Mixed Contaminants Research Articles

Interactions and Toxicity of Cu-Zn mixtures to Hordeum vulgare in Different Soils Can Be Rationalized with Bioavailability-Based Prediction Models.

Soil contamination with copper (Cu) is often associated with zinc (Zn), and the biological response to such mixed contamination is complex. Here, we investigated Cu and Zn mixture toxicity to Hordeum vulgare in three different soils, the premise being that the observed interactions are mainly due to effects on bioavailability. The toxic effect of Cu and Zn mixtures on seedling root elongation was more than additive (i.e., synergism) in soils with high and medium cation-exchange capacity (CEC) but less than additive (antagonism) in a low-CEC soil. This was found when we expressed the dose as the conventional total soil concentration. In contrast, antagonism was found in all soils when we expressed the dose as free-ion activities in soil solution, indicating that there is metal-ion competition for binding to the plant roots. Neither a concentration addition nor an independent action model explained mixture effects, irrespective of the dose expressions. In contrast, a multimetal BLM model and a WHAM-Ftox model successfully explained the mixture effects across all soils and showed that bioavailability factors mainly explain the interactions in soils. The WHAM-Ftox model is a promising tool for the risk assessment of mixed-metal contamination in soils.

Thresholds of copper phytotoxicity in field-collected agricultural soils exposed to copper mining activities in Chile

It has been argued that the identification of the phytotoxic metal thresholds in soil should be based on field-collected soil rather than on artificially-contaminated soils. However, the use of field-collected soils presents several difficulties for interpretation because of mixed contamination and unavoidable covariance of metal contamination with other soil properties that affect plant growth. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with perennial ryegrass (Lolium perenne L.). The total Cu content in soils was the best predictor of plant growth and shoot Cu concentrations, while soluble Cu and pCu2+ did not well correlate with these biological responses. The effects of Pb, Zn, and As on plant responses were not significant, suggesting that Cu is a metal of prime concern for plant growth in soils exposed to copper mining activities in Chile. The effects of soil nutrient availability and shoot nutrient concentrations on ryegrass response were not significant. It was possible to determine EC10, EC25 and EC50 of total Cu in the soil of 327mgkg−1, 735mgkg−1 and 1144mgkg−1, respectively, using the shoot length as a response variable. However, the derived 95% confidence intervals for EC10, EC25 and EC50 values of total soil Cu were wide, and thus not allowing a robust assessment of metal toxicity for agricultural crops, based on total soil Cu concentrations. Thus, plant tests might need to be performed for metal toxicity assessment. This study suggests shoot length of ryegrass as a robust response variable for metal toxicity assessment in contaminated soils with different nutrient availability.

ChemInform Abstract: Chemical Immobilization of Metals and Metalloids by Phosphates

AbstractReview: 148 refs.

Rapid Detection of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari in Fresh Chicken Meat and By-Products in Bangkok, Thailand, Using Modified Multiplex PCR

A multiplex PCR assay for simultaneous detection and differentiation of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari was developed and validated to assess the occurrence of these bacteria in fresh chicken meat and by-products in Bangkok, Thailand, by using a new combination of four previously published PCR primers for C. jejuni, C. coli, C. lari, and a universal 16S rDNA gene as an internal control. The specificity was determined by using 13 strains of other bacteria. With pure culture DNA, the detection limit was 0.017 ng/PCR for C. jejuni and C. coli and was 0.016 ng/PCR for C. lari. It can detect 10 CFU of C. jejuni, C. coli, and C. lari in 2 g of chicken meat within a 16-h enrichment time. Our multiplex PCR assay was applied for identification of Campylobacter spp. in 122 supermarket samples and 108 fresh market samples. Of the 230 samples evaluated by multiplex PCR, 54.0, 3.3, and 10.7% of supermarket samples were positive for C. jejuni, C. coli, and mixed C. jejuni and C. coli, respectively, and 56.5 and 33.3% of fresh market samples were positive for C. jejuni and mixed C. jejuni and C. coli, respectively. No sample was positive for C. lari. Fresh market samples had significantly higher C. jejuni and C. coli contamination than those from supermarkets (relative risk: 1.3; P = 0.0001). Compared with the culture method (a gold standard), the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of multiplex PCR were 97.7, 86.8, 96.1, 92.0, and 95.2%, respectively. No significant difference was observed between results from two methods (P = 0.55). Therefore, the established multiplex PCR was not only rapid and easy to perform but had a high sensitivity and specificity to distinguish between C. jejuni, C. coli, and C. lari, even in samples containing mixed contamination. Our study indicated that fresh chicken meat and by-products from fresh markets were significantly less hygienic than those from supermarkets.

An in-depth analysis of actinobacterial communities shows their high diversity in grassland soils along a gradient of mixed heavy metal contamination

Several previous studies indicated that Actinobacteria may be enriched in soils with elevated content of heavy metals. In this study, we have developed a method for the in-depth analysis of actinobacterial communities in soil through phylum-targeted high-throughput sequencing and used it to address this question and examine the community composition in grassland soils along a gradient of heavy metal contamination (Cu, Zn, Cd, Pb). The use of the 16Sact111r primer specific for Actinobacteria resulted in a dataset obtained by pyrosequencing where over 98 % of the sequences belonged to Actinobacteria. The diversity within the Actinobacterial community was not affected by the heavy metals, but the contamination was the most important factor affecting community composition. The most significant changes in community composition were due to the content of Cu and Pb, while the effects of Zn and Cd were relatively minor. For the most abundant actinobacterial taxa, the abundance of taxa identified as members of the genera Acidothermus, Streptomyces, Pseudonocardia, Janibacter and Microlunatus increased with increasing metal content, while those belonging to Jatrophihabitans and Actinoallomurus decreased. The genus Ilumatobacter contained operational taxonomic units (OTUs) that responded to heavy metals both positively and negatively. This study also confirmed that Actinobacteria appear to be less affected by heavy metals than other bacteria. Because several Actinobacteria were also identified in playing a significant role in cellulose and lignocellulose decomposition in soil, they potentially represent important decomposers of organic matter in such environments.

Synergistic effect of Cu adsorption on the enhanced photocatalytic degradation of bisphenol A by TiO2/titanate nanotubes composites

The synergistic effect of Cu(II) adsorption on the enhanced photodegradation of bisphenol A (BPA) by TiO2/titanate nanotube (TNTs) was investigated under UV light irradiation. TNTs were fabricated by hydrothermal method and calcined at 500 °C for 4 h (TNT-500) to adsorb Cu(II) as well as to increase the photocatalytic activity. The TNT-500 exhibited an excellent adsorption ability on copper ions and the adsorption isotherm of Cu(II) followed the Langmuir model with the maximum adsorption capacity of 54 mg/g at pH 5. In addition, the photocatalytic activity of TNT-500 toward BPA degradation was significantly enhanced by factors of 20–34 after the adsorption of 5–40 mg/g Cu(II). The pseudo-first-order rate constant (kobs) for BPA photodegradation was highly dependent on Cu(II) concentration and an optimized value of 20 mg/L was obtained. The reaction rate of BPA by optimized Cu-loaded TNT-500 was 5.2 times higher than that of P25 TiO2. In addition, the photocatalytic activity of Cu-loaded TNT-500 was significantly enhanced at pH > 4.8 and can be recycled for at least 5 times to completely photodegrade BPA under 365 nm UV light irradiation. Results obtained in this study clearly indicate that TNTs are promising nanomaterials for coupled removal of Cu(II) and BPA in aqueous solutions which can open an avenue to develop an effective strategy for removal of mixed contaminants in water and wastewater treatment.

Quantitative surveys of Salmonella and Campylobacter on retail raw chicken in Yangzhou, China

To assess the risks to consumers from Salmonella and Campylobacter in whole raw chickens sold in Yangzhou City, 12-month quantitative surveys were performed in succession. In this study, 480 samples were collected from supermarkets and wet markets from 2011 to 2013. The examination method of Salmonella was optimized from the most probable number (MPN), and the level of Campylobacter contamination was tested using the direct plating method. These results showed that the positive rates of Salmonella and Campylobacter were 33.8% and 51.3%, respectively, and the corresponding mean values of enumeration were 0.524 MPN/g and 1473.49 colony-forming units/g. For prevalence and loads of Salmonella, there was no significant difference between supermarkets and wet markets. However, for Campylobacter, the contamination level of wet markets was greater compared to supermarkets. Seasonality was observed in both qualitative and quantitative studies for both pathogens, with summer being the high-incidence season. Diversity among Salmonella isolates was high in terms of serovar, and the dominant serotypes were Salmonella Typhimurium (34.6%) and Salmonella Enteritidis (16.7%). Diversity of Campylobacter isolates demonstrated that Campylobacter jejuni (45.5%) and Campylobacter coli (30.9%) were the most common species, except for the mixed contamination. Survey results indicated that there was a need for more interventions to minimize the exposure of consumers to Salmonella and Campylobacter.

Investigation of carbonate dissolution for the separation of magnesium hydroxide and calcium sulphate in a magnesium hydroxide-calcium sulphate mixed sludge

South Africa is experiencing a large environmental problem due to uncontrolled discharge of acid mine water into public water courses. The need for neutralisation and desalination of acid mine drainage is a significant issue in South Africa and the sludges that result from mine wastewater treatment usually contain elevated levels of mixed contaminants derived from those originally contained in the wastewater. A more reasonable approach to ultimate sludge disposal is to view the sludge as a resource that can be recycled or reused. Carbon dioxide and a sludge mixture consisting of Mg(OH) 2 and CaSO 4 ·2H 2 O are by-products from acid mine drainage treatment processes. This study was carried out to explore the feasibility of separating Mg(OH) 2 from CaSO 4 ·2H 2 O through dissolution of Mg(OH) 2 by accelerated carbonation in a pressurised, completely-mixed reactor. The effects of temperature and pressure, and of both together, on the dissolution of the sludge mixture with time were investigated. Parameters monitored included alkalinity, pH, conductivity and Ca 2+ , Mg 2+ and SO 4 2- concentrations. OLI Analyser Studio Version 9.0 software was used for modelling predictions of chemical speciation of the mixtures. The optimum separation capacity for the Mg(OH) 2 -CaSO 4 ·2H 2 O sludge mixture was determined to be 99.34% Mg 2+ and 0.05% Ca 2+ in the aqueous phase when contacted with CO 2 at a temperature of 5°C and pressure of 150 kPa. The model predictions were in agreement with the experimental findings. Temperature and pressure have a significant impact on the dissolution of the mixed sludges when contacted with CO 2 . Keywords : Carbonation, gypsum, dissolution, reclamation, carbon dioxide, sludge disposal

Optimal Removal of Cadmium from Heavily Contaminated Saline–Sodic Soil Using Integrated Electrokinetic-Adsorption Technique

Saline–sodic soil inherently exhibits extreme characteristics which challenge getting it remediated from mixed contaminants. In this study, the feasibility of removal of cadmium (Cd) in saline–sodic clay soil in presence of mixed pollutants was investigated. Fifteen (15) experimental runs, each having residence time of three (3) weeks, were designed and conducted according to Box-Behnken design to evaluate the effects of contaminants initial concentration (20–100 mg/kg), voltage gradient (0.2–1 v/cm) and polarity reversal (12–48 h) on Cd removal efficiency. The Cd removal efficiency fitted experimentally verified quadratic model (prediction error of 18.60 %) with insignificant lack of fit based on 5 % significant level (R2 = 0.9917 and p initial contaminant concentration > polarity reversal rate. The optimal conditions considering optimization of all effecting parameters (both factors and responses) were found to be at voltage gradient = 0.47 V/cm; polarity reversal rate = 19.77 h; initial contaminant concentration = 65.44 mg/kg which yielded highest Cd remedial efficiency of 86 % at 22.45 kWhr/m3/mg energy expenditure. The study demonstrated the viability of employing integrated-adsorption technology for the removal of Cd from contaminated saline–sodic clays under extreme soil and contamination conditions. It also further underscores the intricacy of obtaining a common optimal remediation conditions for the different pollutants presence in saline–sodic soil contaminated with mixed pollutants.

Historical profiles of PCB in dated sediment cores suggest recent lake contamination through the "halo effect".

We investigated the major sources of polychlorinated biphenyls (PCB) and interpreted the environmental fate processes of these persistent organic pollutants in the past and current PCB contamination of three large, urbanized, French peri-alpine lakes. Dated sediment cores were analyzed in order to reconstruct and compare the historical contamination in all three lakes. Stratigraphic changes of PCB contents and fluxes were considered as revealing the temporal dynamics of PCB deposition to the lakes and the distribution of the seven indicator congeners (further referred to as PCBi) as an indicator of the main contamination origin and pathway. Although located within a single PCB industrial production region, concentration profiles for the three lakes differed in timing, peak concentration magnitudes, and in the PCBi congeners compositions. PCBi fluxes to the sediment and the magnitude of the temporal changes were generally much lower in Lake Annecy (0.05-2 ng·cm(-2)·yr(-1)) as compared to Lakes Geneva (0.05-5 ng·cm(-2)·yr(-1)) and Bourget (5-290 ng·cm(-2)·yr(-1)). For all three lakes, the paramount contamination occurred in the early 1970s. In Lakes Annecy and Bourget, PCB fluxes have declined and plateaued at 0.5 and 8 ng·cm(-2)·yr(-1), respectively, since the early 1990s. In Lake Geneva, PCB fluxes have further decreased by the end of the XX(th) century and are now very low. For the most contaminated lake (Lake Bourget), the high PCBi flux (5-290 ng·cm(-2)·yr(-1)) and the predominance of heavy congeners for most of the time period are consistent with a huge local input to the lake. This still high rate of Lake Bourget is explained by transport of suspended solids from one of its affluents, polluted by an industrial point source. Intermediate historical levels and PCBi distribution over time for Lake Geneva suggest a mixed contamination (urban point sources and distant atmospheric transport), while atmospheric deposition to Lake Annecy explains its lowest contamination rate. The presently low contamination levels recorded in Lake Geneva correspond to atmospheric inputs, but the recent PCBi distribution of Lake Annecy, enriched in relatively heavy congeners, reveals a contamination by the neighboring Lake Bourget, following a halo effect of about 40 km radius.

Enhanced tolerance and remediation to mixed contaminates of PCBs and 2,4-DCP by transgenic alfalfa plants expressing the 2,3-dihydroxybiphenyl-1,2-dioxygenase

Polychlorinated biphenyls (PCBs) and 2,4-dichlorophenol (2,4-DCP) generally led to mixed contamination of soils as a result of commercial and agricultural activities. Their accumulation in the environment poses great risks to human and animal health. Therefore, the effective strategies for disposal of these pollutants are urgently needed. In this study, genetic engineering to enhance PCBs/2,4-DCP phytoremediation is a focus. We cloned the 2,3-dihydroxybiphenyl-1,2-dioxygenase (BphC.B) from a soil metagenomic library, which is the key enzyme of aerobic catabolism of a variety of aromatic compounds, and then it was expressed in alfalfa driven by CaMV 35S promoter using Agrobacterium-mediated transformation. Transgenic line BB11 was selected out through PCR, Western blot analysis and enzyme activity assays. Its disposal and tolerance to both PCBs and 2,4-DCP were examined. The tolerance capability of transgenic line BB11 towards complex contaminants of PCBs/2,4-DCP significantly increased compared with non-transgenic plants. Strong dissipation of PCBs and high removal efficiency of 2,4-DCP were exhibited in a short time. It was confirmed expressing BphC.B would be a feasible strategy to help achieving phytoremediation in mixed contaminated soils with PCBs and 2,4-DCP.

Effect of grain size and heavy metals on As immobilization by marble particles.

The effect of grain size and the interaction of heavy metals on As sorption by marble waste with different particle sizes was investigated. Acidic solutions containing only arsenic and a mixture of arsenic, lead, zinc, and cadmium were put in contact with the marble waste. The amount of metal(loid)s that were immobilized was calculated using the difference between the concentration in the acidic solution and in the liquid phase of the suspensions. Approximately 420 μg As m(-2) was sorbed onto the marble grains, both nonspecifically and specifically, where ≥ 80 % of the total arsenic in the acidic solution remained soluble, which suggests that this amendment is not effective to immobilize arsenic. However, in mixed contamination, relatively stable Pb-Ca arsenates were formed on the surface of the marble particles, and the soluble arsenic was reduced by 95 %, which indicates that marble particles can effectively immobilize arsenic and lead when both appear together.

Simultaneous removal of mixed contaminants by organoclays — Amoxicillin and Cu(II) from aqueous solution

The treatment of mixed contaminants in wastewater faces a significant challenge because of the distinct fate and transport mechanism of metals and organic contaminants. The present study explored the possibility of organoclays used to simultaneously remove amoxicillin (AMX) and Cu(II) from wastewater. The adsorption of AMX onto organobentonite (DK1) was 6 times higher than that using bentonite (control), while adsorption of Cu(II) on DK1 showed comparable results as that using bentonite. Adsorption isotherms indicated that AMX was well described by Langmuir isotherms, while Cu(II) adsorption data fitted well with Freundlich isotherms, and adsorption kinetics of both could be explained by the first-order and pseudo-second-order kinetic models. The exothermic nature of simultaneous adsorption of AMX and Cu(II) onto DK1 was disclosed by the thermodynamic study. Furthermore, DK1 was characterized using EDS and XRD, which confirmed the simultaneous adsorption of AMX and Cu(II) onto DK1 by evaluation of their morphologies and chemical compositions. Finally, the simultaneous adsorption of AMX and Cu(II) onto DK1 occurred through partition for AMX and ion-exchange for Cu(II). DK1 was further used to remove AMX and Cu(II) from industrial wastewater. More than 34.8% AMX and 43.6% Cu(II) were removed, indicating its great potential removal of mixed organic and metal contaminants.

Simultaneous removal of co-contaminants: acid brilliant violet and Cu2+ by functional bimetallic Fe/Pd nanoparticles

Effluents from the textile industry often contain dyes and metals that are a serious environmental concern. It is a challenge to develop a method for simultaneous removal of mixed contaminants. In this study, kaolinite supported bimetallic Fe/Pd (K–Fe/Pd) is firstly reported to be used for simultaneous catalytic removal of acid brilliant violet (ABV) and Cu2+ in aqueous solution, where the presence of kaolinite as a stable supporter and disperser maintains the reactivity of Fe0 as a reductant, while Pd0 as a catalyst accelerates the reaction. This was confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and batch experiments. 96.23 % of ABV and 100 % of Cu2+ was removed using K–Fe/Pd within 60 min, while only 77.50 % of ABV and 99.45 % of Cu2+ using K–Fe, and 19.75 % of ABV and 4.00 % of Cu2+ using kaolinite was removed, respectively. However, both efficiency and rate of removal in the mixed solution were higher than that of the single one regarding both ABV and Cu2+, which is attributable to the formation of in situ trimetallic Cu/Fe/Pd in the mixed solution. Different factors impacting on the removal of ABV–Cu2+ using K–Fe/Pd showed that the catalytic reduction decreased when pH, initial concentration, and temperature increased. Finally, the reuse and application of K–Fe/Pd in dyeing wastewater led to a removal efficiency of 96.35 % for ABV and 100 % for Cu2+, respectively.

Enhanced soil washing process for the remediation of PBDEs/Pb/Cd-contaminated electronic waste site with carboxymethyl chitosan in a sunflower oil-water solvent system and microbial augmentation.

An innovative ex situ soil washing technology was developed to remediate polybrominated diphenyl ethers (PBDEs) and heavy metals in an electronic waste site. Elevated temperature (50 °C) in combination with ultrasonication (40 kHz, 20 min) at 5.0 mL L(-1) sunflower oil and 2.5 g L(-1) carboxymethyl chitosan were found to be effective in extracting mixed pollutants from soil. After two successive washing cycles, the removal efficiency rates for total PBDEs, BDE28, BDE47, BDE209, Pb, and Cd were approximately 94.1, 93.4, 94.3, 99.1, 89.3, and 92.7 %, respectively. Treating the second washed soil with PBDE-degrading bacteria (Rhodococcus sp. strain RHA1) inoculation and nutrient addition for 3 months led to maximum biodegradation rates of 37.3, 52.6, 23.9, and 1.3 % of the remaining total PBDEs, BDE28, BDE47, BDE209, respectively. After the combined treatment, the microbiological functions of washed soil was partially restored, as indicated by a significant increase in the counts, biomass C, N, and functioning diversity of soil microorganisms (p < 0.05), and the residual PBDEs and heavy metals mainly existed as very slow desorbing fractions and residual fractions, as evaluated by Tenax extraction combined with a first-three-compartment model and sequential extraction with metal stability indices (I R and U ts). Additionally, the secondary environmental risk of mixed contaminants in the remediated soil was limited. Therefore, the proposed combined cleanup strategy is an environment-friendly technology that is important for risk assessment and management in mixed-contaminated sites.

New phosphate-based binder for stabilization of soils contaminated with heavy metals: Leaching, strength and microstructure characterization

Cement stabilization is used extensively to remediate soils contaminated with heavy metals. However, previous studies suggest that the elevated zinc (Zn) and lead (Pb) concentrations in the contaminated soils would substantially retard the cement hydration, leading to the deterioration of the performance of cement stabilized soils. This study presents a new binder, KMP, composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The effectiveness of stabilization using this binder is investigated on soils spiked with Zn and Pb, individually and together. Several series of tests are conducted including toxicity characteristic leaching (TCLP), ecotoxicity in terms of luminescent bacteria test and unconfined compressive strength. The leachability of a field Zn- and Pb- contaminated soil stabilized with KMP is also evaluated by TCLP leaching test. The results show that the leached Zn concentrations are lower than the China MEP regulatory limit except when Zn and Pb coexist and for the curing time of 7 days. On the other hand, the leached Pb concentrations for stabilized soils with Pb alone or mixed Zn and Pb contamination are much lower than the China MEP or USEPA regulatory limit, irrespective of the curing time. The luminescent bacteria test results show that the toxicity of the stabilized soils has been reduced considerably and is classified as slightly toxic class. The unconfined compressive strength of the soils decrease with the increase in the Zn concentration. The stabilized soils with mixed Zn and Pb contaminants exhibit notably higher leached Zn concentration, while there is lower unconfined compressive strength relative to the soils when contaminated with Zn alone. The X-ray diffraction and scanning electron microscope analyses reveal the presence of bobierrite (Mg3(PO4)2·8H2O) and K-struvite (MgKPO4·6H2O) as the main products formed in the KMP stabilized uncontaminated soils; the formation of hopeite (Zn3(PO4)2·4H2O), scholzite (CaZn2(PO4)2·2H2O), zinc hydroxide (Zn(OH)2), and fluoropyromorphite (Pb5(PO4)3F) in the soils are the main mechanisms for immobilization of Zn and Pb with the KMP binder. The change in the relative quantities of the formed phosphate-based products, with respect to the Zn concentration and presence of mixed Zn and Pb contaminants, can well explain the measured impact of the Zn concentration levels and presence of both Zn and Pb contaminants on the unconfined compressive strength of the KMP stabilized soils.

Evaluation of Biochar as a Potential Filter Media for the Removal of Mixed Contaminants from Urban Storm Water Runoff

AbstractUrban storm water runoff can carry a wide range of contaminants, many of which exceed federal maximum contaminant levels, into surface water resources (e.g., rivers and lakes). The use of filtration systems has received greater attention for its potential to remove particulate matter and other contaminants. Biochar is expected to have excellent potential as an adsorbent or filter given its large surface area and microporous structure. This study evaluated the potential use of biochar as a filter media through a series of column experiments. A column with an inner diameter of 7 cm (2.75 in.) and a length of 61 cm (24 in.) using biochar as filter media was constructed to examine its effectiveness for the removal of mixed contaminants [total suspended solids (TSS), nutrients, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and E. coli] from synthetic storm water. The results demonstrated that this filter reduced the TSS in the storm water effluent by an average of 86% and the concentrations of...

Evaluation of soil washing process with carboxymethyl-β-cyclodextrin and carboxymethyl chitosan for recovery of PAHs/heavy metals/fluorine from metallurgic plant site

Polycyclic aromatic hydrocarbons (PAHs)/heavy metals/fluorine (F) mixed-contaminated sites caused by abandoned metallurgic plants are receiving wide attention. To address the associated environmental problems, this study was initiated to investigate the feasibility of using carboxymethyl-β-cyclodextrin (CMCD) and carboxymethyl chitosan (CMC) solution to enhance ex situ soil washing for extracting mixed contaminants. Further, Tenax extraction method was combined with a first-three-compartment model to evaluate the environmental risk of residual PAHs in washed soil. In addition, the redistribution of heavy metals/F after decontamination was also estimated using a sequential extraction procedure. Three successive washing cycles using 50g/L CMCD and 5g/L CMC solution were effective to remove 94.3% of total PAHs, 93.2% of Pb, 85.8% of Cd, 93.4% of Cr, 83.2% of Ni and 97.3% of F simultaneously. After the 3rd washing, the residual PAHs mainly existed as very slowly desorbing fractions, which were in the form of well-aged, well-sequestered compounds; while the remaining Pb, Cd, Cr, Ni and F mainly existed as Fe–Mn oxide and residual fractions, which were always present in stable mineral forms or bound to non-labile soil fractions. Therefore, this combined cleanup strategy proved to be effective and environmentally friendly.

Competitive Reduction of Nitrate, Nitrite, and Nitrobenzene in Fe0-Water Systems

AbstractTreating mixed contaminants with zerovalent iron (Fe0) for environmental remediation requires a thorough understanding of the competition among electron acceptors. The authors conducted aqueous batch tests to determine competitive reduction of nitrate, nitrite, and nitrobenzene by Fe0 under varying conditions. Results indicate that nitrate reduction by Fe0 was accompanied by substantial Fe0 oxidation by water. Nitrite and nitrobenzene were concomitantly reduced by Fe0, forming a lepidocrocite (γ-FeOOH) coating on the Fe0 grains. When present together, nitrite and nitrobenzene reduction proceeded without apparent interference from nitrate. Nitrate reduction, however, did not occur in the presence of nitrite or nitrobenzene. Adding aqueous Fe(II) facilitated nitrate reduction by Fe0, but not until the lepidocrocite coating on the Fe0 grains was transformed to magnetite (Fe3O4), a process that is significantly accelerated by surface-bound Fe(II). This study illustrates the relative reactivity of Fe0 ...

Sr Isotope Zoning in Plagioclase from Parinacota Volcano (Northern Chile): Quantifying Magma Mixing and Crustal Contamination

We present analyses of Sr isotope zoning by microdrilling and thermal ionization mass spectrometry in plagioclase crystals from Parinacota volcano (Central Volcanic Zone, northern Chile), which were analysed for major and minor element zoning in a previous study. Although the isotopic range of the bulk-rock samples is small at this volcano (0·7067–0·7070, except for one flow of mafic andesite at 0·7061), significant variations are seen (0·70649–0·70700) within and between plagioclase crystals. A general negative correlation is observed between Sr isotope composition and Sr concentration in the liquid in equilibrium with each plagioclase zone, as calculated from chemical zoning data and partition coefficients. Additional scatter is superimposed on this general trend, indicating a decoupling between isotopic and chemical variations for Sr. In one dacite sample a detailed isotopic profile shows increasing contamination during crystal growth, except for an abrupt decrease correlated with a dissolution surface and interpreted as a recharge event. We apply energy-constrained recharge, assimilation and fractional crystallization modelling to the melt evolution recorded in the chemical and isotopic zoning in this crystal. Results suggest 20% assimilation of the local wall-rock gneiss, at high initial temperatures. The isotopic data confirm the involvement of two contrasting mafic magmas, which are sampled at flank cinder cone vents. One (Lower Ajata) has a low Sr content with high 87Sr/86Sr, the other (Upper Ajata) has a high Sr content with lower 87Sr/86Sr. In some samples from Parinacota, the isotopic composition of plagioclase crystal rims or groundmass crystals is significantly higher than that of the high 87Sr/86Sr mafic magma. In others, where chemical zoning profiles suggest that recharge was from the low 87Sr/86Sr magma, the 87Sr/86Sr of the groundmass and crystal rims is higher than expected. This indicates either additional parent magmas to the two previously identified, or further crustal assimilation, either at lower crustal depths, before crystallization of plagioclase, or just after the last recharge. Our results illustrate the complexity of magma–crust interaction beneath Parinacota, which is likely to be representative of many other Central Andean volcanoes formed on thick crust. Such complex interactions can be revealed by combined study of chemical and isotopic zoning in plagioclase (in a textural petrographic context), despite a small whole-rock isotopic range. The distinct contamination patterns of various samples suggest an important role for the geometry, location and evolution of the magma plumbing system and, in general, variations of the thermal and compositional structure of the crust underneath the volcano.