Physiological Effects Of Magnetic ?Fe₃O₄? Nanoparticles And Their Reducing Effects On The Toxicity Of Heavy Metals In The Seedlings Of Cucumber And Wheat

Due to their anticipated high-volume production and widespread use in coming years,engineered nanomaterials will inevitably be released into the environment and interact with plants during manufacture,use,and disposal.This dissertation focused on the physiological effects of magnetic?Fe₃O₄?nanoparticles on cucumber and wheat plants.Magnetic?Fe₃O₄?nanoparticles were synthesized by reduction method using vitamin C or ethylene glycol as a reductant for 6 nm and 50-100 nm,respectively.The obtained magnetic?Fe₃O₄?nanoparticles were characterized by transmission electron microscopy?TEM?,scanning electron microscopy?SEM?,X-ray powder diffraction?XRD?,thermogravimetric analysis?TGA?,vibrating sample magnetometer?VSM?,and Fourier transform infrared spectroscopy?FTIR?.The mean size,size distribution,and zeta potential of 50 mg/L magnetic?Fe₃O₄?nanoparticles?6 nm,50 nm,100 nm?or bulk-Fe₃O₄ were measured by Dynamic Light Scattering?DLS?.In this work,experiments were performed based on two main steps after synthesized of magnetic?Fe₃O₄?nanoparticles:1.The phytoxicity effects of Fe₃O₄ NPs?6 nm,50 nm,100 nm?,and bulk were evaluated in cucumber?Cucumis sativus L?and wheat?Triticum aestivum L?plants grown in hydroponic conditions in terms of growth parameters,biomass production,TEM observation,antioxidant enzyme activities,and MDA content.The results show that,among the synthesized nano-Fe₃O₄?6 nm,50 nm,and 100 nm?,only the small size?6 nm?was observed to have significant inhibition on fresh and dry biomass of cucumber and wheat plants.Nano-and bulk-Fe304 treatments?21days?caused more oxidative stress in cucumber plants than wheat.Cucumber plants grown under lowest concentrations of 50 mg/L nano-Fe₃O₄?6 nm?were affected by a decrease in biomass and enzyme activities compared to the control.However,at higher concentration of nano-Fe₃O₄ dosage?2000 mg/L?,there was significant increase in biomass and enzymatic activities?SOD and POD?respectively.The phytotoxicity effects of the different sizes of nano-Fe₃O₄ particles and bulk-Fe304 might depend on the chemical composition,the structure properties/particle sizes,the concentration in the tested medium,the time of incubation,as well as the plant species.2.The effects of Fe₃O₄ NPs and bulk on phyotoxicity of heavy metals were investigated on the seedlings of cucumber and wheat in two times.Firstly,we evaluated the effects of Fe₃O₄ NPs?6 nm,50 nn,100 nm?,and bulk on the toxicity of Cd in the seedlings of both cucumber and wheat.The experimental treatments included four concentrations?0,50,500,and 2000 mg/L?of nano-or bulk and 25 mg/l of Cd.The results showed that,among the nano-Fe₃O₄ with different sizes?6 nm,50 nm and 100 nm?and bulk-Fe₃O₄,only the addition of nano-Fe₃O₄?6 nm?significantly decreased the Cd accumulation,Cd-induced seedling growth inhibition and oxidative stress in the seedlings of both cucumber and wheat.To understand if nano-Fe304?6 nm?particles can reduce the toxicity of other heavy metals,new experiments were performed to investigate their mitigation effects on the toxicity of four heavy metals?Pb,Zn,Cd,and Cu?in wheat and cucumber seedlings.These experiments were performed with 2000 mg/L of Fe₃O₄ NPs,1 mM and 10 mM of heavy metals.The results showed that,nano-Fe₃O₄?2000 mg/L?did not change the toxicity of the tested heavy metals at high concentration?10 mM?in the seedlings of both cucumber and wheat.Addition of magnetic?Fe₃O₄?nanoparticles?2000 mg/L?in each metal solution?1 mM?,significantly decreased the growth inhibition and activated protective mechanisms to alleviate oxidative stress induced by heavy metals in the wheat and cucumber seedlings.The reducing effects of nano-Fe₃O₄ against heavy metals stress could be dependent on the increase in the enzyme activity?SOD and POD?,but also their adsorption capacity of heavy metals.Our results may imply a size and species-dependent protective effect of magnetic nanoparticles against the toxicity of heavy metals during the seedling growth.