Impact of CaO, fly ash, sulfur and Na2S on the (im)mobilization and phytoavailability of Cd, Cu and Pb in contaminated soil

• Effect of amendments on immobilization of HMs and plant uptake was studied.
• CaO, FA, sulfur and Na2S reduced the DTPA-extractable Cd, Cu, and Pb in soil.
• The amendments have increased the solubility of Cd, Cu, and Pb in soil system.
• Shoots of Chinese cabbage accumulated more Cd, Cu, and Pb compared to roots.
• Sulfur reduced soil pH (3.6) and did not support the growth of Chinese cabbage.

Soil heavy metals pollution is a serious problem worldwide due to its potential human health risks through food chain. Therefore, a sustainable solution is needed to efficiently remediate HMs contaminated soils. Our study aimed to assess the impact of CaO, fly ash, sulfur, and Na2S on the immobilization of Cd, Cu, and Pb and their uptake by Chinese cabbage (Brassica rapa chinensis) in a contaminated soil. The concentration of DTPA-extractable Cd, Cu, and Pb was significantly decreased as compared to control in treated soil. However, the solubility of Cd, Cu, and Pb has increased at greater extent in soil system which favored the uptake of metals in roots and shoots of Chinese cabbage. In general, Cd uptake was significantly increased in shoots followed by roots as compared to control. In addition, Cu has also same trend of increased uptake in shoots as compared to roots. However, the uptake Pb in shoots was considerably increased in Na2S treated samples whereas roots have shown great potential for Pb uptake in CaO treated samples as compared to control. Although, sulfur treatments had efficiently immobilized metals but reduced soil pH to highly acidic level which restricted the growth of Chinese cabbage in sulfur treated samples. We assume that sulfur amendment could be applied for immobilization of metals in alkaline soils rather than acidic soils to achieve better immobilization results. In order to achieve sustainable phytoextraction of Cd, Cu, and Pb using CaO, FA, and Na2S, the non-edible hyperaccumulators species are suggested to be investigated in future studies.