The uptake of uranium by Eleocharis dulcis (Chinese water chestnut) in the Ranger Uranium Mine constructed wetland filter

Eleocharis dulcis has proliferated in a constructed wetland used to treat uranium mine runoff water, where it rapidly accumulates significant quantities of uranium (U) in its roots and relatively little in its stems. We investigated the mechanism of U uptake and accumulation by E. dulcis using field-sampling techniques and microcosm test work. Results from the microcosm trials and outcomes from statistical tests of field sampled macrophyte, water and sediment indicate that the primary source of U for E. dulcis is the water column. Basipetal translocation of U to the plant's roots was indicated by significant correlations between the U content of stems, taproots and rhizomes and XPS detection of U inside root segments. U sequestering from sediment interstitial water by Fe hydroxides on root surfaces was also evident. No basipetal translocation was evident following the 28-day duration of the microcosm experiments, indicating that it is a longer-term process.     

Sorption and oxic degradation of the explosive CL-20 during transport in subsurface sediments

The abiotic sorption and oxic degradation processes that control the fate of the explosive CL-20, Hexanitrohexaazaisowurtzitane, in the subsurface environment were investigated to determine the potential for vadose and groundwater contamination. Sorption of aqueous CL-20 is relatively small (K(d) = 0.02-3.83 cm3 g(-1) for 7 sediments and 12 minerals), which results in only slight retardation relative to water movement. Thus, CL-20 could move quickly through unsaturated and saturated sediments of comparable composition to groundwater, similar to the subsurface behavior of RDX. CL-20 sorption was mainly to mineral surfaces of the sediments, and the resulting isotherm was nonlinear. CL-20 abiotically degrades in oxic environments at slow rates (i.e., 10s to 100s of hours) with a wide variety of minerals, but at fast rates (i.e., minutes) in the presence of 2:1 phyllosilicate clays (hectorite, montmorillonite, nontronite), micas (biotite, illite), and specific oxides (MnO2 and the ferrous-ferric iron oxide magnetite). High concentrations of surface ferrous iron in a dithionite reduced sediment degraded CL-20 the fastest (half-life < 0.05 h), but 2:1 clays containing no structural or adsorbed ferrous iron (hectorite) could also quickly degrade CL-20 (half-life < 0.2 h). CL-20 degradation rates were slower in natural sediments (half-life 3-800 h) compared to minerals. Sediments with slow degradation rates and small sorption would exhibit the highest potential for deep subsurface migration. Products of CL-20 oxic degradation included three high molecular weight compounds and anions (nitrite and formate). The 2-3.5 moles of nitrite produced suggest CL-20 nitro-groups are degraded, and the amount of formate produced (0.2-1.2 moles) suggests the CL-20 cage structure is broken in some sediments. Identification of further degradation products and CL-20 mineralization rates is needed to fully assess the impact of these CL-20 transformation rates on the risk of CL-20 (and degradation product) subsurface movement.     

Occurrence and abatement of volatile sulfur compounds during biogas production

Volatile sulfur compounds (VSCs) in biogas originating from a biogas production plant and from a municipal sewage water treatment plant were identified. Samples were taken at various stages of the biogas-producing process, including upgrading the gas to vehicle-fuel quality. Solid-phase microextraction was used for preconcentration of the VSCs, which were subsequently analyzed using gas chromatography in combination with mass spectrometry. Other volatile organic compounds present also were identified. The most commonly occurring VSCs in the biogas were hydrogen sulfide, carbonyl sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide, and hydrogen sulfide was not always the most abundant sulfur (S) compound. Besides VSCs, oxygenated organic compounds were commonly present (e.g., ketones, alcohols, and esters). The effect of adding iron chloride to the biogas reactor on the occurrence of VSCs also was investigated. It was found that additions of 500-g/m3 substrate gave an optimal removal of VSCs. Also, the use of a prefermentation step could reduce the amount of VSCs formed in the biogas process. Moreover, in the carbon dioxide scrubber used for upgrading the gas, VSCs were removed efficiently, leaving traces (ppbv levels). The scrubber also removed other organic compounds.     

Electrochemical monitoring of methylparathion degradation in an acid aqueous medium in presence of Cu(II)

A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o,4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2-7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH < or = 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 x 10(-3) s(-1) at pH 2, 5.5 x 10(-3) s(-1) at pH 4 and 9.0 x 10(-3) s(-1) at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.     

Removal of nickel (II) from aqueous solutions using marine macroalgae as the sorbing biomass

In the present study biosorption technique, the passive accumulation of metals by biomass, is used for the removal of nickel from aqueous medium. The brown algae, Sargassum sp., in its natural and acid treated forms are used as a low cost sorbent. The adsorption characteristics of nickel on Sargassum sp. are evaluated as a function of time, pH, adsorbent dosage and initial concentration of nickel. The equilibrium adsorption data are fitted to Freundlich and Langmuir adsorption isotherm models and the model parameters are evaluated. Both the models represent the experimental data satisfactorily. The adsorption follows Lagergren first order kinetic model. The monolayer adsorption capacities of natural and acid treated forms of algae as obtained from Langmuir adsorption model are found to be 181 and 250mg g(-1) respectively.     

Synthesis of effects in four Arctic subregions

An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints--or facilitation--of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function, species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.     

Cosolvent effect on the catalytic reductive dechlorination of PCE

Reductive dechlorination of chlorinated organic contaminants is an effective approach to treat this widespread group of environmentally hazardous substances. Metalloporphyrins can be used to catalyze reduction reactions by shuttling electrons from a reducing agent (electron donor) to chlorinated organic contaminants, thus rendering them to non-chlorinated acetylene, ethylene or ethane as major products. Iron, nickel and vanadium oxide tetraphenyl porphyrins (TPPs) were used as models of non-soluble metalloporphyrins that are common in subsurface environments, and hence may inflect on the ability to use natural ones. The effect of cosolvents on metalloporphyrins is demonstrated to switch the reduction of tetrachlorethylene (PCE) from no reaction to complete PCE transformation within 24 h and the production of final non-chlorinated compounds. Variations in product distributions for the different metalloporphyrins indicate that changes in the core metal can influence reaction rates and effective pathways. Furthermore, different cosolvents can generate varied product distributions, again suggesting that different pathways and/or rates are operative in the reduction reactions. Comparison of different cosolvent effects on PCE reduction using vitamin B12--a soluble natural metalloporphyrinogen--as the catalyst shows less pronounced differences between reactions in various cosolvent solutions versus only aqueous solution.     

Uncertainties and recommendations

An assessment of the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, made within the Arctic Climate Impacts Assessment (ACIA), highlighted the profound implications of projected warming in particular for future ecosystem services, biodiversity and feedbacks to climate. However, although our current understanding of ecological processes and changes driven by climate and UV-B is strong in some geographical areas and in some disciplines, it is weak in others. Even though recently the strength of our predictions has increased dramatically with increased research effort in the Arctic and the introduction of new technologies, our current understanding is still constrained by various uncertainties. The assessment is based on a range of approaches that each have uncertainties, and on data sets that are often far from complete. Uncertainties arise from methodologies and conceptual frameworks, from unpredictable surprises, from lack of validation of models, and from the use of particular scenarios, rather than predictions, of future greenhouse gas emissions and climates. Recommendations to reduce the uncertainties are wide-ranging and relate to all disciplines within the assessment. However, a repeated theme is the critical importance of achieving an adequate spatial and long-term coverage of experiments, observations and monitoring of environmental changes and their impacts throughout the sparsely populated and remote region that is the Arctic.     

Effects of the mosquito larvicide GB-1111 on bird eggs

Golden Bear Oil (GB-1111; legal trade name for GB-1313) is a petroleum distillate used in the United States and other countries as a mosquito larvicide. As part of an evaluation of the potential effects of GB-1111 on birds, fertile eggs of mallards (Anas platyrhynchos) and bobwhite (Colinus virginianus) were incubated in the laboratory, and treated on day 4 of incubation with external applications equivalent to either 0, 1/3, 1, 3 or 10 times the maximum rate (X) of 47 l/ha (5 gal/A) of field application of GB-1111. Hatching success was significantly reduced in mallards treated at 3 and 10 times the maximum field application, with a calculated approximate LD50 of 1.9 times the maximum field application. Most mortality occurred within a week of treatment. Hepatic P450-associated monooxygenase activity (ethoxyresorufin-O-dealkylase; EROD) was negatively related to dose. In the 3X group there was a significant increase in the concentration of hepatic reduced glutathione (GSH) but a decrease in protein-bound thiols (PBSH). Hatching success of bobwhite was marginally reduced at the highest level of treatment (10X). Other effects at this level in bobwhite included a significant increase in incidence of abnormal embryos or hatchlings, lower body and liver weights, and a two-fold increase in hepatic microsomal EROD activity in hatchlings. The recommended maximum rate of field application of GB-1111 is unlikely to impair the survival or development of bobwhite embryos but is potentially toxic to mallard embryos under conditions of larvicide drift or spray overlap.     

Polychlorinated biphenyls and chlorinated pesticides in mussels from the Egyptian Red Sea coast

The residues of 17 organochlorine pollutants were analyzed in bivalve Brachiodontes sp. collected from 11 different locations in April 2000 along the Egyptian Red Sea coast. The pollutants studied were 10 individual polychlorinated biphenyl (PCB) congeners, alpha,alpha,alpha-hexachlorocyclohexane (HCHs), cyclodienes (heptachlor, heptachlorepoxide, aldrin, dieldrin) and dichlorodiphenyltrichloroethanes (DDTs) (p,p'-DDE, p,p'-DDD and p,p'-DDT). The concentration of total DDTs ranged between 125 and 772 ng/g of wet weight whereas the concentration of the PCBs, HCHs and cyclodienes ranged from 6.7 to 66.4 ng/g; 16.2 to 183.4 ng/g and 8.8 to 221.6 ng/g of wet weight, respectively. The levels are low to moderate in relation to the published data from other coastal areas. The present results indicate low to moderate PCBs and pesticides contamination in the investigated mussels except DDTs.