A pot culture experiment was conducted to assess the effect of modified bentonite application on lead (Pb) uptake by spinach (Spinacia oleracea cv. All Green). Amendment of soil with humic acid functionalized bentonite @ 7.5 g kg-1 significantly improved the plant growth by 74.7, 128.8 and 122.6 % in first, second and third harvest, respectively over control. The metal concentration of spinach reduced to 2.17, 1.74 and 1.32 mg kg-1 for Pb at first, second and third harvest, respectively on application of 7.5 g kg-1 humic acid bentonite (T10). However, Fe-bentonite, GHA-bentonite and Humic acid-bentonite reduced Pb content in spinach at all the applied doses, but application at 7.5 g kg-1 soil was found most significant as compared to control. Between the treatments, highest dry weight of spinach plant was recorded at higher dose of Humic acid-bentonite followed by GHA-bentonite and Fe-bentonite. The hazard quotient (HQ) for metal uptake through consumption of spinach was significantly reduced by application of bentonite @ 7.5 g kg-1 as it immobilises heavy metals in polluted soil.

Functionalized clays, phytoremediation, metal contamination, risk assessment

The present study highlights the positive effects of using humic acid functionalized bentonite clay on the growth and heavy metal tolerance of spinach plants. The addition of functionalized bentonite had a significant and positive impact on the biomass production of spinach during all three harvest times, leading to a substantial increase in plant growth compared to the unamended soil. The study's findings revealed that using humic acid functionalized bentonite at an application rate of 7.5 g kg-1 proved most effective in immobilizing heavy metals like Pb. By introducing functionalized bentonite, the chemical adsorption of heavy metals increased, leading to a reduction in their mobility in plants. Bentonite's high surface area and enhanced adsorptive capacity effectively immobilized heavy metals in the soil, reducing their bioavailability and uptake by plants. The reduction in the hazard quotient of heavy metals in spinach was attributed to the decreased metal uptake by plants as a result of their immobilization in the soil due to the application of humic acid functionalized bentonite. The approach outlined in this research allows for the application of modified bentonite in soil to decrease the mobility and availability of heavy metals to plants, consequently reducing the health risks associated with consuming vegetables grown in metal-contaminated soils.

A. Naveenkumar, K.M. Manjaiah, V.K. Sharma, Prasenjit Ray, Renu Pandey, R.N. Sahoo, Rajesh Kumar, T.K. Das, Md. Basit Raza, Siyaram Meena and Ravi Saini (2023). Assessing the Impact of Functionalized Bentonite in Reducing Lead content and uptake in Spinach (Spinacia oleracea cv. All Green). Biological Forum – An International Journal, 15(8): 135-140.