In-situ stabilization of potentially toxic elements in two industrial polluted soils ameliorated with rock phosphate-modified biochars

The present study was aimed at determining the efficacy of rock phosphate (RP) 3% loaded in a green coconut shell, chicken manure, and vegetable waste to make green coconut-modified biochar (GMB), chicken manure modified-biochar (CMB), and vegetable waste-modified biochar (VMB) in the fixation of Cr, Pb, Cu, Zn, Ni, and Cd in Sharafi goth and Malir polluted soils. The impact of RP impregnated with organic waste material to produce modified biochars (MBs) on stabilizing PTEs from polluted soils and reducing their uptake by mustard plant has not yet been thoroughly investigated. All modified BCs in 0.5, 1, and 2% doses were used to stabilize Cr, Pb, Cu, Zn, Ni, and Cd in two polluted soils and to reduce their uptake by the mustard plant. The obtained results revealed that the maximum mustard fresh biomass was 17.8% higher with GMB 1% in Sharafi goth polluted soil and 25% higher with VMB 0.5% in Malir polluted soil than in the control treatment. After applying modified BCs, immobilization of Cr, Pb, Cu, Ni, and Cd was observed in both soils and it reduced the uptake of these elements by mustard plants. On the other hand, although Zn mobilization increased by 0.38% for CMB 0.5% and by 5.9% for VMB 0.5% in Sharafi goth polluted soil, as well as by 3.15% for GMB 1%, 6.34% for GMB 2%, and 4.78% for VMB 0.5% in Malir polluted soil, this was due to changes in soil pH and OM. It was found that GMB 1%, CMB 0.5%, and VMB 0.5% have the potential to increase Zn uptake by mustard, while VMB 2% can reduce the element uptake by the plant. Redundancy analysis showed that soil chemical parameters were negatively correlated with PTEs in both soils and reduced their uptake by mustard. The present study revealed that MBs can stabilize PTEs in industrial and wastewater soils polluted with multiple metals and reduce their uptake by plants. • Impact of rock phosphate-modified biochars on the fixation of PTEs in two soils was investigated. • Modified biochars potentially stabilize PTEs in both polluted soils. • Modified biochars clearly reduced the uptake of PTEs by mustard plant. • Changes in fresh and dry biomasses of mustard were observed after applying modified biochars. • Long-term ex-situ trials must be conducted to assess the potential of different modified biochars.