Electrokinetic-enhanced remediation of actual arsenic-contaminated soils with approaching cathode and Fe0 permeable reactive barrier

Purpose

The aim of this study was to investigate the remediation efficiency of actual arsenic-contaminated soils by electrokinetic (EK)-enhanced remediation with approaching cathode and Fe⁰ permeable reactive barrier (PRB).

Materials and methods

Experiments were conducted in a lab-made apparatus consisting of the anode reservoir, the soil specimen chamber, and the cathode reservoir.

Results and discussion

In this study, the enhanced combination methods (approaching cathode and Fe⁰-PRB) were assisted for EK remediation of actual arsenic-contaminated soils under a voltage gradient of 1 V/cm and a treatment period of 96 h. Experimental results showed that arsenic accumulated in the anode sections (I, II) of the soil by employing EK alone with an arsenic removal rate of less than 5%. In contrast, EK-enhanced remediation with either approaching cathode (EK/AC) or Fe⁰-PRB (EK/PRB) reduced the arsenic concentrations in both central and anode sections of the soil and afforded the removal rates of 20% in both cases. However, EK-enhanced remediation with the combination of approaching cathode and Fe⁰-PRB (EK/PRB/AC) reached the removal efficiency of 45% without arsenic accumulation in any soil sections. This phenomenon is mainly caused by the approaching cathode that creates an alkaline environment to promote the migration of arsenic, as well as PRB filled with Fe⁰ that achieves the adsorption and immobilization of arsenic.

Conclusions

The highest remediation efficiency was achieved in the EK/PRB/AC test, which was attributed to the fact that the combination of this two methods solved the problem of arsenic accumulation in treated soil and ensured a more thorough arsenic removal. Furthermore, enhanced remediation efficiency does not elevate the costs.

     

Microbial Diversity and Bioactive Substances in Disease Suppressive Composts from India

The present study aimed to investigate microbial communities in seven Indian composts and their potential for biocontrol of Fusarium oxysporum f. sp. lycopersici. In addition, identification of bioactive substances in disease suppressive composts was also attempted. Composts were chosen based on disease suppressiveness and subjected to molecular microbial analyses. Total genomic DNA from the composts was extracted and amplified with polymerase chain reaction using primers targeting the 18S rRNA and 16S rRNA genes of fungi and bacteria, respectively. Denaturing gradient gel electrophoresis (DGGE) fingerprinting and DNA sequencing were used to identify the fungal and bacterial targets. Phylogenetic analysis of the fungal 18S rRNA ITS gene sequences showed that phylum Ascomycota was dominant in all composts, while in the bacterial 16S rRNA gene sequences, the phylum Proteobacteria was dominant. Some fungi in disease suppressive composts grouped phylogenetically close to F. oxysporum. Bacterial sequences with close similarity (>95% identity) with Actinobacterium showed a strong presence only in disease suppressive composts. Disease suppressive composts formed a separate group in the cluster analysis of 18S rRNA ITS and 16S rRNA gene sequences. Gas chromatography-time of flight-mass spectrometry was performed with compost extracts to determine if bioactive substances were present in disease suppressive composts. The analysis of compost organic matter showed a negative association of disease suppressiveness with phloroglucinol, sitosterol, and monoenoic fatty acid, while cholesterol and certain organic acids were positively associated with suppressiveness.     

Effect of <Emphasis Type="Italic">Silene vulgaris</Emphasis> and Heavy Metal Pollution on Soil Microbial Diversity in Long-Term Contaminated Soil

In this study, we analysed the impact of heavy metals and plant rhizodeposition on the structure of indigenous microbial communities in rhizosphere and bulk soil that had been exposed to heavy metals for more than 150 years. Samples of the rhizosphere of Silene vulgaris and non-rhizosphere soils 250 and 450 m from the source of emission that had different metal concentrations were collected for analyses. The results showed that soils were collected 250 m from the smelter had a higher number of Cd-resistant CFU compared with the samples that were collected from 450 m, but no significant differences were observed in the number of total and oligotrophic CFU or the equivalent cell numbers between rhizosphere and non-rhizosphere soils that were taken 250 and 450 m from the emitter. Unweighted pair group method with arithmetic mean (UPGMA) cluster analysis of the denaturing gradient gel electrophoresis (DGGE) profiles, as well as a cluster analysis that was generated on the phospholipid fatty acid (PLFA) profiles, showed that the bacterial community structure of rhizosphere soils depended more on the plant than on the distance and metal concentrations. The sequencing of the 16S rDNA fragments that were excised from the DGGE gel revealed representatives of the phyla Bacteroidetes, Acidobacteria, Gemmatimonadetes, Actinobacteria and Betaproteobacteria in the analysed soil with a predominance of the first three groups. The obtained results demonstrated that the presence of S. vulgaris did not affect the number of CFUs, except for those of Cd-resistant bacteria. However, the presence of S. vulgaris altered the soil bacterial community structure, regardless of the sampling site, which supported the thesis that plants have a higher impact on soil microbial community than metal contamination.     

Fate of the herbicides glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron in two Finnish arable soils

The fate of five herbicides (glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron) was studied in two Finnish sugar beet fields for 26 months. Soil types were sandy loam and clay. Two different herbicide-tolerant sugar beet cultivars and three different herbicide application schedules were used. Meteorological data were collected throughout the study and soil properties were thoroughly analysed. An extensive data set of herbicide residue concentrations in soil was collected. Five different soil depths were sampled. The study was carried out using common Finnish agricultural practices and represents typical sugar beet cultivation conditions in Finland. The overall observed order of persistence was ethofumesate > glyphosate > phenmedipham > metamitron > glufosinate-ammonium. Only ethofumesate and glyphosate persisted until the subsequent spring. Seasonal variation in herbicide dissipation was very high and dissipation ceased almost completely during winter. During the 2 year experiment no indication of potential groundwater pollution risk was obtained, but herbicides may cause surface water pollution.     

Previous exposure advances the degradation of an anthropogenic s-triazine regardless of soil origin

Purpose

Previous investigations—field samplings and laboratory experiments—support the hypothesis that the degradation of s-triazines is enhanced in previously exposed as compared to pristine soils in terrestrial environments. Despite this, bottlenecks of soil sampling and various soil modification practices in microcosm studies have made it difficult to guarantee that previous contamination history enhances contaminant degradation regardless of soil origin in terrestrial ecosystems. We test the hypothesis that the degradation of simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) is enhanced in previously exposed soils as compared to pristine soils in 10 l buckets at the mesocosm scale.

Materials and methods

We collected soil at three separate sites consisting of a previously exposed and a pristine field. At every field, soil was collected at three separate plots and simazine degradation (days 0 and 65) and the response to atzB degrader gene primers (days 0 and 110) were followed. We analyzed the results using analysis of covariance (ANCOVA). Previous exposure and field site were assessed as fixed factors and initial simazine concentration and abiotic soil conditions as covariates.

Results and discussion

After the 65-day exposure, remaining simazine concentrations depended on previous exposure but not on collection site. The response to atzB gene primers was positive in all mesocosms where simazine degradation had been rapid. Soil moisture, pH, and organic matter content were insignificant. If soil moisture was not included in the ANCOVA model, previous exposure did not appear as a significant factor.

Conclusions

The results support the hypothesis that simazine is degraded more rapidly in previously exposed soils as compared to pristine environments, provided that degradation genes are available. Previously exposed soil might be used to enhance the degradation of simazine in recently contaminated terrestrial soils, supposing that the central requirements for microbial growth are adequate.     

Plant invasiveness and target plant density: high densities of native Schima wallichii seedlings reduce negative effects of invasive Ageratina adenophora

Economically feasible strategies to cope with invasive species are urgently needed. Plant density can be increased to reduce competitive effects on target plants. This study indicates that increasing native plant density can be used to reduce the effect of invasive Ageratina adenophora. Seedlings of an indigenous tree species, Schima wallichii, were grown in pots containing uninvaded or invaded soil, with or without A. adenophora leaf litter on the soil surface. Schima wallichii seedlings were also grown at four densities under four levels of A. adenophora leaf litter. Root and shoot biomass and length were measured as response parameters in both bioassays. Schima wallichii growth was inhibited by A. adenophora leaf litter and invaded soil. High litter levels reduced S. wallichii root length and dry weight at low plant densities. The inhibition disappeared at high S. wallichii plant densities. As A. adenophora did not inhibit S. wallichii growth at high plant densities, adjustments of seedling density should be studied as a possible management strategy for invasion by A. adenophora and potentially by other exotic plant species. As density‐dependent growth inhibition is the key characteristic of chemical interference, we propose that phytotoxins contribute to A. adenophora invasion particularly at low densities of native seedlings.     

Soil vapor extraction of wet gasoline-contaminated soil made possible by electroosmotic dewatering–lab simulations applied at a field site

Purpose

Soil restoration is still mainly carried out ex situ by excavating and replacing the contaminated soil. In situ remediation would reduce the costs of soil transportation and this way, the problem is not merely transferred elsewhere. The present study introduces a field case where the aged, oil-contaminated soil in a former fuel station in Finland was treated in situ sequentially with different methods.

Materials and methods

Several approaches, including soil vapor extraction and biostimulation with electrokinetic pumping, were performed in the field. After these treatments, the dense original portion of the soil beneath the gasoline pump location, ca 100 m³, was still contaminated with petroleum-derived volatile organic compounds (VOCs), with concentrations of nearly 10,000 mg kg^?1 measured at some hotspots. After a period of electroosmotic water circulation, the electrical field (0.5 V cm^?1, DC) was kept connected for 6 months without addition of water, leading to dewatering and warming of the soil.

Results and discussion

In contrast to the situation with the original wet soil, VOCs, in lab conditions, were found to volatilize very efficiently from the dewatered soil. When the soil vapor extraction treatment was renewed using perforated tubing installed horizontally at ca 1 m depth in the dewatered soil at the contaminated site, the treatment was efficient and the soil was decontaminated in 5 months. The final VOC concentrations were on average 190 mg kg^?1 (n = 13) with the highest value of 700 mg kg^?1 at one hotspot. After a risk evaluation, the site was concluded to be sufficiently clean for industrial use.

Conclusions

Since with many former fuel stations, the contamination consists of both volatile fractions that are difficult to degrade by biological means and heavier compounds for which biostimulation is often suitable, a combination of different methods may be worth pursuing.

     

Chlorinated and methylated dibenzothiophenes in sediment samples from a river contaminated by organochlorine wastes

Eleven sediment samples from the lower Kymijoki River were analyzed for the occurrence of polychlorinated and polymethylated dibenzothiophenes (PCDT and PMeDTs). The area was heavily polluted by wastes from a pulp chlorobleachery and by leakage from a factory producing wood preservative chlorophenol formulation Ky-5. Levels in the sediments were from <5 to 400, 200 and 50 pg g^-1 dw for tetra, penta and hexa-CDT, respectively. The concentrations of mono, di, tri and tetra-MeDTs were in the range of 1–5, 5–85, 5–500 and 15–2300 ng g^-1 dw, respectively. PCDT contents in surface sediment (0–3 cm layers) decreased by distance downstream from the bleachery and Ky-5 factory similar to those of the bound polychloroguaiacols (PCG) and polychlorinated dibenzofurans (PCDF). In contrast, PMeDT contents showed a steep increase by distance with a maximum at 32 km downstream.     

Bioaccumulation of POPs from contaminated sediment to lamprey<Emphasis Type="Italic">(lampetra fluviatilis l.</Emphasis>) larva

Background  Adult sea lampreys, a delicate food species catch from Baltic Sea rivers, migrate from sea and spawn to sediments of still river water areas. Their larva live there four years before return to sea. The few published studies of toxicity of the sediment contaminants to the lamprey larva, however, do not include chlorinated persistent organic pollutants (POPs), thus far. Kymijoki River in southeast Finland is known for high polychlorinated POP contamination which has been measured to accumulate in several bottom fauna and fish species. Goal of the Study  To obtain the first screening results of the bioaccumulation power of POPs from sediment to lamprey larva during their life stage in the contaminated sediment. The accumulated dioxin-type of toxic load (TEQ) was also studied as a possible human hazard. Methods  Surface sediment and lamprey larva were sampled from four localities of the lower Kymijoki River and analysed for MeO-PBDEs, PBDEs, PCBs, PCDDs, PCDEs, PCDFs, and PCDTs by solvent extraction, column clean up and GC/MS procedures. The larva were sorted to seven composites according to locality and (for one place) size of the specimens (to classes of small, medium and large individuals). From the analysis results, TEQ values for composites and the bioaccumulation factors from dry sediment to fresh larva (BSAF), from dry sediment to larva lipid (BSAFlw) and from sediment organic carbon to larva lipid (BSAFoc) were calculated. Results and Discussion  TEQ load was highest (about 500 pg g^-1 ww) in large larva composite due to high bioaccumulation of PCB 118, 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (D66) and toxic penta- to octa-CDFs. A high positive significant correlation was found between weight and length of larva. Instead, lipid content had no significant correlations with weight and length of larva. Larva lipid or sediment organic carbon did not correlate significantly with any of the calculated BSAF, BSAFlw and BSAFoc values. Therefore, statistical comparisons between substance properties and bioaccumulation rate were possible for BSAF alone. These comparisons indicated a slightly significant increase of PCBs, but very significant decrease of PCDF bioaccumulation from sediment to larva by increase of the number of chlorine atoms (NCI) in the molecule. This property of highly chlorinated PCDFs indicates, as found earlier for local fish, a kinetic control of bioaccumulation by slow release from sediment back to water and the food chain. Recommendation and Outlook  The results obtained point out that bioaccumulation of POPs in lamprey larva is a possible source of toxic hazard to human food consumption and to development of lamprey species. Therefore, both larva and adult lampreys should be studied further for significance of their POP contamination compared with other experiences on impact of POPs to human and wildlife.