To reveal the degradation capacity of bacteria in PAH polluted soil and rhizosphere we combined bacterial extradiol ring-cleavage dioxygenase and 16S rRNA analysis in Betula pubescens rhizoremediation. Characterisation of the functional bacterial community by RFLP revealed novel environmental dioxygenases, and their putative hosts were studied by 16S rRNA amplification. Plant rhizosphere and PAH amendment effects were detected by the RFLP/T-RFLP analysis. Functional species richness increased in the birch rhizosphere and PAH amendment impacted the compositional diversity of the dioxygenases and the structural 16S rRNA community. A shift from an Acidobacteria and Verrucomicrobia dominated to an Alpha- and Betaproteobacteria dominated community structure was detected in polluted soil. Clone sequence analysis indicated catabolic significance of Burkholderia in PAH polluted soil. These results advance our understanding of rhizoremediation and unveil the extent of uncharacterized functional bacteria to benefit bioremediation by facilitating the development of the molecular tool box to monitor bacterial populations in biodegradation.

Activated carbon (AC) can help overcome toxicity of pollutants to microbes and facilitate soil bioremediation. We used this approach to treat a Histosol and an Alluvial soil historically contaminated with PCB (4190 and 1585 mg kg−1, respectively; primarily tri-, tetra- and pentachlorinated congeners). Results confirmed PCB persistence; reductions in PCB extractable from control and AC-amended soils were mostly due to a decrease in tri- and to some extent tetrachlorinated congeners as well as formation of a bound fraction. Mechanisms of PCB binding by soil and AC were different. In addition to microbial degradation of less chlorinated congeners, we postulate AC catalyzed dechlorination of higher chlorinated congeners. A large decrease in bioavailable PCB in AC-amended soils was demonstrated by greater clover germination and biomass. Phytotoxicity was low in treated soils but remained high in untreated soils for the duration of a 39-month experiment. These observations indicate the utility of AC for remediation of soils historically contaminated with PCB. Activated carbon promotes remediation of soils historically contaminated with PCB.

Landfill leachates usually need to be treated before discharged, and using soil–plant systems for this has gained substantial interest in Sweden and in the UK. A three-year field study was conducted in central Sweden to quantify plant response, treatment efficiency and impact on groundwater quality of landfill leachate irrigation of short-rotation willow coppice (Salix). Two willow varieties were tested and four irrigation regimes in sixteen 400-m2 plots. The willow plants did not react negatively, despite very high annual loads of nitrogen (≤2160 kg N/ha), chloride (≤8600 kg Cl/ha) and other elements. Mean annual growth was 1.5, 9.8 and 12.6 tonnes DM/ha during years 1–3. For one of two willow varieties tested, relative leaf length accurately predicted growth rate. Irrigation resulted in elevated groundwater concentrations of all elements applied. Treatment efficiency varied considerably for different elements, but was adequate when moderate loads were applied. Short-rotation willow coppice was successfully used for treating a strong landfill leachate in central Sweden over three years.

The impact of residual PAHs (2250 ± 71 μg total PAHs g−1) following enhanced natural attenuation (ENA) of creosote-contaminated soil (7767 ± 1286 μg total PAHs g−1) was assessed using a variety of ecological assays. Microtox™ results for aqueous soil extracts indicated that there was no significant difference in EC50 values for uncontaminated, pre- and post-remediated soil. However, in studies conducted with Eisenia fetida, PAH bioaccumulation was reduced by up to 6.5-fold as a result of ENA. Similarly, Beta vulgaris L. biomass yields were increased 2.1-fold following ENA of creosote-contaminated soil. While earthworm and plant assays indicated that PAH bioavailability was reduced following ENA, the residual PAH fraction still exerted toxicological impacts on both receptors. Results from this study highlight that residual PAHs following ENA (presumably non-bioavailable to bioremediation) may still be bioavailable to important receptor organisms such as earthworms and plants. Residual PAHs in creosote-contaminated soil following enhanced natural attenuation impacted negatively on ecological receptors.

An eco-restoration system to remove excess nutrients and restore the agricultural ecosystem balance was proposed and applied from August 2006 to August 2008 in a residential-cropland complex area (1.4 × 105 m2) in Kunming, western China, where the self-purifying capacity of the agricultural ecosystem had been lost. The proposed eco-restoration system examined includes three main foci: farming management, bioremediation, and wastewater treatment. The results showed that the removal efficiencies of total phosphorus (TP) and total nitrogen (TN) from the complex wastewater were 83% and 88%, respectively. The Simpson’s diversity indices of macrophytes and zoobenthos indicated that the system had increased macrophyte and zoobenthic diversity as well as improved growth conditions of the plankton habitats. The results demonstrated that the proposed eco-restoration system is a promising approach for decreasing the output of nutrients from soil, improving agricultural ecosystem health, and minimizing the downstream eutrophication risk for surface waters.

We studied nutrient removal by Phragmites australis in the Albujón rambla, the main drainage system that discharges into the Mar Menor, a Mediterranean coastal lagoon of high conservation interest, but highly threatened by point and nonpoint pollution derived from tourism and agricultural activities. We measured aerial biomass and N and P concentrations in both aboveground and belowground tissues of common reed during an annual cycle that included two cutting events and two periods of reed growth (one at the end of summer after cutting and another at the beginning of spring, following their natural cycle). The temporal variation of N and P concentrations was related to the phenology of the plant and cutting events. The maximum nutrient concentrations were recorded in young stems in the initial stages of the autumn growing season (35.86 mg N g⁻¹ and 2.38 mg P g⁻¹). The phosphorus dynamics showed evidence of translocation processes related with growth activity, although no evidence of N translocation was found. In November and in summer, when aerial growth ceases because of the hard conditions, the P concentration in rhizomes was higher than in stems, while in spring and in September, the period of maximal growth, the reverse relation was found. The highest total amounts of the two elements in the aboveground biomass (0.54 Tm N ha⁻¹ and 0.25 Tm P ha⁻¹) were reached in July, coinciding with the highest biomass (3.72 kg DW m⁻²), which then decreased to approximately half in August. Nutrient content in the aboveground tissues was highly dependent on the ammonium and nitrate water concentrations. In addition, the N content was inversely related to the Corg/N of sediments, while the P content was influenced positively by the phosphorous concentration of the water. Common reed of the Albujón rambla corresponds to the assimilation type, adapted to nutrient-rich habitats, which is characterized by a pronounced external N cycle and P internal reserves. Based on the results obtained, we propose a management plan for common reed to help control eutrophication of the Mar Menor lagoon. This would bring forward reed cutting to the beginning of summer, instead of August, coinciding with the time of maximum aerial biomass, greater nutrient retention, and lower risk of strong precipitation.

The purpose of this study was to understand the dynamic conditions of soil/organic mixtures in order to contribute to the study of remediation processes at hydrocarbon spill sites. Induced polarization (IP) and physical, chemical, and microbiological parameters for uncontaminated and artificially contaminated soil samples with diesel oil were evaluated under controlled conditions (constant temperature and soil moisture) during a period of 12 months. In contaminated samples, the resistivity and IP parameters (chargeability and polarizability) decreased during 8 months and remained relatively stable between 8 and 12 months. The observed reduction on resistivity and IP parameters was related to the increase on the granular aggregation of the soil and a decrease on total porosity, caused by diesel-degrading microorganisms. The behavior of the IP parameters observed after 8 months can be explained by a reduction in the microbial activity and, consequently, a decrease of the degradation rate of diesel. In the studied loamy soil with high content of organic matter (96.16 g/kg), the results demonstrate that IP time domain measurements can be used in the evaluation of the evolution of the hydrocarbon degradation even when the concentration is not very high.

The influence of inoculum preparation and cell density on the efficiency of Cr(VI) removal was assessed with two chromate-resistant yeasts, Pichia jadinii M9 and Pichia anomala M10, isolated from textile wastewaters. Batch cultures in yeast nitrogen base (YNB)′ liquid medium (YNB without amino acids and ammonium sulfate plus sucrose and ammonium sulfate) containing 1-mM initial Cr(VI) concentrations revealed that heavy metal removal in both isolates was substantially affected by the inoculation procedure. Inocula with high initial density or pregrown in a nutritionally rich medium (Malt Czapek) were found to be key factors in order to achieve successful Cr(VI) decontamination. In contrast, low-density inocula and/or synthetic media-precultured cells were shown to negatively influence Cr(VI) disappearance, either by increasing the time for complete degradation or by reducing the percentage of heavy metal removed. These results emphasized the relevance of the selection of an appropriate inoculum culture medium and the positive influence of increasing one order of magnitude inoculum cell density in order to achieve successful and rapid Cr(VI) removal. Under these considerations, the selected yeasts, P. jadinii M9 and P. anomala M10, exhibited a remarkable ability to tolerate and completely remove Cr(VI) concentrations up to 1 mM, thus being candidates for potential applications in bioremediation of Cr(VI)-contaminated environments.

The release of heavy metals in aquatic systems due to the discharge of industrial wastewaters is a matter of environmental concern. Heat-inactivated cells of a flocculent strain of Saccharomyces cerevisiae were used in the bioremediation, in a batch mode, of a real electroplating effluent containing Cu, Ni, and Cr. In this approach, no previous reduction of Cr(VI) to Cr(III) was required. Cr(VI) was selectively removed (98%) by yeast biomass at pH 2.3. At this pH, Cr(VI) is mainly in the form of HCrO ₄ ⁻ and yeast surface is surrounded by H⁺ ions, which enhance the Cr(VI) interaction with biomass binding sites by electrostatic forces. Subsequently, pH of the effluent was raised up to 6.0; this pH maximizes the efficiency of cations removal since at this pH the main binding groups of yeast cells are totally or partially deprotonated. The passage of effluent through a series of sequential batches, at pH 6.0, allowed, after the third batch, the removal of Cu(II), Ni (II), Cr total, and Cr(VI) in the effluent to values below the legal limit of discharge. The strategy proposed in the present work can be used in plants for the treatment of heavy metals rich industrial effluents containing simultaneously Cr(VI) and Cr(III).

Investigations were made on living strains of fungi in a bioremediation process of three metal (lead) contaminated soils. Three saprotrophic fungi (Aspergillus niger, Penicillium bilaiae, and a Penicillium sp.) were exposed to poor and rich nutrient conditions (no carbon availability or 0.11 M d-glucose, respectively) and metal stress (25 µM lead or contaminated soils) for 5 days. Exudation of low molecular weight organic acids was investigated as a response to the metal and nutrient conditions. Main organic acids identified were oxalic acid (A. niger) and citric acid (P. bilaiae). Exudation rates of oxalate decreased in response to lead exposure, while exudation rates of citrate were less affected. Total production under poor nutrient conditions was low, except for A. niger, for which no significant difference was found between the poor and rich control. Maximum exudation rates were 20 µmol oxalic acid g⁻¹ biomass h⁻¹ (A. niger) and 20 µmol citric acid g⁻¹ biomass h⁻¹ (P. bilaiae), in the presence of the contaminated soil, but only 5 µmol organic acids g⁻¹ biomass h⁻¹, in total, for the Penicillium sp. There was a significant mobilization of metals from the soils in the carbon rich treatments and maximum release of Pb was 12% from the soils after 5 days. This was not sufficient to bring down the remaining concentration to the target level 300 mg kg⁻¹ from initial levels of 3,800, 1,600, and 370 mg kg⁻¹in the three soils. Target levels for Ni, Zn, and Cu, were 120, 500, and 200 mg kg⁻¹, respectively, and were prior to the bioremediation already below these concentrations (except for Cu Soil 1). However, maximum release of Ni, Zn, and Cu was 28%, 35%, and 90%, respectively. The release of metals was related to the production of chelating acids, but also to the pH-decrease. This illustrates the potential to use fungi exudates in bioremediation of contaminated soil. Nonetheless, the extent of the generation of organic acids is depending on several processes and mechanisms that need to be further investigated.