Remediation of Pb contaminated soils by phytoextraction and amendment induced immobilization : biological aspects

Abstract

This study examines the biological aspects related to alternative remediation strategies for Pb contaminated soils: EDTA induced Pb phytoextraction and amendment induced immobilization of soil Pb by means of inorganic soil amendments. The physiological effects of Pb-EDTA and EDTA were studied on bean plants (Phaseolus vulgaris L. Limburgse vroege), grown under strictly controlled conditions on a Hoagland nutrient solution. Addition of Pb-EDTA to the growth medium increased the capacity of enzymes belonging to three different compartments of defence mechanisms against oxidative stress in roots and primary leaves, before effects on plant morphology or chlorophyll content were observed. Pb-EDTA further drastically reduced Ca, Fe, Mn and Zn content in primary leaves. EXAFS analysis revealed that only 60-70% of all Pb in leaves was complexed to EDTA. Our data did not permit to conclude whether the observed phytotoxic response is due to the presence of Pb-EDTA, unchelated Pb or their combination. SPOD appeared to be an early biomarker for Pb-EDTA induced stress, possibly due to its role in cell wall lignification. Addition of EDTA alone decreased Fe, Mn, and Zn content in primary leaves of bean plants but did not induce any stress reaction. ...