Tributyltin partitioning in sediments: effect of aging

The effect of aging on the solid/pore-water partitioning and desorption behaviour of tributyltin (TBT) in sediments was examined. Three sediment samples with contrasting physical and chemical properties were spiked with 10 mg/kg TBT and aged under sterile conditions for periods of time ranging from 1 to 84 days. Aging had a negligible effect on partitioning and desorption behaviour in a sandy sample with very low organic carbon content (0.2% w/w). In contrast, for samples with larger amounts of organic carbon (2.6% and 4.8% w/w), aging caused substantial increases in TBT sorption. For these samples, apparent distribution coefficients (KD,app) obtained from sequential 2 h desorption experiments also exhibited a twofold increase between spiked sediments subjected to aging for 1 day and 84 days. This study demonstrates that aging effects may be an important aspect of TBT fate in contaminated sediments.     

Effect of chromium on the fatty acid composition of two strains of Euglena gracilis

The effect of hexavalent chromium on fatty acid composition was studied in two strains of Euglena gracilis; UTEX 753 (from the Culture Collection of Algae of Texas University, USA) and MAT (isolated from a highly polluted River). Both were grown in photoauxotrophic and photoheterotrophic conditions and exposed to two metal concentrations, one below and one above IC50. The high malondialdehyde (MDA) levels (3 to 7-fold) obtained with chromium concentration above IC50, suggested the existence of metal-induced lipid peroxidation. Total lipid content increased only with concentration below IC50, whereas it was inhibited by higher metal concentration. Photoheterotrophic control strains exhibited a significantly higher proportion of saturated and polyunsaturated fatty acids. Polyunsaturated acids were most affected by chromium, especially those related to chloroplast structures. Ultra-structure studies showed clear thylakoid disorganization in all treated cells. The results indicate that hexavalent chromium affects levels of fatty acids, especially those related to photosynthetic activity.     

Dip-angle influence on areal DNAPL recovery by co-solvent flooding with and without pre-flooding

A two-dimensional (2D) laboratory model was used to study effects of gravity on areal recovery of a representative dense non-aqueous phase liquid (DNAPL) contaminant by an alcohol pre-flood and co-solvent flood in dipping aquifers. Recent studies have demonstrated that injection of alcohol and co-solvent solutions can be used to reduce in-situ the density of DNAPL globules and displace the contaminant from the source zone. However, contact with aqueous alcohol reduces interfacial tension and causes DNAPL swelling, thus facilitating risk of uncontrolled downward DNAPL migration. The 2D laboratory model was operated with constant background gradient flow and a DNAPL spill was simulated using tetrachloroethene (PCE). The spill was dispersed to a trapped, immobile PCE saturation by a water flood. Areal PCE recovery was studied using a double-triangle well pattern to simulate a remediation scheme consisting of an alcohol pre-flood using aqueous isobutanol ( approximately 10% vol.) followed by a co-solvent flood using a solution of ethylene glycol (65%) and 1-propanol (35%). Experiments were conducted with the 2D model oriented in the horizontal plane and compared to experiments at the 15 degrees and 30 degrees dip-angle orientations. Injection was applied either in the downward or upward direction of flow. Experimental results were compared to theoretical predictions for flood front stability and used to evaluate effects of gravity on areal PCE recovery. Sensitivity experiments were performed to evaluate effects of the alcohol pre-flood on PCE areal recovery. For experiments conducted with the alcohol pre-flood and the 2D model oriented in the horizontal plane, results indicate that 89-93% of source zone PCE was recovered. With injection oriented downward, results indicate that areal PCE recovery was 70-77% for a 15 degrees dip angle and 57-59% for a 30 degrees dip angle. With injection oriented upward, results indicate that areal PCE recovery was 57-60% at the 30 degrees dip angle, which was similar to PCE recovery for injection in the downward flow direction. Lower areal PCE recovery at greater dip angles in either direction of flow was attributed to DNAPL swelling and migration, flood front instabilities and bypassing of the displaced fluid past the extraction wells during the alcohol pre-flood. Additional results demonstrate that the use of an alcohol pre-flood can be beneficial in improving DNAPL recovery in the horizontal orientation, but pre-flooding may reduce areal recovery efficiency in dip-angle orientations. This study also demonstrates the use of theoretical perturbation (fingering) analysis in predicting NAPL recovery efficiency for flooding processes in remediating aquifers with dip angles.     

Anthropogenic metal enrichment of snow and soil in north-eastern European Russia

Trace metal composition of winter snowpack, snow-melt filter residues and top-soil samples were determined along three transects through industrial towns in the Usa basin, North-East Russia: Inta, Usinsk and Vorkuta. Snow was analysed for Ag, Al, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr and Zn using ICP-MS (Ca and K by F-AAS for Vorkuta only), pH and acidity/alkalinity. Filter residues were analysed for: Al, Ba, Ca, Cd, Cu, K, Mg, Mn, Ni, Pb, Sr and Zn using F-AAS and GF-AAS; top-soil samples were analysed for Ba, Cu, Mg, Mn, Na, Ni, Pb, Sr, Zn using F-AAS. Results indicate elevated concentrations of elements associated with alkaline combustion ash around the coal mining towns of Vorkuta and Inta. There is little evidence of deposition around the gas and oil town of Usinsk. Atmospheric deposition in the vicinity of Vorkuta, and to a lesser extent Inta, added significantly to the soil contaminant loading as a result of ash fallout. Acid deposition was associated with pristine areas whereas alkaline combustion ash near to emission sources more than compensated for the acidity caused by SO2.     

The influence of time on lead toxicity and bioaccumulation determined by the OECD earthworm toxicity test

Internationally agreed standard protocols for assessing chemical toxicity of contaminants in soil to worms assume that the test soil does not need to equilibrate with the chemical to be tested prior to the addition of the test organisms and that the chemical will exert any toxic effect upon the test organism within 28 days. Three experiments were carried out to investigate these assumptions. The first experiment was a standard toxicity test where lead nitrate was added to a soil in solution to give a range of concentrations. The mortality of the worms and the concentration of lead in the survivors were determined. The LC50s for 14 and 28 days were 5311 and 5395 microgPb g(-1)soil respectively. The second experiment was a timed lead accumulation study with worms cultivated in soil containing either 3000 or 5000 microgPb g(-1)soil. The concentration of lead in the worms was determined at various sampling times. Uptake at both concentrations was linear with time. Worms in the 5000 microg g(-1) soil accumulated lead at a faster rate (3.16 microg Pb g(-1)tissue day(-1)) than those in the 3000 microg g(-1) soil (2.21 microg Pb g(-1)tissue day(-1)). The third experiment was a timed experiment with worms cultivated in soil containing 7000 microgPb g(-1)soil. Soil and lead nitrate solution were mixed and stored at 20 degrees C. Worms were added at various times over a 35-day period. The time to death increased from 23 h, when worms were added directly after the lead was added to the soil, to 67 h when worms were added after the soil had equilibrated with the lead for 35 days. In artificially Pb-amended soils the worms accumulate Pb over the duration of their exposure to the Pb. Thus time limited toxicity tests may be terminated before worm body load has reached a toxic level. This could result in under-estimates of the toxicity of Pb to worms. As the equilibration time of artificially amended Pb-bearing soils increases the bioavailability of Pb decreases. Thus addition of worms shortly after addition of Pb to soils may result in the over-estimate of Pb toxicity to worms. The current OECD acute worm toxicity test fails to take these two phenomena into account thereby reducing the environmental relevance of the contaminant toxicities it is used to calculate.     

Uranium transport around the reactor zone at Bangombé and Okélobondo (Oklo): examples of hydrogeological and geochemical model integration and data evaluation

The sites at Bangombé and Okélobondo (Oklo) in Gabon provide a unique opportunity to study the behaviour of products from natural nuclear reactions in the vicinity of reactor zones which were active around two billion years ago. The Commission of the European Communities initiated the Oklo Natural Analogue Programme. One of the principal aims was to study indications of present time migration of elements from the reactor zones under ambient conditions. The hydrogeological and hydrochemical data from the Oklo sites were modelled in order to better understand the geochemical behaviour of radionuclides in the natural system, by using independent models and by comparing the modelling outcome. Two modelling approaches were used: M3 code (hydrochemical mixing and mass balance model), developed by the Swedish Nuclear Fuel and Waste Management Company (SKB) and HYTEC (reactive transport model) developed by Ecole des Mines de Paris. Two different reactor zones were studied: Bangombé, a shallow site, the reactor being at 11 m depth, and OK84 at Okélobondo, situated at about 450 m depth, more comparable with a real repository location. This allowed the validation of modelling tools in two different sedimentary environments: one shallow, with a more homogeneous layering situated in an area of meteoric alteration, and the other offering the opportunity to study radionuclide migration from the reaction zone over a distance of 450 m through very heterogeneous sedimentary layers. The modeling results indicate that the chemical reactions retarding radionuclide transport are very different at the two sites. At Bangombé, the decomposition of organic material consumes oxygen and at Okélobondo the oxygen is consumed by inorganic reactions resulting, in both cases, in uranium retardation. Both modelling approaches (statistic with M3 code and deterministic with HYTEC code) could describe this situation. The goal of this exercise is to test codes which can help to describe and understand the processes taking place at the sites, validate the models with in situ data, and thus build confidence in the tools used for future site characterization. Ultimately, this allows identifying and selecting processes and parameters that can be used as input into repository performance assessment calculations and modelling exercises.     

Effect of pH control at the anode for the electrokinetic removal of phenanthrene from kaolin soil

Polycyclic aromatic hydrocarbon (PAH)-contaminated soils exist at numerous sites, and these sites may threaten public health and the environment because many PAH compounds are toxic, mutagenic, and/or carcinogenic. PAHs are also hydrophobic and persistent, so conventional remediation methods are often costly or inefficient, especially when the contaminants are present in low permeability and/or organic soils. An innovative technique, electrokinetically enhanced in situ flushing, has the potential to increase soil-solution-contaminant interaction and PAH removal efficiency for low permeability soils; however, the electrolysis reaction at the anode may adversely affect the remediation of low acid buffering capacity soils, such as kaolin. Therefore, the objective of this study was to improve the remediation of low acid buffering soils by controlling the pH at the anode to counteract the electrolysis reaction. Six bench-scale electrokinetic experiments were conducted, where each test employed one of three different flushing solutions, deionized water, a surfactant, or a cosolvent. For each of these solutions, tests were performed with and without a 0.01 M NaOH solution at the anode to control the pH. The test using deionized water with pH control generated a higher electroosmotic flow than the equivalent test performed without pH control, but the electroosmotic flow difference between the surfactant and cosolvent tests with and without pH control was minor compared to that observed with the deionized water tests. Controlling the pH was beneficial for increasing contaminant solubilization and migration from the soil region adjacent to the anode, but the high contaminant concentrations that resulted in the middle or cathode soil regions indicates that subsequent changes in the soil and/or solution chemistry caused contaminant deposition and low overall contaminant removal efficiency.     

Sorption of As(V) ions by akaganéite-type nanocrystals

A priority pollution problem, the removal of arsenate oxyanions from dilute aqueous solutions by sorption onto synthetic akaganéite (beta-FeO(OH)) was the aim of the present study. This is an innovative inorganic adsorbent material prepared in the laboratory, following a new method of preparation. The effect of akaganéite and arsenate concentration, the contact time, temperature, solution pH value, and ionic strength variation on the treatment process was mainly investigated during this study. Typical adsorption isotherms were determined, which were found to fit sufficiently the typical Langmuir equation. The mechanism of sorption was examined by electrokinetic, X-ray diffraction, Fourier transmission infrared and scanning electron microscopy measurements. Promising results were obtained, due to the favourite characteristics of the adsorbent applied.     

Metal ion removal from water by sorption on paper mill sludge

Chromatographic columns packed with paper mill sludge are employed for metal ion recovery from water. The breakthrough curves show that cadmium, copper, lead and silver are removed from acid solutions (pH 2, 4); the affinity series is Pb(II)>Cu(II)>Ag(I)>Cd(II). Both the amount of metal retained and the metal-matrix interaction are pH dependent; the sorptive capacity increases with increasing pH. When the metals are present together at the same initial concentrations a competition among the different ions occurs although the affinity order remains unchanged. In metal recovery from the paper mill sludge column, the total amount of the cadmium and copper is displaced by HCl 1.0 M, 65% of the lead by HCl 0.1 M and 75% of the silver by HNO(3) 0.1 M. More than 95% of copper and lead and less than 20% of cadmium were recovered with HCl 0.1 M when the metals were present at the same time.     

Congener-specific accumulation of polychlorinated biphenyls in ovarian follicular wall follows repeated exposure to PCB 126 and PCB 153. Comparison of tissue levels of PCB and biological changes

OBJECTIVE: Small (SF), medium (MF) and large (LF) preovulatory porcine follicles were isolated and incubated in an Erlenmeyer flask containing 5 ml of medium with addition of PCB 126 or PCB 153 to test differences in their accumulation in the follicular wall. METHODS; The follicles were incubated in M199 medium at 37 degrees C with constant shaking at 70 rpm, for 6 days. The media were changed every day and repeated dose 25 pg/ml of PCB 126 or 25 ng/ml of PCB 153 was added each day till 6 days of culture. Media were collected every day and frozen for steroid analysis by RIA. 24 h after the last treatment follicles were frozen for further polychlorinated biphenyls (PCB) content analysis. PCB concentrations in the follicular wall were analysed by mass spectrometry. RESULTS: 3.3%; 3.6% and 5.6% of total PCB 126 dose, and 71%; 71.4% and 30.4% of total PCB 153 dose accumulated in SF, MF and LF follicles, respectively. The accumulative effect of PCB was manifested by the disruption of estradiol (E2) secretion. In SF antiestrogenic action of PCB 126 was observed during the whole time of exposure while PCB 153 decreased E2 till 4 days of culture and then estrogenic action was observed. In MF, both these congeners decreased E2 till 5 days of exposure and then estrogenic actions were noted with the highest magnification in the case of PCB 126. In LF both PCB studied increased E2 till 3 days of exposure with the highest magnification of PCB 126, then antiestrogenic action was noted. Testosterone secretion was generally affected in a pattern oposite to that of E2 suggesting action on P450arom activity. CONCLUSION: The results of these studies demonstrated that disruption of aromatization process in the follicles following repeated exposure to both congeners is not directly correlated with the bioaccumulation or amount of PCB within the follicular wall.