Influence Of Biochar On Uptake And Bioaccumulation Of Engineered Nano-particles(ENPs)in Food Crops

In recent years'nanotechnology-based products are used extensity in every field of life,releasing massive quantities of engineered nano-particles(ENPs)in the environment,posing a potential threat for the ecosystem safety.ENPs interaction with plants can affect their health.Moreover,plants are the primary producers in the terrestrial environment and dietary consumption of food plants/crops containing ENPs can transfer these nano-pollutants to humans through the food chain.Thus,it is crucial to immobilize and reduce the bioavailability of ENPs in food crops by using a sustainable and renewable source such as biochar.As biochar has been applied successfully for the remediation of both organic and inorganic pollutants.However,little is known about biochar interaction with nano-pollutants.Biochar is a carbon-rich material usually obtained from the waste biomass by thermochemical conversion process in an inert or oxygen-limited atmosphere.Benefits of biochar included but not limited to improve soil physico-chemical characteristics for favorable plant growth and economical crop yield,remediation of environmental pollutants,sequestration of carbon and energy source.In this study,we produced the biochar under variable pyrolysis operating conditions and characterize using an array of techniques such as SEM,Raman,XRF,FTIR,XPS,TGA,XRD,Brunauer-Emmett-Teller(BET)and Elemental Analyzer.Characterization results indicated that favorable type of biochar for C-sequestration and adsorption of environmental contaminants has produced at relatively high temperature(?500 ?),extended retention time(90 min),lower heating(1 ? min-1)and sweep gas flow(20 Sccm)rates and fine biomass particle size(<200 mesh).Moreover,produced biochar was applied for the remediation of ENPs.Food crops,wheat {Triticum aestivum L.),rice(Oryza sativa L.)and maize(Zea mays L.)were exposed to different concentrations(0,100,200,500,1000 and 2000 mg L-')of silver(Ag),cerium dioxide(CeO2)and titanium dioxide(TiO2)ENPs without and with biochar amendment(@2%w/v)under hydroponics exposure system.In alone ENPs treatments,TEM-EDS results revealed the cellular uptake and plants tissues localization of ENPs in the nano-form and disturb the plant growth as well as photosynthesis and gas exchange related physiological traits.Conversely,biochar amendment with ENPs substantially reduced the plant's tissues accumulated mass of respective element confirmed by ICP-MS analysis and subsequently alleviated the phyto-toxic effects of ENPs.Meanwhile,biochar also promoted the plant growth by improving biomass production,root and shoot elongation as well as assimilation of macro-and micronutrients.Biochemical and EPR analysis confirmed that the mechanism of nano-toxicity in plants is oxidative stress through the production of reactive oxygen species(ROS)mainly superoxide(O2·-)radical.Moreover,XPS and FTIR results of ENPs-biochar complex revealed the role of carboxylate,hydroxyl,and sulfur surface functionalities of biochar in ENPs immobilization.These results indicated that biochar addition is an effective method to inhibit the bioavailability and accumulation of ENPs in food crops for the nano-safety of plants and ecosystem.