Heavy metal remediation in soil with chemical amendments and its impact on activity of antioxidant enzymes in Lettuce (Lactuca sativa) and soil enzymes

Abstract

Chemical amendments have been used to remediate soils contaminated with heavy metals. However, there is little understanding on the impacts of these amendments on the physiological and biochemical functions of plants and soil. This study used in situ microcosm experiment to understand the effect of chemical amendments on antioxidant and soil enzyme activity in plant and soil with respect to heavy metal reduction. Three chemical amendments—acid mine drainage sludge (AMDS), limestone (LS), and steel slag (SS)—were applied to soil at 3, 5, and 10% mixing ratios, and lettuce (Lactuca sativa) was cultivated in that soil for 30 days. The results showed that bioavailable Cd and Pb in soil was reduced by 9.8–40.5% and 4.2–92.5%, respectively. The most efficient amendment for heavy metal reduction was AMDS. The uptake of Cd and Pb also decreased by 0.5–66.1 and 21.6–79.5%, respectively, depending on the amendment type and application ratio. The activity of three antioxidants—catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)—was generally higher than the control with no amendments. This result indicated that there was minimal inhibition of antioxidant activity due to the reduction of heavy metal uptake. Also, no significant difference was observed in chemical amendments applied soil compared to control in terms of soil enzyme activity. However, correlation analysis between heavy metal concentration in soil and two soil enzyme activities showed that significantly negative correlation (p < 0.01) was observed between bioavailable Pb in soil and acid-phosphatase activity. This result might indicate that impact of bioavailable Pb was much higher than Cd in terms of inhibition of soil enzyme activity. Overall, the application of chemical amendments to heavy metal polluted had a positive effect on plant physiological function and soil enzyme activity with a reduction in bioavailable heavy metals in soil and plants.