Surfactant-assisted removal of 2,4-dichlorophenol from soil by zero-valent Fe/Cu activated persulfate

The organic compounds contaminated soil substantially threatens the growth of plants and food safety.In this study,we synthesis zero-valent bimetallic Fe/Cu catalysts for the degradation of 2,4-dichlorophenol(DCP)in soils with persulfate(PS)in combination of organic surfactants and exploring the main environmental impact factors.The kinetic experiments show that the 5%(mass)dosage of Fe/Cu exhibits a higher degradation efficiency(86%)of DCP in soils,and the degradation efficiency of DCP increases with the increase of the initial PS concentration.Acidic conditions are favorable for the DCP degradation in soils.More importantly,the addition of Tween-80,and Triton-100 can obviously desorb DCP from the soil surface,which enhances the degradation efficiency of DCP in soils by Fe/Cu and PS reaction system.Furthermore,the Quenching experiments demonstrate that SO_(4)^(-1)·and·OH are the predominant radicals for the degradation of DCP during the Fe/Cu and PS reaction system as well as non-radical also exist.The findings of this work provide an effective method for remediating DCP from soils.

A highly porous animal bone-derived char with a superiority of promoting nZVI for Cr(Ⅵ)sequestration in agricultural soils

Paddy soil and irrigation water are commonly contaminated with hexavalent chromium[Cr(Ⅵ)]near urban industrial areas,thereby threatening the safety of agricultural products and human health.In this study,we develop a porous and high specific area bone char(BC)to support nanoscale zero-valent iron(n ZVI)and apply it to remediate Cr(Ⅵ)pollution in water and paddy soil under anaerobic conditions.The batch experiments reveal that BC/n ZVI exhibits a higher removal capacity of 516.7 mg/(g·n ZVI)for Cr(Ⅵ)than n ZVI when normalized to the actual n ZVI content,which is 2.8 times that of n ZVI;moreover,the highest n ZVI utilization is the n ZVI loading of 15%(BC/n ZVI15).The Cr(Ⅵ)removal efficiency of BC/n ZVI15 decreases with increasing p H(4–10).Coexisting ions(phosphate and carbonate)and humic acid can inhibit the removal of Cr(Ⅵ)with BC/n ZVI15.Additionally,BC exhibits a strong advantage in promoting Cr(Ⅵ)removal by n ZVI compared to the widely used biochar and activated carbon.Our results demonstrate that reduction and coprecipitation are the dominant Cr(Ⅵ)removal mechanisms.Furthermore,BC/n ZVI15 shows a significantly higher reduction and removal efficiency as well as a strong anti-interference ability for Cr(Ⅵ)in paddy soil,as compared to n ZVI.These findings provide a new effective material for remediating Cr(Ⅵ)pollution from water and soil.

Rice(Oryza sativa L.)seedlings enriched with zinc or manganese:Their impacts on cadmium accumulation and expression of related genes

Cadmium(Cd)contamination in paddy soils means that the rice produced there may be unsafe for human consumption.A hydroponic study was conducted to enrich rice seedlings with zinc(Zn)or manganese(Mn),and the uptake and transport characteristics of Cd in these Zn-and Mn-rich seedlings were subsequently investigated using a greenhouse pot trial.The results showed that hydroponic cultivation in 10-50μmol L^(-1) Zn(ZnSO_(4)·7 H_(2)O)or50-250μmol L^(-1) Mn(MnSO_(4)·H_(2)O)for 30 d had no significant impact on rice growth,while the accumulation of Zn and Mn was 7.31-18.5 and 25.4-47.7 times higher,respectively,than in the control(no Zn or Mn addition).The accumulation of Cd in the Zn-and Mn-rich rice plants was 26.3%-38.6% and 34.4%-44.5% lower than that in the control,respectively,and the translocation factors of Cd from roots to shoots also decreased by 23.3%-41.3% and 25.3%-37.0%,respectively,after transplanting to Cd-contaminated soils.Furthermore,the relative expression levels of OsIRT1(Oryza sativa iron-regulated transporter 1)were downregulated by 40.1%-59.3% and 16.0%-25.9%,respectively,in the Zn-and Mn-rich seedling roots.This downregulation may indicate a possible mechanism contributing to the reductions in Cd absorption.Field experiments confirmed that the Zn-and Mn-rich seedlings produced brown rice(unpolished rice grains)with significantly decreased concentrations of Cd(34.2%-44.4%).This study provides an innovative method for reducing the food safety risks from rice grown on slightly to moderately Cd-contaminated paddy soils.

Selected dark sides of biomass-derived biochars as environmental amendments

With the rapid increase in the application of biochars as amendments, studies are needed to clarify the possible environmental risks derived from biochars to use safely the biomass resources. This work reported selected dark sides of maize straw-and swine manurederived biochars pyrolyzed at 300 and 500°C. During the pyrolysis processes, total heavy metals in the biochars were enriched greatly accompanying with considerable emission of the heavy metals into atmosphere and the trends became increasingly obvious with pyrolysis temperature. Meanwhile, the biochars showed distinctly decreased available heavy metals compared with raw feedstocks, which could be mainly attributed to the sorption by the inorganics in the biochars. The water-and acid-washing treatments significantly increased the releasing risks of heavy metals from biochars into the environments. Electron paramagnetic resonance analysis indicated that persistent free radicals, emerged strongly in the biochars as a function of the aromatization of biomass feedstocks, were free from the influence of water-, acid-, or organic-washing of the biochars and could remain stable even after aged in soils for 30 days. Dissolved biochars, highly produced during pyrolysis processes, showed distinct properties including lower molecular weight distribution while higher aromaticity compared with soil dissolved organic carbon.The results of this study provide important perspectives on the safe usage of biochars as agricultural/environmental amendments.

Influence of soil type and genotype on Cd bioavailability and uptake by rice and implications for food safety

Cadmium （Cd） entering the human body via the food chain is of increasing concern. This study investigates the effects of soil type and genotype on variations in the Cd concentrations of different organs of nine rice plants grown on two types of soils with two Cd levels. Cd concentrations in nine rice cultivars varied significantly with genotype and soil type （P 〈 0.01）. The Cd concentration was higher in red paddy soil （RP） than in yellow clayey paddy soil （YP）. The average Cd concentrations of different organs in three rice types were indica 〉 hybrid 〉 japonica for the Cd treatments and controls. The polished grain concentration in YP and RP soils had a range of 0.055--0.23 mg/kg and 0.13-0.36 mg/kg in the Cd treatment, respectively. Two rice cultivars in YP soil and five rice cultivars in RP soil exceeded the concentration limits in the Chinese Food Hygiene Standard （0.2 mg/kg）. The Cd concentrations in roots, stems, and leaves were all significantly and positively correlated to that in polished grain in a single test. The Cd concentrations in polished grain were positively and significantly （P 〈 0.01） correlated with the calculated transfer factors of stem to grain and leaf to grain Cd transfer. The results indicated that the variations of Cd concentration in grain were related to Cd uptake and the remobilization of Cd from stem and leaf to grain. Also, the cultivars with a strong tendency for Cd-accumulation should be avoided in paddy soil with low soil pH and low organic matter content to reduce the risks to human health from high Cd levels in rice.

Genotypic variations in the accumulation of Cd exhibited by different vegetables

It is an important approach to use the Cd-contaminated soils properly by growing low accumulator or excluder plants for Cd to produce safe foods. To find the suitable vegetable species for growing in Cd-contaminated soils, in the present study the variations in the Cd accumulation for twenty eight vegetable species and several cultivars of five common vegetables （cowpea, kidney pea, bitter gourd, cucumber and squash） were investigated in two soil Cd levels （1 and 2 mg/kg Cd）. Experimental results showed that highly significant differences in Cd concentration were evident among 28 vegetables. For example, spinach Cd concentrations were 110-fold and 175-fold higher than that of sweet pea under the 1 and 2 mg/kg Cd exposures, respectively. For Cd accumulation, the order of vegetable species was： leafy vegetables solanaceous vegetables kale vegetables root vegetables allimus melon vegetables legumes. Distinctive differences were also identified when comparing different cultivars of the five common vegetables with an average range of 0.003–0.094 mg/kg Cd. Our results indicated that a large genotypic variation existed among vegetable species or cultivars when subjected to Cd exposure. Therefore, it is important and feasible to elect/breed vegetable species/cultivars with low accumulation of Cd, especially in mildly Cd-contaminated soils.

Effects of rape straw and red mud on extractability and bioavailability of cadmium in a calcareous soil

Screening of cost-effective soil amendments is important to develop ＂in situ＂ remediation techniques for cadmium （Cd） contaminated soils. In this study, different soil amendments, including red mud, a by-product of the alumina industry, and acid-treated, nano-treated by nanoparticle milling, nano and acid-treated red muds, zeolite, corn straw, and rape straw, were evaluated to immobilize Cd in two added levels （2 and 5 mg Cd·kg^-1 soil） in a calcareous soil by single and sequential extractions and by cucumber （Cucumis sativus L.） pot experiments. Results indicated that cruciferous rape straw significantly decreased the concentrations of water soluble, extractable Cd in soils, and Cd in cucumber plants, and it was more effective than gramineous corn straw. Also, red mud generally decreased the extractability and bioavailability of Cd added to calcareous soils more effectively than zeolite. Furthermore, the efficiency of red mud could be increased by the treatment of nano-particle milling due to the increase in specific surface area of red mud. It is potential to use rape straw and red mud as soil amendments to develop a cost-effective and efficient ＂in situ＂ rernediation technology for Cd mildly contaminated calcareous soils.

Field evidence of decreased extractability of copper and nickel added to soils in 6-year field experiments

The phytotoxicity of added copper （Cu） and nickel （Ni） is influenced by soil properties and field aging. However, the differences in the chemical behavior between Cu and Ni are still unclear. Theretbre, this study was conducted to investigate the extractability of added Cu and Ni in 6-year field experiments, as well as the link with their phytotoxicity. The results showed that the extractability of added Cu decreased by 6.63% （5.10% 7.90%）, 22.5% （20.6e,~~23.9%）, and 6.87% （0~17.9%） on average lbr acidic, neutral, and alkaline soil from 1 to 6 years, although the phytotoxicity of added Cu and Ni did not change significantly from 1 to 6 years in the long term field experiment. Because of dissolution of Cu, when the pH decreased below 7.0, the extractability of Cu in alkaline soil by EDTA at pH 4.0 could not reflect the effects of aging. For Ni, the extractability decreased by 18.1% （10.1e/~33.0%）, 63.0% （59.2% 68.8%）, and 22.0% （12.4% 31.8%） from 1 to 6 years in acidic, neutral, and alkaline soils, respectively, indicating the effects of aging on Ni were greater than on Cu. The sum of ten sequential extractions of Cu and Ni showed that added Cu was more extractable than Ni in neutral and alkaline soil, but similar in acidic soil.

Distinct roles of pH and organic ligands in the dissolution of goethite by cysteine

Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils,while the roles of pH and organic ligands in this process are poorly understood.Herein,the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands.Our results showed that cysteine exhibited a strong reactivity towards goethite-a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to0.1 hr^(-1).However,a large portion of Fe(Ⅱ) appeared to be "structural species" retained on the surface.The decline of pH was favorable to generate more Fe(Ⅱ) ions and enhancing tendency of Fe(Ⅱ) release to solution.The decline of generation of Fe(Ⅱ) by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite.Interestingly,the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(Ⅱ) release from 0.09 to 0.15 hr-1;nevertheless,they negligibly affected the overall generation of Fe(Ⅱ) in opposition to the pH effect.Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds(S-S) to generate cystine through oxidative dehydration,and subsequently,inducing electron transfer from cysteine to the structural Fe(Ⅲ) on goethite;meanwhile,those organic ligands act as Fe(Ⅱ) "strippers".The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils.