DC Electric Fields Promote Biodegradation of Waterborne Naphthalene in Biofilter Systems.

Biofiltration is a simple and low-cost method for the cleanup of contaminated water. However, the reduced availability of dissolved chemicals to surface-attached degrader bacteria may limit its efficient use at certain hydraulic loadings. When a direct current (DC) electric field is applied to an immersed packed bed, it invokes electrokinetic processes, such as electroosmotic water flow (EOF).

Taxis-enhanced mineralization and co-metabolism of PAHs by bacteria in micrometer-scale environments.

Polycyclic aromatic hydrocarbons (PAHs) are associated with micropores in sediments and soils. This limits the bioaccessibility of these compounds via existing bioremediation technologies, as biodegradation is strongly influenced by the ability of bacteria to access different sizes of pores. In this work, we employed naphthalene and pyrene as model contaminants to evaluate the transformation capacity of the soil bacterium Pseudomonas putida G7 (2 × 1 μm) via mineralization and co-metabolic activity, respectively.

Taxis-mediated bacterial transport and its implication for the cometabolism of pyrene in a model aquifer.

One of the main problems in contaminated soils is that many toxic substances, such as PAHs, which are found in areas close to aquifers and groundwater, are difficult to access and degrade via traditional methods of remediation. The use of controlled bacterial mobility through chemotaxis has been shown to be efficient in increasing the dispersion of pollutant-degrading organisms, increasing the biodegradation rates of pollutants. In this study, using percolation columns as model aquifers, the mobilization of the Pseudomonas putida G7 strain to a distant pyrene source was demonstrated using γ-aminobutyric acid and artificial root exudates as strong chemoeffectors.

Integrating bioavailability measurements in persistence testing of partially biodegradable organic chemicals in soil.

Overestimation of risk is one of the main problems in environmental risk assessments if only total concentration of organic pollutants is considered. In this study, we integrated bioavailability measurements into persistence testing of pollutants in soil to show that it is the key to have a more realistic environmental risk assessment (ERA). To this integration, two standardized methods were used: OECD 307, as persistence test, and ISO 16751: 2020, to bioavailability measurements based on 20 h extractions with a strong adsorbent (Tenax), using pyrene and carbamazepine as model test substances.

Risk reductions during pyrene biotransformation and mobilization in a model plant-bacteria-biochar system.

The productive application of motile microorganisms for degrading hydrophobic contaminants in soil is one of the most promising processes in modern remediation due to its sustainability and low cost. However, the incomplete biodegradation of the contaminants and the formation of the intermediary metabolites in the process may increase the toxicity in soil during bioremediation, and motile inoculants may mobilize the pollutants through biosorption. Therefore, controlling these factors should be a fundamental part of soil remediation approaches.

Chemotactic Bacteria Facilitate the Dispersion of Nonmotile Bacteria through Micrometer-Sized Pores in Engineered Porous Media.

Recent research has demonstrated that chemotactic bacteria can disperse inside microsized pores while traveling toward favorable conditions. Microbe-microbe cotransport might enable nonmotile bacteria to be carried with motile partners to enhance their dispersion and reduce their deposition in porous systems. The aim of this study was to demonstrate the enhancement in the dispersion of nonmotile bacteria ( VM552, a polycyclic aromatic hydrocarbon-degrader, and sp.

Use of natural sorbents for accelerated bioremediation of grey forest soil contaminated with crude oil.

Due to the extensive oil extraction and transportation that occurs in oil-producing countries, many lands remain contaminated because of accidental leakages. Despite its low cost and environmentally safe nature, bioremediation technology is not always successful, mainly because of the soil toxicity to the degrading microbial populations and plants. Here we report a three-year microfield experiment on the influence of natural sorbents of mineral (zeolite, kaolinite, vermiculite, diatomite), organic (peat), carbonaceous (biochar) origin, and a mixed sorbent ACD (composed of granular activated carbon and diatomite) on the bioremediation of grey forest soil contaminated with weathered crude oil (40.

Nature-based approaches to reducing the environmental risk of organic contaminants resulting from military activities.

As is the case with many other industrial activities, the organic contaminants at military-impacted sites may pose significant hazards to the environment and human health. Given the expected increase in defense investments globally, there is a need to make society aware of the risks of emissions of organic contaminants generated by military activities and to advance risk minimization approaches. The most recent advances in environmental analytical chemistry, persistence, bioavailability and risk assessment of organic contaminants indicate that efficient risk reductions through biological means are possible.

Role of tactic response on the mobilization of motile bacteria through micrometer-sized pores.

A major cause of high bioremediation endpoints is the limited bioaccessibility to residual contaminants resting in soil pores with diameters close to the size exclusion limit of bacterial cells. Under nongrowing conditions and in the absence of hydraulic flow, we examined how the tactic behavior of motile, contaminant-degrading Pseudomonas putida G7 cells (2 × 1 μm) influenced passage through membranes with pores ranging in size from 1 μm to 12 μm. The bacteria were spontaneously retained by the membranes - even those with the largest pore size.

Scientific concepts and methods for moving persistence assessments into the 21st century.

The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes.

Determining the bioavailability of benzo(a)pyrene through standardized desorption extraction in a certified reference contaminated soil.

There is a strong need for certified reference materials in the quality assurance of nonionic soil contaminant bioavailability estimations through physicochemical methods. We applied desorption extraction, a method recently standardized as ISO16751, to determine the bioavailable concentration of the most commonly regulated polycyclic aromatic hydrocarbon (PAH), benzo(a)pyrene (BaP), in the reference industrial soil BCR-524 with a certified BaP total concentration of 8.60 mg kg.

Microbial degradation of pyrene in holm oak (Quercus ilex) phyllosphere: Role of particulate matter in regulating bioaccessibility.

In this study we first measured the mineralization of pyrene on leaves of urban holm oak (Quercus ilex) by autochthonous microorganisms and an inoculated PAH degrading bacterium (i.e., Mycobacterium gilvum), selected as a model phyllosphere species, as well as the leaf-water (K) and leaf-air (K) partition coefficients for this chemical.

Root-mediated bacterial accessibility and cometabolism of pyrene in soil.

Partial transformation of pollutants and mobilization of the produced metabolites may contribute significantly to the risks resulting from biological treatment of soils polluted by hydrophobic chemicals such as polycyclic aromatic hydrocarbons (PAHs). Pyrene, a four-ringed PAH, was selected here as a model pollutant to study the effects of sunflower plants on the bacterial accessibility and cometabolism of this pollutant when located at a spatially distant source within soil. We compared the transformation of passively dosed C-labeled pyrene in soil slurries and planted pots that were inoculated with the bacterium Pseudomonas putida G7.

Role of photo- and biodegradation of two PAHs on leaves: Modelling the impact on air quality ecosystem services provided by urban trees.

Urban trees provide important ecosystem services, including air quality improvement. Polycyclic aromatic hydrocarbons (PAHs) are among the most important pollutants in air, due to their elevated concentrations and toxicity. Plants can act as filters of PAHs and as "chemical reactors" for pollutant removal, therefore reducing air concentrations.

Rhizosphere-enhanced biosurfactant action on slowly desorbing PAHs in contaminated soil.

We studied how sunflower plants affect rhamnolipid biosurfactant mobilization of slowly desorbing fractions of polycyclic aromatic hydrocarbons (PAHs) in soil from a creosote-contaminated site. Desorption kinetics of 13 individual PAHs revealed that the soil contained initially up to 50% slowly desorbing fractions. A rhamnolipid biosurfactant was applied to the soil at the completion of the sunflower cycle (75 days in greenhouse conditions).

Impact of bacterial motility on biosorption and cometabolism of pyrene in a porous medium.

The risks of pollution by polycyclic aromatic hydrocarbons (PAHs) may increase in bioremediated soils as a result of the formation of toxic byproducts and the mobilization of pollutants associated to suspended colloids. In this study, we used the motile and chemotactic bacterium Pseudomonas putida G7 as an experimental model for examining the potential role of bacterial motility in the cometabolism and biosorption of pyrene in a porous medium. For this purpose, we conducted batch and column transport experiments with C-labelled pyrene loaded on silicone O-rings, which acted as a passive dosing system.

Adsorptive bioremediation of soil highly contaminated with crude oil.

Due to the extended oil extraction and transportation in Russia and other oil-producing countries, many lands remain contaminated because of accidental spills. This situation requires the cost-effective and efficient remediation of petroleum-contaminated soils. Bioremediation of soils contaminated with high concentrations of crude oil is usually hampered by high toxicity thresholds for microbial degraders.

Rhamnolipid-enhanced solubilization and biodegradation of PAHs in soils after conventional bioremediation.

The application of a rhamnolipid biosurfactant for enhanced solubilization and biodegradation of slowly desorbing polycyclic aromatic hydrocarbons (PAHs) in contaminated soils was determined in this study. The soil samples exhibited different levels of pollution and different bioremediation stages: the first soil originated from a creosote-polluted site, contained 4370 mg kg of PAHs and had not been bioremediated; the second soil was the same as the first but had received bioremediation treatment with nutrient amendment in biopiles for a period of 5 months and contained 580 mg kg of PAHs after this treatment; the third soil was treated by bioremediation for several years to reduce the concentration of PAHs to 275 mg kg . The kinetics of PAH desorption were determined to assess the magnitude of the slowly desorbing fractions present in the polluted soil and to optimize the biosurfactant effectiveness in terms of biodegradation.

Impact of Chemoeffectors on Bacterial Motility, Transport, and Contaminant Degradation in Sand-Filled Percolation Columns.

Chemoeffector-mediated bacterial motility and tactic swimming are major drivers for contaminant accessibility and biodegradation at submillimeter scales. In sand-filled percolated columns we tested how and to what degree chemoeffectors influenced bacterial transport and thereby promoted accessibility and degradation of distantly located C-naphthalene (NAH) at the centimeter scale. Sunflower root exudates and silver nanoparticles (AgNPs) were used as chemoeffectors to stimulate opposing effects of motility and tactic swimming of NAH-degrading Pseudomonas putida G7.

Mycelium-Enhanced Bacterial Degradation of Organic Pollutants under Bioavailability Restrictions.

This work examines the role of mycelia in enhancing the degradation by attached bacteria of organic pollutants that have poor bioavailability. Two oomycetes, Pythium oligandrum and Pythium aphanidermatum, were selected as producers of mycelial networks, while Mycobacterium gilvum VM552 served as a model polycyclic aromatic hydrocarbon (PAH) degrading bacterium. The experiments consisted of bacterial cultures exposed to a nondisturbed nonaqueous phase liquid (NAPL) layer containing a heavy fuel spiked with C-labeled phenanthrene that were incubated in the presence or absence of the mycelia of the oomycetes in both shaking and static conditions.

Mobilization of Pollutant-Degrading Bacteria by Eukaryotic Zoospores.

The controlled mobilization of pollutant-degrading bacteria has been identified as a promising strategy for improving bioremediation performance. We tested the hypothesis whether the mobilization of bacterial degraders may be achieved by the action of eukaryotic zoospores. We evaluated zoospores that are produced by the soil oomycete Pythium aphanidermatum as a biological vector, and, respectively, the polycyclic aromatic hydrocarbon (PAH)-degrading bacteria Mycobacterium gilvum VM552 and Pseudomonas putida G7, acting as representative nonflagellated and flagellated species.

Swimming performance of Bradyrhizobium diazoefficiens is an emergent property of its two flagellar systems.

Many bacterial species use flagella for self-propulsion in aqueous media. In the soil, which is a complex and structured environment, water is found in microscopic channels where viscosity and water potential depend on the composition of the soil solution and the degree of soil water saturation. Therefore, the motility of soil bacteria might have special requirements.

Tactic response of bacteria to zero-valent iron nanoparticles.

The microbial assessment of pollutant toxicity rarely includes behavioral responses. In this study, we investigated the tactic response of Pseudomonas putida G7, a representative of soil bacterium, towards engineered zero-valent iron nanoparticles (nZVIs), as a new end-point assessment of toxicity. The study integrated the characterization of size distribution and charge of nZVIs and tactic reaction response by means of inverted capillary assay and computer-assisted motion analysis of motility behavior.

From Bioavailability Science to Regulation of Organic Chemicals.

The bioavailability of organic chemicals in soil and sediment is an important area of scientific investigation for environmental scientists, although this area of study remains only partially recognized by regulators and industries working in the environmental sector. Regulators have recently started to consider bioavailability within retrospective risk assessment frameworks for organic chemicals; by doing so, realistic decision-making with regard to polluted environments can be achieved, rather than relying on the traditional approach of using total-extractable concentrations. However, implementation remains difficult because scientific developments on bioavailability are not always translated into ready-to-use approaches for regulators.