Asian Research Thesis Index

Abstract

Soil contamination with heavy metals (HMs) is global issue, especially in developing countries where the knowledge and awareness regarding the hazardous contaminants is lacking grossly in rural people. Therefore, they are more vulnerable to toxic contaminants because of improper mining activities and open dumping of wastes. These contaminants with the passage of time make their way to nearby agricultural fields and enter food chain. Present study area has chromium-manganese reservoirs at larger scale and its mining has been continue since long ago. Pi results indicated that, manganese (Mn), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn), are present in higher concentrations from their MPL in nearby agriculture fields, posing potential threats to food safety, human health and soil quality. Use of biochar for the stabilization of selected HMs is environmentally friendly technique. Three different studies were conducted to accomplish objective of the study. The experiment one is about application of biochar to reduce health risks via consumption of rice (Oryza sativa) grown in Cr-Mn mine contaminated soil. Hard wood biochar (HWB) (3% w/w) was applied to three kinds of soil obtained from agriculture fields adjacent to chromium, manganese, and chromium-manganese mix ores. Two varieties of rice (DR83 and IR6) were cultivated in it and stems, leaves and grains were analyzed for HMs. Results revealed that HWB reduced the absorption of HMs significantly (P<0.05) in both varieties of rice. Dietary intake (EDI), hazard quotient (HQ) were reduced significantly (P < 0.01) in V2. HWB reduced Pb concentrations in V1 (22 to 36 %) and V2 (95 to 98%) in rice grains, is particularly more important as exposure to Pb through contaminated rice consumption may cause cancer. The HWB application significantly (P≤0.01) decreased Pb cancer risk via consumption of rice. Hence, the results concluded that HWB effectively decreased the mobility of HMs in amended soils as compare to control soils. Results of the study are in support of the use of HWB to mitigate HMs accumulation in rice and hence reducing the exposure to HMs. In second study the efficacy of HWB was investigated for bioavailability of selected metals (Cr Zn, Cu, Mn and Pb) in degraded soil of mining and their bioaccumulations in vegetables and related health risks. Application of HWB to Cr-Mn mine degraded soil @ 3% to examine the efficacy of HWB for 2nd crop (in crop/vegetable rotation technique). Spinach (Spinaccia oleracea) and Cilantro (Coriandrum sativum) and were cultivated as 2nd crop in the same amended pot, which were previously used for rice cultivation as first crop. HWB reduced the concentrations of Cr, Zn, Cu, Mn, and Pb in cilantro by 25.5%, 37.1%, 42.5%, 34.3%, and 36.2% respectively, in comparison to control. For spinach, reduction was observed for Cr 75.0%, Zn 24.1%, Cu 70.1%, Mn 78.0%, and Pb 50.5% as related to control. HWB significantly decreased (P<0.01) HMs uptake in spinach grown in amended soil. Results obtained from calculation of BAF also indicated that, amendment decreased HMs bioaccumulation in vegetables thus minimized health risk. Third study focused on a remediation technique using poplar wood biochar (PWB) and sugarcane bagasse biochar (SCBB) at 3% and 7% application rates, subsequently called PWB3, PWB7, SCBB3 and SCCB7, for the immobilization of Cr and Pb in mineimpacted agricultural soils. In a greenhouse experiment, lettuce was cultivated in contaminated soil to examine the effect of selected biochars on minimization of HMs bioaccumulation and associated human health risk. Both amendments PWB7 and SCBB7 has reduced the bioavailable Pb and Cr significantly (P<0.01) in amended soil with increase in biomass of lettuce in comparison with control treatment. Risk assessment results signified that PWB and SCBB efficiently reduced the daily intake of metal (DIM) in addition with their associated risk due to lettuce consumption as compared to the control. The Pb human health risk index (HRI) for children and adults were decreased (P<0.01) significantly with SCBB7 in comparison with PWB7 and control treatment. Efficiency of both biochars (SCBB and PWB) at application rate of 7% to reduce Cr and Pb uptake in lettuce was (69%, 73.7%) and (57% ,47.4%) respectively. For both amendments, HRI values for Cr were within safe limits for children and adults. Values of HRI for Pb were not within safe limits except for SCBB7. The results of the study indicated that SCBB7 application to mine impacted agricultural soil effectively increased plant biomass and reduced bioaccumulation, DIM and associated HRI of Cr and Pb as compared to PWB3, PWB7, SCBB3 and the control. Based on above studies results it is concluded that biochar can enhance soil fertility, increase yields and decrease bioaccumulation of HMs. Hence, biochar could play a key role in reclaiming mine-degraded soil and decreasing the possible human health risks.

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