Application of Fe3O4/SA nanoparticles and carbonized rice straw biochar as an efficient adsorbents for heavy metals: physiological study on alfalfa plant

Abstract Background The extensive use of heavy metals in industrial and agricultural fields increases the risk of heavy metals ions accumulation in various plant parts above the maximum permissible limits accepted by FAO and WHO. The objective of this study was to purify irrigation water contaminated with heavy metals to decrease their toxicity on Medicago sativa L. by using Fe 3 O 4 /Salicylic acid (Fe 3 O 4 /SA) nanoparticles or carbonized rice straw biochar (C.R.S) as low-cost sorbents. Results Characterization of synthesized nanoparticles performed using FT-IR, Zeta sizer, Zeta potential analysis, and UV Vis spectroscopy. Fe 3 O 4 /SA nanoparticles with an average size of 365 nm and a Zeta potential of +ve 18.9 mv were recorded. The adsorbents demonstrated significant capacity for purifying contaminated water with lead, cadmium, and nickel. A mixture of the three heavy metals was prepared at two levels, low and high concentrations. At low concentrations, the highest removal efficiency was achieved for Lead by 97.88%, Cadmium by 95.88% using Fe 3 O 4 /SA nanoparticles and 93.93% for Lead using C.R.S. While Nickel was the least effectively removed of the three heavy metals, reaching an efficiency of 79.51% with Fe 3 O 4 /SA nanoparticles. The use of purified water in irrigation was tested on Medicago sativa L.(alfalfa) during early seedling stage. Results showed that heavy metal stress significantly decreased germination percentage by 34%, growth parameters (plumule and radicle length, fresh and dry weight, seedling vigor index, MTI), total soluble proteins and sugars, and the activity of hydrolytic enzymes. At high concentration of heavy metals there was a considerable increase in proline, total phenolics and flavonoids, lipid peroxidation and electrolyte leakage compared to the control. The application of both adsorbents (2 g/L) significantly reduced the inhibitory effects of heavy metals and improved physiological and biochemical indicators through recovery and increase in the activity of hydrolytic enzymes. This led to a notable increase in the germination percentage that reached 99% compared to control 92%, plumule length recovered to 6.5 cm at L. C + C.R.S and radicle length to 3.5 cm at L. C + Fe 3 O 4 /SA nanoparticles, total soluble sugars, and protein content increased. Conversely, there was a significant decrease in the stress indicators, proline to 4.7 mg g⁻¹ f.wt, lipid peroxidation dropped to 28.1 µM g⁻¹ f.wt and antioxidants compounds content also decreased at the treatment L. C + C.R.S. Conclusion The research highlighted that both adsorbents are effective, eco-friendly, and low-cost techniques for removing heavy metals and in turn enhancing water quality which was reflected on alfalfa plant growth irrigated with purified water.