Impact of Simulated Acid Rain on Trace Metals and Aluminum Leaching in Latosol from Guangdong Province,China

Acid rain is one of the most serious ecological and environmental problems worldwide. This study investigated the impacts of simulated acid rain (SAR) upon leaching of trace metals and aluminum (Al) from a soil. Soil pot leaching experiments were performed to investigate the impacts of SAR at five different pH levels (or treatments) over a 34-day period upon the release of trace metals (i.e., Cu, Ni, Pb, Zn, and Fe) and Al from the Latosol (acidic red soil). The concentrations of trace metals in the effluent increased as the SAR pH level decreased, and were highest at the SAR pH = 2.0. In general, the concentrations of Cu, Pb, Fe, and Al in the effluent increased with leaching time at the SAR pH = 2.0, whereas the concentrations of Zn, Fe, and Al in the effluent decreased with leaching time at the SAR pH ≥ 4.0. The increase in electrical conductivity (EC) with leaching time at five different SAR pH levels was primarily due to the concentrations of Al and Fe in the effluent. There were good linear correlations between the effluent Al concentrations and the effluent pH at the SAR pH = 2.0 (R² = 0.87) and pH = 3.0 (R² = 0.83). More soil trace metals and Al were activated and released into the soil solution as the SAR pH level decreased.     

Ultrastructural Responses of the LichenBryoria fuscescensto Simulated Acid Rain and Heavy Metal Deposition

Effects of simulated acid rain and heavy metal deposition onthe ultrastructure of the lichenBryoria fuscescens(Gyeln.) Brodoand Hawksw. were examined in a field study conducted in northernFinland. Lichens were exposed to simulated rain containing twolevels of a mixture of copper (Cu²⁺) and nickel (Ni²⁺) ionsalone or in combination with acid rain (H₂SO₄) at pH 3 over2 months in addition to ambient rainfall. The algal and fungalcomponents responded differently to pH and there was an interactionwith metal toxicity. The algal partner was the most sensitiveto acid rain and heavy metal combinations and had more degeneratecells than the fungal partner. Damage was apparent in chloroplastsand mitochondria, where thylakoid and mitochondrial cristaewere swollen. The fungal partner was the more sensitive to highconcentrations of metal ions in the absence of acidity, suggestingan ameliorating interaction between the metals and acidity.For algae, critical metal concentrations in the thallus were>50 µg g^-1for Cu and >7 µg g^-1for Ni in thepresence of acidity, and >20 µ g g^-1for Ni in the absenceof acidity. Detrimental effects of heavy metals on fungal ultrastructurewere seen when thallus metal concentrations exceeded 400 µgg^-1for Cu and 100 µg g^-1d. wt for Ni. The results suggestthat acid wet deposition containing metal ions may reduce survivalof lichens in northern environments.Copyright 1998 Annals ofBotany Company. Copper, nickel, sulphuric acid, ultrastructure,Bryoria fuscescens(Gyeln.) Brodo and Hawksw., epiphytic lichen, air pollution.     

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.     

天然水中重金属化学形态研究进展

本文介绍了天然水中溶解重金属的形态及其分析方法,着重介绍了阳极溶出伏安法、原子吸收光谱法等重金属形态分析方法,评价了各种分析方法的优缺点并对其进行了展望。     

Leaching Heavy Metals from Contaminated Soil by Using Thiobacillus ferrooxidans or Thiobacillus thiooxidans

Iron- and sulfur-oxidizing bacteria identified as Thiobacillus ferrooxidans and T. thiooxidans were successfully enriched from various soil samples contaminated with heavy metals and organic compounds. Depending on the growth medium, the soil sample, and the type of contaminant, the indigenous isolates solubilized > 50% of most of the heavy metals present in the solid sample (As, Cd, Co, Cr, Cu, Ni, V, Zn, B, Be). Leaching with T. ferrooxidans strains resulted in total extraction of Cd, Co, Cu, and Ni. With sulfur-oxidizing bacteria > 80% of Cd, Co, Cu, and Zn was mobilized from rainwater sludge. Pb and Ba were not detected in the leachate, given the insolubility of their sulfate compounds. An increase in pulp density up to 20%, indicating 6.6% total organic carbon in the soil and rubble leach experiment (sample 557), did not inhibit the growth of the indigenous T. ferrooxidans strain. In view of these results, bioleaching appears to have some potential for remediation of heavy metal contaminated soils.     

Heavy Metals Bioremediation of Soil

Historical emissions of old nonferrous factories lead to large geographical areas of metals-contaminated sites. At least 50 sites in Europe are contaminated with metals like Zn, Cd, Cu, and Pb. Several methods, based on granular differentiation, were developed to reduce the metals content. However, the obtained cleaned soil is just sand. Methods based on chemical leaching or extraction or on electrochemistry do release a soil without any salts and with an increased bioavailability of the remaining metals content. In this review a method is presented for the treatment of sandy soil contaminated with heavy metals. The system is based on the metal solubilization on biocyrstallization capacity of Alcaligenes eutrophus CH34. The bacterium can solubilize the metals (or increase their bioavailability) via the production of siderophores and adsorb the metals in their biomass on metal-induced outer membrane proteins and by bioprecipitation. After the addition of CH34 to a soil slurry, the metals move toward the biomass. As the bacterium tends to float quite easily, the biomass is separated from the water via a flocculation process. The Cd concentration in sandy soils could be reduced from 21 mg Cd/kg to 3.3 mg Cd/kg. At the same time, Zn was reduced from 1070 mg Zn/kg to 172 mg Zn/kg. The lead concentration went down from 459 mg Pb/kg to 74 mg Pb/kg. With the aid of biosensors, a complete decrease in bioavailability of the metals was measured.     

Quantification of Heavy Metals in Mining Affected Soil and Their Bioaccumulation in Native Plant Species

Several anthropogenic and natural sources are considered as the primary sources of toxic metals in the environment. The current study investigates the level of heavy metals contamination in the flora associated with serpentine soil along the Mafic and Ultramafic rocks northern-Pakistan. Soil and wild native plant species were collected from chromites mining affected areas and analyzed for heavy metals (Cr, Ni, Fe, Mn, Co, Cu and Zn) using atomic absorption spectrometer (AAS-PEA-700). The heavy metal concentrations were significantly (p < 0.01) higher in mine affected soil as compared to reference soil, however Cr and Ni exceeded maximum allowable limit (250 and 60 mg kg^?1, respectively) set by SEPA for soil. Inter-metal correlations between soil, roots and shoots showed that the sources of contamination of heavy metals were mainly associated with chromites mining. All the plant species accumulated significantly higher concentrations of heavy metals as compared to reference plant. The open dumping of mine wastes can create serious problems (food crops and drinking water contamination with heavy metals) for local community of the study area. The native wild plant species (Nepeta cataria, Impatiens bicolor royle, Tegetis minuta) growing on mining affected sites may be used for soil reclamation contaminated with heavy metals.     

The Chemophytostabilisation Process of Heavy Metal Polluted Soil

Industrial areas are characterised by soil degradation processes that are related primarily to the deposition of heavy metals. Areas contaminated with metals are a serious source of risk due to secondary pollutant emissions and metal leaching and migration in the soil profile and into the groundwater. Consequently, the optimal solution for these areas is to apply methods of remediation that create conditions for the restoration of plant cover and ensure the protection of groundwater against pollution. Remediation activities that are applied to large-scale areas contaminated with heavy metals should mainly focus on decreasing the degree of metal mobility in the soil profile and metal bioavailability to levels that are not phytotoxic. Chemophytostabilisation is a process in which soil amendments and plants are used to immobilise metals. The main objective of this research was to investigate the effects of different doses of organic amendments (after aerobic sewage sludge digestion in the food industry) and inorganic amendments (lime, superphosphate, and potassium phosphate) on changes in the metals fractions in soils contaminated with Cd, Pb and Zn during phytostabilisation. In this study, the contaminated soil was amended with sewage sludge and inorganic amendments and seeded with grass (tall fescue) to increase the degree of immobilisation of the studied metals. The contaminated soil was collected from the area surrounding a zinc smelter in the Silesia region of Poland (pH 5.5, Cd 12 mg kg^-1, Pb 1100 mg kg^-1, Zn 700 mg kg^-1). A plant growth experiment was conducted in a growth chamber for 5 months. Before and after plant growth, soil subsamples were subjected to chemical and physical analyses. To determine the fractions of the elements, a sequential extraction method was used according to Zeien and Brümmer. Research confirmed that the most important impacts on the Zn, Cd and Pb fractions included the combined application of sewage sludge from the food industry and the addition of lime and potassium phosphate. Certain doses of inorganic additives decreased the easily exchangeable fraction from 50% to 1%. The addition of sewage sludge caused a decrease in fraction I for Cd and Pb. In combination with the use of inorganic additives, a mobile fraction was not detected and an easily mobilisable fraction was reduced by half. For certain combinations of metals, the concentrations were detected up to a few percent. The application of sewage sludge resulted in a slight decrease in a mobile (water soluble and easily exchangeable metals) fraction of Zn, but when inorganic additives were applied, this fraction was not detected. The highest degree of immobilisation of the tested heavy metals relative to the control was achieved when using both sewage sludge and inorganic additives at an experimentally determined dose. The sequential extraction results confirmed this result. In addition, the results proved that the use of the phytostabilisation process on contaminated soils should be supported.     

Strength and Leaching Characteristics of Magnesium Phosphate Cement-Solidified Zinc- Contaminated Soil under the Effect of Acid Rain

Long-term static leaching experiments were conducted to investigate characteristics of magnesium phosphate cement (MPC) solidified/stabilized Zn-contaminated soil under impact of acid rain. Effects of initial pH values of acid rain, binder agent types and compositions, as well as curing age on strength and leaching characteristics of the sample were analyzed. Standard sand was used as raw material, with the content of cement at 15%. Our study used two types of MPC with MgO/KH₂PO₄(M/P) ratio of 3:1 and 6:1 (respectively referred to as M3 and M6), and also ordinary Portland cement with content at 15% (referred to as C15) as test control. Experimental results show that acid rain with pH = 2 has the greatest weakening effect on unconfined compressive strength (q_u) of the sample, while with pH = 4 and 7 such weakening effects on q_u are similar. Research findings also indicate that M6 is the most effective in immobilizing Zn-spiked soils, M3 is next and C15 is the least. The effect of Zn²⁺ on hydration of MPC is much lower than that of C15. Precuring method can improve q_u of the MPC-solidified samples and its resistance to acid rain. Compared with non-renewal, replacing acid rain leachant at designated intervals decreases q_u of the sample.     

Structure of a Microbial Community in Soil after Prolonged Addition of Low Levels of Simulated Acid Rain

Humus samples were collected 12 growing seasons after the start of a simulated acid rain experiment situated in the subarctic environment. The acid rain was simulated with H₂SO₄, a combination of H₂SO₄ and HNO₃, and HNO₃ at two levels of moderate acidic loads close to the natural anthropogenic pollution levels of southern Scandinavia. The higher levels of acid applications resulted in acidification, as defined by humus chemistry. The concentrations of base cations decreased, while the concentrations of exchangeable H⁺, Al, and Fe increased. Humus pH decreased from 3.83 to 3.65. Basal respiration decreased with decreasing humus pH, and total microbial biomass, measured by substrate-induced respiration and total amount of phospholipid fatty acids (PLFA), decreased slightly. An altered PLFA pattern indicated a change in the microbial community structure at the higher levels of acid applications. In general, branched fatty acids, typical of gram-positive bacteria, increased in the acid plots. PLFA analysis performed on the bacterial community growing on agar plates also showed that the relative amount of PLFA specific for gram-positive bacteria increased due to the acidification. The changed bacterial community was adapted to the more acidic environment in the acid-treated plots, even though bacterial growth rates, estimated by thymidine and leucine incorporation, decreased with pH. Fungal activity (measured as acetate incorporation into ergosterol) was not affected. This result indicates that bacteria were more affected than fungi by the acidification. The capacity of the bacterial community to utilize 95 different carbon sources was variable and only showed weak correlations to pH. Differences in the toxicities of H₂SO₄ and HNO₃ for the microbial community were not found.     

模拟酸雨-土壤酸化-杉木、木荷根系生长关系的研究

一、引言酸雨是当今世界重大的环境问题之一,它对生态环境的影响已引起各国政府及人们的极大关注。酸性降水对林木生长的影响目前有两种观点,即“由顶而下论”和“由底而上论”。持前一观点者认为,酸性降水淋洗树木叶子中的镁,伤害了树木的光合作用器官,影响树木的生长,导致森林的衰败。以西德学者     

Leaching Behavior and Risk Assessment of Heavy Metals in a Landfill of Electrolytic Manganese Residue in Western Hunan,China

We analyzed the leaching behavior and chemical speciation of heavy metals in a landfill of electrolytic manganese residue (EMR). The results showed that most of Pb, Cr, As, Cu, and Zn were associated with F4 (residual fraction) and Mn and Co were mainly present in F1 (exchangeable and weak acid soluble fraction). In order to evaluate potential risks of heavy metals to the landfill, modified potential ecological risk index (MPER), potential ecological risk index (PER), index of geo-accumulation (I_geo) assessment, and risk assessment code (RAC) were employed. Ranking order for potential risk based on RAC assessment is Mn > Co > Zn > Cu > Cr = As = Pb. Results from I_geo assessment indicates that Mn poses a potential for high risk to human health and the ecosystem. MPER, which integrates the characteristics of PER and RAC, shows that the potential risks of heavy metals are in the order of As > Cu > Mn > Co > Pb > Cr > Zn. The analysis indicates that Mn, Co, As, and Cu within EMR pose a potential risk when this material is placed in landfills and that these metals should be given particular attention when managing the land disposal of EMR.     

Bioleaching of Heavy Metal Polluted Sediment: Kinetics of Leaching and Microbial Sulfur Oxidation

Remediation of heavy metal polluted sediment through bioleaching using elemental sulfur (S⁰) as the leaching agent can be regarded as a two‐step process: firstly, the microbial oxidation of the added S⁰ to sulfuric acid and, secondly, the reaction of the produced acid with the sediment. Here, both subprocesses were studied in detail independently: oxidized river sediment was either suspended in sulfuric acid of various strengths, or mixed with various amounts of finely ground S⁰ powder (diameter of the S⁰ particles between 1 and 175 μm with a Rosin‐Rammler‐Sperling‐Bennet (RRSB) distribution and an average diameter of 35 μm) and suspended in water. The leaching process was observed by repeated analysis of the suspension concerning pH, soluble sulfate and metals, and remaining S⁰. In the case of abiotic leaching with H₂SO₄, the reaction between the acid and the sediment resulted in a gradual increase in pH and a solubilization of sediment‐borne heavy metals which required some time; 80 % of the finally solubilized heavy metals was dissolved after 1 h, 90 % after 10 h, and 100 % after 100 h. In the case of bioleaching, the rate of S⁰ oxidation was maximal at the beginning, gradually diminished with time, and was proportional to the initial amount of S⁰. Due to its very low solubility in water, S⁰ is oxidized in a surface reaction catalyzed by attached bacteria. The oxidation let the particles shrink, their surface became smaller and, thus, the S⁰ oxidation rate gradually decreased. The shrinking rate was time‐invariant and, at 30 °C, amounted to 0.5 μm/day (or 100 μg/cm²/day). Within 21 days, 90 % of the applied S⁰ was oxidized. Three models with a different degree of complexity have been developed that describe this S⁰ oxidation, assuming S⁰ particles of uniform size (I), using a measured particle size distribution (II), or applying an adapted RRSB distribution (III). Model I deviated slightly from the measured data but was easy to handle, Model II fitted the measured data best but its simulation was complicated, and Model III was intermediate. The amount of soluble sulfate was smaller than the amount of H₂SO₄ added or microbially generated as the H₂SO₄ reacted with the sediment to form in part poorly soluble sulfates. A model has been developed that describes the pH and the soluble sulfate and metals at equilibrium, depending on the amount of H₂SO₄ applied or microbially generated, and that is based on the condition of electrical neutrality, a global metal/proton exchange reaction, and a sulfate‐fixation reaction. In suspension, bioleaching with S⁰ required considerably more time than abiotic leaching with H₂SO₄, but the final pH and metal solubilization were identical when equimolar amounts of leaching agents were applied.     

模拟酸雨对梣叶槭的作用和植物营养

应用光声光谱和调制荧光测量技术研究了模拟酸雨对叶槭（ＡｃｅｒＮｅｇｕｎｄｏＬ．）的短期作用。用ｐＨ值分别为５．６、４．５和３．０的模拟酸雨对相应的三个样本组的梣叶槭树苗进行了为期三个月的跟踪观察和研究。结果表明,用归一化氧信号、光化学能量贮备、归一化可变荧光（ＦＶ／Ｆｍ）、光化学和非光化学叶绿素荧光猝灭等所表示的光合作用活性对这三个样本组的顺序为ｐＨ４．５＞ｐＨ３．０＞ｐＨ５．６。实验证实由于酸度水平增加,酸雨促进了生长率增加。从植物营养角度对结果进行了讨论。     

Role of Simulated Acid Rain on Acer negundo and Plant Nitrition

The short-term effects of simulated acid rain on Acer negundo L. have been investigated using photoacoustic spectroscopy and modulated fluorescence measurements. Three seeding groups of Acer negundo L. were treated with simulated acid rain at pH 3.0, 4.5 and 5.6 levels for three months. The results indicated the photosynthetic activity, expressed in terms of normalized oxygen evolution signal, photochemical energy storage, normalized variable fluorescence (Fv/Fm), photochemical and non-photochemical chlorophyll fluorescence quenching, ranges in the order pH 4.5 > pH 3.0 > pH 5.6. This stimulation effect has been confirmed by increased growth rate observed in relation with increased acidity levels. The nutritional aspects of this favorable effect of the acid rain on plant growth were discussed.     

Epigenetic Modifications Due to Heavy Metals Exposure in Children Living in Polluted Areas

The aim of the present article is to provide a summary of the epigenetic modifications that might occur in children exposed to heavy metals pollutants. It is known that children are more susceptible to environmental pollutants, because their detoxification enzymes are less competent, and this may lead to alterations in chromatin structure or of DNA causing, in turn, epigenetic modifications. Little is currently known about the long-term effects of these changes when occur early in childhood, none-theless there are ethics and practical concerns that make the assessment of DNA modifications difficult to perform in large-scale.     

16S rDNA Pyrosequencing Analysis of Bacterial Community in Heavy Metals Polluted Soils

Soil contamination with heavy metals is a widespread problem, especially prominent on grounds lying in the vicinity of mines, smelters, and other industrial facilities. Many such areas are located in Southern Poland; they are polluted mainly with Pb, Zn, Cd, or Cu, and locally also with Cr. As for now, little is known about most bacterial species thriving in such soils and even less about a core bacterial community—a set of taxa common to polluted soils. Therefore, we wanted to answer the question if such a set could be found in samples differing physicochemically and phytosociologically. To answer the question, we analyzed bacterial communities in three soil samples contaminated with Pb and Zn and two contaminated with Cr and lower levels of Pb and Zn. The communities were assessed with 16S rRNA gene fragments pyrosequencing. It was found that the samples differed significantly and Zn decreased both diversity and species richness at species and family levels, while plant species richness did not correlate with bacterial diversity. In spite of the differences between the samples, they shared many operational taxonomic units (OTUs) and it was possible to delineate the core microbiome of our sample set. The core set of OTUs comprised members of such taxa as Sphingomonas, Candidatus Solibacter, or Flexibacter showing that particular genera might be shared among sites ~40 km distant.     

Geochemical Speciation and Risk Assessment of Heavy Metals in Sediments of a River in Bangladesh

The surface sediment of a downstream river (Paira) connected to the marine ecosystems of the Bay of Bengal was assessed by sequential extraction technique. The objectives of this study were to evaluate the mobility and dynamics of heavy metals and their probable ecological risks. The results revealed high environmental risk of Cd due to higher availability in the exchangeable fraction (21%) and a considerable portion in the carbonate bound fraction due to the special affinity towards carbonate and co-precipitation with its minerals. Toxic metals like Cr, Ni, and Cd are of concern, and can occasionally be associated with adverse biological effects. The risk assessment code (RAC) suggests that the highest mobility of Cd poses a higher environmental risk and threat to the aquatic biota, as well.     

模拟酸雨对3种果树的胁迫效应

以青梅(Prunus mume Sieb.&Zucc.)、龙眼(Dimocarpus longan Lour.)和杨桃(Averrvhoa carambola L.)3种南方果树为材料,研究不同pH值的模拟酸雨对其生理胁迫的效应.在酸雨胁迫下3种果树的叶片叶绿素含量均随pH值的降低有不同程度的下降,叶片伤害率、细胞质膜透性、脯氨酸及丙二醛(MDA)含量则随pH值的降低而上升.抗性较强的龙眼的生理生化指标的变幅最小,其次是杨桃,对酸雨胁迫反应较敏感的青梅变幅最大.     

Heavy Metals Bioconcentration from Soil to Vegetables and Assessment of Health Risk Caused by Their Ingestion

The present study was undertaken to assess the non-carcinogenic human health risk of heavy metals through the ingestion of locally grown and commonly used vegetables viz. Raphanus sativus (root vegetable), Daucus carota (root vegetable), Benincasa hispida (fruit vegetable) and Brassica campestris leaves (leafy vegetable) in a semi-urbanized area of Haryana state, India. Heavy metal quantification of soil and vegetable samples was done using flame atomic absorption spectrophotometer. Lead, cadmium and nickel concentration in vegetable samples varied in range of 0.12–6.54 mg kg^?1, 0.02–0.67 mg kg^?1 and <0.05–0.41 mg kg^?1, respectively. Cadmium and lead concentration in some vegetable samples exceeded maximum permissible limit given by World Health Organization/Food and Agriculture Organization and Indian standards. Much higher concentrations of Pb (40–190.5 mg kg^?1), Cd (0.56–9.85 mg kg^-1) and Ni (3.21–45.87 mg kg^?1) were reported in corresponding vegetable fields’ soils. Correlation analysis revealed the formation of three primary clusters, i.e. Cu–Cd, Cd–Pb and Ni–Zn in vegetable fields’ soils further supported by cluster analysis and principal component analysis. Bioconcentration factor revealed that heavy metals’ uptake was more by leafy vegetable than root and fruit vegetables. Hazard index of all the vegetables was less than unity; thus, the ingestion of these vegetables is unlikely to pose health risks to the target population.