Beneficial effects of tobacco biochar combined with mineral additives on (im)mobilization and (bio)availability of Pb, Cd, Cu and Zn from Pb/Zn smelter contaminated soils

The efficacy of tobacco biochar (TB) alone and in combined with mineral additives: Ca-hydroxide (CH), Ca-bentonite (CB) and natural zeolite (NZ), on immobilization of Pb, Cd, Cu and Zn, via reduce its (bio) availability to plants were investigated. The soils were collected from Tongguan contaminated (TG-C), Fengxian heavily contaminated (FX-HC) and Fengxian lightly contaminated (FX-LC) fields, Shaanxi province, China. The contaminated top soils were treated with low-cost amendments with an application rate of 1% and cultivated by Chinese cabbage (Brassica campestris L.) under greenhouse condition. Results showed that the all amendments (p < 0.05) potentially maximum reduced the DTPA-extractable Pb 82.53, Cd 31.52 and Cu 75.0% with TB + NZ in FX-LC soil, while in case of Zn 62.21% with TB + CH in FX-HC soil than control. The addition of amendments clearly increased dry biomass of Brassica campestris L. as compared with un-amended treatment (except TB + CH). Furthermore, these amendments markedly increased the uptake by plant shoot viz, Cd 10.51% with TB alone and 11.51% with TB + CB in FX-HC soil, similarly in FX-LC Cd increased 5.15% with TB + CH and 22.19% with TB + NZ, respectively. In same trend the Cu uptake in plant shoot was 19.30% with TB + CH in TG-C, whereas 43.90 TB + CH and 19.24% with TB + NZ in FX-LC soil. On the other hand as compared to control Cu accumulation in plant root was observed by TB, TB + CH and TB + CB treatments, while maximum uptake was 62.41% with TB + CH in TG-C soil. Consequently, except TB + CH treatment the chlorophyll content potentially increased in all amendment than control treatment, because of changes in soil EC, pH but increased CEC values after application of amendments. The results of this pot experiment are promising but they will further need to be confirmed with long-term field experiments.