Humic acid reduces lead phytoextraction efficiency of Erythrostemon gilliesii

Abstract

Assisted phytoremediation is extremely promising, but is still in development and needs further study. Therefore, the combination use of Erythrostemon gilliesii and humic acid was studied to aid the efficiency of lead nitrate Pb(NO3)2 phytoextraction. Seedlings were exposed to five simultaneous treatments of Pb(NO3)2 (0, 100, 300, 500, and 700 mg L−1) and humic acid (0 and 300 mg L−1) for three growth months (90 days in summer) and their effects on physiological and morphological traits of plants were recorded. Up to 300 mg L−1, Pb treatments showed apparent positive (stimulative) effects on plant traits, including dry and fresh weight, length, number of leaves, the diameter of collar and root, and root germination. Lead treatments higher than 300 mg L−1 showed negative (repressive) effects on plant growth. A decrease in Pb uptake was observed in simultaneous treatments of humic acid and Pb, which means more Pb remains unabsorbed in the soil. We conclude that E. gilliesii is well-suited to the phytoextraction of Pb in contaminated areas, but humid acid significantly reduces the efficiency of remediation; therefore, the levels of humic acid should be controlled during the remediation process in an area.