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1.
The role of microorganisms in elemental mercury formation in natural waters   总被引：1，自引：0，他引：1  
Gas evasion of elemental Hg (Hg°) from the open ocean plays a prominent role in the global mercury cycle. Elemental Hg is formed primarily by reduction of ionic Hg in the mixed layer of aquatic systems. By culturing phytoplankton in defined media, and by incubating natural seawater and freshwater samples, we have demonstrated that Hg° is produced by microorganisms, with formation rates (0.5 to 10% d?1) similar to those estimated from mass balance studies. Our results also suggest that <3μm microorganisms are the primary Hg reducers in natural waters. Eucaryotic phytoplankton are capable of reducing ionic Hg to Hg° but the rate of reduction is insufficient to account for the observed reduction rates found in incubated field samples. Bacteria are thus the more likely Hg reducers. In seawater, cyanobacteria such asSynecococcus may account for much of the mercury reduction, while in the eutrophic, polluted Upper Mystic Lake north of Boston other procaryotic microorganisms are contributing to the overall Hg reductive capacity of the medium. By reducing ionic Hg, microorganisms play a pivotal role in the aquatic biogeochemistry of Hg, not only by enabling evasion to the atmosphere, but by directly decreasing the amount of ionic Hg available for methylation.  相似文献   

2.
Li  Jinhui  Tang  Hongxiao  Bai  Qingzhong  Nie  Yongfeng  Luan  Zhaokum 《Water, air, and soil pollution》2000,117(1-4):251-261
With the aggravation of acid rain pollution and the enlarging of the acid rain regions in China, the sensitivity evaluation of natural waters to acidification on a regional scale become increasingly important. Acidification models based on a single indicator cannot give much information on aquatic acidification because of their simplicity; yet acidification models based on physical, chemical, hydrological and/or biological processes are not suitable for large scale regional research because of their exceptional complexity. In this paper, a multi-indicator comprehensive model for aquatic acidification sensitivity is proposed and applied. This model comprises some of the most important factors that are considered to influence water acidification, in particular: acid neutralization capacity, acidification capacity, acidification sensitive index, cation exchange capacity of soil, pH of soil, and weathering shuck types of soil-forming. It highlights the key stages of aquatic acidification by acid neutralization capacity, acidification capacity, and acidification sensitivity index. The model thereby estimates the acidification sensitivity of natural waters by using these indicators according to a weighting system. Equal-weight and non-equal-weight approaches are separately used to combine the six indicators into an overall sensitivity index of aquatic acidification. The result derived from an application to China on a national scale indicates the practicability of this approach. In China, the sensitive natural waters emerge in Southern China, which is already a heavy acid rain region, and in Northeastern China where the rainwater is beginning to become much acidic.  相似文献   

3.
The characteristics of electric charge and molecular weight distribution,oxidation-reduction regimes,e.g.Eh and amounts of organic reducing substances produced by milk vetch during anaerobic decomposition process,were studied by using electrochemical methods.Interaction between soils and organic reducing substances was also observed.The results indicate that the organic reducing substances were mainly the organic compounds with negative and amphoteric charges,which were distributed in two groups at anodic peak potentials of 0.25 and 0.69 volt in differential pulse voltammograms,respectively.Their apparent molecular weights are all less than 700 daltons,in which those active in oxidation-reducion reaction were distributed in the fraction with apparent molecular weight less than 200 daltons.The organic reduction substances can be oxidized by manganese oxides in their interaction with soils.  相似文献   

4.
Natural gas storage produced waters (NGSPWs) are brought to the surface when natural gas is reclaimed from underground storage. These waters may have a variety of constituents of concern that need to be treated before the water can be reused or discharged to receiving aquatic systems. The objective of this study was to characterize NGSPWs to discern potential constituents of concern that may limit surface discharge or beneficial reuse of these waters. We conducted a strategic review of literature, analyses of produced water composition records, and analyses of produced water samples provided by natural gas storage companies. Although NGSPWs varied widely in composition, primary constituents of concern included: chlorides (salinity), metals, metalloids, and organic compounds (e.g. oil and grease). Chlorides are the predominant constituent of concern in most NGSPWs. Strategies for risk mitigation of NGSPWs will need to be both robust and site specific to deal with the diverse composition of these waters.  相似文献   

5.
绿肥压青后随郎栽换或未经庸妙就栽秧,常会引起水稻黑根枯苗的“烧秧”现象。一般认为,还原性物质的毒害是引起这一现象的原因之一。然而引起毒害的还原性物质,主要是低铁还是硫化氢或其它还原性物质?则一直不大清楚。近年来不少研究者指出,水和土的氧化还原状况对水稻的生长发育和土壤养分状况有很大影响[1-4],有的研究者指出,对于水稻土的氧化还原体系,应从其彼此相关而又不同的张度因素与数量因素两方面进行研究[5-4],并提出了相应的研究方法[6,7]。按照这些方法,1962年我们在研究绿肥压青后水稻生育期间土壤中还原性物质的动态变化时初步看出[8]:活性有机还原物质在还原性物质总量的变化中起着主要的作用。在此墓础上又于1963年进行了田间小区试验,以探索绿肥压青后土壤中还原性物质舍量的变化及其对水稻生长的影响。现将所得结果整理如下。  相似文献   

6.
Northern Sweden has been regarded as unaffected by acid deposition, but many surface waters in the region fall within the definition of acid surface water (pH < 6.0, alkalinity < 50 mmolc m?3) permanently or during episodes. Approximatly 100 MSEK in spent annually on liming in northern Sweden. This paper summarizes our conclusions from a workshop on natural versus anthopogenic acidification held in February 1995. It was shown that organic substances have a key role in determining the acidity of surface waters in the region, although anthropogenic effects are documented in some coastal systems and in the southern mountain range. Sulfide oxidation occurs by the coast. It appears clear that many surface waters that were naturally acidic have been limed to unnatural pH levels. New criteria to screen liming candidates should be developed, and one such model based on water chemistry data is proposed.  相似文献   

7.
The determination of the structure of humic substances from peat soils and natural waters is a major problem in soil science. Humic substances are chemically heterogeneous and consist of molecules covering a wide distribution of molecular size. A quantity related to both molecular size and structure in the hydrated state is the volume of the humic molecules per unit mass or partial specific volume (ν2). The partial specific volumes of humic substances have been estimated from atom and chemical group volume contributions for 17 proposed structures of fulvic and humic acids taken from the literature. The results show that the partial specific volume reflects the composition of humic substances, decreasing with increase in the carbon: hydrogen (C:H) molar ratio. The more oxidized the humic material the smaller is its partial specific volume. These trends agree with our experimental measurements of partial specific volumes for a range of humic materials (aquatic fulvics, aquatic and peat humics). The predicted values of partial specific volumes for the proposed structures, however, are overestimated by approximately 15% compared to the experimental values. There is little difference between values of ν2 calculated from the detailed humic structures and those calculated from their empirical formulae; calculations of partial specific volumes using a random modelling approach leads to overestimation by approximately 37%. It seems that the estimates based on additivity of atom and chemical group volumes do not take into account an overall contraction of the structures because of hydrophobic interactions. In general terms the values of the partial specific volumes of humic substances suggest they are more compact molecules than globular proteins, and intrinsic viscometry studies suggest that aqueous salt solutions approach θ-solvent conditions for humic substances.  相似文献   

8.
Semi-quantitative biomass-size distributions (BSD's) along a joint axis of individual size provided an integrated illustration of aquatic communities sampled at different taxonomic and trophic levels. The approach was applied within the Swedish ISELAW-programme (integrated studies of the effects of liming acidified waters) to test the general hypothesis that aquatic communities in limed lakes are not systematically different from communities in comparable non-limed circumneutral lakes. Input data included pelagic phytoplankton and zooplankton, sublittoral/profundal macroinvertebrates, and benthic fish, within twelve Swedish lakes (six limed, two acidic and four circumneutral reference lakes). The four compartments were sampled on different spatial scales, but each designed for between-lakes comparisons. There were no clear-cut differences in overall size distribution between the three categories of lakes. The mean BSD of limed lakes was indeed more similar to the mean BSD of circumneutral lakes than to that of two acidic lakes. Due to high variation within categories, however, acifidication status alone can not be used for reliable prediction of BSD in a certain lake.  相似文献   

9.
Irrigation of crops with treated wastewater has the potential to introduce effluent-derived organic microcontaminants into surface waters through agricultural runoff. To determine whether compounds indicative of the presence of treated effluent in irrigation water could be identified in agricultural runoff, surface runoff samples collected from effluent-irrigated and rain-fed cultivated fields were analyzed for a broad spectrum of organic compounds. A variety of compounds was identified that appeared to be associated with irrigation with treated wastewater. These compounds included human pharmaceuticals (e.g., carbamazepine, gemfibrozil, carisoprodol), personal care product ingredients (e.g., insect repellent, polycyclic musks), and alkyl phosphate flame retardant chemicals. Most of these compounds appear not to have been previously reported in agricultural runoff. These compounds were present at concentrations below the few published aquatic toxicology data available; however, their potential to elicit more subtle effects in aquatic organisms cannot be excluded. None of these compounds were detected by broad-spectrum analysis in samples from the same fields during runoff-producing rain events.  相似文献   

10.
Developing procedures for assessing the potential environmental fate and transport of nanomaterials is an active endeavor of the environmental technical research community. Insufficient information exists for estimating the likelihood of nanomaterial deposition on natural surfaces in aquatic environments. This work develops a framework for estimating potential metal oxide nanomaterial self-aggregation through the combined application of recent developments in diffuse layer model surface complexation theory with historical Derjaguin–Landau–Verwey–Overbeek (DLVO) procedures. Findings from the work include: 1) the surface, diffuse layer, and/or zeta potentials of nanomaterials in environmental aqueous systems are likely to have an absolute value less than 25 mV, 2) only nanomaterials with a Hamaker constant as large as 1E-19 J (and an absolute surface potential < 25 mV) will likely aggregate in most environmental aquatic media, 3) natural organic matter coatings may render metal oxide nanomaterials less likely to aggregate in aquatic systems, 4) nanomaterials in aqueous suspension will likely have an absolute surface potential less than their micron-sized counterparts of the same composition, and 5) robust diffuse layer model databases of intrinsic surface site reactivity constants with multivalent aqueous environmental ions will need to be developed in order to provide accurate mechanistic estimates of the surface potential of nanoparticles suspended in aqueous environmental systems.  相似文献   

11.
The indicators of functioning of soil microorganisms in soddy–podzolic soil contaminated with Ni compounds show different ranges of soil ecotoxicity. A halving of soil microorganisms' nitrogen-fixing activity has been shown in slightly acidic soddy–podzolic cultivated soil with a Ni concentration of 150 mg/kg and for noncultivated acidic soils with a Ni concentration 100 mg/kg. The reduction of denitrification activity in cultivated soil has been observed with a Ni concentration of 500 mg/kg, and in uncultivated soil it has been observed at a Ni dose of 100 mg/kg. The inhibition of soil respiration in slightly acidic soil occurred only at the highest dose of Ni, 1000 mg/kg, while in the acidic soil it took place at 300 mg/kg. Biotesting based on bacterial luminescence can be used for determination of soil pollution with heavy metals such as Ni, as well as for the assessment of the toxicity of aqueous environments in contact with contaminated soils.  相似文献   

12.
A simple analytic technique — isotope dilution — was used for determination of the contents of total and methilated Hg in water, sediments, soils and biological objects collected in the basin of the river Katun. The inspected region is located on a territory of two mercury-stibium geochemical provinces. Evaluation of the Hg transport, transformation and bioaccumulation in aquatic and terrestrial ecosystems of the region showed that the main Hg transport occurs on suspended solids after Hg has been washed out from soil and bedrock by water of the river Katun and its tributaries and also by underground waters. Bottom sediments of some rivers of the basin content increased Hg concentrations. This effect is also noted in the sediments of a small reservoir formed on one of the tributaries. The investigations showed that Hg originating from natural sources differs considerably in its biochemical characteristics from Hg compounds coming from anthropogenic sources. So, natural Hg compounds have lower bioavailability for the water and terrestrial organisms of the region.  相似文献   

13.
Because of persistent complaints by downstream users about the deterioration of water quality, the Bow River waters near Calgary, Alberta, were examined for the occurrence and presence of organic compounds. The overall water quality was determined by studying the effects of reservoir-dam, urban, industrial and municipal outfall on the river as it enters and leaves the Calgary city limits. The reservoir-dam and urban run-off do not affect the Bow River water quality. The industrial and municipal outfall, although contributing slightly higher levels of organic carbon compounds to the river, have minimal impact on its water quality. This was indicated by the fact that concentrations of organic compounds in the river waters leaving the Calgary city limits were in the range of those for pristine waters of Alberta. Thus, in terms of organic compounds, the Bow River water quality poses no problem to the downstream users of the river.  相似文献   

14.
Growing interest in the market for humic substances with agricultural applications has led to the development of new potential sources of these compounds other than fossil matrices (e.g. different kinds of lignite), which, until now, have represented the main raw material for the extraction of humus-like products. High quality compost (green compost) obtained through the aerobic biostabilization of selected organic residues, such as vegetable waste from source-collection at garden-produce markets, may be considered for this purpose. Beyond the primary need to develop technically and economically reliable procedures for the extraction of humic substances from compost at the industrial scale, importance must be placed on controlling the influence of such compounds on soil-plant systems. Humates from leonardite, representative of the active agents among humus-based commercial preparations, have been compared in pot trials with humic acids, potassium salts, from green compost in order to evaluate their respective effects on soil microbial activity and plant productivity. Differences between pot blocks amended with humic acids have suggested that humus-like substances extracted from compost seem to exert higher stimulative effects on microbial growth and vegetative biomass production than fossil humates.  相似文献   

15.
A comparison of neutral freshwater lakes and acidic coal mining lakes with respect to both, in-lake alkalinity generation and P mobilization, has been made to predict the extent of the possibility of P remobilisation in acidic mining lakes creating eutrophication. It is hypothesized that the maturing process of an acid mining lake is comparable to the recent history of the increasing productivity observed in SO42--rich freshwater lakes. This hypothesis is based on the observation that (1) with rising pH over time the atomic S:Fe ratio in the acidic waters is increasing because only a fraction of the SO42--S but nearly all Fe is usually buried in the sediment; (2) the potential of their sediments to immobilize P is at present linked to its continuous accumulation at the sediment together with the stock of its binding partners, mainly Fe(III) compounds; (3) the input of organic matter stimulating the SO42- reduction and the formation of insoluble complexes of sulfide with ferrous Fe will enhance not only the generation of alkalinity, but will also increase the mobility and release of P.  相似文献   

16.
The determination of the structure of humic substances from soils and natural waters is an intriguing problem in soil science. Humic substances consist of molecules covering a broad distribution of molecular size and involving different functional groups. Taking this into account, we have chosen smaller model systems with functional groups typically present in humic substances. We investigated theoretically, by quantum chemical calculations, the environmental effects on the complexes formed from the interaction of 2,4‐dichlorophenoxyacetic acid and its anion with acetaldehyde, methanol, methylamine, protonated methylamine, acetic acid and water. The important case of a cation bridge mechanism, with Ca2+ as the bridging cation, is also included into the set of model reactions. It is found that this cation bridge belongs to one of the most stable mechanisms of fixation of organic compounds in soils. According to our calculations the hydroxyl group forms the most stable complexes with 2,4‐D in a polar solvent environment.  相似文献   

17.
Soluble organic matter derived from exotic Pinus species has been shown to form stronger complexes with iron (Fe) than that derived from most native Australian species. It has also been proposed that the establishment of exotic Pinus plantations in coastal southeast Queensland may have enhanced the solubility of Fe in soils by increasing the amount of organically complexed Fe, but this remains inconclusive. In this study we test whether the concentration and speciation of Fe in soil water from Pinus plantations differs significantly from soil water from native vegetation areas. Both Fe redox speciation and the interaction between Fe and dissolved organic matter (DOM) were considered; Fe – DOM interaction was assessed using the Stockholm Humic Model. Iron concentrations (mainly Fe2+) were greatest in the soil waters with the greatest DOM content collected from sandy podosols (Podzols), where they are largely controlled by redox potential. Iron concentrations were small in soil waters from clay and iron oxide‐rich soils, in spite of similar redox potentials. This condition is related to stronger sorption on to the reactive clay and iron oxide mineral surfaces in these soils, which reduces the amount of DOM available for electron shuttling and microbial metabolism, restricting reductive dissolution of Fe. Vegetation type had no significant influence on the concentration and speciation of iron in soil waters, although DOM from Pinus sites had greater acidic functional group site densities than DOM from native vegetation sites. This is because Fe is mainly in the ferrous form, even in samples from the relatively well‐drained podosols. However, modelling suggests that Pinus DOM can significantly increase the amount of truly dissolved ferric iron remaining in solution in oxic conditions. Therefore, the input of ferrous iron together with Pinus DOM to surface waters may reduce precipitation of hydrous ferric oxides (ferrihydrite) and increase the flux of dissolved Fe out of the catchment. Such inputs of iron are most probably derived from podosols planted with Pinus.  相似文献   

18.
Spinosad is a bacterially derived insect control agent consisting of two active compounds, spinosyns A and D. The objective of this paper is to describe the environmental fate of spinosad in aquatic systems. To this end, several studies performed to meet regulatory requirements are used to study the fate and degradation in individual environmental media. Specifically, investigations of abiotic (hydrolysis and photolysis) and biotic (aerobic and anaerobic aquatic) processes are described. Understanding developed from the laboratory-based studies has been tested and augmented by an outdoor microcosm study. Understanding of aquatic fate is a building block for a complete environmental safety assessment of spinosad products (Cleveland, C. B.; Mayes, M. A.; Cryer, S. A. Pest Manag. Sci. 2001, 58, 70-84). From individual investigations, the following understanding of dissipation emerges: (1) Aqueous photolysis of spinosad is rapid (observed half-lives of <1 up to 2 days in summer sunlight) and will be the primary route of degradation in aquatic systems exposed to sunlight. (2) Biotic transformations contribute to spinosad's dissipation, but less so than photolysis; they will be of primary importance only in the absence of light. (3) Spinosad partitions rapidly (within a few days) from water to organic matter and soil/sediment in aquatic systems but not so rapidly as to replace sunlight as the primary route of dissipation. (4) Abiotic hydrolysis is relatively unimportant compared to other dissipation routes, except under highly basic (artificial) conditions and even then observed half-lives are approximately 8 months. Degradation pathways are understood are follows: (1) Degradation primarily proceeds by loss of the forosamine sugar and reduction of the 13,14-bond on the macrolide ring under aqueous photolytic conditions. (2) Degradation to several other compounds occurs through biotic degradation. Degradation under anaerobic conditions primarily involves changes and substitutions in the rhamnose ring, eventually followed by complete loss of the rhamnose ring. Degradation under aerobic conditions was more extensive (to smaller compounds) with the loss of both the forosamine and rhamnose sugars to diketone spinosyn aglycon degradates. (3) Hydrolytic degradation involves loss of the forosamine sugar and water and reduction on the macrolide ring to a double bond at the 16,17-position.  相似文献   

19.
In order to explore the geochemical transformation of trichloroacetic acid to chloroform in fresh waters, an experimental study by using laboratory microcosms was performed. The study confirmed the abiotic transformation of TCA to chloroform with various rate constants, ranging from approx. 3.29×10?4 day?1 to 4.41×10?4 day?1, in different fresh waters at 25± 1 °C. Also, an induction period (5–6 days) was observed before apparent degradation of TCA. Of the four geochemical factors including pH, oxygen, humic substances and ferric ion, the influence of lake HA, extracted from East Lake, on the transformation has been proven to be more substantial. Several model substances of HA, such as acetic acid, citric acid and β-Resorcylic acid etc., were also found to promote chloroform formation. Whilst, the results of pH effect experiments showed that higher yields of chloroform released from TCA solution occurred in the intensified alkaline media (pH = 10), an unusual condition in environment, indicating the limited effect of pH on the transformation under prevailing conditions in natural waters. According to our study, a mathematic model was built and successfully used to simulate TCA transformation to chloroform in fresh waters. Mathematic simulation demonstrates that the rates of decay for chloroform formation, after induction time, are mainly owing to rapid TCA degradation. In addition, biotic experiments indicated that fresh water algae affect TCA transformation to chloroform in varying degrees. The blue alga Anabaena cylindrica remarkably promoted chloroform formation, in weak acid media (pH = 6.5). While, the green alga Chlorella vulgari seems to indistinctively affect chloroform formation, whether in alkaline or weak acidic media. Enzyme or other byproducts of alga, such as citric acid, might play roles in the TCA transformation.  相似文献   

20.
Eurasian Soil Science - Humic substances (HS) are heterogeneous and polydisperse compounds formed in soils, sediments and waters during the decay and transformation of organic residues (the process...  相似文献   

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