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1.
The spatial and temporal distribution of humic substances in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity while positively impacting secondary productivity. In the present investigation, a large shallow lake ecosystem was studied to determine the spatial and seasonal variation of the composition and concentration of humic substances. Concentrations of total dissolved organic matter, humic acid, and fulvic acid were found to display significant spatial distributions (1.3…13.5 mg/L, DOM; 0.1…5.4 mg/L, HA). The distribution is described by using mapping techniques and the analysis of the spatial distribution of the lake. An analysis of the seasonal variations also indicated the dependence of the occurrence of these compounds on meteorological and hydrological conditions. To identify the potential sources of these organic materials, an analysis was made of the ratio of humic and fulvic acid fractions and total DOM. It was found that areas of high DOM concentration coincided with the areas of highest HA percentage of total DOM. Furthermore using the ratio of the normalised concentrations of HA, FA, and residual DOM (< 5000 g/mol) it was found that areas dominated by each are spatially distinct. This confirms the hypothesis that in these shallow lakes, photodegradation and bacterioplankton activity will create a residence time dependent zonation of each component of the total DOM.  相似文献   

2.
In natural waters arsenic normally occurs in the oxidation states +III (arsenite) and +V (arsenate). The removal of As(III) is more difficult than the removal of As(V). Therefore, As(III) has to be oxidized to As(V) prior to its removal. The oxidation in the presence of air or pure oxygen is slow. The oxidation rate can be increased by ozone, chlorine, hypochlorite, chlorine dioxide, or H2O2. The oxidation of As(III) is also possible in the presence of manganese oxide coated sands or by advanced oxidation processes. Arsenic can be removed from waters by coprecipitation with Fe(OH)3, MnO2 or during water softening. Fixed‐bed filters have successfully been applied for the removal of arsenic.The effectiveness of arsenic removal was tested in the presence of adsorbents such as FeOOH, activated alumina, ferruginous manganese ore, granular activated carbon, or natural zeolites. Other removal technologies are anion exchange, electrocoagulation, and membrane filtration by ultrafiltration, nanofiltration or reverse osmosis.  相似文献   

3.
The present paper deals with the modeling of the removal of total arsenic As(T), trivalent arsenic As(III), and pentavalent arsenic As(V) from synthetic solutions containing total arsenic (0.167–2.0 mg/L), Fe (0.9–2.7 mg/L), and Mn (0.2–0.6 mg/L) in a batch reactor using Fe impregnated granular activated charcoal (GAC‐Fe). Mass ratio of As(III) and As(V) in the solution was 1:1. Multi‐layer neural network (MLNN) has been used and full factorial design technique has been applied for the selection of input data set. The developed models are able to predict the adsorption of arsenic species with an error limit of ?0.3 to +1.7%. Combination of MLNN with design of experiment has been able to generalize the MLNN with less number of experimental points.  相似文献   

4.
We performed stable carbon and nitrogen-guided analyses of biomagnification profiles of arsenic (As) species, including total As, lipid-soluble As, eight water-soluble As compounds (arsenobetaine (AB), arsenocholine (AC), tetramethylarsonium ion (TETRA), trimethylarsine oxide (TMAO), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), arsenate (As[V]), and arsenite (As[III])), and non-extracted As in a tropical mangrove ecosystem in the Ba Ria Vung Tau, South Vietnam. Arsenobetaine was the predominant As species (65-96% of water-soluble As). Simple linear regression slopes of log-transformed concentrations of total As, As fractions or individual As compounds on stable nitrogen isotopic ratio (δ15N) values are regarded as indices of biomagnification. In this ecosystem, lipid-soluble As (slope, 0.130) and AB (slope, 0.108) were significantly biomagnified through the food web; total As and other water-soluble As compounds were not. To our knowledge, this is one of the first reports on biomagnification profiles of As compounds from a tropical mangrove ecosystem.  相似文献   

5.
The spatial distribution of As (total As, As (III) and As (V)) in estuarine sediments from the main tributaries of Todos os Santos Bay, BA, Brazil, was evaluated under high and low flow conditions. The concentrations of As were determined using a slurry sampling procedure with hydride generation atomic absorption spectrometry (HG-AAS). The highest concentrations were observed at estuary mouths, and exceeded conservative lower threshold value (Threshold Effects Level; TEL). Due to the oxic conditions and abundance of Mn and Fe (oxyhydr)oxides in the sediments, most inorganic arsenic in the Subaé and Paraguaçu estuaries was present as As (V). Nevertheless, the concentration of As (III) at several locations along the Jaguaripe River were also above the TEL value, suggesting that As may be toxic to biota. In the Subaé estuary, antropogenic activities are the main source of As. At the Jaguaripe and at Paraguaçu estuaries, nevertheless, natural sources of As need to be considered to explain the distribution patterns.  相似文献   

6.
Recent evaluations of acute and chronical toxicity of arsenic resulted in a reduction of the standard value for total arsenic from 40 μg/L to 10 μg/L in drinking water which will be valid in Germany after a transition period as from January 1996. Arsenic is well known as substance of deep groundwaters, mainly of geogenic origin and normally found as As(III) or As(V). As(V) is well removable by flocculation and filtration after adding iron salts. As(III), however, has to be oxidized first to As(V). Therefore, it is important for treatment techniques to be able to distinguish between As(III) and As(V). A modified determination of As(III) using flow injection analysis was installed and optimized in order to investigate whether As(III) may be oxidized to As(V) by bacteria in natural waters. The results showed that at 4°C, no As(III)-oxidation was observed within 14 days. At room temperature, however, in the bacteria-containing samples, an As(III)-oxidation was found starting after 3 to 7 days. After 14 days, no As(III) was left over. In contrast, in the sterile samples, no As(III)-oxidation could be observed within 14 days. These results demonstrated that microbial processes influence the oxidation of As(III) to As(V) in natural waters.  相似文献   

7.
This paper is an experimental investigation into the removal of arsenic species from simulated groundwater by adsorption onto Ca2+ impregnated granular activated carbon (GAC‐Ca) in the presence of impurities like Fe and Mn. The effects of adsorbent concentration, pH and temperature on the percentage removal of total arsenic (As(T)), As(III) and As(V) have been discussed. Under the experimental conditions, the optimum adsorbent concentration of GAC‐Ca was found to be 8 g/L with an agitation time of 24 h, which reduced As(T) concentration from 188 to 10 μg/L. Maximum removal of As(V) and As(III) was observed in a pH range of 7–11 and 9–11, respectively. Removal of all the above arsenic species decreased slightly with increasing temperature. The presence of Fe and Mn increased the adsorption of arsenic species. Under the experimental conditions at 30°C, the maximum percentage removals of As(T), As(III), As(V), Fe, and Mn were found to be ca. 94.3, 90.6, 98.0, 100 and 63%, respectively. It was also observed that amongst the various regenerating liquids used, a 5 N H2SO4 solution exhibited maximum regeneration (ca. 91%) of the spent GAC‐Ca.  相似文献   

8.
In this paper, we determined the concentrations of antimony species (antimonite (Sb(III)), antimonate (Sb(V)) and dissolved inorganic antimony (DISb)) and arsenic, in Bohai Bay seawaters, as well as the relationships of the analytes with environmental factors such as seawater characteristics (e.g., suspended particulate material (SPM), salinity and total organic carbon (TOC)), heavy metals, nutrients and phytoplankton species, and evaluated the sources of arsenic and antimony. Dissolved arsenic and antimony concentrations in the surface waters were ranging spatially from 1.03 to 1.26 ng/ml and 0.386 to 1.075 ng/ml, with mean values of 1.18 and 0.562 ng/ml, respectively. Sb(V) as the prominent chemical species constituted about 89%. Regarding arsenic concentrations in the surface waters, there was a tendency for a small variation. However, antimony species concentrations were much variable than arsenic. The highest arsenic and antimony concentrations were found near the Haihe Estuary. These distribution patterns were controlled mainly by environmental factors, biological activities and sources. In this region, DISb and Sb(V) negatively correlated with salinity. Besides, arsenic and antimony correlated well with the nutrients, chlorophyll a and phytoplankton, implying that arsenic and antimony had been involved in biological cycling. In addition, according to our estimate, about 333.5×108 mg/year of arsenic and 454.2×108 mg/year of antimony reached Bohai Bay via rivers.  相似文献   

9.
This paper deals with kinetics and equilibrium studies on the adsorption of arsenic species from simulated groundwater containing arsenic (As(III)/As(V), 1:1), Fe, and Mn in concentrations of 0.188, 2.8, and 0.6 mg/L, respectively, by Ca2+ impregnated granular activated charcoal (GAC‐Ca). Effects of agitation period and initial arsenic concentration on the removal of arsenic species have also been described. Although, most of the arsenic species are adsorbed within 10 h of agitation, equilibrium reaches after ～24 h. Amongst various kinetic models investigated, the pseudo second order model is more adequate to explain the adsorption kinetics and film diffusion is found to be the rate controlling step for the adsorption of arsenic species on GAC‐Ca. Freundlich isotherm is adequate to explain the adsorption equilibrium. However, empirical polynomial isotherm gives more accurate prediction on equilibrium specific uptakes of arsenic species. Maximum specific uptake (qmax) for the adsorption of As(T) as obtained from Langmuir isotherm is 135 µg/g.  相似文献   

10.
Adsorption and oxidative transformation processes critically affect the mobility and toxicity of arsenic (As) in the environment. In this study, the detoxification of arsenite through adsorption and oxidation by pyrolusite was systematically investigated. Disappearance of aqueous As(III) in the solution can be efficiently achieved using pyrolusite. The As(III) oxidative transformation product arsenate or As(V) was obtained both in the solution and on the pyrolusite surface. The arsenic species adsorbed on pyrolusite exist in two forms: As(III) and As(V). Furthermore, over 64.8% of the adsorbed As cannot be desorbed. They were fixed more stably in the structure of the mineral to achieve a safer removal. Lower As(III) initial concentration increased As(III) detoxification rates. Elevating the reaction pH from 4.5 to 7.9 elicited a slight effect on the disappearance rate of As(III). Efficient As(III) detoxification can be achieved by pryrolusite within the studied pH range. The addition of low‐molecular‐weight carboxylic acids decreased the detoxification rate of As(III) through competition for active sites on pyrolusite. Co‐existing divalent metal ions, such as Ca2+, Ni2+, and Mn2+, also decreased the detoxification rate of As(III). However, the trivalent ion Cr3+ largely increased the detoxification rate through co‐precipitation and adsorption processes.  相似文献   

11.
Concentrations of total arsenic and individual arsenic compounds were determined in livers of cetaceans (Dall's porpoise and short-finned pilot whale), pinnipeds (harp and ringed seals), sirenian (dugong), and sea turtles (green and loggerhead turtles) to characterize arsenic accumulation profiles in higher trophic marine animals. Hepatic arsenic concentrations in sea turtles were highest among the species examined. Chemical speciation of arsenic revealed that arsenobetaine was the major arsenic compound in almost all the species. In contrast, arsenobetaine was a minor constituent in dugong. Dimethylarsinic acid, methylarsonic acid, arsenocholine, tetramethylarsonium ion, arsenite, and an unidentified arsenic compound were also detected as minor constituents. However, the composition of arsenic compounds was different among these species. These results might reflect the differences in the metabolism of arsenic and/or the compositions of arsenic compounds in their preys. To our knowledge, this is the first report on the large variation in the composition of arsenic species in liver of marine mammals and sea turtles.  相似文献   

12.
Gaschromatographic Determination of Diethylenetriaminepentaacetic Acid in Surface Water. A method for the determination of diethylenetriaminepentaacetic acid (DTPA) is reported. The determination is based on the preconcentration on a strong base anion exchange resin, esterification with n-propanol and following gaschromatographic separation using a N-selective detector. The sensitivity of the method, including enrichment, is 1 μg/L in river water. The identity of DTPA in river water was proved by mass spectrography. The method can be used also for the quantitative determination of nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), cyclohexanediaminetetraacetic acid (CDTA) and ethyleneglycolbis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid (EGTA). The method was used to examine river water. An investigation along the river Rhine, taking grab samples from January and february 1992 showed that DTPA was present in some sampling places in similiar concentrations as NTA and EDTA.  相似文献   

13.
Spodic Material for In Situ Treatment of Arsenic in Ground Water   总被引：2，自引：0，他引：2  
The leaching of chromium-copper-arsenic salts from old wood preservation sites is a threat to ground water at many places in Sweden. The installation of in situ reactive barriers is an attractive "passive' technique to prevent the further spreading of contaminants. The use of peat as a reactive barrier material has been suggested for heavy metals, but this material was expected to be unsatisfactory for arsenic (As). Therefore, the feasibility of using spodic B horizon material for the retention of arsenic was tested in laboratory column experiments. Contaminated soil was taken from an old preservation site and leached under conditions designed to imitate the field conditions. The arsenic load during the three-month duration of the test corresponded to a load at the field site during three years. The B horizon material proved to be efficient for retention of arsenic, despite the observation that As(III) dominated the As speciation. The As(III) concentration was reduced from 1 to 3 mg dm−3 to < 0.02 mg dm−3. Pure peat was, as expected, not suited as a reactive barrier for As, and a mixed B horizon/peat reactive barrier also proved unsatisfactory for the removal of As. It is therefore important to separate the B horizon material from any peat that is used to sorb heavy metals. Before applying the B horizon reactive barrier technique in the field, the effect of the naturally occurring variability of the reactive compounds should be tested. The inclusion of oxidizing agents in the barrier could possibly improve the lifetime considerably. Furthermore, the influence of the flow rate should be evaluated since the kinetics of the arsenic adsorption is relatively slow.  相似文献   

14.
Scum formation is a widespread problem in activated sludge nutrient removal plants. It often comes along with an excessive development of the filamentous bacterium “Microthrix parvicella” stabilizing the flotation process. As “M. parvicella” was found to depend on long‐chain fatty acids (LCFA) as sole carbon source not only in vitro but also in situ, some options of in‐situ substrate supply are discussed. Wastewater concentrations of fatty acids in the range of 2 to 15 mg L‐1 and homologue concentrations from synthetic surfactant degradation below 10 mg L‐1 rule out these substrates as source for excessive biomass production. They might, however, well be suitable for start‐up of a “M. parvicella” population. Build‐up of excessive biomass might rely on fatty acid supply originating in cell walls of lysed stationary phase bacteria of long residence time sludge fractions such as scum layers. Moreover, biogenic surfactants such as rhamnolipids have been proved to be an excellent carbon source for excessive biomass production in vitro.  相似文献   

15.
With the Water Framework Directive (WFD) the European Commission (EC) is requested to define environmental quality standards for pollutants to protect aquatic life in surface waters. Quality standards have to be derived by a scientific risk assessment and should not be exceeded. The recommended quality standards are mainly based on long term toxicological tests with algae, crustaceans and fish. The lowest effect concentration is divided by an assessment factor between 10 and 1000, which considers the data quality and quantity. In this work funded by the German Länder Working Party on Water (Länderarbeitsgemeinschaft Wasser – LAWA) environmental quality standards for 40 considered relevant substances were derived for aquatic ecosystems. The data sheets cover the identification of the compounds, their behaviour in the environment (physical‐chemical properties, biotic and abiotic degradation, sorption, bioaccumulation), information about mode of action, uses, analytical determination and available quality criteria. Ecotoxicological effect concentrations for bacteria, algae, protozoa, aquatic plants, crustaceans, fish, amphibians, insects and molluscs are listed. For 17 of the 40 hazardous substances investigated, quality objectives above 1 μg/L were derived. For 12 substances the values were between 0.1 μg/L and 1 μg/L and for 5 substances lower than 0.1 μg/L. Incomplete ecotoxicological data sets of the remaining compounds do not allow the derivation of quality standards. Especially for drugs further ecotoxicological test results are needed.  相似文献   

16.
This study aims to investigate the control of arsenic distribution by biogeochemical processes in the Indian Sundarban mangrove ecosystem and the importance of this ecosystem as an arsenic source for surrounding coastal water. The As(V)/As(III) ratio was found to be significantly lower in both surface and pore waters compared to sea water, which could be attributed to biogeochemical interconversion of these arsenic forms. The biological uptake of arsenic due to primary and benthic production occurs during the post-monsoon season, and is followed by the release of arsenic during the biochemical degradation and dissolution of plankton in the pre-monsoon season. These results suggest that arsenic is immobilized during incorporation into the arsenic-bearing initial phase, and unlikely to be released into pore water until the complete microbial degradation of arsenic-bearing organic compounds.  相似文献   

17.
At specific concentrations oxyanions such as arsenic pose a major threat to human beings and to the environment because of their ability to biomagnify. The World Health Organization has set the drinking water standard at 10 μg l−1 for arsenic. It is in this regard that novel and cheaper methods to detect oxyanions and remove them from the environment are developed. In this work, we have developed sample preparation methods involving solid phase and liquid membrane for the extraction and enrichment of these oxyanions in aqueous environments. Various parameters which govern their optimal extraction and enrichment have been optimised. The manipulation of the liquid membrane extraction process was utilised to selectively extract arsenic (III) which is more toxic as compared to arsenic (V). The liquid membrane consisted of a combination of two organic solvents, and n-undecane and di-n-hexyl ether were used in a combination at various ratios of the two liquid membranes. The means of detection was by graphite furnace atomic absorption spectroscopy (GFAAS) as well as inductively coupled plasma optical emission spectroscopy (ICP-OES). The applicability of the method was tested in real wastewater samples where it was able to remove at least 50% of As (III) with enrichment factors of up to 20.  相似文献   

18.
Monitored natural attenuation is widely applied as a remediation strategy at hydrocarbon spill sites. Natural attenuation relies on biodegradation of hydrocarbons coupled with reduction of electron acceptors, including solid phase ferric iron (Fe(III)). Because arsenic (As) adsorbs to Fe‐hydroxides, a potential secondary effect of natural attenuation of hydrocarbons coupled with Fe(III) reduction is a release of naturally occurring As to groundwater. At a crude‐oil‐contaminated aquifer near Bemidji, Minnesota, anaerobic biodegradation of hydrocarbons coupled to Fe(III) reduction has been well documented. We collected groundwater samples at the site annually from 2009 to 2013 to examine if As is released to groundwater and, if so, to document relationships between As and Fe inside and outside of the dissolved hydrocarbon plume. Arsenic concentrations in groundwater in the plume reached 230 µg/L, whereas groundwater outside the plume contained less than 5 µg/L As. Combined with previous data from the Bemidji site, our results suggest that (1) naturally occurring As is associated with Fe‐hydroxides present in the glacially derived aquifer sediments; (2) introduction of hydrocarbons results in reduction of Fe‐hydroxides, releasing As and Fe to groundwater; (3) at the leading edge of the plume, As and Fe are removed from groundwater and retained on sediments; and (4) downgradient from the plume, patterns of As and Fe in groundwater are similar to background. We develop a conceptual model of secondary As release due to natural attenuation of hydrocarbons that can be applied to other sites where an influx of biodegradable organic carbon promotes Fe(III) reduction.  相似文献   

19.
Stability of arsenopyrite and As(III) in low-temperature acidic solutions   总被引：1，自引：0，他引：1  
Arsenopyrite is one of the most important pri-mary arsenic mineral. In the Eh-pH diagram of the As-O2-S-H2O system, if the total arsenic concentration (TAs) is taken to be 0.75 mg/L, the total sulfur con-centration, 32 mg/L, the temperature, 25℃and the pressure, one atmosphere pressure for the discrimina-tion of arsenic species, it may be found that under hy-pergene conditions, arsenopyrite is a moderately stable mineral. Only in the strongly alkaline and reducing environment can arsenopy…  相似文献   

20.
The quantitative separation of As(III) from a water sample containing As(III) and As(V) in the presence of Fe and Mn in an ion exchange resin (AG1 X8) column for the speciation of arsenic is described. Individual and combined effects of Fe and Mn on the separation of As(III) from the solution have been studied separately. In absence of Fe and Mn, the ratio between the As(T) concentration in the eluent and the As(III) concentration in the original sample has been found to be 0.9717 under optimum process conditions. The presence of Fe(II) in the water sample increased the As(T) concentration in the eluent whereas Mn(II) decreased it. Combined effects of Fe and Mn on the percentage increment in the eluent arsenic concentration have been expressed by additive and interactive models. The interactive model has been developed by a statistical software with a 95 % confidence level. In most of the cases the error on the determination of the As(III) concentration had a minimum when using the interactive model.  相似文献   

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