Chromium in the environment: factors affecting biological remediation

Chromium, in the trivalent form (Cr(III)), is an important component of a balanced human and animal diet and its deficiency causes disturbance to the glucose and lipids metabolism in humans and animals. In contrast, hexavalent Cr (Cr(VI)) is highly toxic carcinogen and may cause death to animals and humans if ingested in large doses. Recently, concern about Cr as an environmental pollutant has been escalating due to its build up to toxic levels in the environment as a result of various industrial and agricultural activities. In this review, we present the state of knowledge about chromium mobility and distribution in the environment and the physiological responses of plants to Cr with the desire to understand how these processes influence our ability to use low cost, environmentally friendly biological remediation technologies to clean up Cr-contaminated soils, sediments, and waters. The use of biological remediation technologies such as bioremediation and phytoremediation for the cleanup of Cr-contaminated areas has received increasing interest from researchers worldwide. Several methods have been suggested and experimentally tested with varying degrees of success.     

Biological technologies for the remediation of co-contaminated soil

Compound contamination in soil, caused by unreasonable waste disposal, has attracted increasing attention on a global scale, particularly since multiple heavy metals and/or organic pollutants are entering natural ecosystem through human activities, causing an enormous threat. The remediation of co-contaminated soil is more complicated and difficult than that of single contamination, due to the disparate remediation pathways utilized for different types of pollutants. Several modern remediation technologies have been developed for the treatment of co-contaminated soil. Biological remediation technologies, as the eco-friendly methods, have received widespread concern due to soil improvement besides remediation. This review summarizes the application of biological technologies, which contains microbial technologies (function microbial remediation and composting or compost addition), biochar, phytoremediation technologies, genetic engineering technologies and biochemical technologies, for the remediation of co-contaminated soil with heavy metals and organic pollutants. Mechanisms of these technologies and their remediation efficiencies are also reviewed. Based on this study, this review also identifies the future research required in this field.     

Environmental impact and bioremediation of seleniferous soils and sediments

Selenium concentrations in the soil environment are directly linked to its transfer in the food chain, eventually causing either deficiency or toxicity associated with several physiological dysfunctions in animals and humans. Selenium bioavailability depends on its speciation in the soil environment, which is mainly influenced by the prevailing pH, redox potential, and organic matter content of the soil. The selenium cycle in the environment is primarily mediated through chemical and biological selenium transformations. Interactions of selenium with microorganisms and plants in the soil environment have been studied in order to understand the underlying interplay of selenium conversions and to develop environmental technologies for efficient bioremediation of seleniferous soils. In situ approaches such as phytoremediation, soil amendment with organic matter and biovolatilization are promising for remediation of seleniferous soils. Ex situ remediation of contaminated soils by soil washing with benign leaching agents is widely considered for removing heavy metal pollutants. However, it has not been applied until now for remediation of seleniferous soils. Washing of seleniferous soils with benign leaching agents and further treatment of Se-bearing leachates in bioreactors through microbial reduction will be advantageous as it is aimed at removal as well as recovery of selenium for potential re-use for agricultural and industrial applications. This review summarizes the impact of selenium deficiency and toxicity on ecosystems in selenium deficient and seleniferous regions across the globe, and recent research in the field of bioremediation of seleniferous soils.     

铜污染土壤的生物修复研究进展

随着工业化与农业化进程的加快,土壤重金属污染问题日益突出。铜(Cu)既是生命体生长发育的必需微量元素,也是重金属污染物之一。土壤中过量的Cu不仅会对植物产生毒害,而且能够通过食物链的富集作用,对人类健康造成严重威胁。生物修复技术作为治理重金属污染土壤的一种新型技术受到广泛关注。文中对生物修复的主要技术如植物修复、微生物修复、植物-微生物联合修复、动物修复等在治理Cu污染土壤方面的研究进展进行综述,以期为重金属污染土壤有效治理和可持续农业的发展提供理论依据。     

Bioremediation of chromium contaminated environments

Bioremediation is the most promising and cost effective technology widely used nowadays to clean up both soils and wastewaters containing organic or inorganic contaminants. Discharge of chromium containing wastes has led to destruction of many agricultural lands and water bodies. Utilisation of chromium(Cr) reducing microbes and their products has enhanced the efficiency of the process of detoxification of Cr(VI) to Cr(III). This review focuses mainly on the current technologies prevalent for remediation like natural attenuation, anaerobic packed bed bioreactors (using live cells, Cr(VI) reductases or their byproducts) and use of engineered microorganisms. Treatment of wastewaters by biosorption or using biofilms and immobilized microbial cells are also discussed.     

EDTA-Enhanced Phytoremediation of Heavy Metals: A Review

The increase in heavy metal terrestrial ecosystems’ contamination through anthropogenic activities is a widespread and serious global problem due to their various environmental and human implications. For these reasons, several techniques, including phytoremediation of heavy metals, have been extensively studied. In spite of significant recent advancement, ethylene diamine tetraacetic acid (EDTA)-enhanced heavy metal phytoextraction as well as related ecological risks are still topical and remain an important area of research. In fact, EDTA favors the solubilization of metals and metalloids in soils, and was therefore extensively studied during the last two decades in order to improve phytoextraction efficiency and reduce treatment duration. This review highlights the recent findings (2010–2012) and mechanisms behind EDTA-enhanced (1) solubilization of heavy metals in soil, (2) mobilization/transport of soluble metals towards plant root zone, and (3) metal absorption by plant roots and translocation towards aerial parts. The review also presents potential risks associated with EDTA-enhanced phytoextraction: (1) environmental persistence of EDTA and/or metal-EDTA complex; (2) potential toxicity of EDTA and/or metal-EDTA complex to plants; and (3) leaching and contamination of groundwater. Moreover, field-scale cost of EDTA-enhanced remediation and the role of EDTA in time required for heavy metal remediation is discussed.     

Hydrocarbon phytoremediation in the family Fabaceae--a review

Currently, studies often focus on the use of Poaceae species (grasses) for phytoremediation of hydrocarbon-contaminated soils. Research into the use of Fabaceae species (legumes) to remediate hydrocarbons in soils has been conducted, but these plants are commonly overlooked due to slower recorded rates of degradation compared with many grass species. Evidence in the literature suggests that in some cases Fabaceae species may increase total degradation of hydrocarbons and stimulate degradative capacity of the soil microbial community, particularly for contaminants which are normally more recalcitrant to degradation. As many recalcitrant hydrocarbons have negative impacts on human and ecosystem health, development of remediation options is crucial. Reconsideration of Fabaceae species for removal of such contaminants may lead to environmentally and economically sustainable technologies for remediation of contaminated sites.     

Computer simulation of uranyl uptake by the rough lipopolysaccharide membrane of Pseudomonas aeruginosa

Heavy metal environmental contaminants cannot be destroyed but require containment, preferably in concentrated form, in a solid or immobile form for recycling or final disposal. Microorganisms are able to take up and deposit high levels of contaminant metals, including radioactive metals such as uranium and plutonium, into their cell wall. Consequently, these microbial systems are of great interest as the basis for potential environmental bioremediation technologies. The outer membranes of Gram-negative microbes are highly nonsymmetric and exhibit a significant electrostatic potential gradient across the membrane. This gradient has a significant effect on the uptake and transport of charged and dipolar compounds. However, the effectiveness of microbial systems for environmental remediation will depend strongly on specific properties that determine the uptake of targeted contaminants by a particular cell wall. To aid in the design of microbial remediation technologies, knowledge of the factors that determine the affinity of a particular bacterial outer membrane for the most common ionic species found in contaminated soils and groundwater is of great importance. Using our previously developed model for the lipopolysaccharide (LPS) membrane of Pseudomonas aeruginosa, this work presents the potentials of mean force as the estimate of the free energy profile for uptake of sodium, calcium, chloride, uranyl ions, and a water molecule by the bacterial LPS membrane. A compatible classical parameter set for uranyl has been developed and validated. Results show that the uptake of uranyl is energetically a favorable process relative to the other ions studied. At neutral pH, this nuclide is shown to be retained on the surface of the LPS membrane through chelation with the carboxyl and hydroxyl groups located in the outer core.     

The Phytomanagement of Trace Elements in Soil

Trace elements (TEs) occur at low concentrations (<1000 mg kg ^?1) in organisms, yet they have a large biological effect, both as essential nutrients and environmental contaminants. Phytomanagement describes the manipulation of soil-plant systems to affect the fluxes of TEs in the environment with the goal of remediating contaminated soils, recovering valuable metals, or increasing micronutrient concentrations in crops. Phytomanagement includes all biological, chemical, and physical technologies employed on a vegetated site. Successful phytomanagement should either cost less than other remediation or fortification technologies, or be a profitable operation, by producing valuable plant biomass products. This may include bioenergy or timber production on contaminated land, a practice that does not reduce food production. We review the components of phytomanagement and the underlying biogeochemical processes, with a view to elucidating situations where this technology may be successfully applied and identifying future research needs. Many full-scale operations have proved the efficacy of plants to reduce contaminant mobility in soils (phytostabilization), particularly when used in combination with other technologies. As a stand-alone technology, the oft-touted use of plants to extract TEs from contaminated soils (phytoextraction) or low-grade ore bodies (phytomining) is unsuitable for most, if not all, sites due to low-extraction rates and problems caused by site heterogeneity, the limited rooting depth of plants and the presence of contaminant mixtures. Unsubstantiated claims about phytoextraction have tarnished the reputation of all “phyto” technologies. Nevertheless, phytoextraction, as part of a larger environmental toolkit, has a role in phytomanagement. The growth, or lack thereof, of profitable companies that provide phytomanagement will indicate its value. A critical knowledge gap in phytomanagement is the integration of the processes that affect plant–TE interactions and the biophysical processes affecting TE fluxes in the root zone, especially the effect of roots on contaminant fluxes.     

修复土地再用生态风险评价方法研究

针对污染土壤的修复技术研究已经取得了很多重要的结果,但是对修复效果的评价研究却相对较少。实际上,在对污染土壤进行物理、化学以及生物修复后,再用前需要根据再用目的对可能残留的污染物或修复剂是否会产生生态安全和人类健康问题进行风险评价。本文着重从修复场地原位观察法、实验室模拟观察法、微宇宙法和现场经验与推导法四方面讨论了如何能够有效、灵敏地诊断污染物对生态系统产生的潜在危害,归纳了生态毒理学实验在评价修复土地再用风险中的作用;并对修复土地再用生态风险评价的发展前景进行了展望,提出了针对性的建议。     

合成生物学技术在环境保护中的应用

合成生物学是一个基于生物学和工程学原理的科学领域,其目的是重新设计和重组微生物,以优化或创建具有增强功能的新生物系统。该领域利用分子工具、系统生物学和遗传框架的重编程,从而构建合成途径以获得具有替代功能的微生物。传统上,合成生物学方法通常旨在开发具有成本效益的微生物细胞工厂进而从可再生资源中生产化学物质。然而,近年来合成生物学技术开始在环境保护中发挥着更直接的作用。本综述介绍了基因工程中的合成生物学工具,讨论了基于基因工程的微生物修复策略,强调了合成生物学技术可以通过响应特定污染物进行生物修复来保护环境。其中,规律间隔成簇短回文重复序列(Clustered Regularly Interspersed Short Palindromic Repeats, CRISPR)技术在基因工程细菌和古细菌的生物修复中得到了广泛应用,生物修复领域也出现了很多新的先进技术,包括生物膜工程、人工微生物群落的构建、基因驱动、酶和蛋白质工程等。有了这些新的技术和工具,生物修复将成为当今最好和最有效的污染物去除方式之一。     

THE BIOTRANSFORMATION,BIODEGRADATION, AND BIOREMEDIATION OF ORGANIC COMPOUNDS BY MICROALGAE1

Rapid growth in the biotechnological industry and production has put tremendous pressure on the biological methods that may be used according to the guidelines of green chemistry. However, despite continuing dramatic increases in published research on organic biotransformation by microorganisms, more research exists with microalgae. Our efforts in transforming chemicals such as organic compounds for the production of functionalized products help to lessen the environmental effects of organic synthesis. These biotransformations convert organic contaminants to obtain carbon or energy for growth or as cosubstrates. This review aims to focus on the potential of microalgae in transformation, conversion, remediation, accumulation, degradation, and synthesis of various organic compounds. However, these technologies have the ability to provide the most efficient and environmentally safe approach for inexpensive biotransforming of a variety of organic contaminants, which are most industrial residues. In addition, the recent advances in microalgal bioactivity were discussed.     

Screening Software for an Innovative In Situ Bioremediation Technology

Innovative in situ treatment technologies show promise as efficient methods for remediating the nation's waste sites. Unfortunately, due to various barriers, some innovative technologies that have been demonstrated at full scale are never transferred for commercial application. The National Research Council (NRC) has recently presented recommendations on how to overcome these barriers (NRC, 1997). User-friendly screening software, which specifically addresses each of the NRC recommendations, is presented for use by site managers to determine the appropriateness of an innovative remediation technology, in situ aerobic cometabolic bioremediation, to clean up a contaminated site with specified hydrogeologic and contaminant characteristics. The software estimates the performance and cost of the technology at the site. Software, such as the one presented, can be used to aid in the transfer and implementation of innovative remediation technologies.     

The impact of uncertainty on phytoremediation project costs

Pollution of the environment by metals and organic contaminants is an intractable global problem, with cleanup costs running into billions of dollars using current engineering technologies. The availability of alternative, cheap and effective technologies would significantly improve the prospects of cleaning-up metal contaminated sites. Phytoremediation has been proposed as an economical and 'green' method of exploiting plants to extract or degrade the contaminants in the soil. To date, the majority of phytoremediation efforts have been directed at leaping the biological biochemical and agronomic hurdles to deliver a working technology, with scant attention to the economic outlook other than simple estimates of the cost advantages ofphytoremediation over other techniques. In this paper we use a deterministic actauarial model to show that uncertainty in project success (the possibility that full clean up may not be realized) may significantly increase the perceived costs of remediation works for decision-makers.     

Rhizosphere Microbial Characterization in Petroleum-Contaminated Soil

Contamination of soil with petroleum compounds is of concern worldwide. Although there are a variety of physical and chemical technologies available to remediate petroleum waste sites, biological methods are often used due to lower cost and public acceptance. Growth and enhanced activity of microbial communities in contaminated soil is a key factor for the success of bioremediation. Establishing vegetation in petroleum-contaminated soil may enhance microbial activity and remediation success even further by providing root exudates to the rhizosphere microorganisms. In this study, microorganisms were characterized in petroleum-contaminated soils and sediments quantitatively and qualitatively based on enumeration and metabolic diversity assessments. Contaminated soils and sediments were obtained from a phytoremediation field demonstration project in California. Microbial numbers in the unvegetated soil, based on plate counts and most probable number of hydrocarbon degraders, were significantly lower than the vegetated soils. Metabolic microbial characterization using BIOLOG was also conducted and based on principle component analysis (PCA), there was a distinct difference between the metabolic diversity of microbial communities in vegetated and unvegetated soils. Results from this research indicate that the presence and type of plants, and level of contamination may greatly influence microbial communities in polluted soils.     

A Critical Review of the Arsenic Uptake Mechanisms and Phytoremediation Potential of Pteris vittata

The discovery of the arsenic hyperaccumulator, Pteris vittata (Chinese brake fern), has contributed to the promotion of its application as a means of phytoremediation for arsenic removal from contaminated soils and water. Understanding the mechanisms involved in arsenic tolerance and accumulation of this plant provides valuable tools to improve the phytoremediation efficiency. In this review, the current knowledge about the physiological and molecular mechanisms of arsenic tolerance and accumulation in P. vittata is summarized, and an attempt has been made to clarify some of the unresolved questions related to these mechanisms. In addition, the capacity of P. vittata for remediation of arsenic-contaminated soils is evaluated under field conditions for the first time, and possible solutions to improve the remediation capacity of Pteris vittata are also discussed.     

酶法催化降解2,4,6-三硝基甲苯的研究进展

2,4,6-三硝基甲苯(TNT)作为一种广泛使用的含能材料,发挥巨大作用的同时也给环境带来了严重的污染,对人类健康构成一定威胁。目前国内外的TNT处置主要有物理、化学、生物及酶法等方法,其中酶法作为一种新兴的方法,显示了良好的应用潜力,受到研究者的广泛关注,。比较了各类处理方法的优缺点,重点介绍近年来涉及TNT降解的酶学研究进展,并对酶法在TNT废水处理和土壤修复中的应用前景进行展望。     

Remediation of contaminated soils with green plants: An overview

Summary Billions of dollars each year are spent on the remediation of contaminated soils in the United States alone. Contaminated soils represent an economic liability as well as a technical challenge. New technologies are needed to address numerous contaminants, especially those that are neither volatile nor mobile in soil solutions. One emerging technology, “phytoremediation”, employs green plants in the remediation process. The technique is relatively new, with few field demonstrations; however, it represents an ever-growing area of research built on a sound technical basis. This technology draws heavily from a wide range of agronomic, biological, and engineering disciplines. Exploiting all plant-influenced biological, microbial, chemical, and physical processes to remediate contaminated sites is the goal of much research in this area. In certain situations, sites remediated with a plant- based technology are expected to have significant economic, aesthetic, and technical advantages over traditional engineering solutions. This paper provides an overview of the phytoremediation area with an emphasis on providing background information and research avenues to plant biologists. Presented in the Session-in-Depth Bioremediation through Biotechnological Means at the 1993 Congress on Cell and Tissue Culture, San Diego, CA, June 5–9, 1993.     

A review on remediation technologies for nickel-contaminated soil

Abstract

With the rapid pace of industrialization and urbanization, the environmental safety of soil is a worldwide concern. In China alone, one-fifth of the arable land is reported to be contaminated with heavy metals including nickel. In this review, current research on nickel remediation, specifically the various remediation technologies including physical and chemical remediation methods, such as immobilization, soil washing, encapsulation, soil replacement, and electrokinetic methods; phytoremediation; and bioremediation, is summarized. Further, the mechanisms underlying the presented remediation technologies, along with their advantages and disadvantages, are discussed. The lacunae in available technologies for nickel remediation are also briefly discussed. The review concludes with a scheme for successful soil remediation.