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1.
The efficacy of cleanup methods in reducing gasoline contamination at spill sites is typically determined by measuring benzene, toluene, xylene (BTX), and total petroleum hydrocarbon (TPH) concentrations in soil samples. Although these values may provide a direct measurement of soil contamination, they may not be indicative of what is transferred to percolating water. This study addresses this issue by measuring TPH, toluene, m‐ and p‐xylene, and naphthalene levels in gasoline‐contaminated soil columns before and after forced‐air venting and relating these values to the aqueous‐phase concentrations measured when water is percolated through the same columns.

Sandy soils with and without organic matter were packed into glass columns. The soils were brought to residual water and residual gasoline saturations by applying a vacuum to a ceramic pressure plate at the column bottom. Venting was performed by passing clean, moist air through the columns. The columns were subsequently leached under unsaturated conditions.

Soil samples were taken from the bottom of the columns upon completion of the venting or leaching phases of the experiments. Toluene, m‐ and p‐xylene, naphthalene, and TPH values were measured in soil samples extracted with either freon or methanol. Aqueous phase concentrations of these compounds were predicted using measured soil concentrations and either Raoult's law or organic matter‐water and fuel‐water partitioning theory (Boyd and Sun, 1990). The predicted results were compared with measured leachate concentrations from the same columns.

Mole fractions estimated from soil concentrations and TPH values used in Raoult's law gave good predictions of aqueous phase concentrations for compounds that had a high mole fraction in the residual nonaqueous phase liquid (NAPL). For compounds at low concentrations in the residual NAPL, an approach using a distribution coefficient that accounted for both the organic matter and residual NAPL in the soil provided better estimates than those based on Raoult's law.  相似文献   


2.
In growth chamber experiments we studied the potential use of elemental sulfur (S8) as an acidifying agent to enhance the uptake of Cd and Zn from three different polluted soils by candidate phytoremediation plants (Brassica juncea, Helianthus annuus, Salix viminalis). Two of the three soils were calcareous, the other slightly acidic. One of the calcareous soils had been contaminated by dust emissions from a nearby brass smelter. The pollution of the other two soils had resulted from sewage sludge applications.

Sulfur was added to soils in quantities of 20 to 400 mmol sulfur kg-1 soil. Plants were grown under fluorescent light in 1.5 l ($OS 13 cm) pots for 28 d.

Within 700 h soil pH decreased significantly in all soils, depending on S8 dosage. In the acid soil, pH decreased from pH 6.5 to about 4 at the highest treatment level, while pH in one of the calcareous soils dropped even below pH 4. The effect was smaller in the second calcareous soil.

NaNO3-extractable Cd and Zn increased up to 26-and 13-fold, respectively, in the acid soil, while in the calcareous soils, maximum increases were 9-and 11-fold, respectively.

Increased NaNO3-extractable concentrations translated well into shoot concentrations (dry matter) in plants. Shoot Zn concentrations in H. annuus, for example, increased from 930 in the controls to 4300 mg kg-1 in the highest S8 treatment. However, effects observed in the plants were generally smaller than in the soils. In addition, in some variants growth was negatively affected, resulting in reduced metal removal from the soils.  相似文献   


3.
Background: The flora of serpentine/ultramafic soils provides an excellent model system for the study of natural selection in plant populations. Streptanthus polygaloides is a nickel hyperaccumulator that is endemic to serpentine soils in the Sierra Nevada of California, and has four floral morphs (yellow, purple, yellow-to-purple and undulate).

Aims: We investigate three hypotheses: (1) the purple morph occurs in colder, wetter climates than the yellow morph; (2) tissue–soil ionic relationships differ among morphs; and (3) morphs occur on soils with differing elemental concentrations.

Methods: We queried herbarium records to investigate patterns of occurrence among the yellow and purple floral morphs, and analysed soil and tissue samples from wild populations of all four morphs.

Results: The purple morph inhabited serpentine outcrops with colder temperatures and greater precipitation levels than the yellow morph. Concentrations of elements in leaf tissue and rhizosphere soil differed little among populations of the morphs, but showed substantial within-site variation.

Conclusions: Our results suggest that a climatic gradient may be responsible for divergence in floral colour among populations of S. polygaloides. Because of the large within-site variation in soil and tissue elemental concentrations, plants appear to have a varied physiological response to edaphic factors, regardless of morph membership.  相似文献   


4.
This work was aimed at evaluating the feasibility of a remediation treatment performed by means of a supercritical carbon dioxide extraction on a sandy soil recently contaminated by light polycyclic aromatic hydrocarbons.

The soil utilized in this study was artificially contaminated by naphthalene and anthracene. The artificial contamination process was intended to simulate a recent accidental spillage of hydrocarbon fuels.

Several extractions, aimed at singling out the operating parameters (pressure, temperature, supercritical fluid mass flow rate) that are able to obtain the residual required concentration (50 mg/kg dry soil) in the shortest time, were carried out on a on-purpose made system.

The best extraction conditions were 120 bar and 40°C for a naphthalene contaminated soil and 200 bar and 80–100°C for an anthracene contaminated soil.

The results obtained in the experimental tests made it possible to build an analytical model able to correlate, for the given soil, the extraction length to the operating parameters such as supercritical fluid density, temperature and mass flow rate.

In order to evaluate the economic feasibility of the process, a unit treatment cost was evaluated for the case of an extraction carried out in a 10 m3 reactor in the presence of the best extraction conditions that were previously determined. The extraction unit cost was therefore equal to 35 000–65 000 €/t for a soil with a starting contaminant concentration equal to 1000 mg/kg of dry soil.  相似文献   


5.
Background: Serpentine ecosystems support different, often unique, plant communities; however, we know little about the soil organisms that associate with these ecosystems. Mycorrhizas, mutualistic symbioses between fungi and roots, are critical to nutrient cycling and energy exchange below ground.

Aims: We address three hypotheses: H1, diversity of mycorrhizal fungi in serpentine soils mirrors above-ground plant diversity; H2, the morphology of mycorrhizas and fungi on serpentine soils differs from that on non-serpentine; and H3, mycorrhizal fungal communities of the same or closely related hosts differ between serpentine and non-serpentine soils.

Methods: This review focuses on whether plant diversity on serpentine soils correlates with the below ground diversity of mycorrhizal fungi.

Results: Studies show that plants and fungi formed abundant ectomycorrhizal and arbuscular mycorrhizal symbioses on and off serpentine soils. No serpentine-endemic fungi were identified. Molecular analyses indicate distinct serpentine isolates for Cenococcum geophilum and for Acaulospora, suggesting adaptation to serpentine soils. While fungal sporocarp assemblages on serpentine sites resembled those off serpentine, fruiting of hypogeous fungi was greatly reduced.

Conclusions: Ectomycorrhizal fungal communities did not differ between soil types; however, arbuscular mycorrhizal communities differed in some cases but not others. The additive response to multiple factors, described as the serpentine syndrome, may explain part of the response by fungi.  相似文献   


6.
The potential to phytoextract uranium (U) from a sandy soil contaminated at low levels was tested in the greenhouse. Two soils were tested: a control soil (317 Bq 238U kg-1) and the same soil washed with bicarbonate (69 Bq 238U kg-1). Ryegrass (Lolium perenne cv. Melvina), Indian mustard (Brassica juncea cv. Vitasso), and Redroot Pigweed (Amarathus retroflexus) were used as test plants.

The annual removal of the soil activity with the biomass was less than 0.1%. The addition of citric acid (25 mmol kg-1) 1 week before the harvest increased U uptake up to 500-fold. With a ryegrass and mustard yield of 15000 kg ha-1 and 10000 kg ha-1, respectively, up to 3.5% and 4.6% of the soil activity could annually be removed with the biomass.

With a desired activity reduction level of 1.5 and 5 for the bicarbonate washed and control soil, respectively, it would take 10 to 50 years to attain the release limit.

A linear relationship between the plant 238U concentration and the 238U concentration in the soil solution of the control, bicarbonate-washed, or citric acid-treated soil points to the importance of the soil solution activity concentration in determining U uptake and hence to the importance of solubilising agents to increase plant uptake.

However, citric acid addition resulted in a decreased dry weight production (all plants tested) and crop regrowth (in case of ryegrass).  相似文献   


7.
The toxicity and mobility of chromium in the environment greatly depends upon its speciation. The reduction of hexavalent chromium to trivalent chromium in a soil environment was examined by spiking three soil types (sandy, clayey, and organic soils) with a common wood preservative solution known as chromated copper arsenate (CCA). Chromium in the CCA preservative solution exists in the hexavalent form. The total and hexavalent chromium concentrations (mg/kg) were measured over a period of 11 months. Leachable chromium concentrations (mg/L) were assessed using the synthetic precipitation leaching procedure (SPLP). The degree and rate of hexavalent chromium reduction were similar for the sand and clayey soil, but much greater for the organic soil. Most of the chromium reduction occurred within the first month of the experiment. At the end of the experiment, approximately 50% of the hexavalent chromium was converted to the trivalent form in the sand and clayey soils. Hexavalent chromium concentrations were below detection in the organic soil at the end of the experiment. Nearly all of the chromium observed in the SPLP leachates was in the form of hexavalent chromium. Chromium leaching was thus greatest in the sand and clay soils where the hexavalent chromium persisted. The results indicate that hexavalent chromium in soils can persist for considerable time periods, in particular in soils with low organic matter content.

  相似文献   


8.
Bench‐scale laboratory experiments were conducted to evaluate the effectiveness of steam injection for in situ remediation of soils contaminated by light nonaqueous‐phase liquids (LNAPLs). Several parametric studies were performed with various combinations of soils, LNAPLs, and steam injection conditions.

An increase in steam injection pressure produced a significant increase in LNAPL recovery efficiency. An increase in steam injection pressure from 12.4 to 44.8 kPa resulted in increased LNAPL recovery efficiency from 86 to 95% after one pore volume of steam injection. Higher steam injection pressure yielded maximum LNAPL recovery efficiency in significantly less time and required a smaller amount of steam than at low pressure.

An increase in soil grain size or an increase in grain‐size‐distribution slope resulted in increased LNAPL recovery efficiency. The final LNAPL residual saturation was approximately 0.5% for coarse‐grained soils and 1.8% for soils with finer grain sizes. Soils with finer grains required more time for treatment than soils with coarser grains.

Steam injection experiments with No. 2 heating oil and with jet fuel showed no significant variation in steam front propagation, temperature profile, and maximum LNAPL recovery efficiency. The LNAPL residual saturation after steam injection was essentially independent of the starting LNAPL saturation.  相似文献   


9.
In Chile, there are several agricultural areas with soils containing high levels of copper of both anthropic and geochemical origin. The diffusive gradient in thin film (DGT) technique is a promising tool for the evaluation of the bioavailability of metals in situ in different environmental systems. The objective of this study was the preparation, validation, and application of DGT to soil solutions and soil containing copper over 1000 mg kg?1.

The results show that a resin gel thickness of 0.3 mm gives the best reproducibility and response in the absorption of copper by DGT. The amount of copper extracted in a period of 4 h by the devices from the soil solution corresponds to 13% of the total metal present in the solution.

The DGT allowed a more representative estimation of the amount of Cu available in the soil, more in agreement with the absence of symptoms of phytotoxicity in cultivated species. This shows that the determination of available Cu by DTPA must be handled cautiously because in soils with high Cu content the amount of metal that can have direct influence on absorption by the plant is overestimated.  相似文献   


10.
Background: High plateaux in the Scottish Highlands are vulnerable to disturbance and erosion, but there is a lack of quantitative measurements of terrain sensitivity.

Aims: To apply new quantitative methods to assess the sensitivity of such terrain to physical stress.

Methods: We investigated two components of the mechanical properties of the terrain on 10 plateaux underlain by several different lithologies: the tensile strength of the vegetation mat and underlying root zone, and the shear and compressional strengths of the substrate.

Results: Significant differences in tensile strength occur amongst plant communities, but there is also large within-site and between-site variation for particular communities. A significant component of such variability is attributable to the proportional representation of co-dominant species within communities, and inter-site variability is partly explained by substrate granulometry: particular communities exhibit lower strength characteristics when rooted in sandy substrates derived from coarse-grained lithologies than the same communities on silt-rich soils derived from fine-grained lithologies.

Conclusions: Terrain sensitivity to physical stress is conditioned by the interaction of vegetation and substrate characteristics. Generally, grass-dominated (particularly Nardus-dominated) communities tend to be most robust, and communities dominated by bryophytes and prostrate Calluna vulgaris are typically most sensitive. We identify a continuum of substrate strength: peat is the most sensitive substrate type, followed by other organic-rich soils, sandy matrix-supported substrates and silt-rich matrix-supported substrates. Clast-supported substrates and openwork blockfields are the most robust substrate types. Because the near-surface layers of mineral substrates are weakest, erosion is likely to remove these to expose the underlying robust but sterile clast-supported layers, altering soil status and inhibiting plant recolonisation on eroded substrates.  相似文献   


11.
Background: Seedling recruitment following fire is an infrequent yet critical demographic transition for woody plants in Mediterranean ecosystems.

Aims: Here we examine whether post-fire seedling recruitment of three widespread Californian chaparral shrubs is affected by local adaptation within an edaphically and topographically complex landscape.

Methods: We reciprocally transplanted 6-month-old seedlings of Adenostema fasciculatum, Ceanothus cuneatus and Eriodictyon californicum to serpentine and sandstone soils, and cool northerly and warm southerly slopes.

Results: At the age of 2 years, none of the species manifested higher survival or growth on ‘home’ compared with ‘away’ soils or slopes, indicating an absence of local adaptation with respect to seedling recruitment in these environments. Seedlings of all species manifested lower survival and relative growth on serpentine soils regardless of seedling source, as well as a variety of other destination and source effects.

Conclusions: The ability of these three species to recruit in new environments, such as in restoration settings or in response to shifting climates, is unlikely to be impeded by a need for seeds from sources that closely match their edaphic or topographic destination.  相似文献   


12.
Context: Carboxymethyl-lysine (CML) results from oxidative stress and has been linked to cardiovascular disease.

Objective: The objective of this study is to investigate the association between sleep-disordered breathing (SDB) – a source of oxidative stress – and CML.

Materials and methods: About 1002 participants in the Cardiovascular Health Study (CHS) were studied.

Results: Women with SDB had significantly higher CML concentration compared with those without SDB (OR?=?1.63, 95%CI?=?1.03–2.58, p?=?0.04). The association was not significant among men.

Discussion: SDB was associated with CML concentration among elderly women but not men in the Cardiovascular Health Study.

Conclusion: Accumulation of CML may be an adverse health consequence of SDB  相似文献   


13.
A method for deriving Site-Specific Assessment Criteria (SSAC) for use when considering risk to human health from chronic exposure to heavy metals (except lead), metalloids, and organic substances in soil, with application to the United Kingdom (UK), is described. The SSAC represents the soil concentration above which an unacceptable risk to human health may be indicated.

The method considers the UK standard land uses (residential with and without plant uptake, allotment gardens, and commercial/industrial) by applying the default exposure factors and algorithms provided. Non-standard land uses can be also considered. Site-specific determinations of contaminant bioaccessibility or of plant-to-soil concentration factors may be used if available.

The method adopts the risk-based source-pathway-receptor pollutant linkage framework and a deterministic methodology. Exposure pathways considered are direct ingestion of soil and dust, consumption of home grown or allotment vegetables, ingestion of soil attached to such vegetables, inhalation of soil vapors outdoors and inhalation of soil vapors indoors. A test for the significance of the dermal pathway is also included.

It is not intended that the method be used to generate or replace UK Soil Guideline Values, because this can only be done by the appropriate authoritative bodies within the UK (Department of the Environment, Food and Rural Affairs and the Environment Agency).  相似文献   


14.
Capsule: Long-term changes in eggshell speckling correlated temporally and spatially with declining soil calcium in an English Great Tit Parus major population.

Aims: Eggshell speckling in the Great Tit correlates with eggshell thickness and calcium availability. We investigated whether eggshell speckling changed in a Great Tit population during a period when soil calcium declined, and estimated changes in eggshell thickness.

Methods: Eggshell pigmentation of 2313 Great Tit clutches was recorded in 1988–2007 across a geological gradient in Wytham Woods, UK. Soil surveys conducted in 1974 and 1991 were repeated in 2008. Temporal and spatial changes in eggshell speckling and soil calcium were examined using generalized linear mixed models. We also estimated the change in eggshell thickness over this period.

Results: Soil-calcium availability declined 1974–2008 especially in calcium-rich limestone areas. A systematic change in eggshell speckling, approximating to a 6.5% reduction in eggshell thickness, occurred between 1988 and 2007. The change was greatest in parts of Wytham that experienced the greatest decline in soil calcium. Hatching success was unaffected.

Conclusion: Soil-calcium availability has declined in Wytham Woods, affecting Great Tit eggshell characteristics. This is the first evidence that declining soil calcium affects birds nesting in calcium-rich areas. Practical applications of these findings are considered.  相似文献   


15.
Background: Species composition of plant communities is shaped by the interplay between dispersal limitation, environmental filters and stochastic events.

Aims: The aim of this work was to investigate the effects of dispersal limitation and environmental filtering on tree recruitment. To accomplish this, we employed the unified neutral theory of biodiversity and biogeography to examine migration within the metacommunity, defined as a set of interacting local communities linked by the dispersal of multiple potentially interacting species.

Methods: We sampled 12,975 individuals with dbh ≥ 1 cm in 26 1-ha permanent plots, including habitats of terra firme, transitional forests, várzea and campinarana, on the upper Madeira River, Brazilian Amazon.

Results: Campinarana drew individuals from outside the metacommunity species pool at a mean probability of recruitment of 0.06, a much lower probability than terra firme (0.31), transitional (0.21) and várzea forests (0.22). Environmental variables, such as water table depth, soil texture and fertility, were related to differences in community assembly.

Conclusions: Species abundance distribution and diversity patterns of plant assemblages in a large river landscape in the Amazon highlight the importance of environmental heterogeneity that conditions beta-diversity. The high variation in recruitment probabilities from the metacommunity species pool to local communities suggests high habitat variability in the process of maintaining patterns of local diversity.  相似文献   


16.
Background: Although lianas are important in forest ecosystems, information on the environmental factors influencing their diversity, structure and habitat associations is scanty.

Aims: This study had the aim of determining variation in liana diversity, structure and habitat associations across different topographic habitats, and the environmental factors influencing them, in the Penang Hill Forest Reserve, Malaysia.

Methods: Liana diversity, structure and habitat associations were examined in 30 plots, 40 m × 40 m, randomly demarcated within three topographic habitats (flatland, slope and valley). The physico-chemical properties of the soils in the plots were determined and the altitude and slope of the plots recorded.

Results: Liana species richness, diversity and structure varied significantly among the topographic habitats. Liana species richness, diversity and abundance variations were related to soil moisture, phosphorus content, pH and altitude, whereas liana diameter and basal area were associated with soil magnesium and slope. A total of eight species had a positive association with the habitat and a further six showed a negative association. Four species had a positive association with the flatland habitat, but only three and two species, respectively, with slope and valley habitats. The slope habitat gave the highest number of species that showed a negative association.

Conclusions: Liana diversity and structure varied between habitats. Some liana species showed different associations with specific habitats. Environmental variables were identified that influence liana diversity, structure and habitat associations. The study provides important information about the factors influencing liana success, and these will be of value in liana conservation and management in tropical forests.  相似文献   


17.
Context: Organophosphorus insecticides (OPs) have been used to control agricultural pests found in Washington state. Farmworkers (FW) have higher exposure to OP pesticides than non-farmworkers (NFW), and FW children may in turn have higher exposure than NFW children.

Objective: To examine the association between the concentration in house dust of five OPs used commonly in pome fruit orchards and the concentration in urine of dialkylphosphate metabolites (DAP), in a cohort of Hispanic FW and NFW and their children.

Methods: Parents and children participated in three data collection periods over the course of one year. Urine samples were evaluated for the DAPs characteristic of OP exposure, and dust from homes and vehicles was evaluated for intact OP residues.

Results: Geometric mean (GM) concentrations of OPs in house and vehicle dust were higher in FW households than NFW households in all agricultural seasons. GM concentration of urinary DAPs was higher for children in FW households than NFW households.

Discussion: Regression analysis found a positive association between OP residues in house dust and the children’s urinary DAPs.

Conclusions: To our knowledge, this study is the first to report an association between pesticides in house dust and their biological metabolites in urine.  相似文献   


18.
Context: Leptin is produced in white adipose tissue, but also in human coronary atherosclerotic lesions.

Objective: The aim of this study is to assess the prognostic value of leptin in patients with proven coronary artery disease (CAD) (N?=?1907).

Methods: AtheroGene is a contemporary CAD cohort study (N?=?3229). Median follow-up time was 3.8 (Quartile 1/3 with 2.8/4.9) years.

Results: Leptin concentration was associated with a hazard ratio (HR) for the fully adjusted model of HR?=?1.32 in women but was not significant in men. The endpoint cardiovascular death and non-fatal myocardial infarction was observed in 167 patients.

Conclusion: In women with known CAD, increased leptin concentration is useful for predicting cardiovascular death and non-fatal myocardial infarction.  相似文献   


19.
Background: Knowledge about vegetation and soil seed bank composition and the processes that contribute to vegetation recovery after the removal of heavy grazing is lacking in sub-alpine ecosystems.

Aims: In order to assess the effects of large herbivores on above-ground vegetation (AGV) and soil seed bank (SSB) characteristics, intensively sheep-grazed areas were compared to adjacent areas where grazing had been removed 10 years previously in a sub-alpine grassland of northern Iran.

Methods: A total of 40 4-m2 (2 m × 2 m) plots were established in each treatment, and soil samples were collected from each plot within a depth of 10 cm. Plant species composition was determined for each plot during the flowering stage of herbaceous species in June 2011. The seedling emergence method was used to estimate SSB composition.

Results: A total of 45 species (23 annuals and 22 perennials) emerged from the soil samples of the grazed area, while the number of species emerged from the soil samples of the previously grazing area was 76 (37 annuals and 39 perennials). The removal of grazing led to a significant increase in species richness and seed density in the SSB. Species turnover of AGV was higher, and that of the SSB was similar for grazed areas compared with areas that were formerly grazed. Detrended correspondence analysis ordination of AGV composition showed a clearly separate structure between grazed plots and plots where grazing has been removed, while the segregation was less clear for SSB composition.

Conclusions: We concluded that restoration of locally degraded sites cannot rely on the SSB when grazing is stopped simultaneously and unvegetated gaps are colonised by vegetative growth rather than by seed.  相似文献   


20.
Context: Several assays of monitoring immune cell function have been developed to enhance therapeutic drug monitoring.

Objective: An in vitro-validated whole-blood assay of phosphorylated ribosomal protein S6 (pS6RP) was evaluated for confounders to monitor the mTOR-inhibitor everolimus (ERL).

Materials and methods: Whole blood samples from 87 heart transplant recipients were analyzed for pS6RP-expression in CD3-positive T-cells by phospho-flow analysis.

Results: ERL blood concentration, laboratory parameters, co-medications, demographic and clinical data were reviewed.

Conclusion: Evaluating the pS6RP-assay revealed that pS6RP is influenced by cyclosporine A (CsA) blood concentration, duration of ERL treatment, co-medication with thiazide diuretics and different metabolic parameters.  相似文献   


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