Biochars effects potentially toxic elements and antioxidant enzymes in Lactuca sativa L. grown in multi-metals contaminated soil

Geogenic and anthropogenic activities can leads to agriculture soil pollution and land degradation. Many cost-effective and environment friendly strategies are applied to improve soil fertility, reduce soil pollution and human health risks caused by consumption of metals contaminated vegetables. In this study we evaluate the effects of rice husk biochar (RHB), biochar from corn cob (CCB) and biochar from peanut shells (PNB) on the bioavailability of potentially toxic elements (PTEs) in soil, its bioaccumulation and antioxidant enzymes activities in Lactuca sativa L. plants. RHB, CCB and PNB amendments significantly (P≤0.05) increased Lactuca sativa L. biomass production (39%, 65% and 100%) as well as soil fertility. Amendments of PNB, RHB and CCB significantly (P≤0.05) increased soil available phosphorous (P), cation exchange capacity (CEC), pH, total nitrogen (TN), total carbon (TC) and dissolved organic carbon (DOC) concentration, but markedly reduced bioavailable concentrations of cadmium (Cd) (31%, 20% and 22%) arsenic (As) (33%, 22% and 27%), and lead (Pb) (46%, 24% and 32%). In addition, CCB and PNB amendments significantly (P≤0.01) decreased the shoot accumulation of Pb, Cd and As, while RHB amendment increased the shoot accumulations of nickel (Ni) and chromium (Cr). The reduction in PTEs accumulation may be linked with increased sorption of PTEs by biochars. Furthermore, amendments of CCB and PNB significantly (P≤0.05) suppressed the activities of SOD (53% and 69%), POD (22%, 31%) but stimulated (38% and 31%) with amendment of RHB. However, RHB, CCB and PNB amendments significantly (P≤0.05) suppressed the activity of CAT (21%, 41% and 48%) in Lactuca sativa L. plants. PNB was the most effective soil amendment as compared with RHB and CCB. However, to fully elucidate the effects of the tested biochars, long-term field trails are needed.