Partitioning of hydrogen peroxide between the gas and liquid phases in the presence of surfactant

Gas-liquid phase partitioning is a key physical property that can predict the environmental fate of a compound between two phases. Several environmental factors have been known to affect the gas-liquid phase partitioning. We investigated the influence of surfactant on the gas-liquid phase partitioning of hydrogen peroxide (H(2)O(2)). The surfactant used was ammonium perfluorooctanoate (APFO). H(2)O(2) solution containing the surfactant was equilibrated in a closed system and gas phase H(2)O(2) concentration was measured by the peroxyoxalate chemiluminescence (PO-CL) method. Gas phase H(2)O(2) concentrations remained constant below the critical micelle concentration (CMC) and increased linearly with surfactant concentration above the CMC, which indicated that surfactant micelles influenced the gas-liquid phase partitioning of H(2)O(2). This result showed that H(2)O(2)-micelle interactions are less favorable than H(2)O(2)-H(2)O interactions. Surfactant monomers did not affect the gas-liquid phase partitioning of H(2)O(2) due to the absence of micelles. Solvent (methanol) effect was also investigated and showed that gas phase H(2)O(2) concentrations increased with the addition of solvent. This indicated the unfavorable interaction of H(2)O(2) with hydrophobic medium compared to hydrophilic one. It is consistent with the result that H(2)O(2)-micelles has a weaker interaction than H(2)O(2)-water because surfactant micelles are hydrocarbon-like organic phase rather than aqueous phase.     

Sulfidation treatment of molten incineration fly ashes with Na2S for zinc, lead and copper resource recovery

The present study focuses on the conversion of heavy metals involved in molten incineration fly ashes to metal sulfides which could be thereafter separated by flotation. The sulfidation treatment was carried out for five molten incineration fly ashes (Fly ash-A to Fly ash-E) by contacting each fly ash with Na(2)S solution for a period of 10 min to 6h. The initial molar ratio of S(2-) to Me(2+) was adjusted to 1.20. The conversion of heavy metals to metal sulfides was evaluated by measuring the S(2-) residual concentrations using an ion selective electrode. The formation of metal sulfides was studied by XRD and SEM-EDS analyses. In the case of Fly ash-A to Fly ash-D, more than 79% of heavy metals of zinc, lead and copper was converted to metal sulfides within the contacting period of 0.5h owing to a fast conversion of metal chlorides to metal sulfides. By contrast, the conversion of about 35% was achieved for Fly ash-E within the same contacting period, which was attributed to a high content of metal oxides. Further, the S(2-) to Me(2+) molar ratio was reduced to 1.00 to minimize Na(2)S consumption and the conversions obtained within the contacting period of 0.5h varied from 76% for Fly ash-D to 91% for Fly ash-C. Finally, soluble salts such as NaCl and KCl were removed during the sulfidation treatment, which brought about a significant enrichment in metals content by a factor varying from 1.5 for Fly ash-D to 4.9 for Fly ash-A.     

Effect of pre-treatment and supporting media on Ni(II), Cu(II), Al(III) and Fe(III) sorption by plant root material

In this work Paspalum notatum root material was used to elucidate the influence of acid leaching pre-treatment and of sorption medium on metal adsorption. Ground P. notatum root was leached with 0.14M HNO(3). Leached root material (LRM) and non-leached root material (NLRM) were employed to flow sorption of Ni(II), Cu(II), Al(III) and Fe(III) in 0.5M CH(3)COONH(4) medium at pH 6.5. For LRM the sorption was also studied in 0.5M KNO(3) medium. The acid pre-treatment increased the sorption capacity (SC) for all ions studied. For the KNO(3) medium, Cu(II) and Fe(III) sorption was higher than in CH(3)COONH(4) and the type of the Ni(II) isotherm's model changed. The Freundlich model was the most representative isotherm model to describe metallic ions sorption. The (1)H NMR spectra showed differences between LRM and NLRM and the acid-basic potentiometric titration elucidated that acid-leaching procedure affected the root material sorption sites once only two predominant sorption sites were found for LRM (phenolic and amine, both able cations sorption) and five sorption sites (two carboxylic, amine and two phenolic) were founded for NLRM.     

Chromate transport through columns packed with surfactant-modified zeolite/zero valent iron pellets

Chromate transport through columns packed with zeolite/zero valent iron (Z/ZVI) pellets, either untreated or treated with the cationic surfactant hexadecyltrimethylammonium (HDTMA), was studied at different flow rates. In the presence of sorbed HDTMA, the chromate retardation factor increased by a factor of five and the pseudo first-order rate constant for chromate reduction increased by 1.5-5 times. The increase in rate constant from the column studies was comparable to a six-fold increase in the rate constant determined in a batch study. At a fast flow rate, the apparent delay in chromate breakthrough from the HDTMA modified Z/ZVI columns was primarily caused by the increase in chromate reduction rate constant. In contrast, at a slower flow rate, the retardation in chromate transport from the HDTMA modified Z/ZVI columns mainly originated from chromate sorption onto the HDTMA modified Z/ZVI pellets. Due to dual porosity, the presence of immobile water was responsible for the earlier breakthrough of chromate in columns packed with zeolite and Z/ZVI pellets. The results from this study further confirm the role of HDTMA in enhancing sorption and reduction efficiency of contaminants in groundwater remediation.     

The influence of EDDS and EDTA on the uptake of heavy metals of Cd and Cu from soil with tobacco Nicotiana tabacum

Phytoextraction, the use of plants to extract contaminants from soils and groundwater, is a promising approach for cleaning up soils contaminated with heavy metals. In order to enhance phytoextraction the use of chelating agents has been proposed. This study aims to assess whether ethylene diamine disuccinate (EDDS), a biodegradable chelator, can be used for enhanced phytoextraction purposed, as an alternative to ethylene diamine tetraacetate (EDTA). EDDS revealed a higher toxicity to tobacco (Nicotiana tabacum) in comparison to EDTA, but no toxicity to microorganisms. The uptake of Cu was increased by the addition of EDTA and EDDS, while no increase was observed in the uptake of Cd. Both chelating agents showed a very low root to shoot translocation capability and the translocation factor was lower than the one of the control. Heavy metals where significantly more phytoavailable than in the control, even after harvesting, resulting in a high heavy metal leaching possibility, probably owing to a low biodegradation rate of EDDS. New seedlings which were transplanted into the EDDS treated pots 7d after the phytoextraction experiment, showed signs of necrosis and chlorosis, which resulted in a significantly lower biomass in comparison to the control. The seedlings on the EDTA treated pots showed no toxicity signs. Contrary to previous opinions the results of this study revealed the chelating agents EDTA and EDDS as unsuitable for enhanced phytoextraction using tobacco.     

Variations in PCB concentrations between genders of six warmwater fish species in Lake Logan Martin, Alabama, USA

We collected and analyzed 955 individual fish (six species) for sexual differences in PCB bioaccumulations from a southeastern, USA reservoir. Using 2-way ANCOVAs, we found significant differences in fillet PCB concentrations between sexes for channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salmoides) and spotted bass (Micropterus punctulatus). Striped bass (Morone saxatilus), black crappie (Pomoxis nigromaculatus) and freshwater drum (Aplodinotus grunniens) did not display differences between sexes in PCB concentrations. We suspect that sexual differences may be due to biological differences in reproduction, relative motility and lipid deposition. For one species (striped bass), sexual differences in PCB concentrations were inconsistent with a study in the Hudson River suggesting that sexual differences in bioaccumulations can change across ecosystems. Two species which did show sexual differences, largemouth bass and channel catfish, are often chosen as representative species (e.g., "piscivore" and "benthivore") in contaminant monitoring in many USA states indicating human consumption and risk management decisions would be improved if an equal number of male and female fish were included in composite PCBs analysis. This could reduce variability in fish PCBs data from which consumption advisories are based.     

Seasonal variations of hydrophobic organic contaminant concentrations in the water-column of the Seine Estuary and their transfer to a planktonic species Eurytemora affinis (Calanoïda, copepoda). Part 1: PCBs and PAHs

Hydrophobic organic contaminants (HOC) (i.e. PAHs and PCBs) were measured in the water column and in Eurytemora affinis samples from the Seine Estuary collected from November 2002 to February 2005. Results showed seasonal variations of both total PCB and PAH levels in the suspended particulate matter (SPM) and in the copepods with maximum levels during winter times. PAH and PCB concentrations in the SPM ranged from 499 to 5819ngg(-1) and from 58 to 463ngg(-1), respectively. Phenanthrene, pyrene and benzo[b+j+k]fluoranthene (B[b+j+k]F) were the predominant PAH compounds in the water column, while CB 101, 118, 153 and 138 were the most abundant PCB congeners. PCBs and PAHs bioaccumulated by E. affinis (EA) varied between 383 and 1785ngg(-1) and 165-3866ngg(-1). CB101, 153, 138 and B[b+j+k] were, respectively, the major compounds of PCB and PAH fingerprints in EA. Thereby, the copepods could reach high accumulation factor (ACF) (91000 for PCBs and 17000 for PAHs). The principal component analyses of contaminant concentrations and environmental parameter datasets distinguished two groups of copepods. The winter time cluster, with high percentage of adult copepods, which bioaccumulated the highest PCB and PAH body-burdens, and the second cluster with juveniles showing the lowest HOC concentrations. Thus, PAH and PCB concentrations in EA exhibited significant correlations with the percentage of adults making up the samples.     

Transport of Sr2+ and SrEDTA2- in partially-saturated and heterogeneous sediments

Strontium-90 has migrated deep into the unsaturated subsurface beneath leaking storage tanks in the Waste Management Areas (WMA) at the U.S. Department of Energy's (DOE) Hanford Reservation. Faster than expected transport of contaminants in the vadose zone is typically attributed to either physical hydrologic processes such as development of preferential flow pathways, or to geochemical processes such as the formation of stable, anionic complexes with organic chelates, e.g., ethylenediaminetetraacetic acid (EDTA). The goal of this paper is to determine whether hydrological processes in the Hanford sediments can influence the geochemistry of the system and hence control transport of Sr(2+) and SrEDTA(2-). The study used batch isotherms, saturated packed column experiments, and an unsaturated transport experiment in an undisturbed core. Isotherms and repacked column experiments suggested that the SrEDTA(2-) complex was unstable in the presence of Hanford sediments, resulting in dissociation and transport of Sr(2+) as a divalent cation. A decrease in sorption with increasing solid:solution ratio for Sr(2+) and SrEDTA(2-) suggested mineral dissolution resulted in competition for sorption sites and the formation of stable aqueous complexes. This was confirmed by detection of MgEDTA(2-), MnEDTA(2-), PbEDTA(2-), and unidentified Sr and Ca complexes. Displacement of Sr(2+) through a partially-saturated undisturbed core resulted in less retardation and more irreversible sorption than was observed in the saturated repacked columns, and model results suggested a significant reservoir (49%) of immobile water was present during transport through the heterogeneous layered sediments. The undisturbed core was subsequently disassembled along distinct bedding planes and subjected to sequential extractions. Strontium was unequally distributed between carbonates (49%), ion exchange sites (37%), and the oxide (14%) fraction. An inverse relationship between mass wetness and Sr suggested that sandy sediments of low water content constituted the immobile flow regime. Our results suggested that the sequestration of Sr(2+) in partially-saturated, heterogeneous sediments was most likely due to the formation of immobile water in drier regions having low hydraulic conductivities.     

Bacteria transport and deposition under unsaturated conditions: the role of the matrix grain size and the bacteria surface protein

Unsaturated (80% water saturated) packed column experiments were conducted to investigate the influence of grain size distribution and bacteria surface macromolecules on bacteria (Rhodococcus rhodochrous) transport and deposition mechanisms. Three sizes of silica sands were used in these transport experiments, and their median grain sizes were 607, 567, and 330 microm. The amount of retained bacteria increased with decreasing sand size, and most of the deposited bacteria were found adjacent to the column inlet. The deposition profiles were not consistent with predictions based on classical filtration theory. The experimental data could be accurately characterized using a mathematical model that accounted for first-order attachment, detachment, and time and depth-dependent straining processes. Visual observations of the bacteria deposition as well as mathematical modelling indicated that straining was the dominant mechanism of deposition in these sands (78-99.6% of the deposited bacteria), which may have been enhanced due to the tendency of this bacterium to form aggregates. An additional unsaturated experiment was conducted to better deduce the role of bacteria surface macromolecules on attachment and straining processes. In this case, the bacteria surface was treated using a proteolitic enzyme. This technique was assessed by examining the Fourier-transform infrared spectrum and hydrophobicity of untreated and enzyme treated cells. Both of these analytical procedures demonstrated that this enzymatic treatment removed the surface proteins and/or associated macromolecules. Transport and modelling studies conducted with the enzyme treated bacteria, revealed a decrease in attachment, but that straining was not significantly affected by this treatment.     

A synchronized amphibian metamorphosis assay as an improved tool to detect thyroid hormone disturbance by endocrine disruptors and apolar sediment extracts

Amphibian metamorphosis assays are used to evaluate potential effects of endocrine disrupting compounds on the thyroid hormone axis. In this study, Xenopus laevis tadpoles are kept in a solution of 0.2% thiourea (TU) to arrest and synchronise them in their development. The advantage of this synchronized amphibian metamorphosis assays is that synchronised tadpoles are available at any time to start metamorphosis experiments, and experimental groups are much more homogenous at the start of experimental exposure compared with groups selected from an untreated pool of animals. The water volume per animal was kept constant throughout the experimental period to overcome the influence of declining numbers of animals per aquarium due to metamorphosis and mortality on the density dependent development of the remaining tadpoles. Clophen A50 (a technical PCB mixture), the single congener 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and apolar sediment extracts that were previously tested positive in the T-Screen, an in vitro proliferation assay for thyroid hormone disruption, were tested in the Synchronized Amphibian Metamorphosis Assay. Endpoints studied were mortality, malformations, body weight, and percentage of metamorphosed froglets at the end of the 60-day experimental period, percentage of tadpoles in different developmental stages, and developmental stage-dependent awarded penalty points. Dietary exposure to Clophen A50 (0.2-50mg/kg food) resulted in a significant increased percentage of tadpoles that did not pass metamorphosis at concentrations higher than 2mg/kg food. Time until metamorphosis in those animals that were able to metamorphose after the 60-days experimental period was significantly decreased. Dietary exposure to PCB 77, a congener that can be readily metabolised, did not result in significant effects in any exposure group (2-500 microg/kg food). Apolar sediment extracts from two of the three sites that are contaminated with a wide variety of chemicals significantly decreased the percentage of metamorphosed animals and significantly increased the number of tadpoles that remained in early and late metamorphic stages. These effects already occurred when the extracts where diluted more than 1000 times (on an organic carbon base) compared to environmental concentrations. The rank of potency was comparable to results obtained with the T-screen. This suggests the presence of thyroid hormone disrupting compounds in the aquatic environment and possible effects of such compounds on animal development in the wild.