Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5mg L(-1). These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.     

Sulphur transformation and deposition in the rhizosphere of Juncus effusus in a laboratory-scale constructed wetland

Sulphur cycling and its correlation to removal processes under dynamic redox conditions in the rhizosphere of helophytes in treatment wetlands are poorly understood. Therefore, long-term experiments were performed in laboratory-scale constructed wetlands treating artificial domestic wastewater in order to investigate the dynamics of sulphur compounds, the responses of plants and nitrifying microorganisms under carbon surplus conditions, and the generation of methane. For carbon surplus conditions (carbon:sulphate of 2.8:1) sulphate reduction happened but was repressed, in contrast to unplanted filters mentioned in literature. Doubling the carbon load caused stable and efficient sulphate reduction, rising of pH, increasing enrichment of S(2-) and S(0) in pore water, and finally plant death and inhibition of nitrification by sulphide toxicity. The data show a clear correlation of the occurrence of reduced S-species with decreasing C and N removal performance and plant viability in the experimental constructed wetlands.     

Spatial variability of arsenic concentration in soils and plants, and its relationship with iron, manganese and phosphorus

Spatial distribution of arsenic (As) concentrations of irrigation water, soil and plant (rice) in a shallow tube-well (STW) command area (8 ha), and their relationship with Fe, Mn and P were studied. Arsenic concentrations of water in the 110 m long irrigation channel clearly decreased with distance from the STW point, the range being 68-136 μg L⁻¹. Such decreasing trend was also noticed with Fe and P concentrations, but the trend for Mn concentrations was not remarkable. Concerning soil As, the concentration showed a decreasing tendency with distance from the pump. The NH₄-oxalate extractable As contributed 36% of total As and this amount of As was associated with poorly crystalline Fe-oxides. Furthermore only 22% of total As was phosphate extractable so that most of the As was tightly retained by soil constituents and was not readily exchangeable by phosphate. Soil As (both total and extractable As) was significantly and positively correlated with rice grain As (0.296 ± 0.063 μg g⁻¹, n = 56). Next to drinking water, rice could be a potential source of As exposure of the people living in the As affected areas of Bangladesh.     

Anthropogenic lead distribution in soils under arable land and permanent grassland estimated by Pb isotopic compositions

The role of land use on fate of metals in soils is poorly understood. In this work, we studied the incorporation of lead in two neighboring soils with comparable pedogenesis but under long-term different agricultural management. Distributions of anthropogenic Pb were assessed from concentrations and isotopic compositions determined on bulk horizon samples, systematical 5-10 cm increment samples, and on 24-h EDTA extracts. Minor amounts of anthropogenic lead were detected until 1-m depth under permanent grassland, linked to high earthworm activity. In arable land, exogenous Pb predominantly accumulated at depths <60 cm. Although the proximity between the two sites ensured comparable exposition regarding atmospheric Pb deposition, the isotopic compositions clearly showed the influence of an unidentified component for the cultivated soil. This work highlights the need for exhaustive information on historical human activities in such anthropized agrosystems when fate of metal pollution is considered.     

Long term changes in atmospheric N and S throughfall deposition and effects on soil solution chemistry in a Scots pine forest in the Netherlands

In a Scots pine forest the throughfall deposition and the chemical composition of the soil solution was monitored since 1984. (Inter)national legislation measures led to a reduction of the deposition of nitrogen and sulphur. The deposition of sulphur has decreased by approximately 65%. The total mineral-nitrogen deposition has decreased by ca. 25%, which is mainly due to a reduction in ammonium-N deposition (−40%), since nitrate-N deposition has increased (+50%). The nitrogen concentration in the upper mineral soil solution at 10 cm depth has decreased, leading to an improved nutritional balance, which may result in improved tree vitality. In the drainage water at 90 cm depth the fluxes of NO₃⁻ and SO₄²⁻ have decreased, resulting in a reduced leeching of accompanying base cations, thus preserving nutrients in the ecosystem. It may take still several years, however, before this will meet the prerequisite of a sustainable ecosystem.     

Anatomical element localization by EDXS in Grevillea exul var. exul under nickel stress

Grevillea exul var. exul, an endemic serpentinic Proteaceae of New Caledonia, was chosen to study the spatial distribution of Ni because this species supports strong content of metals, which can allow important absorptions thus detectable by microanalysis. Fine transversal sections of axenic G. exul var. exul plants grown during 15 days on nickel sulphate medium were examined by EDXS microanalysis. It showed that in Ni treated plants, Ni was concentrated mostly in the phloem compared to the xylem and the epidermis, either in roots or in the basal part of the stems and was mostly in the epidermis in the upper part of the stems and not detectable in the leaves. This metal took the place of P and K in the treated plants whereas the localization of these macroelements was quite uniform in control sections. We assume that a mechanism of phloem loading is implicated to restrict Ni accumulation in G. exul var. exul.     

Dissipation of four forest-use herbicides at high latitudes

Background, aim, and scope  Large-scale deforestation is occurring in subarctic North America following clearing by salvage logging or insect attack. Numerous shrubs, herbs, and deciduous tree species tend to dominate areas on which stands of white spruce have grown. In the absence of economically advantageous mechanical methods, several herbicides have value in efforts to reforest by planting white spruce. Glyphosate, imazapyr, triclopyr, and hexazinone are all capable of selectively removing many competing species, but there is concern about whether they would degrade naturally or persist owing to the frigid climate. Materials and methods  We established test plots with all four herbicides in upland and river bottom sites at 65°N and 58°N latitudes. The northern site has extremely cold winters, with soils that freeze to a depth of 1–2 m, and precipitation of 275 mm/year. The southern site has heavy rain and snowfall, amounting to 2,250 mm/year evenly distributed. Soil seldom freezes deeply. On each test plot, one of the four herbicides was applied at twice the normal operational use rate to facilitate detection. They were applied at the normal timing, with hexazinone, imazapyr, and triclopyr applied in June and glyphosate applied in fall. Soils were sampled immediately after treatment and those samples used as references for dissipation data gathered over the next 11–14 months from soil 0- to 15- and 15- to 45-cm depths. Results  Dissipation rates did not follow first-order rates because freezing conditions slowed most microbial activity. All products dissipated to close to or below detection limits within the time of the study. Dissipation from vegetation was substantially more rapid and depended on the nature of the plants treated as well as the product used. While soil residues dissipated more slowly than in temperate regions, they did display consistent dissipation patterns during above-freezing conditions and also the influence of microbial activity. Mobility was very limited with all products but hexazinone. Discussion  These products dissipate during summer in high latitudes much as they would in temperate climates. Winter changes are small, but are not unlike some changes reported elsewhere under freezing conditions. Unlike many other studies, soil water did not influence dissipation heavily, but the high latitude and semi-arid climate also did not create severely droughty soils. Residues in plants were much higher than those in soils, but denatured the vegetation quickly, leading to unsuitability for forage in any case. Conclusions  Low toxicity of these products and their metabolites combined with consistent dissipation and low mobility suggest that toxic hazard of their use at high latitudes need not be a matter of serious concern to humans, terrestrial wildlife, or aquatic systems. They are safe for use in management and rehabilitation of boreal forests when used properly. Recommendations and perspectives  Dissipation at rates approaching those in warmer climates offer a hypothesis that microflora native to high latitudes may be adapted to destruction of such molecules at lower temperatures than may be indicated by experiments with microflora adapted to warmer climates. Residues pose no observable risk to wildlife or humans in the area of use when products are applied properly. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available for authorized users.     

Functionally relevant microorganisms to enhanced biological phosphorus removal performance at full-scale wastewater treatment plants in the United States

The abundance and relevance ofAccumulibacter phosphatis (presumed to be polyphosphate-accumulating organisms [PAOs]), Competibacter phosphatis (presumed to be glycogen-accumulating organisms [GAOs]), and tetrad-forming organisms (TFOs) to phosphorus removal performance at six full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants were investigated. Coexistence of various levels of candidate PAOs and GAOs were found at these facilities. Accumulibacter were found to be 5 to 20% of the total bacterial population, and Competibacter were 0 to 20% of the total bacteria population. The TFO abundance varied from nondetectable to dominant. Anaerobic phosphorus (P) release to acetate uptake ratios (P(rel)/HAc(up)) obtained from bench tests were correlated positively with the abundance ratio of Accumulibacter/(Competibacter +TFOs) and negatively with the abundance of (Competibacter +TFOs) for all plants except one, suggesting the relevance of these candidate organisms to EBPR processes. However, effluent phosphorus concentration, amount of phosphorus removed, and process stability in an EBPR system were not directly related to high PAO abundance or mutually exclusive with a high GAO fraction. The plant that had the lowest average effluent phosphorus and highest stability rating had the lowest P(rel)/HAc(up) and the most TFOs. Evaluation of full-scale EBPR performance data indicated that low effluent phosphorus concentration and high process stability are positively correlated with the influent readily biodegradable chemical oxygen demand-to-phosphorus ratio. A system-level carbon-distribution-based conceptual model is proposed for capturing the dynamic competition between PAOs and GAOs and their effect on an EBPR process, and the results from this study seem to support the model hypothesis.     

Implications of urine-to-feces ratio in the thermophilic anaerobic digestion of swine waste.

Thermophilic anaerobic digestion of swine manure represents a potential waste treatment technology to address environmental concerns, such as odor emissions and removal of pathogenic microorganisms. However, there are concerns relative to the stability of this process when swine manure is the sole substrate. In this study, the potential of biogas production from swine manure as the sole substrate under thermophilic (50 degrees C) conditions was investigated in the laboratory, to determine whether separation of urine and feces as part of the waste collection process would benefit anaerobic digestion. Effluent from a continuously stirred tank reactor was used as the inoculum for batch tests, in which the substrate contained three different concentrations of urine (urine-free, as-excreted urine-to-feces ratio and double the as-excreted urine-to-feces ratio). Inocula were acclimated to these same urine-to-feces ratios to determine methane production. Results show that both urine-free and as-excreted substrates were not inhibitory to anaerobic inocula. Anaerobic microorganisms can be readily acclimated to substrate with double the as-excreted urine concentration, which contained nitrogen concentrations up to 7.20 g/L. Cumulative methane production reached similar levels in the batch tests, regardless of the substrate urine concentration.     

Emissions tradeoffs among alternative marine fuels: total fuel cycle analysis of residual oil, marine gas oil, and marine diesel oil

Worldwide concerns about sulfur oxide (SOx) emissions from ships are motivating the replacement of marine residual oil (RO) with cleaner, lower-sulfur fuels, such as marine gas oil (MGO) and marine diesel oil (MDO). Vessel operators can use MGO and MDO directly or blended with RO to achieve environmental and economic objectives. Although expected to be much cleaner in terms of criteria pollutants, these fuels require additional energy in the upstream stages of the fuel cycle (i.e., fuel processing and refining), and thus raise questions about the net impacts on greenhouse gas emissions (primarily carbon dioxide [CO2]) because of production and use. This paper applies the Total Energy and Environmental Analysis for Marine Systems (TEAMS) model to conduct a total fuel cycle analysis of RO, MGO, MDO, and associated blends for a typical container ship. MGO and MDO blends achieve significant (70-85%) SOx emissions reductions compared with RO across a range of fuel quality and refining efficiency assumptions. We estimate CO2 increases of less than 1% using best estimates of fuel quality and refinery efficiency parameters and demonstrate how these results vary based on parameter assumptions. Our analysis suggests that product refining efficiency influences the CO2 tradeoff more than differences in the physical and energy parameters of the alternative fuels, suggesting that modest increases in CO2 could be offset by efficiency improvements at some refineries. Our results help resolve conflicting estimates of greenhouse gas tradeoffs associated with fuel switching and other emissions control policies.