Biochar was obtained through pyrolysis of carrot pulp (CP) and then further modified with thiourea (CH₄N₂S). We investigated the effect of carrot pulp biochar (CPB) and modified CPB (MCPB) for adsorption and chemical fractionation of cadmium (Cd) and lead (Pb) in contaminated acidic soil. Application of modified biochar significantly (p < 0.05) increased the pH, soil organic carbon (SOC), and cation exchange capacity (CEC) of the soil, especially at the 8% application rate. The adsorption equilibrium data showed that the adsorption behavior of Cd and Pb could be described more reasonably by the pseudo-second-order kinetic model and the Langmuir isotherm model more accurately fitted the experimental data than Freundlich and Temkin isotherm models. The maximum adsorption capacity of soil treated with MCPB at the 8% application rate for Cd and Pb were 4122.7 and 5219.6 mg kg⁻¹, respectively. Sequential chemical extractions revealed that incorporation soil with MCPB induced the transformation of the acid-soluble fraction of Cd to oxidizable and residual fractions, and the acid-soluble fraction of Pb to reducible, oxidizable, and residual fractions. The results demonstrated that the application of MCPB could effectively immobilize Cd and Pb, thereby reducing their mobility in contaminated acidic soil.

In this study, there is presented a thorough investigation of the effect of biochar produced via pyrolysis of carrot pulp with pre and post-modification by thiourea (CH₄N₂S) at three rates (0, 4%, and 8%) on fractionation of Cu and Zn in acidic soil. The sequential extraction procedure of BCR was utilized for the determination of heavy metals fractionation. According to the FTIR analysis, the thiourea-modified biochar (TMB) had more surface functional groups in comparison with the carrot pulp biochar (CB). The 8% TMB application, was most effective in increasing the CEC, pH, EC, and SOC of the soil than the 8% CB treatment. The BCR test revealed that after the addition of CB and TMB, the acid extractable Cu and Zn decreased considerably. Thiourea-modified biochar was more effective than pristine biochar in decreasing the acid extractable metals fraction. The addition of TMB induced the conversion of the acid extractable fraction of Cu to residual and organic matter bound fractions, and the acid extractable fraction of Zn to residual, organic matter bound and oxides bound fractions. This work suggests that thiourea-modified biochar can be a low-cost and effective amendment for immobilizing Cu and Zn in contaminated acidic soils.

Accumulation of heavy metals in edible crops is amongst major international concerns today. While consuming Lenjan variety of rice is very popular in Iran, limited evidence exists on its safety. Amid increasing public concern about the safety of locally grown and imported rice in the market, a field study was carried out to investigate uptake and translocation of Cd, Pb, Ni, and Zn by a local variety of rice crop ( Oryza sativa ) exposed to contaminated water. At harvest time and in paddy fields, 41 soil and plant samples were collected from four locations of Lenjan, central Iran; irrigated from Zayandeh Rood River. In the laboratory, different parts of the plant were milled, digested via acid digestion method, and then analysed for Cd, Pb, Ni and Zn using atomic absorption spectrophotometry. The results showed that average concentrations of Cd, Pb, Ni and Zn were 1.07, 17.22, 1.73 and 13.75 mg/kg in the plant’s stem; and 1.27, 12.32, 1.099 and 19.39 mg/kg in its grain, respectively. In general, both in the plant’s stem and grain, the Cd and Pb concentrations were much higher than the FAO/WHO standard and labelled as harmful for consumers. Moreover, among the studied heavy metals, Ni transported very weakly, while Cd and Zn conveyed most easily into the plant’s stem and grain. Of course, Pb was the least mobile metal. However, it had highly accumulated in the plant’s stem and grain.