Effect of Humic Acid Functionalized Bentonite on Heavy Metal Uptake by Spinach (Spinacia oleracea cv. All Green) Grown on Metal Contaminated Soil

A pot culture study was conducted to investigate the impact of applying humic acid functionalized bentonite (HA-B) on the uptake of heavy metals by spinach. When the soil was amended with 7.5 g kg-1 of humic acid intercalated bentonite, there was a significant improvement in plant growth. Specifically, plant growth increased by 180.7%, 212%, and 231% during the first, second, and third cuttings, respectively. Additionally, the concentration of metals in the spinach decreased substantially, with reductions of 62.8, 69.7, and 77.7% for Cd and 34.7%, 45.2%, and 64.7% for Ni during the first, second, and third cuttings, respectively, when 7.5 g kg-1 of humic acid functionalized bentonite was applied. Furthermore, the addition of humic acid intercalated bentonite at a rate of 7.5 g kg-1 to the soil significantly lowered the bioconcentration factor (BCF) of metals. The BCF decreased by 36.3%, 40%, and 55.2% for Cd and 15.2%, 13%, and 34.7% for Ni during the first, second, and third cuttings, respectively, indicating a reduced uptake of these metals by the plants. Moreover, the non-cancer health risk through hazard quotient (HQ) computation showed that the risk was significantly reduced due to consumption of spinach by the application of 7.5 g kg-1 of humic acid intercalated bentonite.