Effects of heavy metals on microorganisms and enzymes in soils of lead-zinc tailing ponds.

Taking the soil around the lead-zinc tailings pound in the upper reaches of the Hanjiang River in Shaanxi Province as the research object, with tailings pond as the center, seven different belt zones were divided outwards, the contents of Pb, Cu, Zn, V, Ni, Cd in soil were analyzed, as well as soil basic respiration (SBR), microbial biomass carbon (MBC), microbial metabolic quotient (MMQ), and the activities of catalase, urease, cellulase, invertase and neutral phosphatase were also determined. The purpose was to reveal the intrinsic relationship between soil microbial, enzyme activities and heavy metal pollution, and to establish the characterization system of enzyme activities, soil heavy metal pollution degree, as well as microbial parameters. The results showed that: (1) The potential ecological risk index of six heavy metals was ranked as Cd > Cu > Pb > Ni > Zn > V. Cd was a high potential ecological risk, Cu was a medium potential ecological risk, and Zn, Pb, V and Ni were low potential ecological risk. The comprehensive evaluation result of Hakanson's potential ecological hazard index showed that, Zone I was of high potential risk level, Zone II, III and IV were of medium risk level, and Zone V, VI and VII were of low level. (2) Microbial biomass carbon (MBC) had a significant negative correlation or extremely significant negative correlation with 6 heavy metals, and microbial metabolic quotient (MMQ) had a significant positive correlation or extremely significant positive correlation with 6 heavy metals. MBC and MMQ were effective microbiological indexes to measure the quality status of soil, while SBR was not. (3) Catalase, cellulase, sucrase and neutral phosphatase activity had significant negative correlation with the contents of 6 heavy metals, and they could replicate the pollution degree of substantial metals in the soil. However, urease had no significant correlation with the contents of 6 heavy metals, which could not reflect the pollution degree of soil heavy metals.

Effect of biochar on immobilization remediation of Cd⁃contaminated soil and environmental quality.

PURPOSE: Field experiments were conducted to explore the remediation effects of ordinary biochar and PEI-modified biochar on the Cd-contaminated yellow brown soil, and the improvement of soil environment quality in southern Shaanxi province, so as to provide theoretical basis and technical support for in-situ remediation of Cd-contaminated soil in southern Shaanxi province. RESULTS AND DISCUSSION: Biochar applied in soil could increase the soil pH value, EC, ECEC, and SOC, and improve the soil physical and chemical properties to a certain extent. Biochar in soil could change the chemical form of Cd in soil, effectively passivate Cd in soil and reduce its bio-availability. Biochar could enhance the activities of catalase, urease, alkaline phosphatase and sucrase in soil to different degrees, and the four soil enzymes could be used as indicators of passivation effects of soil Cd by biochar. With biochar treatment, soil aggregates MWD and GMD increased to different degrees, so biochar could enhance soil stability. The biochar could decrease the content of Cd in different parts of wheat, the content of Cd in wheat grains had a highly significant positive correlation with the available content of Cd in soil, and highly significant or significant negative correlations with pH, SOC, EC, ECEC, and the activities of phosphatase, urease and sucrase in soil. Compared with ordinary biochar, the passivation effect of PEI-modified biochar on Cd was more significant. CONLUSIONS: The results of the study indicated that ordinary biochar and PEI-modified biochar could passivate the Cd in soil, and remediate Cd-contaminated soil, and improve the soil environmental quality effectively, compared with ordinary biochar, the PEI-modified biochar produced batter.