Novel approaches for remediation of pesticide pollutants

The use of synthetic pesticides has become an indispensable tool in agriculture for the control of pests. Therefore, the search for remedies and techniques for decontamination and detoxification of a pesticide-contaminated environment has become an important part of the research. Currently, bioremediation seems to be one of the most environmentally safe and cost-effective methods. In nature, the existence of abundant material resources can be used to degrade the environmental pesticide pollutants. At present, a number of microorganisms, capable of degrading pesticides, have been isolated and characterised. For insects, insecticide resistance-associated esterases have been purified and characterised from several insect species, and a new family of cytochrome P450 apparently associated with insecticide resistance in the tobacco budworm, was discovered. Generally, two bioremediation approaches have been used one directly based on microorganisms, and the other involved in isolated enzymes. For the former, in addition to using natural microorganism strains, with genetic techniques certain desirable biodegradation pathways from different organisms are brought together in a single host. However, because of their own limits, especially problems associated with releasing genetically altered microorganisms into the environment, the strategy based on enzymes seems more feasible. In the long term, collaborations between microbiologists, biochemists, and engineers will become increasingly important to efficiently dispose of the pesticide pollutants.     

Enhanced degradation of fluorene in soil slurry by Absidia cylindrospora and maltosyl-cyclodextrin

This study investigates the fungal biodegradation of fluorene, a polycyclic aromatic hydrocarbon, in liquid medium and soil slurry. Fungal strains and cyclodextrins were used in order to degrade fluorene and optimize fluorene bioavailability and degradation in soil slurries. After a procedure of selection in solid and liquid media, maltosyl-cyclodextrin, a branched cyclodextrin was chosen. 47 fungal strains isolated from a contaminated site were tested for biodegradation. Results showed the greater efficiency of "adapted" fungi isolated from contaminated soil vs reference strains belonging to the collection of the laboratory. These assays allowed us to select the most efficient strain, Absidia cylindrospora, which was used in a bioaugmentation process. Bioaugmentation tests were performed in an artificially contaminated non-sterile soil. In the presence of A. cylindrospora, more than 90% of the fluorene was degraded within 288 h, while 576 h were necessary in the absence of fungal bioremediation. It also appeared that biodegradation was enhanced by amendment with previously selected maltosyl-cyclodextrin. The results of this study indicate that A. cylindrospora and maltosyl-cyclodextrin could be used successfully in fluorene bioremediation systems.     

Advances and perspective in bioremediation of polychlorinated biphenyl-contaminated soils

In recent years, microbial degradation and bioremediation approaches of polychlorinated biphenyls (PCBs) have been studied extensively considering their toxicity, carcinogenicity and persistency potential in the environment. In this direction, different catabolic enzymes have been identified and reported for biodegradation of different PCB congeners along with optimization of biological processes. A genome analysis of PCB-degrading bacteria has led in an improved understanding of their metabolic potential and adaptation to stressful conditions. However, many stones in this area are left unturned. For example, the role and diversity of uncultivable microbes in PCB degradation are still not fully understood. Improved knowledge and understanding on this front will open up new avenues for improved bioremediation technologies which will bring economic, environmental and societal benefits. This article highlights on recent advances in bioremediation of PCBs in soil. It is demonstrated that bioremediation is the most effective and innovative technology which includes biostimulation, bioaugmentation, phytoremediation and rhizoremediation and acts as a model solution for pollution abatement. More recently, transgenic plants and genetically modified microorganisms have proved to be revolutionary in the bioremediation of PCBs. Additionally, other important aspects such as pretreatment using chemical/physical agents for enhanced biodegradation are also addressed. Efforts have been made to identify challenges, research gaps and necessary approaches which in future, can be harnessed for successful use of bioremediation under field conditions. Emphases have been given on the quality/efficiency of bioremediation technology and its related cost which determines its ultimate acceptability.     

Chlorophenols and other related derivatives of environmental concern: properties, distribution and microbial degradation processes

Chlorophenols are chlorinated aromatic compound structures and are commonly found in pesticide preparations as well as industrial wastes. They are recalcitrant to biodegradation and consequently persistent in the environment. A variety of chlorophenols derivatives compounds are highly toxic, mutagenic and carcinogenic for living organisms. Biological transformation by microorganisms is one of the key remediation options that can be exploited to solve environmental pollution problems caused by these notorious compounds. The key enzymes in the microbial degradation of chlorophenols are the oxygenases and dioxygenases. These enzymes can be engineered for enhanced degradation of highly chlorinated aromatic compounds through directed evolution methods. This review underscores the mechanisms of chlorophenols biodegradation with the view to understanding how bioremediation processes can be optimized for cleaning up chloroaromatic contaminated environments.     

Phytoremediation to increase the degradation of PCBs and PCDD/Fs

Phytoremediation is already regarded as an efficient technique to remove or degrade various pollutants in soils, water and sediments. However, hydrophobic organic molecules such as PAHs, PCBs and PCDD/Fs are much less responsive to bioremediation strategies than, for example, BTEX or LAS. PCDD/Fs and PCBs represent 3 prominent groups of persistent organic pollutants that share common chemical, toxicological and environmental properties. Their widespread presence in the environment may be explained by their chemical and biological stability. This review considers their fate and dissipation mechanisms. It is then possible to identify major sinks and to understand biological activities useful for remediation. Public health and economic priorities lead to the conclusion that alternative techniques to physical treatments are required. This review focuses on particular problems encountered in biodegradation and bioavailability of PCDD/Fs and PCBs. It highlights the potential and limitations of plants and micro-organisms as bioremediation agents and summarises how plants can be used to augment bacterial activity. Phytoremediation is shown to provide some new possibilities in reducing risks associated with dioxins and PCBs.     

Bioavailability assessment and environmental fate of polycyclic aromatic hydrocarbons in biostimulated creosote-contaminated soil

When hydrocarbon-contaminated soil is subjected to bioremediation technology, hydrocarbon depletion is typically marked by an initially rapid reduction rate. This rate decreases over time and frequently a residual concentration remains in the soil. This kinetic has been attributed primarily to the enrichment of more recalcitrant fractions, as well as to the lack of resting hydrocarbon bioavailability. Thus, at the end of the bioremediation process, a part of the residual hydrocarbon soil concentration represents the non-bioavailable fraction, which is difficult to degrade by microbial populations and which poses a minor hazard. Therefore, determination of the bioavailable fraction in a bioremediation project represents both an estimation of the maximum level of achievable biodegradation, as well as an additional indication of the environmental health hazard. In the present study, aged creosote-contaminated soil was subjected to biostimulation processes, and the bioavailable fraction for several target polycyclic aromatic hydrocarbons (PAHs) was calculated using a mild extraction with cyclodextrines. The amount of PAH extracted corresponded to the desorbing fraction and can be regarded as the bioavailable fraction. The non-desorbing fraction data obtained from this procedure were compared to the remaining PAH concentrations following bioremediation treatment of soil microcosms. These results permitted the establishment of a theoretical biodegradation limit based on the desorbing fraction. In addition, neither accumulation of intermediate metabolites, nor the formation of bound-residues or reduced acute toxicity was observed.     

Dispersal networks for enhancing bacterial degradation in heterogeneous environments

Successful biodegradation of organic soil pollutants depends on their bioavailability to catabolically active microorganisms. In particular, environmental heterogeneities often limit bacterial access to pollutants. Experimental and modelling studies revealed that fungal networks can facilitate bacterial dispersal and may thereby improve pollutant bioavailability. Here, we investigate the influence of such bacterial dispersal networks on biodegradation performance under spatially heterogeneous abiotic conditions using a process-based simulation model. To match typical situations in polluted soils, two types of abiotic conditions are studied: heterogeneous bacterial dispersal conditions and heterogeneous initial resource distributions. The model predicts that networks facilitating bacterial dispersal can enhance biodegradation performance for a wide range of these conditions. Additionally, the time horizon over which this performance is assessed and the network’s spatial configuration are key factors determining the degree of biodegradation improvement. Our results support the idea of stimulating the establishment of fungal mycelia for enhanced bioremediation of polluted soils.     

Molecular perspectives and recent advances in microbial remediation of persistent organic pollutants

Nutrition and pollution stress stimulate genetic adaptation in microorganisms and assist in evolution of diverse metabolic pathways for their survival on several complex organic compounds. Persistent organic pollutants (POPs) are highly lipophilic in nature and cause adverse effects to the environment and human health by biomagnification through the food chain. Diverse microorganisms, harboring numerous plasmids and catabolic genes, acclimatize to these environmentally unfavorable conditions by gene duplication, mutational drift, hypermutation, and recombination. Genetic aspects of some major POP catabolic genes such as biphenyl dioxygenase (bph), DDT 2,3-dioxygenase, and angular dioxygenase assist in degradation of biphenyl, organochlorine pesticides, and dioxins/furans, respectively. Microbial metagenome constitutes the largest genetic reservoir with miscellaneous enzymatic activities implicated in degradation. To tap the metabolic potential of microorganisms, recent techniques like sequence and function-based screening and substrate-induced gene expression are proficient in tracing out novel catabolic genes from the entire metagenome for utilization in enhanced biodegradation. The major endeavor of today’s scientific world is to characterize the exact genetic mechanisms of microbes for bioremediation of these toxic compounds by excavating into the uncultured plethora. This review entails the effect of POPs on the environment and involvement of microbial catabolic genes for their removal with the advanced techniques of bioremediation.     

Review of Separation Technologies for Treating Pesticide-Contaminated Soil

ABSTRACT

Pesticide contamination results from manufacturing, improper storage, handling, or disposal of pesticides, and from agricultural processes. Since most pesticides are mixtures of different compounds, selecting a remedy for pesticide-contaminated soils can be a complicated process. The various available treatment options for remediation fall into three broad categories: containment-immobilization, separation-concentration, and destruction. This paper categorizes pesticides into waste groups based on available treatment options and provides a review of separation treatment options that have been demonstrated to—or show potential to— treat pesticide-contaminated soil. Technologies include radio frequency heating, soil washing, thermal desorp-tion, and solvent extraction.     

Removal of sulfadimethoxine in soil mediated by extracellular oxidoreductases

Sulfadimethoxine (SDM) is an antibiotic commonly used in concentrated animal feeding operations and released into the environment via manure application on agricultural lands. Transformation of antibiotics in soil impacts the likelihood of their entry to water bodies, uptake by plants, and thus their effect on terrestrial and aquatic organisms. We conducted experiments to incubate SDM in a sandy loam soil in the presence of humification enzymes commonly found in natural soil, laccase, horseradish peroxidase, and lignin peroxidase. Incubation with the enzymes led to significant reduction in the fraction of SDM extractable from soil, indicating the formation of bound residues. Such transformation was enhanced when the organic matter content in soil is increased or when certain chemical mediators were used along with laccase. The study provided a basis for understanding the environmental fate of sulfonamides and help with the development of remediation methods to mitigate the release of sulfonamides from soil to water.     

Atrazine biodegradation modulated by clays and clay/humic acid complexes

The fate of pesticides in the environment is strongly related to the soil sorption processes that control not only their transfer but also their bioavailability. Cationic (Ca-bentonite) and anionic (Layered Double Hydroxide) clays behave towards the ionisable pesticide atrazine (AT) sorption with opposite tendencies: a noticeable sorption capacity for the first whereas the highly hydrophilic LDH showed no interactions with AT. These clays were modified with different humic acid (HA) contents. HA sorbed on the clay surface and increased AT interactions. The sorption effect on AT biodegradation and on its metabolite formation was studied with Pseudomonas sp. ADP. The biodegradation rate was greatly modulated by the material's sorption capacity and was clearly limited by the desorption rate. More surprisingly, it increased dramatically with LDH. Adsorption of bacterial cells on clay particles facilitates the degradation of non-sorbed chemical, and should be considered for predicting pesticide fate in the environment.     

Microbial transformation of synthetic estrogen 17α-ethinylestradiol

Natural estrogens such as estrone, 17β-estradiol, estriol, and the particularly recalcitrant synthetic estrogen 17α-ethinylestradiol used as oral contraceptive, accumulate in the environment and may give rise to health problems. The processes participating in their removal from soil, wastewater, water-sediments, groundwater-aquifer material, and wastewater or sewage treatment plant effluents may involve the action of bacterial and microbial consortia, and in some cases fungi and algae. This review discusses the different efficiencies of bacterial degradation of 17α-ethinylestradiol under aerobic and anaerobic conditions, the role of sulfate-, nitrate-, and iron-reducing conditions in anaerobic degradation, and the role of sorption. The participation of autotrophic ammonia oxidizing bacteria and heterotrophic bacteria in cometabolic degradation of estrogens, the estrogen-degrading action of ligninolytic fungi and their extracellular enzymes (lignin peroxidase, manganese-dependent peroxidase, versatile peroxidase, laccase), and of algae are discussed in detail.     

污染物的原位生物处理—生物清消技术

生物清消技术是一种迅速发展的污染物处理的生物技术,用于处理分散在土壤、地下水、海洋和湖泊中的污染物。生物清消技术通过向环境供给营养物、共作基质和供氧,并依靠有机污染物自身的碳源促进天然微生物群体的生长繁殖,也可进一步向污染环境中补充在实验中筛选和增殖的微生物(强化技术)稳定和加速生物降解过程。本文介绍了生物清消的几种方法:生物促进法、生物耕作法、固相清消法、土壤堆制法、生物泥浆法,还介绍了强化技术应用的几个方面。     

In-situ surfactant/surfactant-nutrient mix-enhanced bioremediation of NAPL (fuel)-contaminated sandy soil aquifers

SCOPE AND BACKGROUND: Contamination of soils, aquifers and groundwater by nonaqueous phase liquid (NAPL) pollutants constitutes a major environmental issue of concern, worldwide. The residual (biodegradation-resistant) hydrophobic fuel hydrocarbons entrapped in the soil porous matrix, possess a particular bioremediation challenge due to their becoming virtually immobile, nor desorbable, or water dispersible. Consequently, they are not available as substrates to the micro-organism-based biodegradation. MATERIALS AND METHODS: Our research involves the development of economically feasible, surfactant/surfactant-nutrient mix (SSNM)-enhanced bioremediation methodologies for sustainable, in situ bioremediation of fuel-contaminated aquifers. This requires, methodologically, (a) the optimization, via in vitro 'flow' (columns) lab experiments and screening processes, of an effective mixture for the intended SSNM-enhanced bioremediation; and (b) the study of the combined effect of the optimized SSNM on the solubilization/mobilization and biodegradation of NAPL (fuel) in in vitro site/aquifer-simulated bioremediation. RESULTS AND DISCUSSION: The essence of our findings: (1) kerosene's maximum enhanced mobilization - f = 3.6, compared with that of deionized water, was achieved with an SSNM having the composition of linear alkylbenzene sulfonate (LABS): coco-amphodiacetate (containing N): surfactant-nutrient X (containing both N and P) = 0.15: 0.15: 0.05 g/L, respectively; (2) 62-64% of the initial amount of kerosene in the initially saturated soil matrix, 'packed' in a column, has been eluted from it during approximately 30 days, compared with 68% of kerosene biodegradation in 'vessel' settings, in 21 days. CONCLUSIONS: (1) The indigenous microorganisms present in th vadose zones of fuel-contaminated sandy soil aquifers are potentially capable of unassisted removal of approximately 80% of the initially contained fuel (kerosene), during a period of about 42 days; (2) the major effects of the SSNM addition are (a) enhanced mobilization of the bulky NAPL; and (b) enhanced desorbtion/ solubilization/dispersion of the entrapped NAPL which, in turn, facilitate their enhanced biodegradation. RECOMMENDATIONS AND PERSPECTIVE: Our findings suggest that pre-optimized, biodegradable SSNM is essential for surfactants-based bioremediation of NAPL-contaminated aquifers, in order to make this in-situ methodology both technologically and economically feasible.     

多环芳烃污染土壤生物修复的强化方法

生物降解是去除环境中多环芳烃(PAHs)的重要途径,通过采取一些强化措施,如使用表面活性剂,添加营养物质和提供共代谢底物等,可显著提高PAHs降解速度和程度,为生物修复技术的成功应用提供前提。在分析中,对近年来国内外在PAHs污染土壤生物修复强化方面的研究进展进行了综述。     

Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes

Diffusion, sorption and biodegradation are key processes impacting the efficiency of natural attenuation. While each process has been studied individually, limited information exists on the kinetic coupling of these processes. In this paper, a model is presented that couples nonlinear and nonequilibrium sorption (intraparticle diffusion) with biodegradation kinetics. Initially, these processes are studied independently (i.e., intraparticle diffusion, nonlinear sorption and biodegradation), with appropriate parameters determined from these independent studies. Then, the coupled processes are studied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a second data set. The validated model is then used to conduct a sensitivity analysis, which reveals conditions where biodegradation becomes desorption rate-limited. If the chemical is not pre-equilibrated with the soil prior to the onset of biodegradation, then fast sorption will reduce aqueous concentrations and thus biodegradation rates. Another sensitivity analysis demonstrates the importance of including nonlinear sorption in a coupled diffusion/sorption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions evaluated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption should be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To our knowledge this study is unique in studying nonlinear sorption coupled with intraparticle diffusion and biodegradation kinetics with natural media.     

In situ bioelectrokinetic remediation of phenol-contaminated soil by use of an electrode matrix and a rotational operation mode

In situ bioremediation is a safe and cost-effective technology for the cleanup of contaminated sites, but its remediation rate is usually very slow. This study attempted to accelerate the process of bioremediation by employing non-uniform electrokinetic transport processes to mix organic pollutants and degrading bacteria in soils under in situ conditions (namely, in situ bioelectrokinetic remediation) by use of an electrode matrix and a rotational operation mode. A bench-scale non-uniform electrokinetic system with periodic polarity-reversal was developed for this purpose, and tested by using a sandy loam spiked with phenol as a model organic pollutant. The results demonstrated that non-uniform electrokinetic processes could enhance the in situ biodegradation of phenol in the soil, the efficiency of which depended upon the operational mode of the electric field. Compared with the unidirectional operation and the bidirectional operation, the rotational operation could effectively stimulate the biodegradation of phenol in the soil if adopting appropriate time intervals of polarity-reversal and electrode matrixes. A reversal interval of 3.0 h and a square-shaped electrode matrix with four electrode couples appeared appropriate for the in situ biodegradation of phenol, at which a maximum phenol removal of 58% was achieved in 10d and the bioremediation rate was increased about five times as compared to that with no electric field applied. The results also showed that adopting a small polarity-reversal interval and an appropriate electrode array could produce a high and uniform removal of phenol from the soil. It is believed that in situ bioelectrokinetic remediation holds the potential for field application.     

Biodegradation capability of Absidia fusca Linnemann towards environmental pollutants

The purpose of this work was to study the bioremediation capability of Absidia fusca Linnemann (Zygomycete) towards different classes of xenobiotics (lignin-derived compounds, chloroaromatic compounds, polycyclic aromatic hydrocarbons) the presence of which in contaminated soils, water and sediments poses a significant risk to the environment and human health. Two strains from different origins were compared. One was from an official collection and grown in non-inducing conditions, while the other was isolated during the course of the survey of fungal flora in a polluted soil from Annaba (Algeria). All data were analyzed and results validated via a statistical treatment. We showed the effect of the factors studied (origin of the strain, xenobiotic) but also the interactions between these factors. The strain of A. fusca isolated from a polluted soil was able to efficiently degrade most of the xenobiotics tested, particularly: pentachlorophenol, phenol, catechol, guaiacol and ferulic acid. This property also existed in the other strain but at a very low level.     

Factors inhibiting bioremediation of soil contaminated with weathered oils and drill cuttings

Oily drill cuttings and a soil contaminated with weathered crude oils were treated by enhanced biodegradation under tropical conditions in industrial scaled experiments. Oil contaminants were characterized by gas chromatography and mass spectrometry. This allowed for the identification of a mixture of two crude oils in the contaminated soil. After 12 months of bioremediation process, the removal of hydrocarbons reached by biodegradation an extent of 60% although nutrient amendment with elevated concentration of N-urea had highly detrimental effects on the hydrocarbon degrading fungal populations due to the production of toxic concentration of ammonia gas by nitrification. The saturated hydrocarbons were extensively assimilated, though n-alkanes were not completely removed. Aromatic hydrocarbons were less degraded than saturated whereas resin and asphaltene fractions were, surprisingly, partly assimilated. In laboratory conditions, the residual hydrocarbons in the field-treated materials were 15-20% further degraded when metabolic byproducts resulting from biodegradation were diluted or removed.     

Influence of the application of sewage sludge on the degradation of pesticides in the soil

A study was made of the influence of the application of sewage sludge on the degradation of pesticides in the soil. Two kinds of sludge were used, with different characteristics, one from an urban treatment plant and one from a food processing plant. Three organophosphorus insecticides, fenitrothion, diazinon and dimethoate, were studied. The relative importance was determined of the chemical and biological degradation processes, which involved experiments on soil and sterile soil samples. A comparative study was also made of the degradation of pesticide residues and the evolution of the microbial population. The application of sludge seems to have a complex effect on the degradation of pesticides, determined by the bioavailability and biodegradability of their active ingredient. The biodegradation of pesticide residues brings about alterations in the microorganism population of the soil.