Immobilization of Pb and Cu by organic and inorganic amendments in contaminated soil

Soil contamination with heavy metals has become a global environmental-health concern. A series of greenhouse experiments were conducted to investigate the effects of rice straw, rice straw derived biochar (BC), multi-walled carbon nanotubes, and single superphosphate (SSP) on immobilization of Pb and Cu via sequential extraction of BCR, total characteristics leaching procedure (TCLP), and metals phytoavailability to rapeseed in Pb and Cu spiked soil. Moreover, the residual effect of applied soil amendments on growth and uptake of Pb and Cu in tomato was also investigated in the metals spiked soil. In results, the addition of BC to Pb and Cu spiked soil proved the most effective amendment in modifying the distribution pattern of Pb and Cu from acid-soluble (less bioavailable) to residual fraction (non-toxic), thereby improving the geochemical stability of contaminated soil. The application of BC (6% w/w) reduced the uptake of Pb and Cu in shoot and root by 46 and 36%, and 77 and 58%, respectively. While investigating the residual impact in tomato, the uptake was decreased by 36 and 66% for Pb and 29 and 61% for Cu in shoot and root samples, respectively. With the application of BC (6% w/w), the concentrations of Pb and Cu in the shoot portion of tomato were below the permissible limits as set by the world health organization. The application of SSP was more effective in reducing TCLP-Pb to 0.2 mg L−1 in metals spiked soil compared to the other amendments. However, the bioavailability of Cu was increased with increasing SSP addition. In conclusion, the application of BC was more effective in reducing Pb and Cu phytoavailability through immobilization in contaminated soil compared to the other organic and inorganic amendments.