Time effects of rice straw and engineered bacteria on reduction of exogenous Cu mobility in three typical Chinese soils

Globally,copper(Cu)accumulation in soils is a major environmental concern.Agricultural organic waste and some bacterial species can readily absorb metals in an eco-friendly manner,and thus are commonly used in metal-contaminated soil remediation.This study investigates the change in Cu fractions during the aging process and the time effects of rice straw(RS)and engineered bacteria(EB)(Pseudomonas putida X4/pIME)on reduction of Cu mobility.Three typical Chinese soils(red,cinnamon,and black soils)were incubated with RS or RS+EB in the presence of exogenous Cu for 24 months.The soil physicochemical properties,reactive soil components,Cu fractions,and Cu mobility were determined over time.The Cu mobility factor(MF)values were the lowest in the black soil(6.4-9.2)because of its high organic carbon and clay contents.The additions of both RS and RS+EB accelerated Cu stabilization during the aging process in all three soils.The Cu MF values decreased with time during the initial 20 months;however,the MF values increased thereafter in all soils,which might be due to the reduction of humic substances and amorphous iron oxides and the increase in iron oxides complexed on the organic matter.The reduction rates of Cu MF were similar after 16,24,and more than 24 months in the red,cinnamon,and black soils,respectively,indicating that RS and RS+EB could limit Cu mobility at different times in various soils.The RS treatment showed the greatest efficiency in reducing Cu mobility in the red,cinnamon,and black soils after 12,12,and 8 months of incubation,respectively.The RS+EB treatment was more efficient than the RS treatment in the red soil during the initial 8 months of the incubation period.Our study provides theoretical support for Cu risk assessments and RS supplementation for Cu remediation in different soils.

Effect of Water Quality on Heavy Metal Redistribution and Mobility in Polluted Agricultural Soils in a Semi-Arid Region

Mornag Plain is a coastal area of the Mediterranean basin, which has undergone an agricultural industrial boom. The aim of this study was to investigate the different water qualities used for irrigation on heavy metal mobility in these polluted agricultural soils. The geo-accumulation indices for heavy metals (Ni, Cr, Pb, Cd, Cu, and Zn) revealed that industrial activities and used treated wastewater (TWW) contributed to soil pollution, and water irrigation always decreased this contamination. After long-term use of different water types, high perturbation of heavy metal redistribution has occurred. Groundwater use altered all heavy metal redistributions in the irrigated soil among various soil-solid and soil-solution fractions, as compared to the unirrigated soil. Slight acid water use transferred some metals from different solid phase components into water-soluble and exchangeable fractions. However, TWW use transformed some Ni, Cr, Cd, Cu, and Zn from water-soluble and exchangeable fractions to less labile fractions, particularly into organically bound fractions. Reuse of conventional water within the same soil decreased the whole soil redistribution index values, indicating tendency to return to the pattern of distribution of groundwater-irrigated soil.

Lead stabilization in a polluted calcareous soil using cost-effective biochar and zeolite amendments after spinach cultivation

Biochar has been shown to be an effective organic soil amendment for the in-situ immobilization of lead(Pb).Little research has been done on the effects of biochar and zeolite interactions on Pb immobilization in contaminated calcareous soils.Therefore,the aim of this study was to investigate the effects of different levels of zeolite(2%and 4%,weight:weight)and biochars(3%,weight:weight)prepared from green compost(GB),poultry manure(PB),and municipal waste(MB)on the content of Pb in spinach shoots and Pb stabilization in a greenhouse experiment conducted using a Pb-contaminated calcareous soil.Application of GB and PB significantly decreased the Pb mobility factor(MF)from 2.8%to 4.6%and the cumulative Pb release(diethylenetriamine pentaacetate(DTPA)extraction)from 16.8%to 20.1%in the calcareous soil,which were further enhanced by the combined addition of zeolite,with Pb MF reduction from 4.4%to 8.4%and cumulative Pb release reduction from 24.8%to 28.6%.The enhancement of soil Pb immobilization was attributed to the properties of the amendments,such as high pH,ash content,and phosphorus content(10.5^(-1)1.0,390-435 g kg^(-1),and 2.5-4.3 g kg^(-1),respectively).Results of the soil Pb sequential extraction and Pb release kinetics were highly and significantly correlated with spinach shoot Pb content.Soil chemical data showed that the application of MB with 4%zeolite was the most effective treatment for immobilizing Pb(8.4%reduction in Pb MF and 28.6%reduction in cumulative DTPA-extractable Pb),which is in agreement with the results of the spinach shoot Pb(89.0%reduction in Pb uptake).

Comparative Evaluation between Water Parallel Pricing System and Water Pricing System in China: A Simulation of Eliminating Irrigation Subsidy

The reform in water pricing plays a critical role in agricultural production, which is believed to have great water savings potential. We consider eliminating irrigation subsidies as a simulation and conduct a comparative evaluation between the water parallel pricing system （WPPS） and the water pricing system （WPS）, which are incorporated into two computable general equilibrium （CGE） models, respectively. The results prove that, compared with WPPS, WPS would contribute higher capacities for water savings with more farming imports and less loss in farming output; households in rural and urban areas would benefit from more income and food consumption, which would be matched by increasing farming imports. A policy recommendation is that eliminating the irrigation subsidy should pay more concerns on alleviating the negative effects on farming outputs. Moreover, improvements in agricultural labor mobility and water demand elasticity are needed to enable more focus on the water conservation policy, particularly in WPS.

Root-Induced Changes of pH, Eh, Fe(Ⅱ) and Fractions of Pb and Zn in Rhizosphere Soils of Four Wetland Plants with Different Radial Oxygen Losses

A rhizobox experiment was conducted to compare iron （Fe） oxidation and changes of pH, redox potential （Eh） and fractions of zinc （Zn） and lead （Pb） in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants （Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia） with different radial oxygen loss （ROL） from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe（II） but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors （MF）. Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.