Complexation of Cu2+ and Pb2+ by peat and humic acid

The binding of metal to humic substances is problematical. The approaches for studying metal binding to organic matter are briefly reviewed. Ion-selective electrodes (Cu²⁺ and Pb²⁺) were used to measure metal complexation by a whole peat and an extracted humic acid (HA) fraction. Scatchard plots and calculation of incremental formation constants were used to obtain values for the binding constants for the metals onto both peat and HA. Both the peat and the humic acid had a larger maximum binding capacity for Pb²⁺ than for Cu²⁺ (e.g. at pH = 5 HA gave 0·188 mmol Cu²⁺ g^?1 and 0·564 mmol Pb²⁺ g^?1: peat gave 0·111 mmol Cu²⁺ g^?1 and 0·391 mmol Pb²⁺ g^?1). Overall, the humic acid had a larger metal binding capacity, suggesting that extraction caused conformational or chemical changes. The binding constants (K₁) for Cu²⁺ increased with increasing pH in both peat and humic acid, and were larger in the peat at any given pH (e.g. at pH = 5 HA gave log K₁= 2·63, and peat gave log K¹= 4·47 for Cu²⁺). The values for Pb²⁺ showed little change with pH or between peat and humic acid (e.g. at pH = 5 HA gave log K¹= 3·03 and peat gave log K¹= 3·00 for Pb²⁺). In the peat, Cu²⁺ may be more able to bind in a 2:1 stoichiometric arrangement, resulting in greater stability but smaller binding capacity, whereas Pb²⁺ binds predominantly in a 1:1 arrangement, with more metal being bound less strongly. Whole peat is considered to be more appropriate than an extracted humic acid fraction for the study of heavy metal binding in organic soils, as this is the material with which metals introduced into an organic soil would interact under natural conditions.     

Effect of copper on nitrous oxide reduction in freshwater sediment

The effect of Cu(II) sulfate on N20 reduction was studied in anaerobically incubated freshwater sediment at 15 °C. At Cu concentrations from 100 to 5000 μg g^?1, a concentration-dependent decrease in sediment pH was observed in conjunction with a decrease in N₂0 reduction in Cu²⁺ treated sediment in flask-microcosms analyzed immediately after metal addition. However, if flask-microcosms were amended with Cu²⁺ and then pre-incubated to allow the sediment pH to naturally return to its original pH (7.1), an inhibitory effect was only produced at 5000 μg Cu g^?1 sediment. Copper retention studies showed that up to 96.4% of the added Cu²⁺ (2500 μgg^?1) was retained by sediment.     

Effects of Ca,Mg, K,Na, and pH on Copper Toxicity to Pakchoi (Brassica chinensis L.)

The influence of calcium, magnesium, sodium, and potassium (Ca²⁺, Mg²⁺, Na⁺, K⁺) ions and pH on copper (Cu) toxicity to pakchoi (Brassica chinensis L.) was independently estimated by measuring root elongation in nutrient solutions. Increases in Ca²⁺, Mg²⁺, and hydrogen (H⁺) significantly increased the 5-d EC50Cu_T (expressed as total soluble Cu) by a factor of 12 for all treatments, which clearly demonstrated the limitation of using total Cu concentration to predict Cu toxicity to pakchoi. EC50{Cu²⁺} (expressed as free Cu²⁺ activity) was not significantly influenced by changing the Ca²⁺, Mg²⁺, and H⁺ activities. The nonlinear relationship between EC50{Cu²⁺} and cations indicated that competition for binding sites between Cu²⁺ and cations was not a significant factor in determining toxicity of Cu²⁺ for pakchoi. The lower variation of EC50{Cu²⁺} suggests that free Cu²⁺ activity was a better predictor of toxicity to pakchoi than EC50Cu_T.     

阴离子对可变电荷土壤吸附铜离子的影响机理

根据NO-3、Cl-和SO24-对可变电荷土壤和恒电荷土壤吸附Cu2+的影响的比较,探讨了阴离子对可变电荷土壤吸附Cu2+的影响机理。结果表明,当3种阴离子的浓度相同时,在SO24-体系中铁质砖红壤对Cu2+的吸附率较在NO3-和Cl-体系中大得多,而在浓度相同的3种阴离子体系中,黄棕壤对Cu2+的吸附率相差不大。在离子强度相近的NaCl体系中,砖红壤对Cu2+的吸附率相近。在3种阴离子体系中,随着pH升高,砖红壤对Cu2+的吸附率均增大;但在NO-3体系和Cl-体系中Cu2+的吸附率相近;而在SO24-体系中Cu2+的吸附率最大。随着Na2SO4浓度的增大,铁质砖红壤和砖红壤对Cu2+的吸附率减小。但在0.005 mol L-1和0.05 mol L-1Na2SO4体系中,Cu2+的吸附率大于在不含Na2SO4的体系中者。而在0.5 mol L-1Na2SO4体系中,Cu2+吸附率小于在不含Na2SO4体系中者。在3种浓度的Na2SO4体系中,黄棕壤对Cu2+的吸附率均小于在不含Na2SO4体系中者。总之,阴离子可通过离子强度、专性吸附和形成离子对影响土壤对Cu2+的吸附。在可变电荷土壤中,阴离子对Cu2+吸附的影响机理较在恒电荷土壤中复杂得多。     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

恒电荷土壤胶体对Cu2+ 、Pb2+ 的静电吸附与专性吸附特征

供试土壤胶体对Cu2 、Pb2 的吸附强度用pH50 值表示 ,其大小次序为 :土 >黄绵土、黑垆土 >黄褐土。离子强度实验和表面络合反应机制证明恒电荷土壤胶体对Cu2 、Pb2 的吸附含有专性吸附 ,n值可作为判断专性吸附与静电吸附比例的特征值 ,低pH值时 ,以水解 -络合吸附为主 ;高pH值时 ,以水解 -络合与沉淀吸附为主。静电吸附和专性吸附的比例与pH有关 ,各土壤胶体专性吸附百分数大小为 :黄褐土 >土 >黑垆土 >黄绵土。不同土壤胶体在同一介质中对Cu2 、Pb2 的固有络合常数logKintM 值及固有络合ΔG m 负值大小次序与吸附强度大小一致。在定pH定浓条件下 ,考虑离子之间的相互作用时 ,土壤胶体对重金属离子的吸附过程可用BDM等温式描述。供试土壤胶体对Cu2 、Pb2 专性吸附ΔG m 的大小与固有络合ΔG m 接近且大小次序也一致。     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER. IV. ADSORPTION AND DESORPTION OF Pb2+, Cu2+, Cd2+, Zn2+ AND Ca2+ BY PEAT

The equilibria as well as the rates of adsorption and desorption of the ions Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ca²⁺ by soil organic matter were determined in batch experiments as a function of the amount of metal ions added to an aqueous suspension of HCl-washed peat. Simultaneous determination of the metal ions and hydrogen ions in the solution by atomic absorption spectrophotometry and pH-measurements showed that the adsorption of one divalent metal ion by peat was coupled with the release of two hydrogen ions. Since this equivalent ion-exchange process causes a corresponding increase of the electric conductivity of the solution, the rates of the adsorption and desorption processes were determined by an immersed conductivity electrode. The distribution coefficients show that the selective order for the metal adsorption by peat is Pb²⁺ > Cu²⁺ > Cd²⁺≌ Zn²⁺ > Ca²⁺ in the pH range of 3·5 to 4·5. The slope of -2, as observed in a double logarithmic plot of the distribution coefficients versus the total solution concentration confirms the equivalence of the ion-exchange process of divalent metal ions for monovalent H₃O⁺ -ions in peat. The absolute rates of adsorption, as well as the rates for the fractional attainment of the equilibrium, increase with increasing amounts of metal ions added. This behaviour is also observed for the subsequent desorption of the metal ions by H₃O⁺-ions. At a given amount of metal ions added, the absolute rates of adsorption decrease in the order Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺ > Ca²⁺, while the rates for the fractional attainment of the equilibrium decrease in the order Ca²⁺ > Zn²⁺≌ Cd²⁺ > Pb²⁺ > Cu²⁺. The half times for adsorption and desorption were in the range of 5 to 15 sec.     

Zinc,copper, and nickel availabilities as determined by soil solution and DTPA extraction of a sludge‐amended soil

Abstract

Extracting sludge‐amended soil with DTPA does not always give a reliable measure of plant‐available heavy metals. The major purpose of this greenhouse pot study was to help explain why. Two anaerobically digested sludges from sewages treated with either Ca(OH)₂or FeCl₃were applied to 3‐kg samples of a Mollic Albaqualf previously limed with Ca(OH)₂rates of 0, 2.5, and 10g/pot that resulted in pHs in the check pots of 5.4, 6.2, or 7.7 after the first harvest. Sludge rates provided 0, 200, 40, 800, and 1600 mg Zn kg^‐1of soil. Two consecutive crops of soybeans (Glycine MaxL.) were grown for 42 d each in the greenhouse. DTPA‐extractable, soil‐solution, and plant concentrations of Cu²⁺, Ni²⁺, and Zn²⁺were measured.

Dry matter yields were depressed due to salt toxicity, while DTPA‐extracted Cu²⁺correlated with plant uptake of Cu²⁺for both sludges. DTPA‐extracted Ni²⁺also correlated with plant Ni²⁺from the Ca(OH)₂‐sludge‐amended soil, although DTPA‐extracted Ni²⁺did not correlate with plant uptake of Ni²⁺from the FeCl₃‐sludge‐amended soil, DTPA‐extracted Zn did not correlate with plant uptake of Zn²⁺from any sludge‐amended soil. Soil‐solution composition correlated with plant uptake of Cu²⁺and Ni²⁺in both sludges; it also correlated with plant uptake of Zn²⁺from FeCl₃‐sludge‐amended soil but not from Ca(OH)₂‐sludge‐amended soil. DTPA extraction probably failed with Ni²⁺and Zn²⁺because of (i) its ineffectiveness at low pH, (ii) the inability of DTPA to buffer each soil extract near pH 7.3, and (iii) increased amounts of soluble chelated micronutrients at higher sludge rates and higher soil pHs. Soil‐solution composition seemed to fail only where micronutrient cations in solution probably were present largely as organic chelates     

Influence of microorganisms on Cu speciation in the rhizosphere of forest soils

Our study is one of the first attempts to document the copper (Cu) speciation in the rhizosphere of forest soils and to determine the importance and the influence of the microbial community on Cu speciation. In order to do this, bulk and rhizosphere samples were collected from field sites located close to industrial facilities. The rhizosphere materials were sampled under trembling aspen (Populus tremuloides Michx.) and separated from the bulk soils in the field. A characterization of the microbial populations was made by measuring microbial biomass C and N, urease and dehydrogenase activities. In soil water extracts, chemical properties were also measured, as well as total water-soluble Cu concentration (Cu_WS) and free-ion Cu activity (Cu²⁺). The residual Cu speciation was obtained by modelling, using MINEQL+ 4.5. In all cases, the Cu speciation was dominated by organic forms of Cu, the proportion of which increases with increasing pH. The reverse pH effect was observed for Cu²⁺. Moreover, almost systematically higher concentrations for all Cu variables were reported in the rhizosphere as compared to the bulk soils. The results also showed that microbial variables explained 22% of the distribution of Cu_WS and Cu²⁺ in bulk samples, a proportion that reached 61.5% in rhizospheric samples. In the rhizosphere, relationships between pH, microbial biomass N and Cu²⁺ indicated that microorganisms influenced Cu by modifying the pH of the solution through nitrogen assimilation. Furthermore, links found between urease activity, biomass variables, solid- and liquid-phase organic carbon and Cu_WS suggested that microbial mineralization could partly supply Cu to the solution fraction of the rhizosphere through root decay. This study reveals that microorganisms have a strong influence on Cu speciation in the rhizosphere of forest soils and suggests that a realistic understanding and representation of Cu dynamic in the rhizosphere must take microbial activity into account. Further investigations are needed to identify and establish precisely how microbial processes impact on Cu speciation.     

The behavior of selected chlorinated organic micropollutants in the activated sludge process: A pilot plant study

The effects of Cu(II) sulfate on sediment respiration were investigated in a 3-phase aquatic microcosm, containing a calcareous, southern Ontario stream sediment. In Cu²⁺ treated flask-microcosms, with the pH restored to 7.1, both aerobic and anaerobic CO₂ evolution were unaffected by 5000 jig Cu g^?1 sediment over a 40-day period at 15 °C. Oxygen consumption in sediment was initially unaffected by 5000 μg Cu g^?1. However, after 35 to 40 days, a significant reduction of 28% was observed. The added Cu^?2+ was removed from the water column and the sediment solution. In microcosms containing 5000 μg g^?1 of total Cu, only 1.00 ± 0.76 μg g^?1 was water soluble Cu, and the free cupric cation (Cu²⁺) concentration was below the detection limit of the specific ion electrode (less than 0.01 μg g^?1). Maximum Cu retention (98.6%) was observed at 2800 μg Cu g^?1, above which fractional retention decreased. In a calcareous, organic rich, sediment of pH 7.1, Cu⁺ was essentially unvailable to exert a toxic effect on respiration.     

紫花苜蓿、黑麦草和狼尾草对Cu、Pb复合污染土壤修复能力的研究

随着经济和社会的发展,土壤重金属污染对粮食安全及人类的身体健康构成了巨大的威胁,而目前对于土壤重金属污染的治理主要以植物修复为主。为了寻找适宜修复Cu、Pb复合污染土壤的牧草,采用盆栽试验法,将试验的植物设置9组处理:1组对照组(CK),不添加任何重金属盐;4组单一污染,即单一Cu低(Cu1,200 mg×kg-1)、高浓度(Cu2 400 mg×kg-1),单一Pb低(Pb1 300 mg×kg-1)、高浓度(Pb2 800 mg×kg-1);4组Cu、Pb复合污染(Cu1Pb1、Cu1Pb2、Cu2Pb1、Cu_2Pb_2)。通过比较紫花苜蓿(Medicago sativa)、黑麦草(Lolium perenne)、狼尾草(Pennisetum alopecuroides)的适应能力和富集特征,研究了这3种常见牧草植物对受Cu、Pb复合污染土壤的修复效果。结果表明:1)紫花苜蓿地上部和根部生物量均在Pb1处理组时最大,显著高于其他处理组;黑麦草地上部生物量在Cu1Pb1处理组最大,根部生物量在Pb1处理组最大;狼尾草地上部生物量在Cu_2Pb_2处理组最大,根部生物量在Cu2处理组最大。2)Cu单一污染下,狼尾草抗性系数最大;Pb单一污染下,紫花苜蓿抗性系数最大;Cu-Pb复合污染下,狼尾草的抗性系数较大。高浓度Cu处理组3种牧草植物的地上部生物量、根部生物量和抗性系数均呈现:狼尾草黑麦草紫花苜蓿,且狼尾草显著大于黑麦草和紫花苜蓿。3)种植3种牧草植物后,土壤重金属Cu、Pb含量均有所降低。在一定浓度下,土壤Cu-Pb重金属间会相互促进对方在牧草植物中的吸收。4)3种牧草中紫花苜蓿地上部对Cu的富集系数在Cu_2Pb_2处理组最大,达1.61;黑麦草根部对Cu的富集系数在Cu_2Pb_2处理组最大,达3.80;3种牧草地上部和根部对Pb的富集系数只在黑麦草根部的Cu1Pb1处理组时大于1,达1.46。5)黑麦草对Pb的吸收能力较强,且主要积累在根系;紫花苜蓿对Cu-Pb复合污染综合修复效果最好。紫花苜蓿和黑麦草分别在Cu-Pb复合污染和Pb单一污染土壤中对Pb的转运系数大于1,分别为2.72和2.06,反映其对土壤中的Pb具有富集潜力。综合表明,黑麦草对重金属Pb具有较强的耐性,在Pb单一污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料;紫花苜蓿对重金属Cu、Pb均具有较强的耐性,在重金属Cu单一或Cu-Pb复合污染土壤的植物修复及尾矿废弃地的植被重建中,可优先作为选择的材料。     

Activite des complexes acides humiques-invertase: Influence des cations floculants

-Humic acid (AH) and invertase (I) may be complexed with one of the following cations Ca²⁺, Co²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Al³⁺ or Fe³⁺ in order to study their catalytic activity and longevity. Provided that enough cations are supplied there is an immediate, almost total flocculation with Cu²⁺, Al³⁺ and Fe³⁺, or a slow flocculation with Ca²⁺, Co²⁺ and Mn²⁺ or no flocculation at all with Mg²⁺, depending on the reactivity between organic matter and cation. The six kinds of complexes have very different enzymatic activities in magnitude and longevity.No correlation was found between enzymatic activity and the atomic weight and valency of the cation used to prepare the complex. There is a pH at which flocs occur that is closely related to the pH of the metal chloride and to the affinity of each cation for precipitate; this pH value largely determines the structure of the humic material and consequently the catalytic activity of the enzymatic complex produced. For Cu²⁺, Al³⁺ and Fe³⁺ complexes, the pH values are low, between 1.7 and 3.2 and correspond to high conversion rates if the AH-I-cation reaction time is short; in cases where the reaction time is more protracted, enzyme molecules bound to the outer surface of the micellae are denatured by these very low pH values and the complexes irreversibly lose much of their activity. For Ca²⁺, Co²⁺ and Mn²⁺, the pH values lie between 4.30 and 5.65 and correspond to nearly ten times lower enzymatic activities; here, however, a prolonged reaction enhances activity. For Mg²⁺, the pH is 6.25–6.45; for this value, the humic material remains highly dispersed in buffer and the complex AH_Mg-I cannot be separated.The possibility of a relation between the number of enzyme molecules retained in complexes and the cationic radii on the one hand, and between the longevity of the complexes and the bound-state of humic acid-flocculating cation, on the other hand, is suggested.     

A Comparison of Inorganic Solid Wastes as Adsorbents of Heavy Metal Cations in Aqueous Solution and Their Capacity for Desorption and Regeneration

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and Cr³⁺ was determined at two metal concentrations (10 and 100 mg?L^?1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr³⁺????Pb²⁺????Cu²⁺?>?Zn²⁺?=?Cd²⁺. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO₃ electrolyte were very small, but those removed with 0.01 M HNO₃, and more particularly 0.10 M HNO₃, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO₃ as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.     

Photodegradation of Bisphenol A with ZnO and TiO<Subscript>2</Subscript>: Influence of Metal Ions and Fenton Process

In this study, photocatalytic degradation of bisphenol A (BPA) was investigated using two types of catalysts (TiO₂ and ZnO) with various metal ion concentrations and amounts of added H₂O_2. A kinetic test was performed to observe the changes of BPA over time under UV irradiation in a photocatalytic reactor. Experimental results demonstrated that degradation efficiency of ZnO was higher than that of TiO₂. The degradation rate increased as catalyst dosage increased until reaching optimum dosage, after which degradation rate decreased. The addition of H₂O₂ improved the degradation efficiency of BPA, with the degradation efficiency increasing with the amount of H₂O₂. All metal ions, including Fe²⁺, Ni²⁺, and Cu²⁺, inhibited the degradation of BPA by ZnO at natural pH, whereas Fe²⁺ and Ni²⁺ enhanced degradation efficiency of BPA at acidic pH. Comparison of BPA degradation with H₂O₂ only, ZnO/H₂O₂, Fe²⁺/H₂O₂, and ZnO/Fe²⁺/H₂O₂ revealed that Fe²⁺/H₂O₂ was more efficient than other processes at lower pH (pH?=?3.44), whereas ZnO/H₂O₂ the most efficient at higher pH (pH?=?6.44). These results indicate that ZnO/H₂O₂ process was observed to be the most efficient of all processes. Degradation efficiency of BPA by ZnO was also influenced by additional parameters, including H₂O₂ concentration, metal ions, and solution pH.     

Sorption of cupric,dichromate and arsenate ions in some New Zealand soilds

Concentrated solutions of copper (Cu²⁺), dichromate (Cr₂O^2? ₇) and aresenate (AsO₄ ^3?) ions (CCA solutions) are used extensively in the New Zealand timber preservation industry. These ions are therefore, potential soil pollutants at timber treatment sites. Sorption of these three ions was examined by the surface and sub-surface horizons of two free-draining New Zealand soils over a range of soil solution pH values. Copper sorption by both soils increased substantially with increasing pH and was greater in the surface compared with the sub-surface horizons. Less dichromate was sorbed than the other two ions and wa similar in both surface and sub-surface horizons for each soil. Dichromate sorption increased with decreasing pH. Arsenate sorption from solutions containing all three ions was not greatly different to influenced by changes in soil solution pH. Arsenate sorption was generally greater in the sub-surface horizons of both soils. Sorption from solutions containing all three ions was not greatly different to sorption from solutions containing the single metal ions. Sorption behaviour for each ion is related to its chemistry and the soil chemical properties of each horizon. Results suggest that in the event of soil contamination by CCA solution, the immediate leaching potential of the initial ions species present would increase in the following order: Cu²⁺ < HAsI ₄ ^? ? Cr₂O ₇ ^2? .     

Using electrical signals of microbial fuel cells to detect copper stress on soil microorganisms

A method based on microbial fuel cells (MFCs) was used to evaluate the effects of copper (Cu²⁺) on soil microorganisms. Soil spiked with 50–400 mg kg^?1 of Cu²⁺ as CuCl₂ was incubated for 24 hours before being packed into the MFC anode chambers and assayed for dehydrogenase activity (DHA), substrate‐induced respiration (SIR) and microbial biomass carbon (C_mic). Soil was amended with 5% (w/w) glucose to accelerate ‘start‐up’ and improve power generation, followed by 150 hours of operation. Anode biofilm and soil was extracted to recover total nucleic acids and the 16S rRNA gene was subjected to PCR‐DGGE, sequencing and phylogenetic analysis. Results showed that increases in soil Cu²⁺ concentrations reduced voltage and postponed start‐up. The quantity of generated electrons within 48 hours was 32.5 coulomb (C) in the without‐Cu control and decreased with increasing Cu²⁺ concentrations (11.7, 7.7, 2.0 and 1.3 C under 50, 100, 200 and 400 mg kg^?1 Cu²⁺, respectively). Cyclic voltammetry identified decreased soil electrochemical activity with increasing Cu²⁺ concentrations. The results indicate that Cu²⁺ reduced electrical signals by inhibiting the electrochemical activity, metabolic activity and biomass of microorganisms. The 16S sequences of recovered anodic bacteria were assigned to Firmicutes, including Bacillaceae, Acetobacteraceae, Clostridium, Bacillus and Sporolactobacillus. In general, the DGGE band intensity of anodic bacteria decreased with increasing Cu²⁺ concentrations, except for bands assigned to Firmicutes and Bacillus, which increased with increasing Cu²⁺ concentrations. We suggest that the short‐term electrical signals generated from MFCs with contaminated soil can be used to assess the toxic effect of heavy metal pollutants on soil microorganisms.     

Copper Sorption Characteristics and Activity In a Savanna Acid Soil From Nigeria

The adsorption-desorption, chemical fraction and solubility relations of Cu in a typical savanna soil from Nigeria were studied with a view to elucidating the factors which govern the retention and release of Cu added to the soil as fertilizers and contaminants. Copper adsorption was performed in a KCl medium, and at a pH range of 3.0 to 8.5, using surface and subsurface soil samples of an Alfisol. Copper adsorption curve had a steep slope at low concentration of applied Cu, and a gentle slope at high concentration. Two successive desorptions with 0.01 M KCl recovered between 0 and 6% of sorbed Cu in the surface soil, and between 0 and 3% in the subsurface soil. Fractionation of sorbed Cu showed that between 51 and 62% of the sorbed Cu was in a residual form, whereas the organically-bound form was, on the average, less than 20% of sorbed Cu. Copper sorption increased with increasing pH, which could not simply be explained by pH-dependent charges per se. More than 65% of applied Cu was sorbed at pH ≥ 3.0, far below the point of zero net charge of the soil. The log Cu²⁺-pH activity diagrams showed that Cu²⁺ activities in soil solution were undersaturated with respect to tenorite (CuO) and Cu(OH)_2(c) solubility at the pH range of 4.0 to 7.5, but were supersaturated with respect to cupric ferrite (CuFe₂O₄) solubility except at pH ≤ 4.5. Precipitation of Cu compounds with solubility similar to CuFe₂O₄ might partly account for increasing Cu retention with pH. The strong retention of applied Cu by the soil and its low solubility in the soil solution suggested that the risks of Cu toxicity, and leaching to contaminate ground water and food chain, were Cu-rich wastes to be disposed through this soil, are quite minimal.     

The H+/M2+ exchange stoichiometry of calcium and zinc adsorption by ferrihydrite

The specific adsorption of Ca²⁺ and Zn²⁺ by ferrihydrite results in the net release of H⁺. The rate and H⁺/M²⁺ exchange stoichiometry of this reaction were monitored with a pH-stat. A rapid reaction of less than 6 min was followed by a slower reaction which continued at a diminishing rate for at least 2 days. Adsorption of Ca²⁺ at pH 7.8 and Zn²⁺ at pH 5.4 resulted in the net release of 0.92 and 1.70 mol H⁺/mol M²⁺ adsorbed, respectively. For Zn²⁺ adsorption, this stoichiometry was shown to be independent of pH. These estimates agree well with independent estimates based on the pH dependence of adsorption. The difference between the Ca²⁺ and Zn²⁺ stoichiometries was related to the differing acidity of the –OH₂ ligands attached to the adsorbed ions.     

Adsorption features of Cu(II), Pb(II), and Zn(II) by an ordinary chernozem from nitrate,chloride, acetate,and sulfate solutions

The effect of Cl^?,SO ₄ ^2? , CH₃COO^?, and NO ₃ ^? anions on the adsorption of copper, lead, and zinc by an ordinary chernozem has been studied. The effect of the anions on the adsorption of Cu²⁺, Pb²⁺, Zn²⁺ ions is significant but uncertain. It has been shown that the attendant anions affect the shape of the adsorption isotherms, which are described by the Langmuir, Freundlich, or Henri equations. The constants of the adsorption from a nitrate solution calculated from the Langmuir equation (K _L) decrease in the following order: Cu²⁺ > Pb²⁺ >> Zn²⁺. The values of the maximum adsorption (C _max) decrease in the following order: Cu²⁺ ≥ Zn²⁺ > Pb²⁺ for acetate solutions and in the series Pb²⁺ > Zn²⁺ ≥ Cu²⁺ for nitrate solutions. The values of the Henry constants (K _H) calculated for the adsorption of the same cations from chloride solutions decrease in the same order as the values of K _L. The CH₃COO^? anion has the highest effect on the constant values. The NO ₃ ^? and Cl^? anions “switch their places” depending on the attendant cation, but their effect is always lower than that of the acetate anion. The values of C _max for copper and zinc are most affected by the CH₃COO^? anion, and the adsorption of zinc is most affected by the Cl^? and NO ₃ ^? anions. The assessment of the mobility of the adsorbed cations from the extraction with ammonium acetate (pH 4.8) has shown that the content of the desorbed metals is always lower than the content of the adsorbed cations and varies from 0.025 to 83%. According to their mobility, the adsorbed metals form the following order: Zn²⁺ > Pb²⁺ > Cu²⁺. The effect of the attendant anions on the extractability of the adsorbed cations decreases in the following order: chlorides > sulfates > acetates > nitrates.