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 on the use of enzymes for the detection of organochlorine, organophosphate and carbamate pesticides in the environment

Pesticides are released intentionally into the environment and, through various processes, contaminate the environment. Three of the main classes of pesticides that pose a serious problem are organochlorines, organophosphates and carbamates. While pesticides are associated with many health effects, there is a lack of monitoring data on these contaminants. Traditional chromatographic methods are effective for the analysis of pesticides in the environment, but have limitations and prevent adequate monitoring. Enzymatic methods have been promoted for many years as an alternative method of detection of these pesticides. The main enzymes that have been utilised in this regard have been acetylcholinesterase, butyrylcholinesterase, alkaline phosphatase, organophosphorus hydrolase and tyrosinase. The enzymatic methods are based on the activation or inhibition of the enzyme by a pesticide which is proportional to the concentration of the pesticide. Research on enzymatic methods of detection, as well as some of the problems and challenges associated with these methods, is extensively discussed in this review. These methods can serve as a tool for screening large samples which can be followed up with the more traditional chromatographic methods of analysis.     

微生物降解拟除虫菊酯类农药残留的研究进展

随着拟除虫菊酯类农药使用量不断增加,产生的农药残留问题对生态环境和人类健康造成了危害.对降解拟除虫菊酯类农药的微生物种类、降解酶和降解机制及降解酶基因克隆和构建工程菌等方面进行综述,旨在为研究和开发微生物降解拟除虫菊酯类农药残留提供参考.     

Obsolete pesticide storage sites and their POP release into the environment—an Armenian case study

Organochlorinated pesticides were widely applied in Armenia until the 1980s, like in all former Soviet Union republics. Subsequently, the problem of areas contaminated by organochlorinated pesticides emerged. Environmental, waste and food samples at one pesticide burial site (Nubarashen) and three former pesticide storage sites (Jrarat, Echmiadzin and Masis) were taken and analysed on the content of organochlorinated pesticides, polychlorinated dibenzo-p-dioxins and furans and dioxin-like polychlorinated biphenyls. Gradient sampling and diffusivity-based calculations provided information on the contamination release from the hot spots on a local scale. A risk analysis based on samples of locally produced food items characterised the impact of storage sites on the health of nearby residents. All four sites were found to be seriously contaminated. High pesticide levels and soil and air contamination gradients of several orders of magnitude were confirmed outside the fence of the Nubarashen burial site, confirming pesticide release. A storage in Jrarat, which was completely demolished in 1996 and contained numerous damaged bags with pure pesticides until 2011, was found to have polluted surrounding soils by wind dispersion of pesticide powders and air by significant evaporation of lindane and β-endosulfan during this period. Dichlorodiphenyltrichloroethane-contaminated eggs, sampled from hens roaming freely in the immediate surroundings of the Echmiadzin storage site, revealed a significant health risk for egg consumers above 1E-5. Although small in size and previously almost unknown to the public, storage sites like Echmiadzin, Masis and Jrarat were found to stock considerable amounts of obsolete pesticides and have a significant negative influence on the environment and human health. Multi-stakeholder cooperation proved to be successful in identifying such sites suspected to be significant sources of persistent organic pollutants.     

Bioremediation treatment of hydrocarbon-contaminated Arctic soils: influencing parameters

The Arctic environment is very vulnerable and sensitive to hydrocarbon pollutants. Soil bioremediation is attracting interest as a promising and cost-effective clean-up and soil decontamination technology in the Arctic regions. However, remoteness, lack of appropriate infrastructure, the harsh climatic conditions in the Arctic and some physical and chemical properties of Arctic soils may reduce the performance and limit the application of this technology. Therefore, understanding the weaknesses and bottlenecks in the treatment plans, identifying their associated hazards, and providing precautionary measures are essential to improve the overall efficiency and performance of a bioremediation strategy. The aim of this paper is to review the bioremediation techniques and strategies using microorganisms for treatment of hydrocarbon-contaminated Arctic soils. It takes account of Arctic operational conditions and discusses the factors influencing the performance of a bioremediation treatment plan. Preliminary hazard analysis is used as a technique to identify and assess the hazards that threaten the reliability and maintainability of a bioremediation treatment technology. Some key parameters with regard to the feasibility of the suggested preventive/corrective measures are described as well.     

Perspectives of using fungi as bioresource for bioremediation of pesticides in the environment: a critical review

Pesticides are used for controlling the development of various pests in agricultural crops worldwide. Despite their agricultural benefits, pesticides are often considered a serious threat to the environment because of their persistent nature and the anomalies they create. Hence removal of such pesticides from the environment is a topic of interest for the researchers nowadays. During the recent years, use of biological resources to degrade or remove pesticides has emerged as a powerful tool for their in situ degradation and remediation. Fungi are among such bioresources that have been widely characterized and applied for biodegradation and bioremediation of pesticides. This review article presents the perspectives of using fungi for biodegradation and bioremediation of pesticides in liquid and soil media. This review clearly indicates that fungal isolates are an effective bioresource to degrade different pesticides including lindane, methamidophos, endosulfan, chlorpyrifos, atrazine, cypermethrin, dieldrin, methyl parathion, heptachlor, etc. However, rate of fungal degradation of pesticides depends on soil moisture content, nutrient availability, pH, temperature, oxygen level, etc. Fungal strains were found to harbor different processes including hydroxylation, demethylation, dechlorination, dioxygenation, esterification, dehydrochlorination, oxidation, etc during the biodegradation of different pesticides having varying functional groups. Moreover, the biodegradation of different pesticides was found to be mediated by involvement of different enzymes including laccase, hydrolase, peroxidase, esterase, dehydrogenase, manganese peroxidase, lignin peroxidase, etc. The recent advances in understanding the fungal biodegradation of pesticides focusing on the processes, pathways, genes/enzymes and factors affecting the biodegradation have also been presented in this review article.     

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.     

Destruction of halogen-containing pesticides by means of detonation combustion

Pesticides that contain a halogen functional group have been destructed by means of detonative combustion. The following compounds were examined: (1) atrazine—2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine—herbicide; (2) bromophos—O,4-bromo-2,5-dichlorophenyl O,O-dimethyl phosphorothioate—insecticide; (3) chloridazon—5-amino-4-chloro-2-phenylopyridazin-3(2H)-one—herbicide; (4) linuron—3-(3,4-dichlorophenyl)-1-metoxy-1-methylurea—herbicide; (5) metoxychlor—1,1,1-trichloro-2,2-bis(4-metoxyphenyl)ethane—insecticide and acaricide; and (6) trichlorfon—dimethyl 2,2,2-trichloro-1-hydroxyethylphosphonate—insecticide. Explosive material has been produced on the basis of ammonium nitrate, which served as an oxidizer while the pesticides were used as fuels. Composition of the explosive was adjusted in such a way as to respect thermodynamic parameters. Detonative decomposition of the mixtures has been carried out in shot-holes pre-drilled in soil. Efficiency of the pesticide decomposition has been examined with gas chromatography in order to determine pesticides residues in the environment. It was found that for some, the amount of pesticides in some compounds in the analyzed samples after decomposition was below the determination threshold of the applied method.     

土壤有机农药污染的降解机理与生物修复技术

通过对有机农药在土壤中的环境行为与迁移转化规律综合分析研究,探讨了有机农药污染土壤的生物修复技术,并对生物修复技术进行了前瞻性研究.     

Prioritizing research for trace pollutants and emerging contaminants in the freshwater environment

Organic chemicals have been detected at trace concentrations in the freshwater environment for decades. Though the term trace pollutant indicates low concentrations normally in the nanogram or microgram per liter range, many of these pollutants can exceed an acceptable daily intake (ADI) for humans. Trace pollutants referred to as emerging contaminants (ECs) have recently been detected in the freshwater environment and may have adverse human health effects. Analytical techniques continue to improve; therefore, the number and frequency of detections of ECs are increasing. It is difficult for regulators to restrict use of pollutants that are a human health hazard; scientists to improve treatment techniques for higher priority pollutants; and the public to modify consumption patterns due to the vast number of ECs and the breadth of literature on the occurrence, use, and toxicity. Hence, this paper examines literature containing occurrence and toxicity data for three broad classes of trace pollutants and ECs (industrials, pesticides, and pharmaceuticals and personal care products (PPCPs)), and assesses the relevance of 71 individual compounds. The evaluation indicates that widely used industrials (BPF) and PPCPs (AHTN, HHCB, ibuprofen, and estriol) occur frequently in samples from the freshwater environment but toxicity data were not available; thus, it is important to establish their ADI. Other widely used industrials (BDE-47, BDE-99) and pesticides (benomyl, carbendazim, aldrin, endrin, ethion, malathion, biphenthrin, and cypermethrin) have established ADI values but occurrence in the freshwater environment was not well documented. The highest priority pollutants for regulation and treatment should include industrials (PFOA, PFOS and DEHP), pesticides (diazinon, methoxychlor, and dieldrin), and PPCPs (EE2, carbamazepine, βE2, DEET, triclosan, acetaminophen, and E1) because they occur frequently in the freshwater environment and pose a human health hazard at environmental concentrations.     

Biodegradation of endosulfan by a soil bacterium

A bacterium capable of metabolizing endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine3-oxide) was isolated from cotton-growing soil and effectively shown to degrade endosulfan into endosulfan sulfate. The bacterium degraded 50% of the compound within 3 days of incubation. Endosulfan sulfate was the only terminal product and no other metabolites were formed during the incubation. Endosulfan and its metabolites were analyzed by gas chromatography. The metabolites formed indicated that the organism follows an oxidative pathway for metabolism of this pesticide. Therefore, the present study, microbial degradation of endosulfan by a soil bacterium, may provide a basis for the development of bioremediation strategies to remediate the pollutants in the environment.     

Petroleum Pollutant Degradation by Surface Water Microorganisms (8 pp)

Background, Aims and Scope It is well known that the composition of petroleum or some of its processing products changes in the environment mostly under the influence of microorganisms. A series of experiments was conducted in order to define the optimum conditions for an efficient biodegradation of petroleum pollutant, or bioremediation of different segments of the environment. The aim of these investigations was to show to what extent the hydrocarbons of a petroleum pollutant are degraded by microbial cultures which were isolated as dominant microorganisms from a surface water of a wastewater canal of an oil refinery and a nitrogen plant. Biodegradation experiments were conducted on one paraffinic, and one naphthenic type of petroleum during a three month period under aerobic conditions, varying the following parameters: Inorganic (Kp) or an organic medium (Bh) with or without exposition to light. Methods Microorganisms were analyzed in a surface water sample from a canal (Pančevo, Serbia), into which wastewater from an oil refinery and a nitrogen plant is released. The consortia of microorganisms were isolated from the water sample (most abundant species: Phormidium foveolarum - filamentous Cyanobacteria, blue-green algae and Achanthes minutissima, diatoms, algae). The simulation experiments of biodegradation were conducted with the biomass suspension and crude oils Sirakovo (Sir, paraffinic type) and Velebit (Ve, naphthenic type). After a three month period, organic substance was extracted by means of chloroform. In the extracts, the content of saturated hydrocarbons, aromatic hydrocarbons, alcohols and fatty acids was determined (the group composition). n-Alkanes and isoprenoid aliphatic alkanes, pristane and phytane, in the aliphatic fractions, were analyzed using gas chromatography (GC). Total isoprenoid aliphatic alkanes and polycyclic alkanes of sterane and triterpane types were analyzed by GC-MS. Results and discussion. Paraffinic type petroleums have a significant loss of saturated hydrocarbons. For naphthenic type petroleum, such a trend has not been observed. The most intensive degradation of n-alkanes and isoprenoid aliphatic alkanes (in paraffinic oil) and isoprenoids (in naphthenic oil) was observed using the inorganic medium Kp in the light; the microbial conversion is somewhat lower with Kp in the dark; with organic medium Bh in the light the degradation is of low intensity; with the same medium in the dark the degradation is hardly to be seen. Steranes and triterpanes were not affected by microbial degradation under the conditions used in our experiments. Obviously, the petroleum biodegradation was restricted to the acyclic aliphatics (n-alkanes and isoprenoids). Conclusion Phormidium foveolarum (filamentous Cyanobacteria - blue-green algae) and Achanthes minutissima (diatoms, algae), microbial cultures isolated as dominant algae from a surface water in a wastewater canal of an oil refinery and a nitrogen plant, have degradable effects dominantly involving petroleum hydocarbons. Petroleum microbiological degradation is more intensive when inorganic medium (in the light) is applied. Having in mind that the inorganic pollutants have been released into the canal as well, this medium reflects more the natural environmental conditions. Polycyclic alkanes of sterane and triterpane type, in spite of the fact that these compounds could be degraded, have remained unchanged regarding abundance and distribution. Since this is the case even for naphthenic type petroleum (which is depleted in n-alkanes), it can be concluded that the biodegradation of petroleum type pollutants, under natural conditions, will be restrained to the n-alkane and isoprenoid degradation. Recommendation and Outlook Performed experiments and simulations of petroleum microbiological degradation may serve for the prediction of the fate of petroleum type pollutants, as well as for definition of conditions for bioremediation of some environmental segments.     

洚解菌Pigmentiphagasp．strainD-2对啶虫脒污染土壤的生物修复作用

啶虫脒属于一种新型的氯化烟碱类杀虫剂,被认为是替代有机磷农药的重要品种之一,在世界范围内已经得到了广泛的应用,其在环境中的残留备受关注,利用微生物修复异源污染物是一种有效的措施。在实验室条件下,研究了高效降解菌D-2（噬染料菌属,Pigmentiphagasp．）对被啶虫脒污染土壤的修复作用及其影响因素。结果表明,降解菌株在未灭菌土壤中的降解效果要略好于灭菌土壤,在土壤外源添加降解菌2×10^8cfu／g,温度20～40℃,弱碱性（pH7．5）的条件下,该菌株能有效降解土壤中1～200mg／kg的啶虫脒。啶虫脒施用对土壤种群结构有一定的影响,可以刺激细菌和真菌的生长,从而使土壤微生物群落结构发生改变,而降解菌的施用可缓解啶虫脒对土壤微生物的影响,修复受污染土壤。因此,人工接种降解菌D-2可提高土壤中啶虫脒的降解率,有效降低其在土壤中的残留。     

Biodegradation of Endosulfan by a Soil Bacterium

A bacterium capable of metabolizing endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine3-oxide) was isolated from cotton-growing soil and effectively shown to degrade endosulfan into endosulfan sulfate. The bacterium degraded 50% of the compound within 3 days of incubation. Endosulfan sulfate was the only terminal product and no other metabolites were formed during the incubation. Endosulfan and its metabolites were analyzed by gas chromatography. The metabolites formed indicated that the organism follows an oxidative pathway for metabolism of this pesticide. Therefore, the present study, microbial degradation of endosulfan by a soil bacterium, may provide a basis for the development of bioremediation strategies to remediate the pollutants in the environment.     

Green pre-concentration techniques during pesticide analysis in food samples

The ever-increasing demand for determining pesticides at low concentration levels in different food matrices requires a preliminary step of pre-concentration which is considered a crucial stage. Recently, the parameter of “greenness” during sample pre-concentration of pesticides in food matrices is as important as selectivity in order to avoid using harmful organic solvents during sample preparation. Developing new green pre-concentration techniques is one of the key subjects. Thus, to reduce the impact on the environment during trace analysis of pesticides in food matrices, new developments in pre-concentration have gone in three separate directions: the search for more environmentally friendly solvents, miniaturization and development of solvent-free pre-concentration techniques. Eco-friendly solvents such as supercritical fluids, ionic liquids and natural deep eutectic solvents have been developed for use as extraction solvents during pre-concentration of pesticides in food matrices. Also, miniaturized pre-concentration techniques such as QuEChERS, dispersive liquid–liquid micro-extraction and hollow-fiber liquid-phase micro-extraction have been used during trace analysis of pesticides in food samples as well as solvent-free techniques such as solid-phase micro-extraction and stir bar sorptive extraction. All these developments which are aimed at ensuring that pesticide pre-concentration in different food matrices is green are critically reviewed in this paper.     

室内空气中的化学农药及其检测技术

室内空气中化学农药之所以存在 ,主要因为我们在杀灭室内蚊、蝇、蚤、蚂蚁、蟑螂及老鼠时 ,使用了含化学农药的杀虫剂。目前 ,我国市场上流通的含有化学农药的杀虫剂商品近 1 0 0 0种 ,但从农药的有效成分来看 ,大约有 60余种。它们多属拟除虫菊酯类农药 ,占总数的 50 % ;此外还有氨基甲酸酯类、有机磷类农药等。本文重点介绍室内空气中化学农药的捕集及检测技术     

Sensitized photodecomposition of high disperse pesticide chemicals exposed to sunlight and irradiation from halogen or mercury lamp

The kinetics of sensitized photolysis for four pesticides, deltamethrin (Decis), acrinathrin (Rufast), s-fenvalerate (Sumialpha), and propiconazol (Tilt) in thin films and aerosol particles was investigated under sunlight or the irradiation from halogen or mercury lamp. The peculiarities of principle of the photochemistry of pesticides in high disperse substance state were discussed. The quantum yields of sensitized and direct photolysis were measured, and the phenomenological kinetic mechanism of photolysis was proposed and examined. Four relations between six rate constants of reaction steps of the kinetic mechanism were determined. The use of sensitizers to accelerate the decomposition rates of pesticide pollutants under sunlight could minimize the contamination of agricultural commodities and the adjacent environment. The Shirvanol 2 sensitizer (a by-product of the full treatment of Caspian oils) can regulate decomposition of many pesticides in a wide range of photolysis rates, so that practically any desired lifetime could be really available for either pesticide residues on plant foliage or pesticide aerosol particles in the air.     

酶体外定向分子进化技术:环境生物污染治理中的新星

环境生物技术在环境控制与污染治理中的应用主要是利用微生物降解和转换污染物.一些人类合成的化学物质由于具有高毒性,且难以被自然界微生物降解,已经严重威胁生态环境和人类的健康.生物治理以其低成本、完成矿质化和实现原位处理等特点,成为较好的治理技术.体外定向分子进化技术是一种发现新的生物表型和新酶的好方法,DNA改组是重要的体外分子进化技术,成功地改造了许多在医药、工业和环境保护等的商业酶.综述了近年来体外定向分子进化技术在环境生物污染治理中的研究进展和应用.     

Biodegradation of lindane, methyl parathion and carbofuran by various enriched bacterial isolates

In the present study, lindane (1,2,3,4,5,6-hexachlorocyclohexane), methyl parathion (O-dimethylO-(4-nitro-phenyl) phosphorothioate) and carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) degradation potential of different enriched bacterial cultures were evaluated under various environmental conditions. Enriched cultures behaved differently with different pesticides. Degradation was more in a facultative anaerobic condition as compared to that in aerobic condition. A specific pesticide enriched culture showed maximum degradation of that pesticide irrespective of pesticides and environmental conditions. Lindane and endosulfan enriched cultures behaved almost similarly. Degradation of lindane by lindane enriched cultures was 75 +/- 3% in aerobic co-metabolic process whereas 78 +/- 5% of lindane degradation occurred in anaerobic co-metabolic process. Degradation of methyl parathion by methyl parathion enriched culture was 87 +/- 1% in facultative anaerobic condition. In almost all the cases, many intermediate metabolites were observed. However, many of these metabolites disappeared after 4-6 weeks of incubation. Mixed pesticide-enriched culture degraded all the three pesticides more effectively as compared to specific pesticide- enriched cultures. It can be inferred from the results that a bacterial consortium enriched with a mixture of all the possible pesticides that are present in the site seems to be a better option for the effective bioremediation of multi-pesticide contaminated site.