Sorption of lead ions onto oxidized bagasse-biochar mitigates Pb-induced oxidative stress on hydroponically grown chicory: Experimental observations and mechanisms

This pilot study investigated the affinity of oxidized biochars to sorb lead ions (Pb2+) in aqueous solutions, and its potentiality to serve as bio-filters to detoxify Pb-induced oxidative stress on hydroponically grown chicory. Raw bagasse was slow-pyrolyzed at 600 degrees C to produce original biochar (O-B), which was further oxidized by HNO3 and KMnO4 to generate HNO3-B and KMnO4-B, respectively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), digital selected-area electron diffraction (SAED) and Fourier transform infrared spectroscopy (FTIR) analyses were performed to study physicochemical properties of pre- and post-sorption samples. Kinetic and isothermal batch sorption experiments proved the high affinity of oxidized biochar to Pb2+ ions. Both physisorption and chemisorption mechanisms participated mutually in sorption process. Leaf histochemistry analysis showed various dysfunctions on plants grown under severe Pb-stress including (i) induction of oxidative stress, (ii) deactivation in antioxidant enzymatic and non-enzymatic defense pathways, (iii) defects in plant water status, (iv) disruption in photosynthetic pigments synthesis, and (v) disturbance in the membrane permeability to solute leakage. Biochar filters (particularly KMnO4-B) exhibited a scavenging effect against these adverse effects by reducing Pb-bioavailability. Furthermore, the chemical characteristics of biochar and its derivatives (biochar-derived humic acids) provided additional stimulating effect to plant scavenging mechanisms. This ameliorative effect of biochar filters minimized the dramatic reductions in vegetative measurements of plants grown under severe Pb-stress. Hence, this study provides insights regarding the potentiality to functionalize biochar and its derivatives for heavy metal detoxification. (C) 2018 Elsevier Ltd. All rights reserved.