Humic Acid Decreased Hazardous of Cadmium Toxicity on Lettuce (Lactuca sativa L.)

The binding of Cd to humic acid was studied. The influence of a Cd-humic complex on enzyme activities (superoxide dismutases, peroxidases), availability of Cd, and biomass compared with the behavior of no treatment (control). It was examined through a hydroponics system in lettuce. Treatments were: control (no additions), humic acid (0, 100 and 1000 mg·L^-1), and Cd (0, 2 and 4 mg·L^-1). Enzyme activities increased significantly with increasing rates of cadmium. A significant increase (P<0.05) in cadmium content of leaves result in a considerable decrease in the biomass (P<0.05). It can be concluded that the humic acid applied in the media led to a decrease the metal adsorption by plant. This material can be used to reduce the availability and mobility of heavy metals in the soils, too.