Lead speciation and availability affected by plants in a contaminated soil

Area of Science:

• Environmental Science
• Soil Science
• Biogeochemistry

Background:

• Lead (Pb) speciation in plant rhizospheres influences its mobility and plant uptake.
• Understanding Pb speciation is crucial for assessing Pb fate in soil-plant systems and developing remediation strategies.

Purpose of the Study:

• To investigate how different plant species alter lead speciation and availability in the rhizosphere.
• To evaluate the potential of eucalypt, palisade grass, and Indian mustard for lead phytostabilization.

Main Methods:

• Greenhouse experiment with three plant species and a control.
• X-ray absorption near edge structure (XANES) spectroscopy to determine Pb speciation in soil.
• Measurement of Pb concentration in plant tissues.

Main Results:

• In bulk soil, Pb was mainly associated with illite (Pb-Il) and lead monoxide (PbO).
• Rhizosphere Pb speciation shifted to Pb sorbed to kaolinite (Pb-Ka) and lead acetate ((CH₃COO)₂Pb), indicating complexation by organic acids.
• Palisade grass rhizosphere showed higher (CH₃COO)₂Pb and lower Pb-Ka, correlating with significantly lower Pb uptake by the plant.

Conclusions:

• Palisade grass utilizes low molecular weight organic acids (LMWOAs) to complex and detoxify Pb in the rhizosphere, limiting its uptake.
• The ability of palisade grass to reduce Pb bioavailability suggests its potential for phytostabilization in Pb-contaminated soils.