Phytoextraction of Cadmium from Contaminated Soil Assisted By Microbial Biopolymers

Abstract

Heavy metal contaminated soils remain as a challenging and essential task for environmental engineering. Phytoremediation (plant-based remediation) is effective for the mitigation of large area surface soil contamination, but needs long time and the efficiency is not high. Chemical agents could increase heavy metal bioavailability in soil and bring greater accumulation in plants, but also pose risks to soil, plant growth and ground water environment. In this study, microbial biopolymers, mainly composed of protein and polysaccharide, were obtained from non-induced, copper-induced and cadmium-induced activated sludge culture, and named as ASBP, ASBPCu and ASBPCd, respectively. The influence of microbial biopolymers on phytoextraction of cadmium in contaminated soil was investigated. Microbial biopolymers, compared to other agents, were found to be more effective in improving the phytoextraction of cadmium from soil. In ASBP, ASBPCu and ASBPCd, the cadmium content in plants was found to be 1.52, 1.63 and 1.33 μg (1.9, 2.0 and 1.6 times of the control), respectively. It was also found that in the presence of microbial biopolymers ASBP, ASBPCu and ASBPCd, 10.9%, 26.2% and 13.7% of exchangeable cadmium fraction was extracted from soil matrix to plant or liquid, higher than the control test (4.3%). Microbial biopolymers were more effective in improving cadmium accumulation in plants than other chemical agents. Owing to the benign nature, ease of production, and cadmium binding feasibility, microbial biopolymers may find utility as a new environmentally safe extracting agent for improving phytoextraction of cadmium from contaminated soil.

Microbial Extracellular Polymeric Substances: Ecological Function and Impact on Soil Aggregation

“…Most of the studied EPS are negatively charged, due to the dominance of carboxyl and hydroxyl functional groups, in different proportions depending on EPS composition ( Ding et al, 2018 ). The main factors influencing metal biosorption by EPS are related to the binding sites or their chemical nature, such as pH, metal content, ionic strength, surface properties, as well as EPS molecular weight and degree of branching ( Guibaud et al, 2003 ; Fukushi, 2012 ). For instance, it was demonstrated that the structural conformation of xanthan affects Cu–xanthan bond strength.…”

The Effects of Plant-Associated Bacterial Exopolysaccharides on Plant Abiotic Stress Tolerance

“…Similarly, Abd El-Ghany and Attia [ 85 ] reported a decrease in Cl − ion in faba beans inoculated with an EPS-producing Azotobacter chroococcum strain in combination with melatonin. However, most of the studied bacterial EPS are negatively charged, due to the dominance of carboxyl and hydroxyl functional groups [ 87 , 88 , 89 , 90 , 91 ], indicating that the decrease in chloride anion concentration in PGPR-inoculated plants might not be related to the adsorption capacity of Cl − by EPS.…”

“…The role of bacterial EPS in heavy metal bioremediation has been extensively studied [ 89 ]. Moreover, PGPR are used to accelerate heavy metal phytoremediation [ 151 ].…”