水稻不同生育期土壤微生物区系对模拟Cr（Ⅵ）污水灌溉的响应

通过盆栽试验,分析模拟Cr(Ⅵ)污水灌溉对水稻不同生育时期土壤微生物区系特征的影响.结果表明:(1)土壤细菌数量在低浓度Cr(Ⅵ)(10 mg·L-1)灌溉条件下明显增加而在高浓度Cr(Ⅵ)(50 mg·L-1)灌溉条件下明显降低,土壤真菌、放线菌及钾细菌数量随着Cr(Ⅵ)灌溉浓度的增加而明显降低,而土壤磷细菌数量随着Cr(Ⅵ)灌溉浓度的增加而明显增加;(2)水稻不同生育时期土壤微生物对Cr(Ⅵ)处理的敏感性不同,土壤细菌敏感性生育前期高于生育后期,而土壤真菌及放线菌正好相反;(3)加Si处理对土壤细菌有明显的刺激作用,明显缓解高浓度Cr(Ⅵ)在水稻拔节期和抽穗期对土壤放线菌的抑制作用.与之相反,加Si处理使Cr(Ⅵ)对土壤无机磷细菌数量的刺激作用消失,甚至使抽穗期和成熟期无机磷细菌数量明显低于对照.     

铬污染土壤的微生物修复

采用淋溶实验研究微生物对铬污染土壤中Cr(Ⅵ)的修复,研究培养基成分、培养基添加量及淋溶液pH值对修复效果的影响.结果表明,培养基淋溶能完全修复铬污染土壤中水溶性Cr(Ⅵ),浸出液中Cr(Ⅵ)浓度由初始的700.3mg·L-1降低至检出限以下.单独加入碳源作为培养基时,土壤中Cr(Ⅵ)不能得到完全修复,碳源与氮源结合作...     

水稻对5种重金属累积特征及食用安全研究

为探究土壤中重金属污染对水稻食用安全性的影响,以上海市青浦区现代农业园区水稻和染毒土壤为试验材料,采用温室盆栽土培试验方法研究了镉(Cd)、铅(Pb)、镍(Ni)、铬(Cr)和汞(Hg)5种土壤重金属在不同含量梯度下水稻生物量变化以及水稻籽粒部分累积特征,并基于《食品安全国家标准食品中污染物限量》(GB 2762-2017)和靶标危害指数法(target hazard quotient,THQ)分析了土壤中5种重金属的安全阈值.研究结果表明,Cd、Hg和Cr对水稻地上部分生物量影响表现为"低促高抑"规律,Ni对水稻生物量影响不明显,随着Pb浓度升高,水稻生物量逐渐下降;水稻籽粒对5种重金属富集能力排序为Ni＞Cr＞Cd＞Pb＞Hg,水稻植株部分对5种重金属的富集量大于籽粒部分,富集趋势与籽粒部分相一致,植株部分含量约为籽粒部分的2倍～8倍,水稻籽粒中Cd、Pb、Ni、Cr和Hg含量与土壤中对应重金属含量呈显著正相关线性关系(P＜0.01);依据《食品安全国家标准食品中污染物限量》(GB 2762-2017)中谷物食用安全限量值以及靶标危害指数法,推导出污染区域土壤中各重金属安全阈值为:Cd 0.51 mg·kg-1、Pb 330.33 mg·kg-1、Ni 131.00 mg·kg-1、Cr 231.67 mg·kg-1、Hg 0.93 mg·kg-1.     

重金属铬(Ⅵ)和铅对南京土壤中赤子爱胜蚓生长及繁殖的影响

以南京化学工业园的土壤为研究对象,分析土壤中重金属Cr(Ⅵ)和Pb对赤子爱胜蚓(Eisenia fetida)生长及繁殖的影响.结果表明,与对照组比较,暴露28 d时,较低浓度的Cr(Ⅵ)(4—8 mg·kg-1)和Pb(1000—1500 mg·kg-1)能促进赤子爱胜蚓的生长发育,而较高浓度的Cr(Ⅵ)(32—64 mg·kg-1)和Pb(3000 mg·kg-1)则显著抑制赤子爱胜蚓的生长发育;赤子爱胜蚓的产茧量随着Cr(Ⅵ)和Pb浓度的升高被显著抑制,其中,Cr(Ⅵ)抑制赤子爱胜蚓产茧量的EC50(半数有效浓度)、NOEC(无观察效应浓度)和LOEC(最低观察效应浓度)分别为22.86(20.56—25.42)、8、16 mg·kg-1.Pb抑制赤子爱胜蚓产茧量的EC50、NOEC和LOEC分别为2280.34(2200.90—2362.65)、1500、2000 mg·kg-1;与人工土壤中Cr(Ⅵ)和Pb对赤子爱胜蚓产茧量的28 d-EC50有显著性差异.     

亚铁盐添加的矿物聚合物对Cr(Ⅵ)的解毒与固化研究

中国铬盐生产量及消费量均居世界第一,铬盐生产排放的铬渣量很大,其中Cr(Ⅵ)是一种高毒性物质,是国家重点控制的重金属污染物之一,寻找经济、高效的Cr(Ⅵ)去除方法一直是研究的热点。以煤矸石为原料,以水玻璃和Na OH为碱性激发剂,合成矿物聚合物,用亚铁盐添加的矿物聚合物对Cr(Ⅵ)进行解毒与固化研究,并采用XRD、TEM/EDS、XPS对固化体进行检测。结果发现,当添加的Fe(Ⅱ)与Cr(Ⅵ)摩尔比大于3∶1时,矿物聚合物中总铬浸出的质量浓度小于1 mg·L-1,铬固化率大于99%。以亚铁盐Fe SO4·7H2O作还原剂,矿物聚合物对Cr(Ⅵ)的最大固化量为0.8%。随着Fe SO4·7H2O和Cr(Ⅵ)添加量按3∶1的摩尔比增加,矿物聚合物的抗压强度减小。XRD检测表明,Fe SO4·7H2O和Cr(Ⅵ)添加的矿物聚合物为非晶质结构。TEM/EDS检测表明,矿物聚合物的非晶质结构中含有Fe和Cr。XPS检测结果证明,矿物聚合物中Fe和Cr分别为Fe(Ⅲ)和Cr(Ⅲ)。亚铁盐添加的矿物聚合物对Cr(Ⅵ)的解毒与固化是基于氧化还原反应。在Fe(Ⅱ)和Cr(Ⅵ)添加的矿物聚合物合成过程中,Fe(Ⅱ)被氧化成了Fe(Ⅲ),Cr(Ⅵ)被还原成了Cr(Ⅲ),随后Fe(Ⅲ)和Cr(Ⅲ)被矿物聚合物中的-OAl(-)(OH)3吸引,并被固定在非晶质结构中。     

纳米零价铁去除垃圾渗滤液中铬(Ⅵ)的性能及机理研究

利用柠檬酸处理后的纳米零价铁(NZVI)对铬(Cr(Ⅵ))的去除进行了研究.NZVI对Cr(Ⅵ)的去除率受Cr(Ⅵ)初始浓度、pH值、反应温度和NZVI的浓度等因素影响,在Cr(Ⅵ)初始浓度为20mg·1-1、pH=5.0、NZVI投加量为1.0g·1-1和20℃条件下,Cr(Ⅵ)去处率达到了100%.腐殖酸(HA)与Cr(Ⅵ)可以形成稳定的HA-Cr螯合物,这种螯合物减少了溶液中有效的Cr(Ⅵ)浓度;同时,HA与NZVI的反应减少了NZVI的有效活性位点,HA的存在对NZVI去除Cr(Ⅵ)有竞争抑制的作用.     

膨润土钝化与不同水分灌溉联合处理对酸性稻田土镉污染修复效应及土壤特性的影响

采用盆栽实验方法,研究了膨润土钝化与不同水分灌溉联合处理对酸性稻田土Cd污染修复效应,以及对土壤脲酶活性和氮、磷有效性的影响及其机制.结果表明,与干湿灌溉相比,长期淹水和湿润灌溉可明显降低稻谷生物量.膨润土钝化修复与不同水分灌溉联合处理时稻谷和稻草生物量总体上虽略有增加,但与对照相比并无明显差异.干湿灌溉、湿润灌溉和长期淹水灌溉下,稻米Cd含量分别为0.29、0.38、0.18 mg·kg~(-1),其中与干湿灌溉相比,长期淹水可使稻米镉降低37.93%,而湿润灌溉则使稻米Cd含量增加31.03%.添加膨润土钝化修复后,与干湿灌溉联合处理相比,长期淹水灌溉可使稻米Cd降低45.29%,而湿润灌溉可使稻米Cd增加23.53%.与未钝化处理相比,膨润土钝化修复下,水稻根表Fe(Ⅱ)含量显著增加,但水稻根表Fe(Ⅲ)含量间无明显差异,水稻根表Cd含量显著降低.在未添加膨润土和添加膨润土钝化修复下,长期淹水灌溉处理时土壤脲酶活性比干湿灌溉处理分别降低21.05%和15.79%.在未添加膨润土钝化修复下,不同水分灌溉处理对土壤碱解氮含量无明显影响,但长期淹水灌溉处理比干湿灌溉处理土壤有效磷增加34.92%,而湿润灌溉下土壤有效磷则降低16.99%.不同水分灌溉处理下,膨润土钝化修复对土壤碱解氮和有效磷含量无明显影响.     

外源铅对水稻土微生物量、微生物活性及水稻生长的影响

盆栽试验研究了土壤-水稻-铅-微生物相互作用的体系中,外源铅不同处理水平 (CK、100、300、500、700、900 mg·kg-1 ) 对两种水稻土壤微生物生物量碳、氮, 微生物活性, 水稻生理指标及生物量的影响.结果表明:水稻土壤中微生物量碳、氮, 微生物活性及水稻叶绿素与生物量都随铅处理水平的增大而增加,多数指标在300～500 mg·kg-1铅处理时出现峰值,然后随铅水平的增加而降低,它们的转折点受土壤性质(如颗粒组成,有机质含量等)影响.试验范围内,水稻脯氨酸含量和过氧化物酶活性都随铅处理水平的增大而缓慢增加.体系中土壤微生物指标和水稻生理指标的变化存在一定的相关性,其大小也受土壤类型的制约.试验还表明,土壤微生物量氮、脱氢酶活性及水稻过氧化物酶活性是铅处理后更为敏感的生物学指标.     

碱性介质中还原高浓度Cr(Ⅵ)细菌的分离及其特性

目前国内外处理含铬废水的微生物仅局限于酸性或中性环境,且处理Cr(Ⅵ)的浓度仅为200mg L-1左右,难以工业化应用,尤其是不可能处理诸如铬渣渗滤液之类的碱性含铬废水及铬渣.本研究从铬渣堆埋场附近取得菌样,经富集、分离、驯化,得到能在碱性介质中高效还原Cr(Ⅵ)的无色杆菌属(Achromobacter sp.)菌株,该菌为G-,具有周身鞭毛及可运动性.对其生理及还原Cr(Ⅵ)的特性进行了研究,结果表明该菌嗜碱,好氧,耐盐及高Cr(Ⅵ),在有氧、pH为10.30、30℃等条件下,含Cr(Ⅵ)1 570 mg L-1的废水经该菌处理16 h后浓度降至0.6 mg L-1.处理后的沉淀物中铬以Cr(OH)3的非晶形态存在,其中总铬含量为21.44%,Cr(Ⅵ)检测不出,具有很大的回收价值.图4表3参16     

底泥铬污染的纳米铁粉修复及其土壤酶活性动态

采用纳米铁粉修复Cr(Ⅵ)不同程度污染底泥,通过测定底泥中4种土壤酶活性,分析纳米铁粉修复对Cr(Ⅵ)污染底泥土壤酶活性的恢复情况.结果表明,纳米铁粉修复对底泥Cr(Ⅵ)有很好的去除效果,添加底泥干质量1%的纳米铁粉在16 d内对底泥30～100 mg·kg-1的Cr(Ⅵ)的去除率均高于99.7%.Cr(Ⅵ)污染显著降低了底泥多酚氧化酶、过氧化氢酶、蛋白酶和脲酶的活性.其中多酚氧化酶对Cr(Ⅵ)污染有很好的线性响应,可用于0～100 mg·kg-1底泥Cr(Ⅵ)污染评价.经过16 d的纳米铁粉修复,Cr(Ⅵ)污染底泥的脲酶活性恢复至未污染对照水平,过氧化氢酶活性的恢复效果不明显,多酚氧化酶和蛋白酶活性有待进一步恢复.     

Phytoextraction of Cr(VI) from soil using Portulaca oleracea

Cr(VI) represents an environmental challenge in both soil and water as it is soluble and bioavailable over a wide range of pH. In previous investigations, Portulaca oleracea (a plant local to the United Arab Emirates (UAE)) demonstrated particular ability for the phytoextraction of Cr(VI) from calcareous soil of the UAE. In this publication, the results of the evaluation of P. oleracea phytoextraction of Cr(VI) from UAE soil at higher concentrations are reported. P. oleracea was exposed to nine different concentrations of Cr(VI) in soil from 0 to 400 mg kg^?1. The uptake of Cr(VI) increased as its concentration in soil increased between 50 and 400 mg kg^?1, with the most efficient removal in the range from 150 to 200 mg kg^?1. The total chromium concentrations exceeded 4600 mg kg^?1 in roots and 1400 mg kg^?1 in stems, confirming the role of P. oleracea as an effective Cr(VI) accumulator. More than 95% of the accumulated Cr(VI) was reduced to the less toxic Cr(III) within the plant.     

Influence of iron plaque on chromium accumulation and translocation in three rice (Oryza sativa L.) cultivars grown in solution culture

Hydroponic experiments were conducted to investigate the role of iron plaque on root surface in chromium accumulation and translocation in three rice cultivars (90-68-2, CDR22 and Jin 23A). Rice seedlings were grown under 1.0 mg L^?1 trivalent chromium (Cr(III)) stress with and without phosphorus (P) treatments. P addition significantly increased the shoot and root biomass in all three rice cultivars. In the absence of P, the amounts of iron plaque (DCB-extractable Fe) on the root surface increased resulting in the increase of Cr accumulation in iron plaque. Compared to that with P treatment, Cr concentrations in iron plaque without P treatment were enhanced by 2–3 folds in the three rice cultivars. There was a significantly positive correlation between DCB-extractable Cr and DCB-extractable Fe on the root surface of the three rice cultivars. There were no significant effects on Cr concentration in roots and shoots between P treatments, but significant differences among cultivars were observed. Cultivar Jin 23A had the lowest Cr concentration both in roots and shoots regardless of P treatment. The results suggest that iron plaque could be a trap for immobilising Cr from environment but may not affect Cr uptake and translocation. Screening and breeding the cultivars with low Cr accumulation is considered as the most effective approach in Cr contaminated areas.     

Biosorption potential of Cr(VI) by Kocuria sp. ASB107, a radio-resistant bacterium isolated from Ramsar,Iran

Heavy metal pollution in soil and wastewater is a worldwide environmental issue in which microorganisms play a significant role for its removal. In the present study, biosorption of Cr(VI) by the live and dead cells of Kocuria sp. ASB107, a radio-resistant bacterium, was investigated. The effect of contact time, solution pH, initial hexavalent chromium concentration and adsorbent dose on biosorption efficiency was studied. Also, live cells were further immobilised on various matrices by different techniques and then were examined for tolerance to chromium biosorption. Experimental results indicated that the removal efficiency of chromium increased with decrease in pH, initial Cr(VI) concentration, and also increase in adsorbent dose and the contact time. The maximum removal efficiency of live and dead cells at acidic pH of 4–4.5, contact time of 24 hours, adsorbent dose 1.6?g/100?mL and initial chromium concentration 25?mg/L were 82.4% and 69.2%, respectively. The adsorption data was described well by Langmuir isotherm model. Among all immobilisation techniques tested, cross-linking showed the highest biosorption of Cr(VI). Results indicated that live cells of Kocuria sp. ASB107 were better than dead ones.     

Effects of Cr(III) organic compounds on Lactobacillus plantarum

Biotransformation of Cr(VI) to less toxic Cr(III) has been known to produce insoluble Cr(III) compounds and soluble Cr(III) organic complexes. However, recent research reports have indicated that Cr(III) organic complexes are relatively stable in the environment. Little has been reported on the fate and toxic effects of Cr(III) organic compounds on organisms. In this study, the toxic effects of the soluble Cr(III) organic complexes [Cr(III) citrate, Cr(III) histidine, Cr(III) lactate and Cr(III) glutamate] to a local strain of Lactobacillus plantarum isolated from sauerkraut was investigated. Growth inhibition, viable cell count and lactic acid inhibition were measured to determine the toxicity potential of the test compounds. The EC₅₀ values of Cr(III) citrate, Cr(III) histidine, Cr(III) lactate, and Cr(III) glutamate, calculated from the percent growth inhibition were found to be 56 mg L^?1, 70 mg L^?1, 81 mg L^?1, and 85 mg L^?1, respectively. Similar trend was observed in the viable cell counts and lactic acid production. Cr(VI) was observed to be more toxic than the Cr(III) organic compounds, while inorganic Cr(III) was the least toxic. The severity seemed to increase with increase in chromium compounds’ concentration. The results showed that Cr(III) citrate was the most toxic Cr(III) organic compound, while Cr(III) glutamate was the least.     

Cr (VI) and Fe (III) removal using Cajanus cajan husk

Husk of tur dal (Cajanus cajan) was investigated as a new biosorbent for the removal of Fe (III) and Cr (VI) ions from aqueous solutions. Parameters like agitation time, adsorbent dosage and pH were studied at different initial Fe (III) and Cr (VI) concentrations. The biosorptive capacity of the Tur dal husk was dependent on the pH of the chromium and iron solution, with pH 2 and 2.5 respectively being optimal. The adsorption data fit well with Langmuir and Freundlich isotherm models. The practical limiting adsorption capacity (qmax) calculated from the Langmuir isotherm was 96.05 mg of Cr(VI)/ g of the biosorbent at an initial pH of 2.0 and 66.65 mg/g at pH 2.5. The infrared spectra of the biomass revealed that hydroxyl, carboxyl and amide bonds are involved in the uptake of Cr (VI) and Fe (III) ions. Characterisation of tur dal husk has revealed that it is an excellent material for treating wastewaters containing low concentration of metal ions.     

Uptake,distribution and loss of Cr in the crab Xantho hydrophilus

Uptake of ⁵¹Cr(III) is faster than uptake of ⁵¹Cr(VI), but it occurs mainly on the surface of the animals. Steady state is attained after 28 d. The resulting concentration factor is about 200. Although the uptake of ⁵¹Cr(VI) is slower, it is more intensively distributed into the organs and tissues of the animals. Steady state was not attained during the experiments (35 d); the highest concentration factor reached was about 10. The uptake of both ⁵¹Cr(III) and ⁵¹Cr(VI) seems to be passive. For both chemical forms of chromium, the loss rate is inversely proportional to the exposure time. When the uptake lasted longer, owing to the distribution of Cr(VI) into the organs and tissues, the loss rate of Cr(III) is somewhat faster relative to the loss rate of ⁵¹Cr(VI). The opposite is the case when the uptake of both forms lasts only two days. On the basis of the distribution and loss experiments, we argue that hexavalent chromium in living organisms is reduced to the trivalent form and then complexed with organic molecules.     

1,3,5-triazine-triethylenetetramine polymer: an efficient adsorbent for removal of Cr(VI) ions from aqueous solution

The synthesis of 1,3,5-triazine-triethylenetetramine (TATETA), its characterization by infrared spectroscopy and elemental analysis, and its application for removal of Cr(VI) ions from aqueous solution is reported. The effects of pH, contact time, initial concentration of Cr(VI), sorbent dose, and temperature on adsorption were investigated and optimized by batch adsorption experiments. Adsorption was highest at acidic conditions with an equilibration time of 25 min. The adsorption followed a Langmuir model, with an adsorption capacity of 303 mg g^?1, was second order in its kinetics, and exothermic and thus spontaneous.     

Equilibrium,kinetics and thermodynamics of hexavalent chromium biosorption on pristine and zinc chloride activated Senna siamea seed pods

Hexavalent chromium contamination in water is an issue of huge concern due to its use at a high scale, toxicity and non-biodegradability. Biosorption is a cost effective and unconventional strategy for the elimination of Cr(VI). Here, a novel biosorbent Senna siamea seed pod biomass and its chemically activated form have been investigated for the elimination of hexavalent chromium from aqueous solution. The biosorbent was characterized by using BET, FTIR, FESEM-EDX and TGA techniques. Parameters controlling the biosorption process were optimized as pH 2.0, temperature 30°C, initial Cr(VI) concentration 500?mg/L, biosorbent dose 0.5?g/L. Optimized contact time was 210 and 180 min for pristine biomass and activated carbon, respectively. Langmuir isotherm correlated well with experimental data revealing that the biosorption occurred in monolayer pattern. Maximum biosorption capacity calculated by Langmuir biosorption isotherm was 119.18 and 139.86?mg/g for S. siamea pristine biomass and activated carbon, respectively. Pseudo-second order kinetic model correlated well with experimental data. Thermodynamic studies suggested that the biosorption process occurs in a non-spontaneous, stable and endothermic manner. These interesting findings on Cr(VI) biosorption by S. siamea seed pod biomass and S. siamea zinc chloride activated carbon vouches for its potential application as an unconventional biosorbent.     

Removal of chromium (VI) from water streams: a thermodynamic study

The chemical speciation of water solutions containing chromium oxyanions in various ratios is calculated (with the aid of available computer code Mineql Plus, Geochemist Workbench and Visual Minteq) and discussed. The effect of solution pH, total concentration of each species studied, and the presence of other species in solution are calculated and presented in the form of thermodynamic speciation diagrams. Electrochemical diagram (correlating pH to Eh) has been calculated as well. The conditions of Cr(VI) reduction to Cr(III) and the subsequent solid phase precipitation are given as a function of redox potential and pH. Surface reactions that might occur between the chromate ions in the solution and redox couples as Fe²⁺/Fe³⁺ on the surface of sorbents are also discussed. Moreover, experimental sorption data of hexavalent chromium onto synthetic magnetite are presented and discussed with the aid of the calculated diagrams. A mechanism is elucidated for the efficient removal of Cr(VI) from water streams at low pH values, and zeta potential data of synthetic magnetite with and without Cr(VI) are presented, which agree well with the mechanism proposed.     

Enhancement of extracellular Cr(VI) reduction for anammox recovery using hydrazine: performance,pathways, and mechanism

● N₂H₄ addition enhanced and recovered anammox performance under Cr(VI) stress. ● N₂H₄ accelerated electron transfer of Cr(VI) reduction for detoxification. ● N₂H₄ enhanced anammox metabolism for activity recovery from Cr(VI) inhibition. ● Extracellular Cr(VI) reduction to less toxic Cr(III) was the dominant mechanism. The hexavalent chromium (Cr(VI)) would frequently impose inhibition to anaerobic ammonium oxidation (anammox) process, hindering the efficiency of nitrogen removal in wastewater treatment. Hydrazine (N₂H₄), which is an intermediate product of anammox, participates in intracellular metabolism and extracellular Cr(VI) reduction. However, the roles of N₂H₄-induced intracellular metabolism and extracellular reduction in nitrogen removal under Cr(VI) stress remain unclear. The addition of 3.67 mg/L of N₂H₄ increased the anammox activity by 17%. As an intermediate, N₂H₄ enhanced anammox metabolism by increasing the heme c content and electron transfer system activity. As a reductant, N₂H₄ accelerated the reduction of c-Cyts-mediated extracellular Cr(VI) to the less toxic Cr(III). Extracellular Cr(III) accounts for 74% of the total Cr in a Cr(VI)-stressed anammox consortia. These findings highlight that N₂H₄-induced extracellular Cr(VI) reduction is the dominant mechanism for the survival of anammox consortia. We also found that N₂H₄ increased the production of extracellular polymeric substances to sequester excessive Cr(VI) and produced Cr(III). Taken together, the study findings suggest a potential strategy for enhancing nitrogen removal from ammonium-rich wastewater contaminated with Cr(VI).