistry, University of Redlands
Phytoremediation uses hyperaccumulating plants to take up heavy metals such as lead and cadmium from either water or soil. These plants are resistant to toxic effects and can be harvested and disposed of more economically than other remediation methods. Factors such as pH, naturally-produced or amended chelating agents, salinity, and inter-metal effects have been shown to affect the efficiency of bioconcentration. The uptake of lead by Brassica juncea was studied in hydroponic growth tanks containing a nutrient solution with EDTA and varied concentrations of calcium and lead. The goals of this project were to better understand lead uptake by B. juncea and also to develop a new method of hydroponic planting that improved harvesting of the root system for analysis. Four tanks were grown hydroponically for 11 weeks, 2 with added 50 mgCa2+/L (low Ca ) and 2 with 200 mgCa2+/L (high Ca). Two tanks, one with high and one with low calcium were also grown with 50 mgPb2+/L which had measured lead concentrations in the tank water of 5.9 x10-3 mg Pb2+/L and 4.6 x10-2 mg Pb2+/L, respectively. Low solubility of lead in tank solution occurred because of precipitated phosphate ion in the nutrient solution. After plant harvesting and HNO3/H2O2 digestion, plant and tank water were analyzed for lead, calcium, and magnesium by atomic absorption spectrophotometry. The new method of harvesting allowed analysis of the roots, which had high bioconcentration factors for Pb2+ ranging from 4x104 to 1.5 x 105 depending upon the Ca2+ concentration. The bioconcentration factor is defined by the concentration of lead in the plant (in mg/kg) divided by the concentration of lead in the environment, (in mg/L). These large bioconcentration factors indicate B. juncea’s ability to uptake large amounts of lead from the very low concentrations without suffering toxicity symptoms.