Thus far, members of the genus Dehalococcoides are the only microorganisms known to dehalogenate chlorinated ethenes to ethene and thereby detoxify these common groundwater pollutants. Therefore, it is important to characterize the taxonomic and functional diversity of these key microorganisms and their reductive dehalogenase (RDase) genes in contaminated aquifers for assessing the natural attenuation potential. Little is known about the diversity of RDase genes under field conditions or in laboratory systems under selective pressure during dechlorination activities. Here, we evaluate the diversity of Dehalococcoides sp. and three RDase genes in groundwater as well as in water from a constructed wetland and microcosms setup with contaminated groundwater from the same field site in Bitterfeld (Saxony-Anhalt, Germany). The presence and relative abundance of Pinellas and Cornell subgroups of Dehalococcoides was evaluated by a novel direct sequencing method, which revealed that all sequences were identical and affiliated to the Pinellas subgroup. Contrarily, our results showed remarkable differences at the functional gene level between the systems. Of the vinyl chloride reductase genes, vcrA was detected in samples from the groundwater, wetland, and microcosms, whereas bvcA was only found in wetland and microcosm samples. The trichloroethene dehalogenase gene, tceA could not be detected at all, although complete dehalogenation activity of higher chlorinated ethenes was observed. Our study demonstrates that although the Dehalococcoides 16S rRNA gene sequences retrieved from the investigated systems were identical, the RDase gene diversity varied among the systems, according to the spectrum of the chlorinated ethenes present.

Land use in east China tends to change from paddy rice to vegetables or other high-value cash crops, resulting in high input rates of organic manures and increased risk of contamination with both heavy metals (HMs) and antibiotics. This investigation was conducted to determine the accumulation, distribution and risks of HMs and tetracyclines (TCs) in surface soils and profiles receiving different amounts of farmyard manure. Soil samples collected from suburbs of Hangzhou city, Zhejiang province were introduced to represent three types of land use change from paddy rice to asparagus production, vineyards and field mustard cultivation, and divided into two portions, one of which was air-dried and sieved through 2-, 0.3- and 0.149-mm nylon mesh for determination of pH and heavy metals. The other portion was frozen at -20 °C, freeze-dried and sieved through a 0.3-mm nylon mesh for tetracyline determination. HM and TC concentrations in surface soils of 14-year-old mustard fields were the highest with total Cu, Zn, Cd and ∑TCs of 50.5, 196, 1.03 mg kg(-1) and 22.9 μg kg(-1), respectively, on average. The total Cu sequence was field mustard > vineyards > asparagus when duration of land use change was considered; oxytetracycline (OTC) and doxycycline were dominant in soils used for asparagus production; OTC was dominant in vineyards and chlortetracycline (CTC) was dominant in mustard soils. There were positive pollution relationships among Cu, Zn and ∑TCs, especially between Cu and Zn or Cu and ∑TCs. Repeated and excessive application of manures from intensive farming systems may produce combined contamination with HMs and TCs which were found in the top 20 cm of the arable soil profiles and also extended to 20-40 cm depth. Increasing manure application rate and cultivation time led to continuing increases in residue concentrations and movement down the soil profile.

The electrochemical degradation of the Reactive Red 141 azo dye was done using a one-compartment filter-press flow cell with a boron-doped diamond anode. The response surface methodology (with a central composite design) was used to investigate the effect of current density (10–50 mA cm⁻²), pH (3–11), NaCl concentration ([NaCl]) (0–2.34 g L–¹), and temperature (15–55 °C) on the system’s performance. The charge required for 90 % decolorization (Q ⁹⁰), the fraction of chemical oxygen demand removal after 6 min of electrolysis (COD⁶), and the fraction of total organic carbon removal after 90 min of electrolysis (TOC⁹⁰) were used to model the obtained results. The lowest values of Q ⁹⁰ were attained at pH <4 in the presence of higher values of [NaCl] (>1.5 g L⁻¹), due to the electrogeneration of active chlorine, present mainly as HClO. The value of COD⁶ was not affected by the solution pH, but increased with [NaCl] up to 1.5 g L⁻¹. Higher temperatures (>40 °C) led to a decrease in COD⁶, as a consequence of side reactions. Higher values of TOC⁹⁰, which can be reached only with strong oxidants (such as ·OH and Cl·), were efficiently attained at low [NaCl] values (<0.7 g L⁻¹) in acidic solutions that inhibit the formation of ClO₃ ⁻ and ClO₄ ⁻. Finally, the obtained results allow inferring that most probably the mineralization of the dye starts with an attack on the chromophore group, followed by the degradation of intermediate species.

To assess strategies for mitigating Pb and As transfer into leafy vegetables from contaminated garden soils, we conducted greenhouse experiments using two field-contaminated soils amended with materials expected to reduce metal phytoavailability. Lettuce and mustard greens grown on these soils were analyzed by ICP-MS, showing that some Pb and As transfer into the vegetables occurred from both soils tested, but plant Pb concentrations were highly variable among treatment replicates. Soil-to-plant transfer was more efficient for As than for Pb. Contamination of the leaves by soil particles probably accounted for most of the vegetable Pb, since plant Pb concentrations were correlated to plant tissue concentrations of the immobile soil elements Al and Fe. This correlation was not observed for vegetable As concentrations, evidence that most of the soil-to-plant transfer for this toxic metal occurred by root uptake and translocation into the above-ground tissues. A follow-up greenhouse experiment with lettuce on one of the two contaminated soils revealed a lower and less variable foliar Pb concentration than observed in the first experiment, with evidence of less soil particle contamination of the crop. This reduced transfer of Pb to the crop appeared to be a physical effect attributable to the greater biomass causing reduced overall exposure of the above-ground tissues to the soil surface. Attempts to reduce soil Pb and As solubility and plant uptake by amendment at practical rates with stabilizing materials, including composts, peat, Ca phosphate, gypsum, and Fe oxide, were generally unsuccessful. Only Fe oxide reduced soluble As in the soil, but this effect did not persist. Phosphate amendment rapidly increased soil As solubility but had no measurable effect on either soil Pb solubility or concentrations of Pb or As in the leafy vegetables. The ineffectiveness of these amendments in reducing Pb transfer into leafy vegetables is attributed in this study to the low initial Pb solubility of the studied soils and the fact that the primary mechanism of Pb transfer is physical contamination.

Soil vapor extraction (SVE) is one of the most effective remediation technologies for soil and groundwater contamination. Soil particles can be mobilized by air perturbation during SVE, resulting in the differentiation of porous media, which has not been well addressed. This paper developed a numerical method to study the flow pattern and quantify the change of porous media for the first time. Based on the mass equilibrium and Darcy’s law, a two-phase water–air flow model was constructed with integration of saturation, relative permeability, and capillary pressure during SVE. Relationship between porosity and saturation was deduced and coupled with the two-phase flow model for quantifying change of porous media in real time. Results reveal that both porosity and permeability increase sharply in the early stage of SVE then gradually to a quasi-steady state. These increases in vadose zone tapered off with distance from the SVE screen and the steady period occurred later as well. The influence radius of a single SVE well and the change degree in porosity and permeability of media were proportional to the extraction vacuum and the driving coefficient C, which is more sensitive than extraction vacuum according to the simulation results. Knowledge from this modeling exercise provides a useful tool to estimate the change of remediated zone and assess the environmental risk of remedial activities at real-world contamination sites.

Synthetic hydroxyapatite (HA) and natural phosphate rock (PR) were applied to heavy metal-contaminated soils from sulfide mine areas in Sardinia and Tuscany (Italy). The application of phosphate amendments to the polluted mine waste soils reduced water-soluble concentrations of Co and Ni by about 99 %. In general, phosphate treatment was slightly more effective in reducing water solubility of Co and Ni in the Sardinian soils than in the Tuscan ones. This result suggests that the mineralogical composition of the mine waste soils may impact the effectiveness of metal immobilization. The formation of complexes of the heavy metals on the surface of phosphate grains and partial dissolution of the amendments and precipitation of heavy metal-containing phosphates are the dominant immobilization mechanisms. Between the phosphate amendments, PR was slightly less effective than HA in immobilizing Co and Ni. This result could be attributed to PR inability to provide soluble phosphate. Although with lower effectiveness, the use of PR to immobilize heavy metals from contaminated soils may reduce the risk of phosphate-induced eutrophication due to the application of amendments with highly soluble phosphate.

Reduction of bulk organic matter, nitrogen, and pharmaceutically active compounds from primary effluent during managed aquifer recharge was investigated using laboratory-scale batch reactors. Biologically stable batch reactors were spiked with different concentrations of sodium azide to inhibit biological activity and probe the effect of microbial activity on attenuation of various pollutants of concern. The experimental results obtained revealed that removal of dissolved organic carbon correlated with active microbial biomass. Furthermore, addition of 2 mM of sodium azide affected nitrite-oxidizing bacteria leading to accumulation of nitrite-nitrogen in the reactors while an ammonium-nitrogen reduction of 95.5 % was achieved. Removal efficiencies of the hydrophilic neutral compounds phenacetin, paracetamol, and caffeine were independent of the extent of the active microbial biomass and were >90 % in all reactors, whereas removal of pentoxifylline was dependent on the biological stability of the reactor. However, hydrophobic ionic compounds exhibited removal efficiency >80 % in batch reactors with the highest biological activity as evidenced by high concentration of adenosine triphosphate. © 2013 Springer Science+Business Media Dordrecht.

The aim of this work was to investigate the susceptibility of the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to biodegradation in a range of soils and to identify RDX-degrading organisms using stable isotope probing (SIP). RDX degradation was examined in ten soils, primarily from agricultural areas. RDX biodegradation was observed in six samples and only when the microcosms were not aerated. For one soil, 15N-and 13C-based DNA SIP was used to identify the microorganisms responsible for RDX degradation. Two RDX concentrations were examined (10 and 20 mg/L), however, only the higher concentration resulted in a significant SIP signal. In these ultracentrifugation fractions, one terminal restriction fragment length polymorphism (TRFLP) fragment (260 bp) showed a reliable trend of label uptake. This fragment was of higher relative abundance in the heavier fractions from labeled samples compared with the heavier fractions from the unlabeled control samples, indicating that the organism producing this fragment was responsible for label uptake (hence RDX degradation). Partial 16S rRNA gene sequencing indicated the organisms represented by fragment 260 bp belonged to either Sphingobacteria (phylum Bacteroidetes) or the phylum Acidobacteria. To date, these organisms have not previously been directly linked to RDX degradation. The 16S rRNA sequences were compared with the NCBI database and, in all cases, were most similar to uncultured bacteria. The results suggest SIP is a viable method for discovering novel, previously uncultured, RDX degraders. © Springer Science+Business Media Dordrecht 2013.

Biodegradation of chlorpyrifos was studied in mineral medium and soil with a novel fungal strain JAS1 isolated from a paddy field soil. The molecular characterization based on 18S rRNA sequence homology confirmed its identity as Aspergillus terreus. The 300-mg L⁻¹ chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were completely degraded within 24 h of incubation in the mineral medium. In soil enriched with chlorpyrifos and nutrients (carbon, nitrogen, and phosphorous), A. terreus JAS1 was able to degrade chlorpyrifos and its metabolite TCP (300 mg kg⁻¹ soil) in 24 and 48 h, respectively. The soil was spiked with chlorpyrifos (300 mg kg⁻¹ soil) devoid of nutrients and the fungal strain was capable of degrading both chlorpyrifos and TCP in 24 and 48 h, respectively. The course of the degradation process was studied using high-performance liquid chromatography and Fourier transform infrared analyses. These results showed that the chlorpyrifos-degrading fungal strain had the potential to degrade the pesticide-contaminated agricultural soils even without addition of nutrients.

The use of peracetic acid (PAA) in the disinfection of sanitary effluents has been proposed by various authors. However, there are still doubts about its influence on the physical-chemical characteristics of the effluent after application. In the present study, it was observed that the composition of PAA leads to an increase in organic material, resulting in an increase of approximately 20 mg/L in the chemical oxygen demand of the effluent for every 10 mg/L of PAA applied. According to the kinetic tests, the degradation of PAA in the effluent was represented by a first-order reaction and its half-life in the effluent was estimated at 79 min. The formation of by-products resulting from degradation of PAA in the effluent was evaluated by considering by-products already detected by other authors in disinfection trials, these being nonanal, decanal, chlorophenols, and 1-methoxy-4-methylbenzene, which were not observed in the effluent being studied after application of PAA at a dosage of 10 mg/L. © 2013 Springer Science+Business Media Dordrecht.