Spatial Distribution and Uncertainty Assessment of Potential Ecological Risks of Heavy Metals in Soil Using Sequential Gaussian Simulation

The objective of this study is to assess the spatial distribution and uncertainty of the potential ecological risks of heavy metals in soil using sequential Gaussian simulation (SGS) and the Hakanson potential ecological risk index (PERI). We collected 130 soil samples in an area of 150 km² in the High-Tech Park of Wuhan, China, and measured the concentrations of five heavy metals in soil (i.e., Cd, Cr, Cu, Pb, and Zn). We then simulated the spatial distribution of each heavy metal using SGS, and calculated Hakanson PERIs for individual metals and multiple metals based on the simulated realizations. The spatial uncertainty of the Cd PERI and its occurrence probabilities in different risk grades were further assessed. Results show that the potential ecological risks of Cr, Cu, Pb, and Zn are relatively low in the study area, but Cd indeed reaches a serious level that deserves much attention and essential treatment. The total PERI of multiple heavy metals indicates a moderate grade in most of the study area. In general, combining SGS and the Hakanson PERI appears to be an effective method for evaluating the potential ecological risks of heavy metals in soil and the priority areas for remediation.     

The assessment of soil contamination by heavy metals using geostatistical sequential Gaussian simulation method

Soil contamination by heavy metals is continuously increasing with a great attention in the world. Because, these elements negatively affect living life and the ecosystem. A total of 652 surface soil samples were collected at 100, 200, 400 m regular grid intervals from the study area in Turkey. The observed data does not show normal distribution. Cell declustering was done due to fact that data are not normal. Directional experimental semivariogram of the Cu and Ni showed that both geometric and zonal anisotropy exists in the data. Pb, Zn, Cr and Ba are qualified with omnidirectional experimental semivariogram models. The semivariograms characterized by spherical and Gaussian models of the elements were achieved. Geostatistical sequential Gaussian simulation (SGS) was applied to the study. A hundred simulated realizations depicted the spatial distribution and uncertainty of the elements in the site using a probabilistic approach which produced maps of the heavy metals. These maps showed contaminated and uncontaminated areas in the study site. The results revealed that 23%, 27%, and 24% of the study area at 60% probability were contaminated by the heavy metals including Cu, Cr, and Ni respectively. SGS results have been verified by a number of tests.     

长三角平原区县域土壤磷素流失风险及其空间不确定性的快速评估

磷素是水体富营养化的关键限制因子,其中从农田土壤中流失的磷往往是水体磷素的主要来源。然而,土壤磷素的流失风险不仅与土壤磷素水平直接相关,其他环境因子,如距受纳水体距离、磷肥施用量、地表径流潜力等也强烈影响其流失风险。同时,基于有限样本预测得到的流失风险必然具有一定的空间不确定性。以长三角典型县域金坛区为研究案例,首先结合多个环境因子构建快速磷指数(RPI)评估模型,再利用稳健地统计学方法识别土壤全磷的空间离群值,并利用序贯高斯模型(SGS)模拟土壤全磷可能的空间分布格局,最后将其多个可能的模拟结果及上述主要因子输入到RPI模型,用以快速评估土壤磷素流失风险及其空间不确定性。结果显示,金坛区土壤磷素流失的高风险区和土壤全磷高值区分布格局在研究区北部、中部具有一定的相似性,而在中西部的旱地区两者出现差异性。高风险区主要沿着河流呈现条带状及斑块状分布,较高及以上风险区(快速磷指数值大于0.93)的面积占金坛区面积的65.88%。概率阈值分别设定为0.50、0.75、0.85、0.95时,其超标面积占金坛区总面积分别达到16.71%、5.74%、2.84%、1.04%。引入多个相关环境因子并结合经稳健处理的SGS进行流失风险指数的空间模拟和不确定性评估,可以快速评估区域农田土壤磷素流失风险及不确定性,进而为区域土壤磷素调控提供必要的空间决策支持。     

某焦化场地土壤中多环芳烃分布的三维空间插值研究

为准确界定污染场地土壤中多环芳烃在3维条件下的污染分布范围和受污染土方量,选择我国某焦化污染场地苯并(a)芘分布为研究对象,对比研究Krig-3D、IDW-Shepard、IDW-(Franke/Nielson)以及Nearest Neighbor 4种3维插值方法对界定污染范围的不确定性影响。结果表明,不同3维插值模型计算结果差异较大,交叉验证结果显示Krig-3D插值模型插值精度最高,插值结果能较真实地反映场地实际污染情况。通过修复目标对比确定进一步表明,基于4种插值模型计算所得的污染土壤土方量分别为8.51×105、5.62×105、7.12×105、1.09×106m3,选择合理的插值模型将对预测污染范围的不确定性产生重要影响。研究结果对分析污染范围和修复治理过程土方量确定提供重要参考。     

反距离加权插值法在污染场地评价中的应用

确定污染场地的土壤修复范围在实际操作中存在很大的难度.本文以北方某废弃农药厂为例,结合专家判定采样法与网格采样法,采用地统计学方法中的反距离加权空间插值法,分两种情形将大于土壤环境基准值的区域划定为治理范围.结果表明,由于国家土壤环境二级标准主要适用于农业生产的土地,依据反距离加权空间插值后,以此标准确定的治理范围较大,而基于健康风险水平阈值所确定的修复范围和修复成本较小,较合理且经济可行.采用风险评价的反距离加权插值法确定污染场地的污染范围,为今后的场地评价和土壤修复提供了思路.     

Uncertainty-based dynamic multimedia human health risk assessment for polycyclic aromatic hydrocarbons (PAHs) in a land oil exploitation area

With the increasing development of the petrochemical industry and the growing demand for oil, polycyclic aromatic hydrocarbons (PAHs) pollutions in the environment, especially in petroleum exploitation areas, are caused by the discharge of waste from the petroleum extraction process into an environmental system. This study aims to develop a new health risk assessment approach based on interval dynamic multimedia fugacity (IDMF) model and uncertainty analysis that could analyze the human exposure risk level for PAH contamination. The developed IDM health risk assessment (IDMHRA) approach is applied to assess previous, current, and future risks at a case study site in Daqing, Heilongjiang, China, from 1985 to 2020 for model validation. The human health risk assessment results show that 11 PAHs (NAP, ANT, FLA, PYR, BaA, CHR, BbF, BkF, BaP, IPY, and DBA) in the study site require further remediation efforts in terms of their unacceptable non-carcinogenic and carcinogenic risk. The results of risk source analysis reveal that soil media is the main risk pathway as compared with other exposure pathways. It can be seen that remediation process for soil contamination in the study site is urgently demanded. The assessment results demonstrate that the developed IDMHRA approach provides an effective tool for decision-makers and environmental managers to make remediation decisions in contaminated sites.     

Using hyperaccumulator plants to phytoextract soil Ni and Cd

Two strategies of phytoextraction have been shown to have promise for practical soil remediation: domestication of natural hyperaccumulators and bioengineering plants with the genes that allow natural hyperaccumulators to achieve useful phytoextraction. Because different elements have different value, some can be phytomined for profit and others can be phytoremediated at lower cost than soil removal and replacement. Ni phytoextraction from contaminated or mineralized soils offers economic return greater than producing most crops, especially when considering the low fertility or phytotoxicity of Ni rich soils. Only soils that require remediation based on risk assessment will comprise the market for phytoremediation. Improved risk assessment has indicated that most Zn + Cd contaminated soils will not require Cd phytoextraction because the Zn limits practical risk from soil Cd. But rice and tobacco, and foods grown on soils with Cd contamination without corresponding 100-fold greater Zn contamination, allow Cd to readily enter food plants and diets. Clear evidence of human renal tubular dysfunction from soil Cd has only been obtained for subsistence rice farm families in Asia. Because of historic metal mining and smelting, Zn + Cd contaminated rice soils have been found in Japan, China, Korea, Vietnam and Thailand. Phytoextraction using southern France populations of Thlaspi caerulescens appears to be the only practical method to alleviate Cd risk without soil removal and replacement. The southern France plants accumulate 10-20-fold higher Cd in shoots than most T. caerulescens populations such as those from Belgium and the UK. Addition of fertilizers to maximize yield does not reduce Cd concentration in shoots; and soil management promotes annual Cd removal. The value of Cd in the plants is low, so the remediation service must pay the costs of Cd phytoextraction plus profits to the parties who conduct phytoextraction. Some other plants have been studied for Cd phytoextraction, but annual removals are much lower than the best T. caerulescens. Improved cultivars with higher yields and retaining this remarkable Cd phytoextraction potential are being bred using normal plant breeding techniques.     

Fractional Fuzzy Simulation–Based Health Risk Assessment for Toluene Contaminated Aquifers

This article integrates a fractional fuzzy health risk approach with multi-objective analysis in consideration of multiple exposure pathways in order to assess human health risk in petroleum hydrocarbon (PH)–contaminated aquifers. A PH-contaminated groundwater aquifer located in the Pinggu District of Beijing, China, is then studied for demonstrating the applicability of the proposed approach. The results show that with more fuzzy parameters considered in the risk assessment procedure, the multi-parameter fuzzy (MPF) result is more accurate than that from the single-parameter fuzzy (SPF) model. The comparison results also indicate the advantage of the proposed fractional fuzzy approach in assessing parameter uncertainty. The non-carcinogenic risk assessment results imply that the contaminated groundwater in the study area is in the medium risk level, and remediation plans for soil and groundwater should be considered to ensure safe groundwater utilization.     

基于文献计量的细菌-生物炭协同修复重金属污染土壤研究进展

为提高重金属污染土壤可持续修复效能,研究生物炭与细菌对重金属污染土壤的协同修复作用。基于文献计量学分析及重金属污染土壤修复背景,总结了细菌与生物炭对土壤重金属的稳定化特征及菌炭间的相互作用,分析了单一生物炭或细菌对重金属污染土壤修复的局限性,强调了细菌-生物炭协同修复技术的优势,阐述了细菌与生物炭主要通过离子交换、固定作用、氧化还原作用和迁移作用等重要机制有效修复重金属污染土壤,揭示了细菌-生物炭协同作用在重金属污染土壤修复中的巨大应用价值。文献计量学研究表明,生物炭与细菌对重金属污染土壤的协同修复已得到广泛关注。目前认为:生物炭与细菌的协同作用可有效改良土壤理化性质及提高土壤修复效率,也可促进植物生长及植物修复进程;生物炭对细菌影响具有双重性质,可促进细菌生长,也可能对细菌产生毒害;细菌可改变生物炭的理化性质,进而强化生物炭的重金属固定性能;细菌协同生物炭联合修复重金属污染土壤过程中,生物炭主导吸附和固定,细菌则发挥活化和解毒等功能;优化细菌-生物炭组合形式,发展混合细菌与多种类生物炭协同技术,是复合重金属污染土壤可持续修复亟待解决的重要问题;进一步揭示细菌与生物炭对重金属污染土壤的耦合作用及长效作用机制,规避生物炭生产和应用中的潜在生态健康风险,研发新型高效能细菌与生物炭复合体是细菌协同生物炭可持续修复重金属污染土壤应用领域面临的挑战。     

Mine tailing disposal sites: contamination problems,remedial options and phytocaps for sustainable remediation

Mining practices and the absence of proper mine land reclamation has led to heavy metal contaminated sites with serious impact on the ecosystems and risk for human health. The origin of the contamination is often associated to mine tailing deposits because they are a source of the acid mine drainage (AMD). These areas are devoid of vegetation due to the harsh soil conditions that prevent the rooting of plant species. The remediation of these areas followed by revegetation is necessary to suppress the generation of the AMD and its negative effects on the ecosystems. Conventional remediation technologies for heavy metal contaminated sites are usually not applicable because of the high cost associated with chemicals and energy requirements, as well as the long treatment time to remediate large areas. In this study, the use of phytocapping for the remediation of mine tailing deposits and abandoned mine areas is reviewed. Phytocapping is cost effective, environmentally friendly and has multifunctional role against various problems of mine tailings: it provides erosion control, landscape rehabilitation, enhances the soil properties for further colonization of other more demanding vegetal species, reduces the leachability of metals downwards the groundwater, and favors the immobilization of metals forming less bioavailable species. The most critical step in phytocapping is the developing of the first vegetative cover because of the biotoxicity of the mine soil and mine tailings. Several amendment materials can be used to ameliorate soil conditions creating a favorable environment for the rooting of plants, as well as serving as a source of nutrients. Local plant species with fast growing are preferable because their adaptation to the soil and climate conditions favors their self-propagation.     

Bioavailability of Metals in Soil and Health Risk Assessment for Populations Near an Indian Chromite Mine Area

Soils contaminated with toxic metals may be environmental hazards and sources of exposure to human population. Soils in mining areas are among the most heavily contaminated by metals from the mining activity. This study was focused on metals of interest in bioavailability studies using single and sequential extraction methods. Results of geochemical fractionation suggest that changes in soil characteristics may enhance the mobilization of Cu, Cr, Zn, and Al. The observed metals’ availability pattern was Cr > Cu > Zn > Al. However, the pattern of total contents of metals in soils was Al > Cr > Zn > Cu. Risks to human adults and children from selected metals through soil ingestion was assessed in terms of incremental lifetime average daily dose (LADD), hazard quotient (HQ), and hazard index (HI). The estimated LADDs and HI were within acceptable reference doses and less than 1, respectively, indicating low risk to human populations from the studied metals through soil ingestion in the studied mine area. The generated data may be useful in remediation of contaminated soils with metals.     

基于序贯指示模拟的农田土壤重金属风险区域识别

农田土壤重金属的日益累积已对农作物安全、生态环境和人类健康造成严重威胁,高效、精确地识别农田土壤重金属风险区对农田的环境保护、污染预警和风险管控等有重要意义.以广州市增城区为研究对象,共采集204个农田土壤样点,测定了铜(Cu)、锌(Zn)、铅(Pb)、镉(Cd)、铬(Cr)、砷(As)和汞(Hg)7种重金属含量.针对实际采样数据中存在异常值与偏态分布,以及传统克里格法存在的平滑效应等问题,将序贯指示模拟引入农田土壤重金属的风险识别中,与常用识别方法进行比较,并根据Hakanson风险指数评价进行风险区划.结果表明:(1)对比普通克里格法,在精度相似情况下,序贯指示模拟法较为精细地模拟了重金属的空间分布,平滑效应低,预测的细节表现好;对比指示克里格法,其在划分风险区域时的不确定评估中准确度较高,其误判率仅为4.9%~17.1%,表明其能更好地适用于模拟农田土壤重金属的空间分布和风险识别;(2)增城区的农田土壤重金属均未超标,但在南部的极少数区域存在潜在中等风险,主要成因是包括企业生产、人类活动和河流沉积物等.本研究以序贯指示模拟为基础,有效克服了传统克里格法存在的异常值信息丢失和平滑效应问题,结合Hakanson风险指数法,为非均匀采样的土壤重金属空间风险的识别提供一种新的尝试.     

Chemical Fractionation and Soil-to-Plant Transfer Characteristics of Heavy Metals in a Sludge Deposit Field of the River Ruhr,Germany

The presented study assessed the heavy metal contamination risk in a former sludge deposit field of the River Ruhr in Essen, Germany. Therefore, the temporal and spatial distribution in soils and plants, chemical fractionation, mobilization potential, and transfer characteristics have been investigated. Soil samples, roots and shoots of rushes (Juncus sp.), and stem wood disks of willows (Salix sp.) were analyzed for Zn, Cu, Pb, Ni, Cr, and Cd. Plant available and mobile heavy metal portions have been determined using a sequential extraction procedure. The results show that the soils and the rushes are highly contaminated, although there is a considerable decrease compared to initial concentrations some 20 years ago. The willows show only small heavy metal enrichment. pH induced mobilization potential in soil is high for Cd, Zn and Ni. Additionally, these elements contain high portions of plant-available fractions. High transfer rates from soil to roots and very high rates from roots to shoots of rushes have been determined for Cd and Zn, indicating an accumulation of these elements in shoots of rushes. The rushes reflect the temporal and spatial heavy metal distribution in soil and might thus be used as a bioindicator or for phytoremediation.     

Assessing the spatial uncertainty in soil nitrogen mapping through stochastic simulations with categorical land use information

This study explores the capability of an extended sequential Gaussian simulation algorithm with incorporation of categorical land use information (SGS-CI) for simulating spatial variability of soil total nitrogen (TN) contents and assessing associated spatial uncertainty. 402 sampled data in soil TN contents in a county scale region and the categorical land use map data of the study area were used to perform sequential simulations for comparing the SGS-CI algorithm and the conventional SGS algorithm, and 135 validation samples were used to assess the improvement of SGS-CI over SGS in prediction accuracy and uncertainty reduction. Results showed that the validation data were more strongly correlated with the optimal prediction (i.e., E-type estimates) data of SGS-CI than with those of SGS, and the mean error and the root mean square error of the optimal prediction using SGS-CI were smaller than those using SGS. SGS-CI also performed slightly better than SGS in uncertainty modeling in terms of accuracy plots and goodness statistic G. In addition, because demands for soil total nitrogen by different crops are usually different in agricultural practice, we showed that SGS-CI could be used to assess spatial uncertainty of deficiency or abundance degrees of soil TN based on demands of different crops in different land use types. Therefore, SGS-CI may provide an effective method for improving prediction accuracy and reducing uncertainty in soil TN prediction.     

污染场地土壤生态风险评估研究进展

随着我国快速城市化以及产业结构的调整,遗留下了大量的污染场地,发展和实施污染场地土壤生态风险评估是进行大规模污染场地修复行动的必要条件。本文围绕污染场地土壤生态风险评估的科学原理、框架构建及技术方法等方面的关键问题: 1)评估框架的场地实际针对性;2)概念模型的不确定性;3)土壤复合污染毒性机制;4)评估终点筛选;5)评估方法和框架构建等展开讨论,指出土壤复合污染的制毒机制,即污染物生物有效性和联合效应是污染场地土壤生态风险评估的关键科学问题。耦合美国环保局四步法和欧盟层级法的“证据-权重法”评估框架适用于野外复杂环境条件下的土壤污染生态风险评估。建议今后重点开展以下5个方面的工作: 1)污染场地土壤生态风险评估技术框架与风险管控技术框架之间的联合;2)概念模型研究;3)基于过程的场地土壤污染物反应运移模型研究;4)场地土壤复合污染生态毒理学机制研究;5)生态系统高水平生态风险评估终点研究。旨在为形成我国本土污染场地土壤生态风险评估技术指南提供理论基础和构架。     

Methodology for using contaminated soil leachability testing to determine soil cleanup levels at contaminated petroleum underground storage tank (UST) sites

The costs of environmental remediation at leaking petroleum underground storage tank (UST) sites are influenced significantly by soil cleanup levels. The use of conservative generic soil cleanup levels may be inappropriate at some sites contaminated by leaking petroleum USTs. At many contaminated sites, a primary objective of site remediation is long‐term protection of water resources (e.g., groundwater) from pollution. Leaching of pollutants from residual soil contamination to groundwater is a primary consideration in establishing site‐specific soil cleanup levels at fuel‐contaminated sites. The use of laboratory soil leachability testing methods may be useful in objectively evaluating the leaching potential of contaminants from residual soil contamination and estimating potential groundwater impacts. Developing soil cleanup levels that are protective of water resources must include a technically sound integration of site‐specific soil leachability data and contaminant attenuation factors. Evaluation of the leaching potentials of soil contaminants may also provide essential supplementary information for other site characterization methods that may be used to evaluate risks to human health. Contaminant leachability testing of soils may provide a cost‐effective and technically based method for determining soil cleanup levels that are protective of groundwater resources at contaminated petroleum UST sites.     

Liming to remediate Ni contaminated soils with diverse properties and a wide range of Ni concentration

Historic emissions from a Ni refinery at Port Colborne, Ontario, caused Ni contamination of regional soils and raised concerns about potential Ni phytotoxicity. Previous tests revealed that if these soils were made alkaline and fertilized with Mn and other common nutrients as needed to maintain fertility of such alkaline soils, full remediation (prevention of Ni phytotoxicity) would be obtained. This experiment was conducted to test this method of remediation on diverse soils from Port Colborne, and to evaluate chemical extraction tests which would be predictive of plant uptake and potential for Ni phytotoxicity in Ni-contaminated soils. Ten soils with varied levels of Ni contamination and varied soil properties were amended with limestone or nitric acid to raise or lower pH so that a wide pH range could be examined for the soils. For lower Ni organic and mineral soils near the Ontario remediation limit (200 mg/kg), neither crop suffered Ni phytotoxicity at any pH tested. Only when more highly contaminated soils were strongly acidic did Ni phytotoxicity occur. Phytotoxic soils were fully remediated by making soils alkaline even for these Ni-sensitive crop species. Only the most contaminated organic soil remained slightly toxic – but this soil was remarkably contaminated (over 1.1% of Ni). The Sr nitrate extraction method was much more effective in predicting plant Ni concentrations than the DTPA method. This test provides an inexpensive soil extraction result highly predictive of potential for Ni phytotoxicity across soils.     

Sequential extraction and speciation of Ba,Cu, Ni,Pb and Zn in soil contaminated with automotive industry waste

Abstract

Sequential extraction or fractionation of heavy metals in the solid phase and their speciation in soil solution are important tools for assessing changes resulting from land use and/or pollution. The distribution of the various forms of Ba, Cu, Ni, Pb and Zn was evaluated in soil samples taken from a polluted area, and the speciation of cations and anions in a soil solution contaminated with automotive industry waste. We evaluated the sequential extraction and speciation of Ba, Cu, Ni, Pb and Zn in a Leptosol associated with a Cambisol and contaminated with automotive industry waste. Soil samples were collected at 0-0.2 m (a mix of soil and waste); 0.2-0.4 m (waste only), and 0.4-0.6 m (soil only) both in the polluted area and in two contiguous unpolluted areas: a sugarcane plantation and a forest fragment. Total concentrations of metals in the polluted area were above limits for intervention established by European Community regulations. Cu was mostly distributed in the residual and in the oxide-bonded fractions, except for the waste-only sample, in which the carbonate-bonded fraction was significant. Zn was concentrated in the residual and carbonate-bonded fractions, while Ba, Ni and Pb predominated in the residual fraction of the contaminated samples. Metals in the soil solution were predominantly in the hydroxyl forms, except for Ba, which was mostly in the ionic form (Ba²⁺).     

镍污染土壤植物采矿技术关键过程及其研究进展

植物采矿是利用超积累植物高量吸收土壤中的重金属,并从中提取、冶炼金属产品,在修复污染土壤的同时实现金属的资源化。全世界广泛分布着自然风化的镍污染土壤,植物采矿因其重要的环境、生态及资源价值,被作为一种环境友好且具备经济效益的土壤修复技术,在此类地区具有广阔的应用前景。该植物采矿技术关键过程主要包括超积累植物镍高选择性根际环境响应、植物镍高效吸收转运以及生物质中镍高附加值资源化等过程。近30年,污染土壤中镍的植物采矿已经在美国、阿尔巴尼亚、马来西亚等多个国家进行了野外实践,取得了良好效果。然而,相关技术在我国的研究与应用仍然处于起步阶段。文中通过综述植物采矿技术的关键过程的研究进展,发现其中的瓶颈,为接下来植物采矿的科学研究和技术在全世界推广提供理论基础和技术指导。     

西北黄土区石油污染土壤原位微生物生态修复试验研究

通过对西北黄土石油开采区石油污染土壤生物强化原位微生物生态修复方法的试验研究,充分利用强化原位微生物菌群辅以物理和化学方法与土壤环境相结合的微生物生态技术,进行了土壤中石油的降解与修复试验研究,试验结果显示,土壤中平均石油含量在2754mg/kg时,经过lld～32d强化原位微生物生态修复技术的修复,土壤中石油含量降解可达40.92%～80.37%,验证了微生物生态修复技术在西北黄土区土壤石油污染修复的有效性,探索了推广应用的可行性.