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The combined use of electrokinetic remediation and phytoremediation to decontaminate metal-polluted soils: a laboratory-scale feasibility study.

The use of a combination of electrokinetic remediation and phytoremediation to decontaminate two metal-polluted soils has been demonstrated in laboratory-scale reactors. One soil was heavily contaminated with copper, the other with cadmium and arsenic (2500 microg g(-1) Cu; 300-400 microg g(-1) Cd and 230 microg g(-1) As, respectively). Test reactors with two separated chambers, each with a capacity of 5.25 kg soil, were constructed, then the respective chambers were filled with either a mixture of the polluted soil and a control topsoil (75:25) or topsoil alone. Reactors were sown with perennial ryegrass (Lolium perenne cv Elka) and a constant voltage of 30 V was applied continually across the soils in each reactor. Soil sampling took place at the start and the end of the test run, whilst plant foliage was sampled after approximately 3 weeks (both reactors) 6 weeks (Cd soil reactor only) and at the conclusion of each test run (98 days Cu soil, 80 days Cd soil). Soil and plant metal concentrations were measured, together with soil pH. Results showed that in both soils there was a significant re-distribution of metals from anode to cathode in the test reactors, coupled with an enhancement of plant Cu uptake in the cathode region for the Cu soil. Patterns of plant Cd uptake were less clear cut and were not as clearly related to the redistribution of Cd measured in the soil. There was significant acidification of soil at the anode in each test reactor, but soil pH in other parts of the reactor changed little during the course of the experiment. Plant growth was affected at the anode, but was not affected in other parts of the reactor. There was no visual evidence of metal toxicity in the ryegrass in either polluted soil. Some effects on soil fungi were apparent, with a stimulation of Fusarium infection of ryegrass in the cathode region of all reactors and the appearance of sporophores of Coprinus in the same location. It is concluded that the combination of the two techniques represents a very promising approach to the decontamination of metal polluted soils that now requires validation in field conditions.

Arsenic↗

Evaluation of genotoxicity of combined soil pollution by cadmium and imidacloprid.

Cadmium (Cd) is one of the important pollutants of soil and the genotoxicity of Cd-contaminated soil was studied in combination with imidacloprid. The single cell gel electrophoresis or comet assay was used to quantify DNA strand breaks as a measure of DNA damage induced by Cd and imidacloprid contamination in soil. The soil was artificially contaminated by Cd (0.0, 0.2, 0.5, 1.0, 2.0 mg x kg(-1) dry soil) or Cd (0.0, 0.2, 0.5, 1.0, 2.0 mg x kg(-1) dry soil) and imidacloprid (0.5 mg x kg(-1) dry soil). Roots of Vicia faba were exposed to the contaminated soil for 2 h at 25 degrees C and were used in the comet assay. DNA damage was measured as the values of percentage of nuclei with tails, tail length, tail DNA, tail moment (TM), and Olive tail moment (OTM). DNA damages of root tips of Vicia faba increased after Cd treatment and there were dose-related increases in DNA damage measured as these parameters. However, the addition of imidacloprid further increased the DNA damage. These data confirmed the genotoxic effect of Cd to plants, and that the combined pollution with imidacloprid can enhance the genotoxicity of Cd.

Cadmium↗

Assessment of antibiotic resistance genes in soils polluted by chemical and technogenic ways with poly-aromatic hydrocarbons and heavy metals.

Anthropogenic activities are leaving lots of chemical footprints on the soil. It alters the physiochemical characteristics of the soil thereby modifying the natural soil microbiome. The prevalence of antimicrobial-resistance microbes in polluted soil has gained attention due to its obvious public health risks. This study focused on assessing the prevalence and distribution of antibiotic-resistance genes in polluted soil ecosystems impacted by industrial enterprises in southern Russia. Metagenomic analysis was conducted on soil samples collected from polluted sites using various approaches, and the prevalence of antibiotic-resistance genes was investigated. The results revealed that efflux-encoding pump sequences were the most widely represented group of genes, while genes whose products replaced antibiotic targets were less represented. The level of soil contamination increased, and there was an increase in the total number of antibiotic-resistance genes in proteobacteria, but a decrease in actinobacteria. The study proposed an optimal mechanism for processing metagenomic data in polluted soil ecosystems, which involves mapping raw reads by the KMA method, followed by a detailed study of specific genes. The study's conclusions provide valuable insights into the prevalence and distribution of antibiotic-resistance genes in polluted soils and have been illustrated in heat maps.

Soil Pollutants↗

[Modeling of dynamics of microorganisms quantity in the soil polluted by heavy metals].

Microflora of soils polluted by heavy metals was the subject of monitoring investigations. Basing on the experimental data obtained with the use of interactive system ASTRID by the method of group accounting of arguments, mathematical models were constructed which describe the dynamics of microorganisms quantity, depending on the number of ecological factors and presence of heavy metals in the soil. The models allow one to predict the number of microorganisms in the soil under certain parameters of the environment, to determine "critical" deviations from the predicted values as well as to renew the intermediate data for obtaining uniform series of ecological researches. Prospects of the use of the inductive approach for modeling of microbiological processes in the soil have been demonstrated.

Environmental Monitoring↗

Distribution and location of polycyclic aromatic hydrocarbons (PAHs) and PAH-degrading bacteria within polluted soil aggregates.

A study was conducted to determine the location and distribution of PAH and PAH-degrading bacteria in different aggregate size fractions of an industrially polluted soil. The estimation of PAH-degrading bacteria using an MPN microplate technique indicated that these bacteria are most numerous in the aggregate size fractions corresponding to fine silt (2-20 microm) and clay (<2 microm) compared to larger fractions or unfractionated soil. PAH concentrations were also highest in the aggregate size fraction corresponding to fine silt. Similar results were found in a spiked soil (incubated for 6 months) with similar carbonated minerals. Transmission electron microscopy observations showed that the autochtonous PAH-degrading bacteria were embedded in the aggregates where PAHs were abundant. In spite of this extensive co-localisation PAH degradation was limited during 6 months incubation. This indicates that factors other than spatial distribution and PAH degrading ability control degradation rates. The fine silt fraction of the industrial soil had an elevated C/N ratio (35) compared to the clay fraction (C/N: 16). Thus the fraction which assumably had the highest specific surface area contained less PAH but similar numbers of PAH-degraders. N thus seem to play an important role in the long term, but as PAH degradation was low in fine size fractions, other sources/factors were probably limiting (easily degradable C, P org, O2 etc.). Based on these findings, soil particle organization and structure of soil aggregates appear to be important for the characterization of a polluted soil (localization and sequestration). Manipulations that modify aggregation in polluted soils could thus potentially influence the accessibility and biodegradability of PAHs.

Bacteria↗

[The ecologo-hygienic problem of soil pollution].

The article covers the ecologo-hygienic aspects of anthropogenic soil pollution, and important directions of research into its sanitary protection. The authors adduce data concerning the levels of actual soil pollution with chemicals and biological agents (microbiological and helminthological ones) in various centers of population, and discuss the variants of solving the ecologo-hygienic problems of soil protection in Russian Federation.

Environmental Illness↗

[Lead absorption by weeds from lead-polluted soil].

A pot experiment with red soil was installed in 2002 and 2003 to study the impact of lead pollution on weed growth, its lead and nutrients uptake, and AMF colonization. The results showed that lead pollution had no significant influence on weed growth, and the absorbed lead was mainly accumulated in root system. The impact of lead pollution on nutrients uptake by weeds was depended on weed species, their growth stages, and kinds of nutrients. No significant difference was found between lead treatment and control in nutrient contents except potassium in Digitaria adscendens at its early growth stages, and lead had little influence on the absorption of nutrients by Kummerowia striata, Ixeris chinensis, Digitaria adscendens and Echinochloa crusgalli var. mitis. The phosphorus content in Ixeris chinensis and Digitaria adscendens at their ripen stage sampled from lead-polluted soil was significantly higher than that from control, while the nitrogen content in matured Echinochloa crusgalli var. mitis sampled from polluted soil was significantly lower than that from the control. There existed great difference of mycorrhizal colonization among various weed species. The infection rate of Kummerowia striata and Digitaria adscendens showed a slight difference between lead treatment and control both at vegetative and ripen stage. Lead pollution hindered the colonization of Ixeris chinensis. In lead-polluted soil, the AMF infection rate of Ixeris chinensis was 45.52% at vegetative stage and 74.64% at ripen stage, while in the control, it was 69.44% at vegetative stage and 82.21% at ripen stage. Echinochloa crusgalli var. mitis, an annual weed, showed an opposite response of AMF colonization to lead pollution. The colonization rate of AMF in Echinochloa crusgalii var. mitis root was higher under lead pollution condition, being 82.45% at vegetative stage and 91.36% at ripen stage, while in the control, it was 59.19% and 78.28%, respectively.

Absorption↗

[Mathematical simulation of accumulation of opportunistic micromycetes in petroleum-polluted soils].

The impact of pollution of different types of soils (leached chernozem, grey wood and dark-grey wood soils) with petroleum and its products on the size, species-specific composition, and accumulation of opportunistic micromycetes was studied in long-term field microallotment and laboratory conditions. Petroleum and its refining products were shown to increase the size of micromycetes and to change their structure and species diversity. A mathematical model has been developed, which describes the time course of changes in the size of mushroom propagules under different environmental conditions.

Fungi↗

[The distribution and natural degradation of cyanide in goldmine waste-solid and polluted soil].

The farmland and river were seriously polluted by cyanide because one goldmine tailing dam collapsed in 1995. 3 and 4 years after the accident, the cyanide distribution in the polluted farmland and the abandoned tailing dam was studied. The results indicated that natural degradation of cyanide in soil section was slower than in natural water body. The cyanide transference in soil section was similar to freely soluble salts. In arid and semiarid area, cyanide can be highly enriched in the salt shell which content degrading 4 years even higher than the fresh tailing slurry. One side the viscidity layer in the soil section can partly prevent cyanide transference to groundwater, on the other side the result can cause the cyanide highly enrich in the viscidity layer. According to character of cyanide natural degradation in soil the measurement of prevention and cure soil pollution by goldmine tailing dam collapsing was brought forward.

Cyanides↗

Chelate-induced phytoextraction of metal polluted soils with Brachiaria decumbens.

Chelate-induced phytoextraction with high biomass plant species has been proposed for the clean-up of heavy metal polluted soils. In the current work, the effect of the application of two different chelating agents, i.e. EDTA and EDDS, on the metal phytoextraction capacity of Brachiaria decumbens was studied. Although EDTA was, in general, more effective in soil metal solubilization, EDDS, a chelate less harmful to the environment, was more efficient inducing metal accumulation in B. decumbens shoots than EDTA. Indeed, in a moderately heavy metal polluted soil, EDDS caused a 2.54, 2.74 and 4.30-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. In this same soil, EDTA caused a 1.77, 1.11 and 1.87-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. EDDS was also more effective than EDTA in stimulating the translocation of metals from roots to shoots. B. decumbens plants were able to grow in the metal polluted soils showing no visible symptoms of phytotoxicity, which suggests their metal tolerance. Finally, B. decumbens, a fast-growing, high biomass, aluminum tolerant plant species, that has a well-established agronomic system, fulfills most of the requirements for chemically-induced phytoextraction.

Biomass↗

Assessment of the bioavailability of PAHs in rats exposed to a polluted soil by natural routes: induction of EROD activity and DNA adducts and PAH burden in both liver and lung.

In order to assess bioavailability of polycyclic aromatic hydrocarbons (PAHs) present in soils, male laboratory rats were exposed to litters of control and polluted soils. After 88+/-2 h of exposure, several biomarkers were measured in both liver and lung. When rats were exposed to SIV soil, contaminated by a mixture of at least 13 PAHs, (1) only 2 or 3 PAH compounds were detected in liver and lung; (2) cytochrome P450-dependent monooxygenase activity, followed by 7-ethoxyresorufin O-deethylase (EROD) activity measurement, was highly induced in liver (13-fold-induction) and lung (up to 78-fold); and (3) DNA adducts were significantly increased. For what concerns soil artificially contaminated by only one PAH (phenanthrene or B[a]P), EROD activity was not or fully induced, respectively. These results demonstrate the occurrence of a high bioavailability of PAHs to mammals in natural conditions of exposure. First results concerning DNA adducts must be profound, but they already show that a short exposure of mammals to PAH-polluted soils can lead to potential genotoxic effects. EROD activity can be used as a sensitive biomarker in both liver and lung of rats maintained on litters of soils in the laboratory, and such a test can be used routinely to contribute to risk assessment.

Animals↗

Soil solution dynamics of Cu and Zn in a Cu- and Zn-polluted soil as influenced by gamma-irradiation and Cu-Zn interaction.

A pot experiment was conducted to study soil solution dynamics of Cu and Zn in a Cu/Zn-polluted soil as influenced by gamma-irradiation and Cu-Zn interaction. A slightly acid sandy loam was amended with Cu and Zn (as nitrates) either singly or in combination (100 mg Cu and 150 mg Zn kg(-1) soil) and was then gamma-irradiated (10 kGy). Unamended and unirradiated controls were included, and spring barley (Hordeum vulgare L. cv. Forrester) was grown for 50 days. Soil solution samples obtained using soil moisture samplers immediately before transplantation and every ten days thereafter were used directly for determination of Cu, Zn, pH and absorbance at 360 nm (A360). Cu and Zn concentrations in the solution of metal-polluted soil changed with time and were affected by gamma-irradiation and metal interaction. gamma-Irradiation raised soil solution Cu substantially but generally decreased soil solution Zn. These trends were consistent with increased dissolved organic matter (A360) and solution pH after gamma-irradiation. Combined addition of Cu and Zn usually gave higher soil solution concentrations of Cu or Zn compared with single addition of Cu or Zn in gamma-irradiated and non-irradiated soils, indicating an interaction between Cu and Zn. Cu would have been organically complexed and consequently maintained a relatively high concentration in the soil solution under higher pH conditions. Zn tends to occur mainly as free ion forms in the soil solution and is therefore sensitive to changes in pH. The extent to which gamma-irradiation and metal interaction affected solubility and bioavailability of Cu and Zn was a function of time during plant growth. Studies on soil solution metal dynamics provide very useful information for understanding metal mobility and bioavailability.

Copper↗

Effect of toluene as gaseous cosubstrate in bioremediation of hydrocarbon-polluted soil.

The stimulation of the microbial population by a more bioavailable supplementary carbon source and by a surfactant pretreatment was studied in petroleum hydrocarbon-polluted soils bioremediation. Two types of soils were used, Soil A which had been recently polluted and the aged Soil B. They contained 52.4 and 50.4 g of total petroleum hydrocarbons per kg of dry soil, respectively. The effect of passing a continuous small stream of air containing a low concentration of gaseous toluene through packed 0.5 l (Ø=5.5 cm) columns was studied. For Soil A, after 62 days the THPs degradation was 28% higher in the toluene treated columns than in controls. In aged Soil B the effect of toluene was not significant, probably due to bioavailability limitations. With Soil B, the combined effect of toluene as cosubstrate and a surfactant pretreatment was studied and the hydrocarbons degradation was 29% higher in the toluene-amended columns than in the controls. Toluene removal was higher than 99% in all cases. Surfactant addition increased hydrocarbon degradation when toluene was also added suggesting that the biological reaction was the limiting process. The study shows the possibilities of using gaseous substrates, such as toluene, for the in situ or ex situ treatment of petroleum hydrocarbon-polluted soil in processes limited by the biological reaction. The main advantage of the treatment is that the compound can be easily and directly delivered to the polluted soil through the venting system.

Biodegradation, Environmental↗

Soil pollution by oxidation of tailings from toxic spill of a pyrite mine.

On the 25th April 1998, toxic water and tailings from a pyrite mine of Aznalcóllar (southern Spain) spilled into the Agrio and Guadiamar River Basin affecting some 40 km2. In five sectors throughout the basin, we monitored the physical and chemical properties of the tailings as well as the degree of pollution in the soils on four different sampling dates: 5 May, 20 May, 4 June and 22 July 1998. The characteristics of the tailings deposited on the soils are shown to be related to distance from the spill. The oxidation rate of the tailings and the solubilization of the pollutant elements were more pronounced in the middle and lower sectors of the basin, where the particle size was finer, the sulfur content higher and the bulk density less. The increases in water-soluble sulfates, Zn. Cd and Cu were very rapid (the highest values being reached 25 days after the spill) and intense (reaching 45% of the total Cu, 65% of the total Zn and Cd). Meanwhile, the increases in water-soluble As, Bi, Sb, Pb and Tl were far lower (ranging between 0.002% of the total Tl and 2.5% of the total As) and less rapid in the case of As, Bi and Pb (the highest values for these elements being reached 40 days after the spill). These soluble elements infiltrated the soils with the rainwater, swiftly augmenting the soil pollution. Twenty-five days after the spill, when the rainfall ranged between 45 and 63 mm, the first 10-cm of the soils in the middle and lower sectors of the basin exceeded the maximum concentration permitted for agricultural soils in Zn, Cu and Tl. At 40 days after the spill, when the rainfall ranged between 60 and 89 mm, all the soils reached or exceeded the maximum permitted concentrations for As and Tl. Nevertheless, the pollutants tended to concentrate in the first 10 cm of the soils without seriously contaminating either the subsoil or the groundwaters. Consequently, a rapid removal of the tailings and the ploughing of the first 25-30 cm of the soils would be urgent measures to diminish pollutant concentration in the soils affected by the spill.

Environmental Monitoring↗

Chemometric analysis of soil pollution data using the Tucker N-way method.

N-way methods, particularly the Tucker method, are often the methods of choice when analyzing data sets arranged in three- (or higher) way arrays, which is the case for most environmental data sets. In the future, applying N-way methods will become an increasingly popular way to uncover hidden information in complex data sets. The reason for this is that classical two-way approaches such as principal component analysis are not as good at revealing the complex relationships present in data sets. This study describes in detail the application of a chemometric N-way approach, namely the Tucker method, in order to evaluate the level of pollution in soil from a contaminated site. The analyzed soil data set was five-way in nature. The samples were collected at different depths (way 1) from two locations (way 2) and the levels of thirteen metals (way 3) were analyzed using a four-step-sequential extraction procedure (way 4), allowing detailed information to be obtained about the bioavailability and activity of the different binding forms of the metals. Furthermore, the measurements were performed under two conditions (way 5), inert and non-inert. The preferred Tucker model of definite complexity showed that there was no significant difference in measurements analyzed under inert or non-inert conditions. It also allowed two depth horizons, characterized by different accumulation pathways, to be distinguished, and it allowed the relationships between chemical elements and their biological activities and mobilities in the soil to be described in detail.

Journal Article↗

Bioremediation of pulp and paper mill effluent by a novel fungal consortium isolated from polluted soil.

Two basidiomycetous fungi (Merulius aureus syn. Phlebia sp. and an unidentified genus) and a deuteromycetous fungus (Fusarium sambucinum Fuckel MTCC 3788) were isolated from soils affected with effluents of a pulp and paper mill over several years. These isolates were immobilized on nylon mesh and the consortium was used for bioremediation of pulp and paper mill effluent in a continuously aerated bench-top bioreactor. The treatment resulted in the reduction of color, lignin and COD of the effluent in the order of 78.6%, 79.0% and 89.4% in 4 days. A major part of reductions in these parameters occurred within first 24h of the treatment, which was also characterized by a steep decline in the pH of the effluent. During this period, total dissolved solids, electrical conductivity and salinity of the effluent also registered marked decline. It is pertinent to note that this is the first report of bioremediation of pulp and paper mill effluent by an immobilized fungal consortium.

Biodegradation, Environmental↗