Metal Transport and Bioavailability in Soil Contaminated with CCA-Treated Wood Leachates

A laboratory study was conducted to investigate metal transport and accumulation within soils contaminated with As, Cr, and Cu from CCA-treated wood leachates. New blocks of CCA-treated wood were leached using synthetic rainwater. Soil columns were constructed and filled with three different soils, including a sandy soil, an organic soil and a clay soil. The leachate was applied intermittently until 80 pore volumes were eluted through each column. Metal concentrations (Cu, Cr, and As) were measured in the leachate before passage through the columns as well as in each elutriate fraction collected. Chemical analysis was complemented with toxicity testing using Ceriodaphnia dubia, Selenastrum capricornutum, and MetPLATE?. Following application of 80 pore volumes of leachate, the columns were dissected and the profile of the metal concentrations within each column was determined. A comparison of the arsenic, chromium and copper leaching patterns found arsenic to be the most mobile, with copper the most retained in the soil columns (As < Cr < Cu). Transport patterns of As differed in the three soil types, with observed mobility highest in the sandy soil and lowest in the clay soil. The three metals accumulated in the top layer of soil. Arsenic posed the greatest risk when soil concentrations were compared to risk-based target levels. Although metals were detected in soil elutriates, no toxicity was detected in any of the soil column elutriates using any of the three toxicity assays.     

植物修复——治理土壤重金属污染的新途径

介绍了重金属污染土壤的植物修复的概念、原理与研究动态以及重金属超积累植物的特性 ,及其在治理污染土壤中的潜力 ,为土壤重金属污染的整治及其生态的修复提出新途径。     

我国土壤重金属污染植物吸取修复研究进展

我国从上世纪90年代中后期开始土壤重金属（含类金属砷）污染的植物吸取修复研究及技术探索,先后发现了一批具有较高研究价值和应用前景的铜、砷、镉、锰等重金属的积累或超积累植物,并从重金属耐性和超积累生理机制、植物吸取修复的根际过程与机制、吸取修复强化措施和修复植物处置与资源化利用等方面进行了研究,同时开展了植物吸取修复技术的示范与应用,已有一些较成功的植物修复工程应用案例,使我国重金属污染土壤植物修复技术,尤其是植物吸取修复技术在国际上产生了较强的影响力。本文就近年来我国土壤重金属污染植物吸取修复研究进展进行了综述,并对今后的发展趋势进行了展望。     

Effects of Anions on the Capacity and Affinity of Copper Adsorption in Two Variable Charge Soils

Effects of nitrate,(NO₃⁻) chloride (Cl⁻), sulfate (SO₄^2-, and acetate (Ac⁻) on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were evaluated in two Fe and Al enriched variable charge soils from Southern China. The maximum adsorption of Cu²⁺ (M, a parameter from the Langmuir isotherm model) in the presence of different anions decreased in the order Cl⁻ > Ac⁻ > NO₃⁻ > SO₄^2- for both soils. The clayey loamy soil (mixed siliceous thermic Typic Dystrochrept, TTD), developed on the Arenaceous rock, adsorbed less Cu²⁺ than the clayey soil (kaolinitic thermic Plinthudults, KTP), derived from the Quaternary red earths, regardless of anion type present in the medium. The affinity of adsorbed Cu²⁺ to both soils could be characterized by the Kd (distribution coefficient) values and successive extraction of the adsorbed Cu²⁺ with 1-mol NH₄Ac L⁻¹. The log₁₀Kd value was smaller for the TTD soil than for the KTP soil and decreased in the order of Cl⁻ > NO₃⁻ > SO₄^2- > Ac⁻ at low initial Cu²⁺ concentrations (≤40 mg Cu²⁺L⁻¹), whereas at 80 mg Cu²⁺L⁻¹, the log₁₀Kd value was similar for NO₃⁻, SO₄^2-, and Ac⁻, but was slightly higher for Cl⁻. Complete extraction of Cu²⁺ adsorbed in the presence of Ac⁻ was achieved. Influence of NO₃⁻ and SO₄^2- on the affinity of adsorbed Cu²⁺ was similar, but the effects of Cl⁻ depended on the initial Cu²⁺ concentrations. The extracted percentage of the adsorbed Cu²⁺ in the presence of NO₃⁻ or SO₄^2- increased with increasing Cu²⁺ adsorption saturation. The presence of Cl⁻, NO₃⁻, or SO₄^2- markedly decreased the equilibrium solution pH for both soils with increasing initial Cu²⁺ concentrations, and the delta pH values at the highest Cu²⁺ level were 0.5, 0.63, and 0.55 U for the TTD soil and 0.79, 0.84, and 0.93 U for the KTP soil, respectively for the three anions. The presence of Ac⁻ had a minimal influence on the equilibrium solution pH because of the buffering nature of the NaAc/HAc medium which buffered the released protons. The effects of anions on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were dependent on anion types and were apparently related to the altered surface properties caused by anion adsorption and/or the formation of anion– Cu²⁺ complexes.     

福建漳州菜园土壤重金属污染评价及防治

调查福建省漳州市菜园土壤重金属Cd、Pb、Hg、Cr及非金属有害元素As含量,并采用单项污染指数法和综合污染指数法进行评价。结果表明,以福建土壤背景值为评价标准,漳州市部分菜园土壤受到重金属污染,单项污染指数的顺序为Cd(2.39) >Hg(2.00) >Pb(1.40) >Cr(0.63) >As(0.57),污染元素主要为Cd、Pb、Hg,其中Cd、Hg为中度污染;综合污染指数为1.75,属轻度污染。而以土壤环境质量二级标准为评价标准,其综合污染指数为0.14,污染等级为未受污染。     

Assessment of Heavy Metal Pollution in Urban Agricultural Soils of Jilin City,China

Due to rapid industrialization and urbanization during the last two decades, contamination of urban agricultural soils by heavy metals is on an increase all over China. In this study, fifty soil samples were collected from urban vegetable fields in a chemical industrial area and non chemical industrial area in Jilin City to investigate the heavy metal pollution level. The mean Pb, Cr, Cu, Ni, Zn, and Cd contents (30.84, 65.65, 26.41, 23.07, 135.14, and 0.1434 mg kg^?1 dry weight, respectively) in the urban vegetable soils were higher than their corresponding natural background values. The principal component analysis (PCA) was performed to identify the possible sources of metal contamination in the study area. The results indicated that Cu and Zn were mainly from industrial activities, while Pb and Cd were derived from traffic activities and agricultural activities, and Cr and Ni tended to be from parent material. The distribution of comprehensive pollution index values showed that Pb, Cr, Cu, Ni, Zn, and Cd concentrations in most of the agricultural fields did not exceed the baseline values affecting the safety of agricultural production and human health according to the soil environmental quality standard of China, indicating an insignificant contamination of these metals in Jilin City.     

A Confidence Region Approach for Assessing Equivalence in Variability of Bioavailability

The problem for assessment of equivalence in variability of bioavailability between two drug products is considered. Similar to the method for assessing bioequivalence in average bioavailability proposed by Chow and Shao (1990), an exact confidence region approach is derived when the intersubject variance is known. When the intersubject variance is unknown, a large sample approximation is considered. The proposed method for assessing equivalence of variability of bioavailability appears to be asymptotically uncorrelated with that of Chow and Shao (1990) for average bioavailability. As a result, the proposed method in conjunction with the method proposed by Chow and Shao (1990) constitutes a confidence region approach for assessing population bioequivalence. An example concerning a bioequivalence trial with 24 healthy volunteers is provided to illustrate the proposed method.     

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.     

Comparison of Extractants for Removing Heavy Metals from Contaminated Clayey Soils

This article describes the removal of heavy metals from contaminated clayey soils by soil washing using various extractants. Two clayey soils, kaolin, a low buffering soil with pH of 5, and glacial till, a high buffering soil with pH of 8, were used to represent various soil conditions. These soils were spiked with chromium (Cr), nickel (Ni), and cadmium (Cd) to simulate improper disposal of typical electroplating waste constituents. The following extracting solutions were investigated for the removal of heavy metals from the soils: deionized water, distilled water, and tap water; acetic acid and phosphoric acid; chelating agents ethylenediaminetetraacetic acid (EDTA) and citric acid; and the oxidizing agents potassium permanganate and hydrogen peroxide. The effect of extractant concentration on removal of heavy metals was also investigated. Complete removal of Cr was achieved using 0.1?M potassium permanganate for kaolin, while a maximum of 54% was removed from glacial till. A maximum Ni removal of 80% was achieved using tapwater for kaolin, while a maximum removal of 48 to 52% was achieved using either 1?M acetic acid or 0.1?M citric acid for glacial till. A maximum Cd removal of 50% was achieved using any of the extractants for kaolin, while a maximum removal of 45 to 48% was obtained using either acids or chelating agents for glacial till. Overall, this study showed that complete removal of Cr, Ni, and Cd from clayey soils is difficult to achieve using the soil-washing process, and also the use of one extractant may not be effective in removing all metals. A sequential extraction using different extractants may be needed for the removal of multiple metal contaminants from clayey soils.     

Environmental Monitoring of Heavy Metal Status and Human Health Risk Assessment in the Agricultural Soils of the Jinxi River Area,China

Soil contamination with heavy metals is one of the main environmental concerns in China, mainly owing to rapid industrialization and mining activities in certain areas. The current study aimed at monitoring the levels of heavy metals in soils of the industrial areas along the Jinxi River and surrounding Lake Qingshan. In addition, a health risk assessment for humans in contact with these soils was also conducted. The results revealed that the soils of the studied areas were contaminated with Cr, Cu, As, Se, Cd, Pb, and Zn and that the industrial activities were the main source of soil contamination therein. Furthermore, soils of the sites adjacent to Lin’an city exhibited higher levels of heavy metals than the upstream and Lake Qingshan sites. Most of the studied heavy metals tended to concentrate in the fine soil fractions (PM100, PM10, and PM2.5). Calculation of the hazard index (HI) revealed that humans, especially children, have potential health risks. Moreover, As was found to contribute to more magnitude of cancer risks. Thus, we concluded that the unmanaged development negatively affects the Chinese environment and human health. Furthermore, fine fractions of soil particles should be considered for risk assessment.     

Heavy Metal Contamination in the Brownfield Soils of Cleveland

The results esults of a survey of heavy metal contamination at Cleveland area brownfields and public spaces are presented. Soils were analyzed using a 24?h, 1N HCl extraction procedure. The study was conducted to seek brownfield soils that manifest properties of “old” sequestered contamination and to develop a better understanding of the nature and extent of heavy metal burdens at brownfield sites in the Greater Cleveland area. The results indicated that Cleveland brownfields commonly yield soil burdens well above remediation triggers for residential soils and often yield values above industrial remediation triggers. It was also discovered that public areas in the vicinity of brownfields commonly have heavy metal contamination significantly above background levels and occasionally above residential remediation triggers. These results indicate that brownfields redevelopment initiatives should proceed with caution. The appropriate remediation goals or restrictions must be imposed to control urban exposure to heavy metal contamination.     

Relevance of Rhizosphere Research to the Ecological Risk Assessment of Trace Metals in Soils

The chemical, mineralogical, and microbial properties of the rhizosphere of a range of forested ecosystems were studied to identify the key processes controlling the distribution and fate of trace metals at the soil–root interface. The results of our research indicate that: (1) the rhizosphere is a soil microenvironment where properties (e.g., pH, organic matter, microbes) and processes (nutrient and water absorption, exudation) differ markedly from those of the adjacent bulk soil; (2) the rhizosphere is a corrosive medium where the weathering and neoformation of soil solid phases are enhanced; (3) the concentrations of solid-phase and water-soluble trace metals like Cd, Cu, Ni, Pb, and Zn are generally higher in the rhizosphere as shown by both macroscopic and microscopic approaches; (4) a larger fraction of water-soluble metals is complexed by dissolved organic substances in the rhizosphere; and (5) soil microorganisms play, either directly or indirectly, a distinct role on metal speciation, in particular Cu and Zn, in the rhizosphere. These results improve our capacity to estimate metal speciation and bioavailability at the soil–root interface. Furthermore, the research emphasizes the crucial physical position occupied by the rhizosphere with respect to the process of elemental uptake by plants and its key functional role in the transfer of trace metals along the food chain. We conclude that the properties and processes of the rhizosphere should be viewed as key components of assessments of the ecological risks associated with the presence of trace metals in soils.     

Sources and Ecological Risk Assessment of Heavy Metal(loid)s in Agricultural Soils of Huzhou,China

To identify sources of heavy metal(loid) (HM) contamination in agricultural soils of Huzhou, surface soil samples were sampled from 89 different agricultural regions in 2012. Concentrations of heavy metal(loid)s, along with pH, total phosphorus (TP), total nitrogen (TN), and soil organic matter (SOM), were determined. Ecological risk was then assessed using a modified Hakanson ecological risk index, and the sources of contamination were determined using principal component analysis (PCA). Mean concentrations of heavy metal(loid)s were 10.26, 23.21, 83.75, 22.81, 0.25, 61.86, 33.03, and 0.15 mg kg^?1 for As, Cu, Zn, Ni, Cd, Cr, Pb, and Hg, respectively. Cu, Zn, Ni, Cr, Cd, Hg, and Pb were correlated positively with TP and there were obvious positive correlations among Cu, Zn, Ni, Cr, and Cd. Risk index (RI) values varied from 39 to 1246 with a mean value of 137. Enrichment of Pb, Zn, Cu, and especially Cd can be attributed to excessive use of nitrogen and phosphorus fertilizers containing heavy metals, as well to surface irrigation and natural soil formation. While the ecological risk of most agricultural soils in Huzhou is low, it is recommended that the use of phosphate and nitrogen fertilizers be restricted and production technology be improved to reduce the heavy metal(loid) concentrations. Results suggest that the Chinese environmental quality standard for soil should be revised to better address heavy metal(loid) contamination.     

Chelate-Enhanced Phytoremediation of Soils Polluted with Heavy Metals

In general, hyperaccumulators are low biomass, slow-growing plants. High biomass non-hyperaccumulator plants by themselves are not a valid alternative for phytoextraction as they also have many limitations, such as small root uptake and little root-to-shoot translocation. In this context, chemically-induced phytoextraction (based on the fact that the application of certain chemicals, mostly chelating agents, to the soil significantly enhances metal accumulation by plants) has been proposed as an alternative for the cleaning up of metal polluted soils. But chelate-induced phytoextraction increases the risk of adverse environmental effects due to metal mobilization during extended periods of time. In order to minimize the phytotoxicity and environmental problems associated with the use of chelating agents, nowadays, research is being carried out on the gradual application of small doses of the chelating agent during the growth period. However, EDTA utilization in the future will most likely be limited to ex situconditions where control of the leachates can be achieved. There are other mobilizing agents which are much less harmful to the environment such as citric acid, NTA, and particularly EDDS. Research should also be aimed towards more innovative agronomic practices. Environmentally safe methods of chelate-induced phytoextraction must be developed before steps towards further development and commercialization of this remediation technology are taken. Most importantly, more applied projects in this field are needed to clarify the real potential and risks of this technology.     

Current Research on Heavy Metal Binding Complexes of Plants

Heavy metal binding complexes found in the cytoplasm of plant cells are widely reported to be responsible fox metal resistance. It is believed that these metal binding complexes may play an important role in the accumulation of heavy metal and preventing them from entering the ptant metabolic pathways. This review summarizes information on purification, characterization and properties of these molecules. In view of their inducibility, low molecular weight, specific optical characteristics (high absorption at 254nm and low absorption at 280 nm), high cysteine content and high capacity for binding heavy metal, these complexes were once proposed to be metallothionein-like molecules. However differing from metallothionein of animal system, heavy metal binding complexes in plants are comprised mainly of three amino acids with a unique structure of (γ-Glu-Cys)n-Gly ((γ-EC)nG) (n=2—11). With the presence of γ-carboxyl group peptide linkage, the complexes are thought not to be synthesized via mRNA but the product of biosynthetic pathway using glutatkione as precursor.     

重金属污染对蛙蟾类毒性的研究进展

基于近20年的大量相关资料,综述了重金属对蛙蟾类毒性影响方面的研究,介绍了实验动物和实验方法,综合了重金属对蛙蟾类在形态、器官、组织、细胞和分子水平上毒害的主要表现,从重金属致毒过程、环境因素、物种、发育、重金属积累、联合毒性等角度初步分析了重金属对蛙蟾毒性大小的影响因素和毒性作用的主要机理,归纳了蛙蟾的几种抗毒/解毒/避毒反应,对开展进一步的研究提出建议.     

The Adsorption Properties of Agricultural and Forest Soils Towards Heavy Metal Ions (Ni,Cu, Zn,and Cd)

Adsorption of Cu, Cd, Ni, and Zn in single and multi-metal solutions by agricultural and forest soils was investigated in batch sorption experiments. The results showed significant differences in sorption capacities of the studied soils. The selectivity order was as follows: agricultural soil? top forest soil > bottom forest soil. The adsorption sequence Cu > Zn > Ni > Cd was established for the agricultural and bottom forest soil, while the order for the top forest soil was Cu > Ni > Zn > Cd. The experimental isotherms for the metal sorption were described satisfactorily by the Freundlich and Langmuir models. The competitive adsorption experiment indicated a reduction in the amount of metals adsorbed by the soils from the multi-metal solution compared to the single metal solution. Properties of the soils, such as pH, content of clay and organic matter, exchangeable bases and hydrolytic acidity, showed a significant influence on adsorption capacities of the studied soils.     

Heavy Metal Concentration in the Urban Environment of Addis Ababa,Ethiopia

This work assesses the issue of whether the measured concentrations of heavy metals in soil, rocks, surface and ground waters in Addis Ababa can be related to anthropogenic contamination or natural weathering of rocks. Heavy metal analyses of rocks, soils, streams, springs and boreholes have been carried out to identify the presence of potentially harmful solutes. The maximum concentration of total chromium measured is 269 ppm in the northern, industry-free zone of Addis Ababa in the B ₂-horizon of soil profile (cambisol). The Ni/Cr ratio in the rocks is higher than soils, which could indicate the presence of high concentrations of Cr in soils is from weathering processes. A comparative study of different samples collected from various parts of the city indicates that the chemical composition of the hydrothermally affected volcanic rocks plays an important role in increasing heavy metal concentration in the study area. The fresh country rocks contain relatively low concentrations of heavy metals, as shown by background values. The statistical evaluation indicates that the hydrothermally altered rocks contain far higher mean heavy metal concentrations than the fresh acidic rocks (background values). Consequently, soils derived from altered rocks are enriched with respect to heavy metals. From this study it was possible to observe that the rock and soil outcrops of Addis Ababa are anomalously rich in heavy metals derived from hydrothermal activity. Therefore, heavy metal concentrations in the surrounding rocks and soils are related to geogenic sources whereas anthropogenic contribution as a cause of these concentrations is minor.     

Decorative Landscaping Rock as a Source for Heavy Metal Contamination,Las Vegas,Nevada

Recent drought coupled with population growth throughout the southwestern United States has increased the demand for water-efficient landscaping alternatives. As a result, xeriscaping has become a popular approach to landscaping in arid climates. Currently, no regulations control the mineralogy of decorative rocks that are used in these applications. Eight public sites were examined in Las Vegas, NV, where green and white salt crusts appeared on recently emplaced decorative rocks. The landscaping rocks, underlying soil, surface salt crusts, irrigation water runoff, and plants were analyzed for mineralogy and/or chemistry. Pyrite and high levels of copper were identified in the decorative rock. Acid-rock drainage caused by pyrite oxidation has concentrated copper in salt efflorescences, and As, Cu, Mo, Pb, and Cr in plant tissues. These metals are not known to occur naturally in Las Vegas Valley soils, and our results indicate that their source is the landscaping aggregate. These highly soluble salt crusts have the potential to contaminate the environment, and increase the risk of human exposure. Additionally, expenses resulting from plant mortality and infrastructure damage due to increased sulfate production are undesirable. This research supports the development of regulations preventing the use of sulfide-bearing rocks in future landscaping applications.