Zn-Cu Interaction Affecting Zn Adsorption and Plant Availability in a Metal-Contaminated SoilA

In a previous greenhouse experiment, we showed that there was an interaction between Cu and Zn, which affected growth and metal uptake by young barley plants grown on soil to which Cd, Cu, Pb, and Zn had been added. We suggested that the underlying mechanism was the control of the amount of plant-available Zn by competitive adsorption between Cu and Zn. In order to test this hypothesis, the adsorption of Zn alone, and in the presence of added Cd, Cu and Pb, has been measured using the same soil. Following adsorption, the extractability of the Zn in CaCl2 solution was measured. The adsorption isotherms showed that of the added metals only Cu had a large effect on Zn adsorption. The effect of Cu was to reduce Zn adsorption and to increase the amount of CaCl2-extractable (i.e. plant-available) Zn, in agreement with the conclusions from the greenhouse experiment. The magnitude of the effect of Cu on plant-available Zn was similar in both experiments.

Liquefaction of metal-contaminated giant reed biomass in acidified ethylene glycol system:Batch experiments

Giant reed is a suitable pioneer plant for metal-contaminated soil phytoremediation,however,it is imperative to dispose the metal-contaminated biomass after harvesting.The liquefaction of metal-contaminated giant reed biomass in ethylene glycol system with sulfuric acid as catalyst for the precursors of polyurethane compounds was studied.The results show that giant reed biomass from metal-contaminated soil is potentially liquefied and significantly affected by solvent/solid ratio,liquefaction temperature and liquefaction time （P〈0.05）.The liquefaction rate of biomass in acidified ethylene glycol system can reach 85.2% with optimized conditions of 60 min,170 ℃,3% sulfuric acid and solvent/biomass ratio of 5：1.The hydroxyl value of liquefied products is of 481 mg KOH/g while reactive hydroxyl groups of them are abundant,which is promised as potential precursors for polyurethane compounds.The solvent liquefaction is a potential method to dispose the metal-contaminated biomass,however,the containing-metal liquefied products should be studied deeply in order to get the suitable precursors in future.

Global perspectives and future research directions for the phytoremediation of heavy metal-contaminated soil:A knowledge mapping analysis from 2001 to 2020

In total,9,552 documents were extracted from the Web of Science Core Collection and subjected to knowledge mapping and visualization analysis for the field of phytoremediation of HM-contaminated soil(PHMCS)with CiteSpace 5.7 R3 software.The results showed that(1)the number of publications increased linearly over the studied period.The top 10 countries/regions,institutions and authors contributing to this field were exhibited.(2)Keyword co-occurrence cluster analysis revealed a total of 8 clusters,including“Bioremediation,”“Arsenic,”“Biochar,”“Oxidative stress,”“Hyperaccumulation,”“EDTA,”“Arbuscular mycorrhizal fungi,”and“Environmental pollution”clusters(3)In total,334 keyword bursts were obtained,and the 25 strongest,longest duration,and newest keyboard bursts were analyzed in depth.The strongest keyword burst test showed that the hottest keywords could be divided into 7 groups,i.e.,“Plant bioremediation materials,”“HM types,”“Chelating amendments,”“Other improved strategies,”“Bioremediation characteristics,”“Risk assessment,”and“Other.”Almost half of the newest topics had emerged in the past 3 years,including“biochar,”“drought,”“health risk assessment,”“electrokinetic remediation,”“nanoparticle,”and“intercropping.”(4)In total,9 knowledge base clusters were obtained in this study.The studies of Ali et al.(2013),Blaylock et al.(1997),Huang et al.(1997),van der Ent et al.(2013),Salt et al.(1995),and Salt(1998),which had both high frequencies and the strongest burst scores,have had the most profound effects on PHMCS research.Finally,future research directions were proposed.

Phosphate-induced differences in stabilization efficiency for soils contaminated with lead, zinc, and cadmium

Phosphates can cost-effectively decrease the mobility of Pb in contaminated soils. However, Pb always coexists with other metals in soil, their competitive reactions with phosphates have not been tested. In this study, the abilities of KHzPO4, K2HPO4, and K3PO4 to stabilize Pb, Zn, and Cd in soils contaminated with a single metal or a ternary metal for different phosphorus/metal molar ratios were investigated. Results indicated that the stabilization efficiency of KH2PO4, K2HPO4, and K3PO4 for Pb, Zn, and Cd in single metal contaminated soil （P/M ratio 0.6） was 96.00%-98.74%, 33.76%-47.81%, and 9.50%-55.79%, respectively. Competitive stabilization occurred in the ternary system, Pb exhibited a strong competition, the stabilization efficiency of Zn and Cd reduced by 23.50%- 31.64%, and 7.10%--39.26%, respectively. Pyromorphite and amorphous lead phosphate formed with excess KH2PO4 or K2HPO4 addition, while K3PO4 resulted in the formation of a hydroxypyr- omorphite precipitate. Amorphous Zn and Cd phosphates and hydroxides were the primary products. The immobilization rate of Zn and Cd depends on pH, and increased significantly in response to the excess phosphate application. This approach provides insight into phosphate-induced differences in stabilization efficiency in soils contaminated with multiple metals, which is of theoretical and engineering significance.

Responses of Carbonic Anhydrase to Cadmium in the Zinc/Cadmium Hyperaccumulator Picris divaricata Vant.

A number of higher plants are able to hyperaccumulate cadmium(Cd). However, it is unknown whether cadmium(Cd) plays a biological functional role in the carbonic anhydrase(CA) of hyperaccumulators. A hydroponic experiment was conducted to explore the potentially physiological function of Cd in CA and the accumulation and tolerance of Cd in the Zn/Cd hyperaccumulator Picris divaricata Vant. P. divaricata was exposed to nutrient solutions with six Cd concentrations(0, 5, 10, 25, 50 and 75 μmol L^(-1)). After 12 d, plants were harvested for the analysis of plant biomass, Cd concentration and CA activity. The Cd concentrations in plant increased with the increasing Cd in nutrient solution, reaching 640 and 3 100 mg kg^(-1) in shoot and root, respectively, at the 75 μmol L^(-1) Cd treatment. Meanwhile, plant growth was enhanced by the Cd treatments at 5–25 μmol L^(-1), but it was significantly inhibited when the plants were exposed to solutions with higher Cd concerntrations(50 and 75 μmol L^(-1)). Exposure to Cd significantly increased the CA activity in P. divaricata, which reached a maximum value of 21.27 U mg^(-1) proteins at the 25 μmol L^(-1)Cd treatment, and the CA activity and shoot Cd concentration were positively correlated at solutions Cd of ≤ 25 μmol L^(-1). Moreover, two protein bands appeared on the denatured gel electrophoresis of purified CA, indicating that P. divaricata may have CA isomers with their respective molecular weights at around 60 and 55 k Da, at least one of which is Cd-bound. In addition, trace amounts of Cd in purified CA significantly increased with the supplied Cd concentration in nutrient solution(5–25 μmol L^(-1)). The results suggested that Cd may play a biological role by enhancing the activities and forming the active Cd-specific CA in the hyperaccumulator P. divaricata.