Assessment of heavy metal bioremediation potential of bacterial isolates from landfill soils

Indiscriminate disposal of wastes on landfills has led to increase in heavy metal contamination in landfill soils. However, the ability of the indigenous microorganisms to remediate the polluted environment can be of great influence in reclamation of such soils. The objectives of this study were to assess the bioremediation potential of the screened indigenous bacteria and evaluate the effects of carbon source and pH in the enhancement of the bioremediation process. Bacterial isolates from landfill sites were screened for their capability to utilize heavy metal (Cd and Pb). Nutrient Agar was supplemented with five different concentrations of each metal (25 to 600 mgL^-1). Viable counts of the isolates were taken four times at two days interval. Pseudomonas aeruginosa, Klebsiella edwardsii and Enterobacter cloacae were selected based on their tolerance to heavy metal for remediation process. Peptone broth was also supplemented using different concentrations of heavy metals. The remediation process was assessed by monitoring the growth of biomass using UV spectrophotometer at 600 nm and the residual heavy metal was evaluated after 8 days of incubation using AAS. Pseudomonas aeruginosa exhibited the highest bioremediation potential among the bacterial isolates with 58.80 and 33.67 remediation percentage in 50 mg Cd L^-1 and 300 mg Pb L^-1 . However, higher remediation percentage (79.87 and 92.41) was observed by Klebsiella edwardsii through addition of carbon source (5 g/L) and varying the pH (6) of the media in the heavy metal contaminated medium. The results of this study indicate that the effectiveness of the indigenous bacteria in remediation process can be enhanced through the addition of carbon source and increase pH for effective reclamation of contaminated soil.     

The Distribution of Metals in Soils and Pore Water at Three U.S. Military Training Facilities

Small arms firing ranges at military training facilities can have enormous heavy metal burdens (percent level) in soils. Currently there are few published works that quantify the metal content of soils and waters at military installations or speculate on the potential for migration of these contaminants into groundwater. This article documents metals in soils and waters at nine small arms training ranges at three military installations in the U.S. Soil samples were collected from the surface and shallow subsurface. The results demonstrated that lead, antimony, copper, and zinc were the principal contaminants of interest and mapping a site's lead and copper surface distributions would adequately define the extent of impacted soil. Lower metal concentrations at three of the ranges reflected previous remediation by means of physical separation and mechanical removal of metallic fragments followed by fixation treatment with Maectite^TM. Except for the treated ranges where mixing had occurred, subsurface soil samples indicated limited vertical migration. Several of the ranges were also monitored for trace element migration in the vadose zone by means of suction-cup lysimeters. This pore-water sampling indicated ceramic suction-cup lysimeters are useful for assessing relative concentrations but require care in evaluation because of potential sorption losses. Monitoring of soil water at ranges should include antimony and zinc; the former because, in contrast to the other metals, it is typically soluble in an anionic form, and the latter because of its greater solubility and mobility.     

Heavy Metal Speciation in Sediments and the Associated Ecological Risks in Rural Rivers in Southern Jiangsu Province,China

Heavy metal speciation and the associated ecological risks were investigated, using a European Community Bureau of Reference sequential extraction procedure, in sediments from the residential, mixed (residential and industrial), and agricultural areas of rural rivers in southern Jiangsu Province, China. Compared with the background values in Jiangsu Province soils, Cd was the metal with the highest contamination level, especially in the mixed area, followed by Cu and Zn. In the sediment samples from the agricultural area, the heavy metal concentrations were no more than two times greater than the background values. There were higher proportions of Cd in the acid-soluble fraction, Cr in the residual fraction, and Pb in the reducible fraction in the three areas. The heavy metal mobility was mainly controlled by the acid-soluble and reducible fractions. Cd could pose extremely high risks to the environment. In addition, the risks of heavy metal to the environment in the three areas followed the order: mixed area > residential area > agricultural area. Furthermore, a risk assessment code analysis showed that most of the sediment samples were classified as being of high to very high risk in the residential and mixed areas because of their Cd, Ni, and Zn concentrations. Heavy metal pollution in the residential and mixed areas is generally serious, and immediate remediation measures need to be taken.     

Contamination Levels Remaining in Aznalcóllar Spill-Affected Soils (Spain) Following Pyritic Sludge Removal

Potentially toxic elements (PTE) in aqua regia extracts were analyzed by ICP in order to determine the remaining degree of contamination of the selected points along Agrio and Guadiamar rivers. The studied area was affected in 1998 by the accidental spillage from a flotation plant for complex sulfides located at Aznalcóllar (Spain), it was covered by acidic waters and pyritic sludge. Emergency response for the remediation of the contaminated soils, for avoiding greater ecological impact, and waiting for possible ulterior remedial actions, was the removal of the superficial sludge. Sampling was done after the sludge removal operations 1 year after the spill, at different depths down to 300?cm. The results show that the soils affected are still contaminated by several PTE at different degrees and depths depending on their particular conditions. In general, superficial soil samples became highly contaminated. The contamination of soils is due, in general, to processes of sludge infiltration and PTE leaching. The sludge infiltration is due, in part, to the heavy machinery used to remove the sludge. A moderate degree of contamination remains in some soils down to 120 or 300?cm.     

解磷微生物修复土壤重金属污染研究进展

土壤重金属污染问题日益严重,具有普遍性、隐蔽性、表聚性、不可逆性等特点,已经成为环境污染治理中的热点、难点问题。解磷微生物能够依靠自身的代谢产物或通过与其他生物的协同作用,将土壤中的难溶性磷转化为可供植物吸收利用的磷,具有多重植物促生长功能和重金属解毒能力,可在重金属毒害水平下,促进植物生长、提高植物抗病能力、克服重金属对植物生长的不利影响,从而增强重金属修复植物的生存竞争力。从解磷微生物的研究现状入手,介绍了解磷微生物对土壤重金属污染的修复能力,综述了解磷微生物对土壤重金属污染修复的作用机制,分析了目前解磷微生物在重金属修复过程中存在的问题,并提出了今后研究的方向,为重金属污染土壤的修复提供了新思路。     

Heavy Metal/Metalloid Indexing and Balances in Agricultural Soils: Methodological Approach for Research

Heavy metal(loid) accumulation in agricultural soils is a threat to the soil capacity, quality, and productivity. It also increases human exposure to heavy metal(loid)s via consumption of contaminated plant-based foods. The detrimental effects of soil contamination also deteriorate the environment of plants and animals. For sustainable agriculture, therefore, the soil must be protected from toxic levels of heavy metal(loid)s. Studies on heavy metal(loid) balances in agricultural soils are important in predicting future risks to sustainable production from agro-ecological zones and human exposure to heavy metal(loid)s. The latest and continuous indexing of the problem seems a prerequisite for sustainable agriculture. This review provides some background information and then summarizes key methodological approaches for studies on indexing and balance of heavy metal(loid)s in agricultural soils. In the end, important soil and health indices are explained that may be useful in understanding the extent of the problem. The provided information would contribute to sustainable heavy metal(loid) management in the agricultural soils, high crop production, better soil protection, and ultimately to human health.     

重金属污染的植物修复及相关分子机制

随着近代工业的发展,土壤重金属污染问题日益严重。重金属即使在极低浓度下仍然可以对人畜造成健康上的威胁,因此迫切需要有效的修复方法对土壤进行修复。生物修复,特别是植物修复目前已经成为重金属污染修复的重要手段之一,了解相关植物的重金属解毒和积累分子机制是提高修复效率、解决重金属污染问题的基础。文中以土壤修复方式为起点,结合植物吸收积累重金属以及解毒的相关分子机制研究,探讨了植物修复的发展现状以及趋势。     

重金属污染土壤植物修复的研究进展和应用前景

土壤污染是当今面临的一个严峻的问题。其中重金属污染尤为严重。因此重金属污染土壤的修复日益受到各国政府和学者的重视。植物修复技术作为一种绿色安全的技术以其潜在的高效、经济及生态协调性成为当前国际学术界研究的热点领域。就植物修复技术的概念、方法原理、植物修复技术的研究历史和现状以及优点、应用前景作了系统阐述,并介绍了国内外开展的一些应用性实例。指出了植物修复技术当前还存在的问题。对今后发展的方向。作出了几点展望。     

Mycorrhizal and Endophytic Fungal Colonization in Arrhenatherum elatius L. Roots According to the Soil Contamination in Heavy Metals

The aim of this work was to jointly study non-mycorrhizal (dark septate fungi) and mycorrhizal (arbuscular mycorrhizae) colonization along a large range of heavy metal pollution in soil in order to determine the effective contribution of each type of endophytes in relation to heavy metal uptake and tolerance. Hence, eight sites were chosen in the mining area of northern France with respect both to a large range of heavy metal contamination (Cd, Pb, Zn) and monospecific colonization by Arrhenatherum elatius. Root colonization with both arbuscular mycorrhizae (AM) and dark septate fungi (DSF) as well as spore density in rhizospheric soil were estimated in relation to soil characteristics. Mycorrhizal infestation (hyphae, arbuscules and vesicles) was adversely affected by soil pollution almost to exclusion. The intensity of colonization with DSF was very low in presence of AM in non-contaminated soils but higher in polluted soils. The effect of the fungal colonization on the heavy metal tolerance of Arrhenatherum elatius is discussed.     

Investigation of the extent of contamination of heavy metals in agricultural soil using statistical analyses and contamination indices

To examine the level of contamination of Eshghabad region, Neyshabur, the concentration of heavy metals in soil was measured. For this purpose, 37 samples were taken from surface soil and the total concentration of heavy elements was measured by inductively coupled plasma (ICP). The mean concentration of Pb, Ni, Cu, Zn, and Fe was obtained to be 195, 87.3, 22.8, 274.8, and 2.5%, respectively. Using five valid indicators, the intensity of metal contamination in soil was calculated and compared. Furthermore, using statistical analyses, the relationships between the elements, their origins, and the spatial distribution of metals across various stations were investigated. The results indicated that the mean value of all of the studied metals (except for iron and copper) is greater than the mean concentration of metals in the Earth's crust. The indicators showed very high contamination for lead, while low to medium contamination for other elements of interest in the farming soils of the region. Statistical analyses indicated that there is a relatively similar contamination intensity across all of the studied stations. Considering the quality standards, the soils of this region are threatened by contamination of lead.     

Analysis of Worldwide Naphthalene Surface Soil Regulatory Guidance Values

Many environmental regulatory jurisdictions worldwide specify the maximum soil contamination mass burdens that may occur without prompting a regulatory response. For residential surface soils, these regulatory guidance values (RGVs) are generally based on human (often child) health risks from inhalation, ingestion, and dermal exposure to contamination. RGVs have been promulgated for more than 1,200 soil contaminants. Of these, naphthalene is the most frequently regulated contaminant. The 234 known naphthalene RGVs range from a minimum of 0.0289 mg/kg to a maximum of 16,000 mg/kg and span 5.7 orders of magnitude. Analysis illustrates that, although there are small non-random clusters of values, and there may be statistically significant differences between the values used in the U.S. and elsewhere around the world, the overall distribution of numbers strongly resembles (r = 0.9953) that of a log-normal random variable. Results of Monte Carlo uncertainty analysis applied to the U.S. Environmental Protection Agency risk model are presented to approximate the range of the naphthalene RGV span that can be attributed to uncertainty in cancer or non-cancer risk formulations. Uncertainty in the cancer risk formulation could account for approximately 41% of the RGVs. Uncertainty in the non-cancer risk formulation could account for a different 22% of the RGVs, but the cancer risk model generally yields the binding (lowest) value. The implications of these widely variable RGVs for health risk and remediation costs are discussed and methods of reducing variability are suggested.     

Heavy Metals in Agricultural Soils of the Mouriki-Thiva Area (Central Greece) and Environmental Impact Implications

The heavy metal content of 51 surface soil samples from the agricultural region of Mouriki-Thiva (central Greece) was investigated by a combination of mineralogical (X-ray diffraction and scanning electron microscopy) and geochemical (aqua regia and 0.5 M HCl extractions) methods in order to determine the levels of contamination, as well as the origin, distribution and mobility of selected metals. The geology of the area includes ultrabasic rocks, and consequently the soils have anomalous values in Ni (621-2639 mg/kg) and Cr (134-856 mg/kg). Whereas Cr is mainly hosted in the crystal structure of chromite, Ni is primarily mobilized from olivine and serpentine. Nickel, and to a lesser extent Cr, were also found to be absorbed in Fe oxides. The results of a single 0.5 HCl leach revealed significant differences in the mobility and potential bioavailability of Ni and Cr in representative soil samples; Nickel is substantially more labile, and as a result a potential amount of this metal is readily available to the plants. The whole area is heavily contaminated by Ni and Cr and consequently the monitoring of the agricultural products of the region for their heavy metal content is strongly recommended.     

Ecological risk assessment of metals in roadside agricultural soils: A modified approach

The threat of metal contamination of roadside agricultural soils poses severe ecological risks throughout the globe due to dual contamination by intensive agriculture and traffic-related activities. Therefore, the present study was conducted to assess ecological risks posed by metals (Cd, Co, Cr, Cu, Fe, Mn, Pb, and Zn) in intensively cultivated roadside agricultural soils of Punjab, India. The results of the contamination assessment factors i.e. Contamination Factor (CF) and Enrichment Factor (EF) indicated that the studied soils were moderately to highly contaminated with metals. It was observed that the Modified Risk Index (MRI), which is based upon EF, indicated the ecological risks of metals more efficiently than the traditional Ecological Risk Index (RI), which is based upon CF in the present study. The MRI values indicated that the metals posed considerable to high risk in 67.86% samples as compared to only 7.14% samples based upon RI values. Thus, MRI can be considered as a more efficient risk indicator in comparison to RI. Spatial distribution maps of MRI indicated to higher metal contamination in inner urban parts of study area due to higher traffic and industrial activities.     

高砷区植物的生态与化学特征

 土壤砷污染是一种十分严重的环境问题,但目前尚无经济有效的治理方法。利用各种重金属的耐性与富集植物修复重金属污染土壤是当前的研究热点。通过对两个中国典型的砷矿区（炼砷区）土壤与植物的系统调查与采样分析,发现若干种植物对砷具有极强的耐性和不同程度的富集能力。砷在不同植物中的含量分别为：蜈蚣草（Pteris vittata）羽片1 600 mg·kg-1 DW,剑叶凤尾蕨(Pteris ensiformis)地上部1 230 mg·kg-1 DW,酸模(Rumex acetosa)地上部 440 mg·kg-1     

Methodological considerations for determining cleanup limits for uranium in treated and untreated soils

Uranium‐contaminated soils are present at various locations across the U.S. where uranium was processed for nuclear fuels or atomic weapons. Important issues in dealing with such contamination include the assessment of the potential health risks associated with human exposures to the residual uranium and the determination of safe levels of U in soils that have been treated by a given technology. This paper reviews pertinent aspects of the health risks posed by uranium in soils and discusses various methodological considerations that must be dealt with in developing cleanup limits for U in treated soils. Of special concern is the development of remediation limits that are closely tied to a set of monitoring requirements for determining compliance with derived limits. Key issues addressed include characterization of the bioavailability of uranium compounds in food and water, determination of a safe level of uranium in kidney tissue, estimation of the health risks associated with the uranium daughter products radium and radon, assessment of the potential for ground‐water contamination, biogeochemical characterization of soil‐treatment processes, and specification of appropriate monitoring and statistical protocols for analyzing treated and untreated soils.     

丛枝菌根在植物修复重金属污染土壤中的作用

丛枝菌根（Arbuscular mycorrhizae，AM）是自然界中分布最广的一类菌根，AM真菌能与陆地上绝大多数的高等植物共生，常见于包括重金属污染土壤在内的各种生境中。在重金属污染条件下，AM真菌可以减轻重金属对植物的毒害，影响植物对重金属的吸收和转运，在重金属污染土壤的植物修复中显示出极大的应用潜力。重点介绍了AM真菌对植物重金属耐性的影响及其在植物提取和植物稳定中的应用等方面的进展，讨论了未来研究所面临的任务和挑战。     

土壤复合污染的联合修复技术研究进展

复合污染是土壤污染的主要存在形式,其中重金属、有机污染物等是主要的污染源。例如,共存于土壤中铅和镉会发生交互作用,从而增强了镉的迁移能力。此前单一的物理、化学、生物等修复手段对复合污染的修复效果并不明显。联合修复技术的使用可以在一定程度上克服使用单一的修复手段存在的缺点,提高修复效率、降低修复成本。最近有研究表明,综合利用化学氧化和超声波方法可以在很短的时间内将土壤中的甲苯和二甲苯完全氧化为CO和CO2。介绍了综合利用物理、化学、生物等方法对土壤复合污染修复的进展,并对研究中需要注意的问题及未来的发展趋势说明。     

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.     

In Vitro Health Risk Assessment of Ingesting Metal-Enriched Soils and Dusts in a Chinese Mining City

To evaluate the potential health hazards caused by extensive vanadium–titanium magnetite mining, bioavailability and bioaccessibility of metals were assessed in the pluralistic mining–agriculture–residential city of Panzhihua, China. Intensive mining and related heavy traffic may have contributed to Ni, Cr, and Zn contamination and Mn and V accumulation in soils and road dusts. The metal bioavailability estimated by water extraction was significantly lower than metal bioaccessibility on the basis of the simple bioaccessibility extraction test. The bioaccessible metal concentrations were significantly and positively correlated with soil/dust total metal concentrations (p < .05). However, bioavailable metal concentrations exhibited no relationship with total metal concentrations except for V. The bioaccessibility of metals significantly varied and exhibited the following order: Pb > Zn > Mn > Ni > V > Cr. Health risk assessment indicated that the carcinogenic and non-carcinogenic risks posed by these metals were at an acceptable level, but Cr in soils of the mining area and V in surface soils along the Jinsha River were close to the safe level for children. Therefore, the potential health risk attributed to the exposure of children to metals in surface soils and road dusts in such areas should not be overlooked.     

重金属污染土壤修复技术中有关淋洗剂的研究进展

淋洗法是修复污染土壤的一种很有效的方法 ,是对污染土壤生物修复的一种补充 ,使污染土壤修复的系统化成为可能。淋洗法就是使用淋洗剂来清洗土壤 ,使土壤中污染物随淋洗液流出 ,然后对淋洗液及土壤进行后续处理 ,从而达到修复污染土壤的目的。而淋洗剂的选择是影响这一技术效率高低的主要因素之一。本文对目前淋洗剂的应用情况 ,作用机制进行了总结和评价。探讨了天然有机酸、生物表面活性剂等对环境影响小的淋洗液的应用前景。并根据“以废治污”的指导思想提出并分析了以柠檬酸废水和味精废水作为淋洗剂修复重金属污染土壤的可行性。