Statistical Analysis of BTEX Surface Soil Regulatory Guidance Values

Residential surface soil regulatory guidance values (RGVs) specify the threshold at which soil contamination requires action. Usually, these are risk-based values based on child ingestion, inhalation, and dermal exposure. Benzene, toluene, ethylbenzene, and xylenes (BTEX) are among the five most commonly regulated soil contaminants in the United States and worldwide. More than 100 regulatory jurisdictions have established surface soil RGVs for BTEX compounds. Analysis of these values indicates that they vary by several orders of magnitude and appear to fit a lognormal random variable model with values well dispersed across the number spans. The RGVs applied to benzene are statistically distinct from those applied to TEX contamination, but the TEX values appear to be statistically indistinguishable. The magnitude of difference between TEX RGVs of different jurisdictions appears to be more significant than differences in the T, E, and X values specified by any one jurisdiction. Although value distributions are dominated by randomness, some contain clusters of points that are unlikely to be random and may represent consensus on appropriate values. Where “consensus clusters” exist, they should be identified and explored. The mechanistic explanations for cluster values may yield methods of reducing RGV variability.     

Worldwide Residential Soil Regulatory Guidance Values for Chlorinated Methanes

In many environmental jurisdictions worldwide, surface soil contamination is regulated using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. Three of the four chlorinated methanes are among the seven most frequently regulated synthetic surface soil contaminants. There are at least 80 U.S. regulatory jurisdictions and at least 30 international jurisdictions with guidance values for at least one of the chlorinated methanes, yielding as many as 106 values (for dichloromethane) for the same regulatory consideration. This analysis explores the variability of these values. Results indicate that the values span at least 5 orders of magnitude and are distributed in patterns similar to a lognormal random variable, but fit distributions that are statistically distinct. The distributions also contain value clusters that may imply emerging consensus about appropriate regulatory levels or demonstrate the impact of regulatory leadership to suppress variability. Simulation based on the current U.S. Environmental Protection Agency risk analysis model are used to estimate the degree to which value ranges may be attributed to uncertainty in exposure models. Approximately 50% of guidance values fall within the 95% confidence interval uncertainty bounds of risk model results.     

Evaluating an Electrokinetically Driven Extraction Method for Measuring Heavy Metal Soil Contamination

Measuring the heavy metal burden of “old contamination” soils (soils with aged contamination) can be challenging. Many laboratory procedures are currently in use and these can yield a wide range of burden estimates for the same soil. The appropriate extraction method selection depends on the intended use of the information and on compatibility with the procedures used to generate the “reference” data to which results are compared. In this work, results for an extraction based on the electrokinetic mobilization of old contamination heavy metals were compared to the results of established single analyte and sequential extraction methods. Accomplishing extractions electrokinetically offers promise for simplifying processes and for evaluating the electrokinetic remediation potential of old contamination soils. On the brownfield soils tested, electrokinetic extraction identified an average of 82% of the soil’s Cr, Cu, Pb, and Zn burden relative to Environmental Protection Agency Method 3050B extractions. However, results also indicated that neither of these methods were successful at extracting all of the sequestered (residual) fraction of heavy metals and thus underestimated the total contamination burden of the soil.     

Worldwide Residential Soil Regulatory Guidance Values for Chlorinated Ethenes

Surface soil contamination is often regulated by using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. In the United States, there are at least 88 value sets, and another 35 worldwide, that provide guidance for at least one chlorinated ethene. Trichloroethene is the most commonly regulated chlorinated ethene (118 values) and may be the most commonly regulated synthetic organic surface soil contaminant. Cis- and trans-1,2-dichloroethene are the least regulated chlorinated ethenes. Overall, there are 617 guidance values for specific chlorinated ethenes plus another 32 for mixed isomers of dichlorethene. This analysis explores the origin, magnitude, and form of the variability of these values. Results indicate that values span from 4.9 to 6.6 orders of magnitude and follow distributions similar to lognormal random variables. However, distributions include value clusters similar to values advocated by the U.S. Environmental Protection Agency (USEPA) or the Canadian Council of Ministers of the Environment (CCME). Although only 9.5% of the regulatory guidance values (RGVs) are identical to USEPA or CCME values, 55% of these fall within the uncertainty bounds estimated for USEPA risk models. Results suggest that stronger national leadership and reduced risk model uncertainty could be effective in reducing the RGV variability of chlorinated ethenes.     

Worldwide Residential Soil Regulatory Guidance Values for Chlorinated Ethanes

Surface soil contamination is often regulated using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. In the United States, there are at least 89 value sets (and worldwide there are another 29) that provide guidance for at least one of the nine chlorinated ethanes. The most commonly regulated chlorinated ethane is 1,2-dichloroethane (108 values), and it is the third most commonly regulated synthetic organic surface soil contaminant. Pentachloroethane (17 values) is the least regulated chlorinated ethane. Overall, there are at least 690 guidance values for chlorinated ethanes. This analysis explores the origin, magnitude, and form of the variability of these values. Results indicate that the values span from 3.7 to 7.6 orders of magnitude and are distributed in patterns similar to log-normal random variables. Less than 20% of these values are similar to those of national regulatory agencies such as the U.S. EPA or the Canadian Council of Ministers of the Environment, but more than 60% of the values fall within the 95% confidence interval bounds of the uncertainty in U.S. EPA risk model calculations.     

Analysis of Regulatory Guidance Values for Residential Surface Soil Arsenic Exposure

Residential surface soil regulatory guidance values (RGVs) specify the threshold at which soil contamination requires action. Usually, RGVs are risk-based values based on child ingestion, inhalation, and dermal exposure. The U.S. Environmental Protection Agency, 45 U.S. states, and 27 other nations have developed arsenic surface soil RGVs. Regulating arsenic poses unusual problems because it presents both cancer and noncancer risks, and its background concentration often exceeds health-based risk levels. Statistical analyses are presented to characterize 119 arsenic surface soil RGVs. State values vary between 0.039 and 200 mg/kg. Worldwide values vary between 1.7 and 687 mg/kg. The U.S. and worldwide values resemble lognormal probability distributions but the data cannot be mingled since worldwide values are significantly higher. An analysis of 40 arsenic background studies yielding averages between 1.3 and 45.1 mg/kg is also presented. Monte Carlo simulations of screening model calculations are used to explore the impact of coefficient uncertainty. Results indicate that 95% of cancer-based results should fall between 0.004 and 2.7 mg/kg and 95% of noncancer results should fall between 1.0 and 40 mg/kg. Although U.S. state arsenic RGVs vary by 3.7 orders of magnitude, most values appear to fall within the bounds of plausible risk- and background-based values.     

Preliminary Evaluation of Microbially Mediated Precipitation of Cadmium, Chromium, and Nickel by Rhizosphere Consortium

Elevated heavy metal soils and water contamination have been shown to impose toxic effects on plants, animals, and human health. The extent of toxicity depends on the nature of the metals, soil and aquatic system characteristics, and the complex interactions between metals and the environment. Recent studies have shown that metal–microbe interactions may be effective for the remediation of contaminated media. This study investigated the effectiveness of an isolated rhizosphere bacterial consortium for treating an aqueous solution containing 600 mg/L of Cd, Cr, and Ni. The consortium was resistant to the metal toxicity as evidenced by an increase of population density of more than 6×1011?cfu/mL. The microbial activity facilitated a reduction in aqueous metal concentration with a metal precipitation selectivity of Cr?Cd>Ni.     

Influence of Metal Loading on the Mode of Metal Retention in a Natural Clay

Clay, which is a natural fine-grained soil, was subjected to various levels of contamination by the heavy metal Zn, in a series of batch sorption experiments conducted at pHs of 3–7. Zinc speciation in the soil was subsequently analyzed using a sequential extraction technique, which fractionated the retained Zn into exchangeable, carbonate, reducible, organic, and residual fractions. The results showed that when Zn loading increased, the increase in Zn sorption by the clay was rather limited in acidic conditions. The Zn distribution between the dissolved phase and each fraction of the sorbed phases could be described with either the Freundlich or the Langmuir adsorption equations. If favorable pH existed, at high Zn loadings, precipitation was the most effective process of Zn removal from the dissolved phase. At low Zn loading levels, a relatively higher proportion of Zn was retained in the more persistent fractions. These findings indicated that the predominant mode of heavy metal retention in a soil can be significantly influenced by the level of soil contamination by the metal, in addition to geochemical factors and behaviors of the metal itself.     

Periprosthetic humeral fractures: mechanisms of fracture and treatment options

The mink (Mustela vision) is a top trophic level species that readily bioaccumulates environmental pollutants and is considered to be a sensitive indicator of ecosystem health. Spatial trends in levels of organochlorine and heavy metal contaminant burdens were determined from 1991 to 1995 for wild mink from western Northwest Territories (NWT), Canada. Tissue samples from 207 mink from seven communities were analyzed for residues of 63 organochlorines and 10 heavy metals. All groups of organochlorines were detected in mink livers at relatively low levels; maximum community means were 9.52 ng/g sigma DDT and 73.07 ng/g sigma PCB (sum of 43 congeners). There was a general trend of decreasing organochlorine burdens along a northerly or westerly gradient for some groups of compounds, primarily sigma DDT, sigma PCB, sigma chlordane and dieldrin. Toxic equivalents (TEQs) of mink liver tissue were low, with the maximum community mean of 0.28 pg/g wet weight (5.5 pg/g lipid weight). Levels of heavy metal burdens in liver and kidney tissues were found to be relatively low, with the exception of Hg, which was found at moderate levels. There was no obvious geographic trend to the pattern of heavy metal burdens. The available evidence suggests that long-range atmospheric transport is the main source of the organochlorine contaminants observed. Local conditions (geology, water and soil chemistry, diet, etc.) may determine heavy metal burdens. Levels of contaminants in NWT mink appear to be one to two orders of magnitude lower than levels observed to cause reproductive impairment, reduced survival of kits, or lethality in adult mink. In the western NWT mink may be the best indicator to assess trends in environmental contaminants and ecosystem health; periodic monitoring is recommended.     

赣州市土壤重金属形态分布特征及污染评价

以赣州市6大功能区土壤重金属为研究对象,采取表层0~20cm土壤共50个样品,测定土壤中重金属Pb、Zn、Cu、Cd和Cr含量并分析其来源,采用改进BCR连续提取法进行形态分析,结合次生相与原生相分布比值法、单因子指数法进行污染评价。结果表明研究区土壤中Pb和Cu元素变异系数较大,重金属Zn, Cu和Pb之间相关性显著。通过单因子指数法评价结果可以看出,赣州市6大功能区都受到重金属Cd的重度污染,居民区和工业区受到重金属Cr的轻度污染,交通区受到重金属Pb和Zn的轻度污染。研究区土壤重金属Cd、Cr、Cu、Pb、Zn形态都以残渣态为主,次生相与原生相比值都是小于1的属于无污染。      

基于模糊数学的矿区土壤重金属污染评价——以信丰稀土矿区为例

根据土壤重金属污染评价具有的模糊性和渐变性特点,建立模糊数学污染评价模型分析重金属的污染程度.结果显示单个重金属无污染,矿区综合土壤质量等级为1级,评价分值为97.034,属于安全水平. 在此基础上,与传统的污染指数对比分析,单因子污染指数显示Ni和Pb为轻度污染,地累积指数显示Pb为中度污染,内梅罗指数和潜在生态危害指数显示为无污染和轻微生态危害.研究表明:模糊评价法不仅可以对土壤重金属进行评价,还可以建立隶属度函数描述土壤重金属污染状况的模糊性和渐变性,解决传统污染指数评价法存在的不足,比传统污染指数评价法更为客观、准确,可以作为一种有效的矿区土壤重金属污染程度的评价方法.      

模糊数学模型在土壤重金属污染评价中的应用

针对传统的土壤环境重金属受污染程度评价标准不统一、定性指标难以定量化的问题,建立了适用于土壤中Cd等重金属污染状况评价的模糊数学模型。应用Matlab软件的Matlab-FIS工具分析了白银市白银区附近的土壤中重金属污染情况,评价结果显示该区域土壤受到了一定程度的重金属污染,采样点中层土壤受污染程度高于表层土壤,远离工业区的土壤质量好于工业区附近的土壤。研究表明,模糊评价法可以精确地对土壤中重金属综合污染进行评价,解决了传统的单因子指数评价法存在的不足之处,比单因子指标评价法更为客观、准确。     

Respiratory symptoms and pulmonary function in coal miners: looking into the effects of simple pneumoconiosis

Most soil quality guidelines do not distinguish among the various forms of metals in soils; insoluble, nonreactive, and nonbioavailable forms are deemed as hazardous as highly soluble, reactive, and toxic forms. The objective of this study was to better understand the long-term effects of copper on microorganisms in relation to its chemical speciation in the soil environment. Carbon mineralization processes and the global structure of different microbial communities (fungi, eubacteria, actinomycetes) are still affected after more than 50 years of copper contamination in 20 soils sampled from two different agricultural sites. The microbial respiration lag period (LP) preceding the beginning of mineralization process increases with the level of soil copper contamination and is not significantly affected by other environmental factors such as soil pH and soil organic matter (SOM) content. The total copper concentration showed the best correlation with the LP when each site is considered separately. However, when considering the whole set of data, soil solution free Cu2+ activity (pCu2+) is the best predictor of Cu toxicity determined by LP (quite likely because pCu2+ integrates the soil physicochemical variability). The maximum mineralization rate (MMR), even if well correlated with the pCu2+, appears not to be a good biomonitor of copper contamination in soils since it is highly sensitive to soil characteristics such as SOM content. This study emphasizes the importance of the physicochemical properties of the environment on soil heavy metal toxicity and on soil toxicological measurements. These properties must be characterized in soil toxicological studies with respect to (1) their interactions with heavy metals, and (2) their direct impact on the selected biological test. The measurement of pCu2+ to characterize the level of soil contamination and of lag period as a bioindicator of metal effects in the soil are recognized as useful tools for the evaluation of the biological quality of soils.     

Evaluation of Chemical Treatments for a Mixed Contaminant Soil

Treatability tests were conducted on soil from the reservoir No. 2 burning ground at the former Plum Brook Ordnance Works in Sandusky, Ohio. This soil is contaminated with explosives 2,4,6-trinitrotolune (TNT) and 2,4/2,6-dinitrotoluene (DNT), polychlorinated biphenyls (PCB, Aroclor 1260), as well as lead. Lime treatment (alkaline hydrolysis) and persulfate oxidation were tested individually and in combination to treat explosives and PCBs. Lime treatment removed 98% of TNT, 75% of DNT, and 80% of PCBs. Similar removal levels were found for persulfate treatment as well as lime followed by persulfate. The percentage of contaminant removal was found to be independent of initial contaminant concentrations. Treatments of the most contaminated soil did not meet the preliminary remediation goals for explosives or PCBs but would allow for disposal in a nonhazardous waste landfill. Treatment of soil with lower initial concentrations easily met the residential (most stringent) preliminary remediation goals of 16, 61, and 0.22?mg?kg?1 for TNT, 2,6-DNT, and PCB (Aroclor 1260), respectively. Neither alkaline hydrolysis nor persulfate oxidation transferred more than 0.02% of the lead from the soil into the reaction waters. Lead was successfully stabilized via phosphate addition.     

Enhanced Soil Flushing for Simultaneous Removal of PAHs and Heavy Metals from Industrial Contaminated Soil

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are environmental concerns and must be removed to acceptable levels. This paper evaluates different flushing agents to enhance the remediation of soil contaminated with PAHs and heavy metals at a former manufactured gas plant site. Four flushing column tests at a constant hydraulic gradient of 1.2 were conducted using four different flushing agents, which included deionized water, chelant (0.2?M EDTA), surfactant (5% Igepal CA-720), and cyclodextrin (10% hydroxypropyl-β-cyclodextrin or HPCD). Additional column tests using Igepal and HPCD at a lower hydraulic gradient of 0.2 were conducted to investigate the effects of rate-limited desorption or solubilization of PAHs. The results showed that the EDTA produced the maximum metal removal from the soil compared with deionized water, Igepal, and HPCD under different hydraulic gradient conditions. The 0.2?M EDTA flushing solution removed approximately 25–75% of the toxic heavy metals found in the soil. None of the PAHs were removed from the soil when deionized water and EDTA were the flushing solutions. The PAHs removal efficiencies in the Igepal and HPCD systems decreased as the hydraulic gradient decreased. However, the surfactant-enhanced systems were more efficient in removing PAHs from the soil than the HPCD systems under high- and low-hydraulic gradients. The results also demonstrated that the removal of PAHs in surfactant-enhanced systems depended upon the micelles formation, whereas in the HPCD-enhanced systems, it depended upon the sterioselective diffusion of the PAHs to the nonpolar cavity of the HPCD. Overall, this study showed that the contaminant removal in soil flushing systems depends on the flushing solution affinity and selectivity toward the target contaminant and the existing hydraulic gradient condition.     

Effects of Road Salts on Heavy Metal Mobility in Two Eastern Washington Soils

Heavy metals deposited on road surfaces and transferred to roadside environments by rainfall and snowmelt runoff can have serious impacts on receiving ecosystems. Infiltration is an effective best management practice for controlling metal contamination in runoff, although metals retention within infiltration facilities depends on a number of factors, including metal species, soil characteristics, and influent water quality concentrations. In cold climates, deicing compounds have been shown to mobilize heavy metals putting receiving waters at risk. This study ascertains the effects of two widely used road salts (NaCl and MgCl2) on heavy metal mobility in two eastern Washington soils. Infiltration experiments were conducted using a basic soil, exhibiting a soil pH of 8.3, taken from a highway infiltration pond site in Spokane Washington and an acidic soil, exhibiting a soil pH of 5.9, taken from an infiltration pond site in Richland Washington. Three concentrations of each salt were percolated through both soils using continuous flow soil columns. Leachate samples were collected and analyzed for dissolved metals, organic matter, and pH. Experiments were also performed without salt and used as controls. Results indicate that metal mobilization can occur by a number of mechanisms including cation exchange, chloride complex formation, and colloid dispersion (release of organic matter and/or clay that can complex metal species). Sodium chloride resulted in the largest release of copper and lead via indirect mobilization of organic matter. The magnesium salt had less of an effect on lead and copper but had a much greater effect on the mobilization of cadmium. Releases of metals during or immediately following salt application produced concentrations that ranged from 50% to 1000% greater than the concentrations released from the control experiments.     

Enhanced Electrokinetic Remediation of Heavy Metals in Glacial Till Soils Using Different Electrolyte Solutions

Previous electrokinetic remediation studies involving the geochemical characterization of heavy metals in high acid buffering soils, such as glacial till soil, revealed significant hexavalent chromium migration towards the anode. The migration of cationic contaminants, such as nickel and cadmium, towards the cathode was insignificant due to their precipitation under the high pH conditions that result when the soil has a high acid buffering capacity. Therefore the present laboratory study was undertaken to investigate the performance of different electrolyte (or purging) solutions, which were introduced to either dissolve the metal precipitates and/or form soluble metal complexes. Tests were conducted on a glacial till soil that was spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, under the application of a 1.0 VDC/cm voltage gradient. The electrolyte solutions tested were 0.1M EDTA (ethylenediaminetetraacetic acid), 1.0M acetic acid, 1.0M citric acid, 0.1M NaCl/0.1M EDTA, and 0.05M sulfuric acid/0.5M sulfuric acid. The results showed that 46–82% of the Cr(VI) was removed from the soil, depending on the purging solution used. The highest removal of Ni(II) and Cd(II) was 48 and 26%, respectively, and this removal was achieved using 1.0M acetic acid. Although cationic contaminant removal was low, the use of 0.1M NaCl as an anode purging solution and 0.1M EDTA as a cathode purging solution resulted in significant contaminant migration towards the soil regions adjacent to the electrodes. Compared to low buffering capacity soils, such as kaolin, the removal of heavy metals from the glacial till soil was low, and this was attributed to the more complex composition of glacial till. Overall, this study showed that the selection of the purging solutions for the enhanced removal of heavy metals from soils should be primarily based upon the contaminant characteristics and the soil composition.     

潼关金矿区农田土壤Cd污染分析

潼关金矿区是中国重要的黄金产地。在金矿石的开采及选冶生产过程中,矿石中的有毒重金属Cd会污染矿区周围环境。文中以133件土壤样品Cd含量为基础,研究了该矿区土壤Cd的分布特征。土壤Cd含量范围为0.00~45.20mg/kg,部分样品的Cd含量极高,受污染程度严重。土壤Cd累积污染超标倍数表明,研究区42.11%的样品土壤受到轻度污染,15.03%的样品土壤属于中度以上污染。农田土壤Cd含量的空间分布显示,土壤Cd含量较高的范围与矿业活动的污染源基本一致,说明矿业活动对土壤Cd含量影响较为明显。通过尾矿渣中Cd的分析,进一步证明金矿生产活动是造成土壤Cd污染的主要原因。     

小秦岭典型地段植物重金属污染特征分析

在研究区采集了132组植物样品,并对样品中As、Hg、Cu、Zn、Pb、Cd、Cr、Ni 8种重金属含量进行了测试,采用环境指数作为植物重金属污染评价方法来描述受污染程度,得出了不同种类植物的重金属污染状况。通过对比分析富集系数,研究了重金属在植物中的富集特征。其研究结果表明:不同植物中重金属含量超标倍数和吸收量明显不同,显示出选择性富集特征。该次采集的所有植物中As、Hg的含量都不超标;红薯中Cd和Pb的含量超标倍数最高,玉米中Zn的含量超标倍数最高,Cu也比较容易在粮食作物中累积且以红薯最为突出;蔬菜中Pb、Cd、Zn的含量超标倍数最高,以白萝卜、白菜最为突出;水果中Pb的含量超标倍数最高,且苹果和柿子都较为突出。该次采集的植物对Pb的吸收能力都很强,只有玉米对Zn的吸收能力比其对Pb的吸收能力略强。受到重金属污染的土壤所种植的粮食、蔬菜和水果均有不同程度的富集,其对重金属吸收强弱的排序分别为:白菜、白萝卜和胡萝卜中,PbZnCuNiCrCdHgAs;红薯和茄子中,PbCuZnNiCrHgCdAs;南瓜和苹果中,PbCuZnNiCrHgAsCd;柿子中,PbNiCuZnCrHgAsCd;玉米中,ZnPbCuNiCrHgAsCd;西红柿中,PbZnCuNiCrAsCdHg。     

微生物对重金属元素作用机理综述

我国土壤重金属污染问题日益严峻,对于土壤重金属污染的治理已成为环境保护方面的一个热点．当前土壤重金属污染处理方法有物理、化学、生物方法．其中物理、化学方法成本高,且容易造成二次污染;而微生物方法以其低成本,且微生物因其种类多且易得而受到越来越多的重视．利用微生物的溶解作用能够淋滤出污染土壤中的结合态重金属离子;利用微生物的氧化还原作用能够改变重金属离子的价态,使其毒性降低;利用微生物的固定作用能够降低重金属的迁移性;利用菌根联合作用能够对重金属污染进行联合治理修复．文中介绍了微生物对重金属的溶解、氧化还原、固定以及菌根联合作用的机理,并指出了这一领域日后的研究方向,希望能对日后这方面的相关研究有所裨益．