土壤重金属污染评价指标的研究进展

土壤重金属污染评价指标主要有：土壤重金属总含量，有效含量，土壤酶活性以及植物中毒临界含量等。由于受重金属污染的土壤中往往伴有多种重金属元素以及元素之间的交互作用，使得临界值的确定更为复杂，目前评价土壤重金属复合污染的方法主要是综合指数法。     

重金属有效态与土壤环境质量标准制订

制订合适的土壤环境质量标准是评价土壤健康质量及食品安全的核心问题,而土壤重金属有效态对制定土壤环境质量标准具有重要意义。土壤重金属有效态主要指植物有效态,它与重金属形态关系密切。影响土壤重金属有效态的因素很多,主要包括:土壤pH值、氧化还原电位、CEC、有机质含量、粒径组成(黏粒含量)、铁铝锰氧化物含量、植物种类、土壤微生物、土壤温度的高低、重金属来源等。化学试剂浸提法是测量重金属生物有效性的常用方法,所用化学试剂主要有三类:弱(稀)酸、络合剂和中性盐,中性盐由于对土壤pH值影响小而受到重视。我国现行土壤质量标准采用土壤重金属总量和pH两个因素为依据,但是不少学者认为,该标准仅适用于重金属有效态较高的土壤,而不能反映重金属有效态含量较低土壤的实际状况。     

Comparison and Evaluation of Extraction Media and Their Suitability in a Simple Model to Predict the Biological Relevance of Heavy Metal Concentrations in Contaminated Soils

Abstract

The concentrations of heavy metals in agricultural soils are increasing gradually from various diffuse sources. The metals can transfer from contaminated soils into the growing plants or may affect the respiration rate of soil microorganisms.

In the first part of this paper, the following simple model to predict the biorelevant metal concentration in anthropogenically or artificially contaminated soils is reported: log M_p = α + β log [M_NaNO3] log M_R = α' + β' log [M_NaNO3] log M_P = log Metal concentration in test plant (mg/kg dry weight) log M_R = log percent Redution in the respiration or enzyme activity [M_NaNO3] = Metal concentration in NaNO3-soil extract (mg/kg soil) α and β & α' + β' = Intercepts and slopes of the linear regression lines.

The model has been tested in laboratory experiments, in growth experiments either in a greenhouse or in the field. Also, an attempt is made to present a theoretical interpretation.

Critical concentrations are calculated with the help of the relationship between metal concentration in soil solution [M_NaNO3] and metal concentration in plants. The critical concentration, which is able to induce either phyto- or zootoxic concentrations in the plant parts (productive or vegetative) or reduce their growth or to reduce significantly the growth of soil microorganisms, are found to be uniform in a wide range of soils (pH 3 to 8 and CEC 10–50 millimol/100g soil), the critical concentrations of NaNO₃ in soil extracts are comparable with the values obtained with plant growth experiments in nutrient solution and also with the concentrations obtained from soil respiration experiments reported in literature.     

Assessment of mobility of heavy metals in two soil types by use of column leaching experiments and chemometric evaluation of elution curves

The objectives of this study were to evaluate the mobility of heavy metals (HMs) in two types of soils (acidic forest soil and neutral agricultural soil) by leaching with calcium chloride solution in column experiments. The screening properties of neutral agricultural soil towards pollution by heavy metals (Ni, Cu, Zn and Cd) are approximately 10 times higher than those of acid forest soil. The neutral agricultural soil, polluted artificially by one pore volume (PV) of an HMs solution of concentration 200 mg L^?1, can screen the leaching of these metals over several hundreds of years. The higher apparent desorption rate and per cent desorption of HMs (especially Cd) in acid forest soil indicated a higher potential of intensive migration of the metals across the profile and indicated potential risk of Cd pollution for this type of soil. The latest approach of artificial neural networks to describe transport of HMs in soil has been also evaluated. Using a simple three-layer perceptron topology with three hidden neurons, the experimental data could be simulated. The results suggested that the pH of soil is a major factor controlling the retention of the heavy metals in the soils.     

Preliminary investigation of Spartina alterniflora for phytoextraction of selected heavy metals in soils from Southwest Louisiana

Spartina alterniflora plants were collected at the Rockefeller Wildlife Refuge near Lake Charles, Louisiana for phytoremediation (phytoextraction) studies. In order to determine whether the plant would thrive in different soils and undergo phytoremediation, three soils were used and analyzed: experimental controlled soil (minimum heavy metal contamination), spiked soil (spiked with 100 ppm of selected heavy metals of Cr, Cu, Pb, Fe and Zn) collected from a local store and contaminated soil collected from the known contaminated (with metals) Bayou d'Inde in Lake Charles, Louisiana. The plant grew evenly in each of the three soils. Based on the inductively coupled plasma-optical emission spectrometric determination of the plant in each soil, it was shown that S. alterniflora exhibited potential for phytoremediation of metals in soils via phytoextraction into the roots.     

Development of Resin Membranes as a Sensitive Indicator of Heavy Metal Toxicity in the Soil Environment

Abstract

Ion exchange resins in contact with soil can act as a sink for metal cations, thereby simulate the action of plant roots. Ion exchange resins in membrane form offer additional advantages in ease of use and handling. A procedure was developed to assess the bioavailability of four heavy metals Cd, Cr, Ni and Pb via direct in soil burial. A growth chamber experiment with three representative crops (oats, radish and lettuce) was set up to determine the phytotoxic levels of the four heavy metals. The critical levels varied widely from crop to crop, and soil to soil. Lettuce was most sensitive to high concentration of metals. The toxic effects are more pronounced on sandier textured soils.     

Desorption of Heavy Metals from Typical Soil Components (Clay,Peat) with Glycine

Abstract

Natural organic chelating agents take part in the mobilization and translocation of heavy metals in unpolluted and polluted soils. They also have to be considered as possible extracting agents for the decontamination of heavy metal polluted soils. For an assessment of the desorption capability of glycinc, heavy metals (Cd, Cu, Ni, Pb, Zn) were adsorbed onto typical soil components (bentonite and peat). The metal loaded sorbents were resuspended in aqueous solutions of glycine at pH 7.0 and 4.5 and the quantities of the desorbed metals were analysed in the liquid phase. Furthermore, the dependency of the desorption rate on the duration of experiments and the metal content were investigated. The remobilization of heavy metals from bentonite by glycine at pH 7.0 decreases following the order Cu > Ni > Zn > Cd > Pb and ranges from 95% to 9.5%. The desorption rate was significantly lower at pH 4.5 and in suspensions of peat.     

Ornamental Plant Efficiency for Heavy Metals Phytoextraction from Contaminated Soils Amended with Organic Materials

Accumulation of heavy metals (HMs) by ornamental plants (OPs) from contaminated agriculture soils is a unique technique that can efficiently reduce the metal load in the food chain. Amaranthus tricolor L. has attractive characteristics acquiring a higher growth rate and large biomass when grown at heavy metal contaminated soils. Site-specific detailed information is not available on the use of A. tricolor plant in metal phytoremediation from the polluted sites. The study aimed to enhance the uptake of HMs (Pb, Zn, and Cu) via amending poultry litter extract (PLE), vinasse sugarcane (VSC), and humic acid (HA) as natural mobilized organic materials compared to ethylene diamine tetraacetic acid (EDTA), as a common mobilized chemical agent by A. tricolor plant. The studied soils collected from Helwan, El-Gabal El-Asfar (Cairo Governorate), Arab El-Madabeg (Assiut Governorate), Egypt, and study have been conducted under pot condition. Our results revealed all organic materials in all studied soils, except EDTA in EL-Gabal El-Asfar soil, significantly increased the dry weight of the A. tricolor plant compared to the control treatment. The uptake of Pb and Zn significantly (p > 0.05) increased due to applying all organic materials to the studied soils. HA application caused the highest uptake as shown in Pb concentration by more than 5 times in Helwan soil and EDTA by 65% in El-Gabal El-Asfar soil while VSC increased it by 110% in El-Madabeg soil. Also, an increase in Zn concentration due to EDTA application was 58, 42, and 56% for Helwan, El-Gabal El-Asfar, and El-Madabeg soil, respectively. In all studied soils, the application of organic materials increased the remediation factor (RF) than the control. El-Madabeg soil treated with vinasse sugarcane gave the highest RF values; 6.40, 3.26, and 4.02% for Pb, Zn, and Cu, respectively, than the control. Thus, we identified A. tricolor as a successful ornamental candidate that, along with organic mobilization amendments, most efficiently develop soil health, reduce metal toxicity, and recommend remediation of heavy metal-contaminated soils. Additionally, long-term application of organic mobilization amendments and continued growth of A. tricolor under field conditions could be recommended for future directions to confirm the results.     

Heavy Metals Desorption from Synthesized and Natural Iron and Manganese Oxyhydroxides: Effect of Reductive Conditions

Reductive conditions in soils can lead to the dissolution of iron and manganese oxyhydroxides, releasing heavy metal pollutants (e.g., Pb and Cd) bound to them. The present study used hydroxylamine as a reducing agent. Laboratory batch experiments were conducted, varying pH and hydroxylamine concentrations, with artificially contaminated synthetic amorphous Fe(OH)(3s) and MnO(2) and with a polluted cultivated soil. Until conditions were reductive enough to dissolve solids, remobilization of metals depended on their surface complexation constant and readsorption of metal was possible. However, if conditions were sufficiently reductive, all solids were dissolved and metals were released into solution. A straightforward surface complexation model for cation desorption was carried out to support these results. Copyright 2000 Academic Press.     

Characterization of Heavy Metals in Soil Near Coal Mines and a Power Plant in Huainan,China

The environmental and health hazards posed by heavy metals are significant due to their toxicity and bioavailability. Thirty-two soil samples were collected from residential areas around three coal mines and a power plant to assess the environmental and health implications caused by mining activities. The concentrations of heavy metals in soil were determined by inductively coupled plasma mass spectrometry. To evaluate the risk levels, the geo-accumulation index and health risk assessment were determined. The concentrations of metals in power plant soil were generally higher than those in coal mine soil, suggesting a higher release during coal combustion. The results demonstrate that the soils in the vicinity of Xinzhuangzi Mine and Luohe Power Plant are moderately contaminated by arsenic and cadmium. The analysis of the health risk of the metals indicated that the non-carcinogenic and carcinogenic adverse effects to residents due to heavy metal exposure are negligible. However, more attention should be paid around the power plant for the unacceptable level of carcinogenic risk. Based on the results of the environmental and health risk assessment, priority control components in Huaian have been identified. The study provides a comprehensive assessment of soil heavy metal implications derived from mining activity in this region in China and is helpful for pollution control and environmental management.     

Stability and Mobility of Metal-Humic Complexes Isolated from Different Soils

The contamination of potable water aquifers by heavy metals is one of the most severe environmental threats. For the transport of heavy metals from various types of contaminated sites into the ground water and also into surface water aquifers, humic substances (HS) are recognized to be of main importance. Dissolved in natural waters humic substances are readily complexed with a variety of metal ions. Therefore, humic substances are of cardinal importance for the migration and, consequently, the pollution of ground waters with heavy metals. Our paper presents the results of a comprehensive comparison of several isolated humic acids of soils of different origin (different geochemical milieu) and their metal complexes. Two polluted sites in Germany, which differ in their geochemical milieu (pH-value) were selected. The aim of our experiments was to describe the properties of terrestrial humic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon activation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded humic acid on an XAD-8 resin column, the partition of metals mobilized by humic acids could be quantified. There are correlations of the formation of metal-humic complexes with the soil pedogenes, with the pH-value as well as with the humic acid concentration.     

Comparison of chromium and nickel uptake of plants grown in different soils

The chromium and nickel uptake of ryegrass has been examined in pot experiments in extremely different soils, poor sandy and fertile black chernozem. The effect of calcium carbonate doses and nitrogen supply on heavy metal uptake of the plant has been studied for chromium and nickel loadings (0–100 mg/kg Cr³⁺ or Ni²⁺) applied as inorganic salts. The ability to uptake Cr³⁺ and Ni²⁺ differs significantly and is highly affected by the characteristics of soils, and depends on the metal investigated. The heavy metal uptake of the plant differs significantly in acid, colloid deficient sandy soils; while artificial chromium contamination did not modify the dry-matter production in the pots in either soil, a large quantity of nickel reduced the yields significantly. Nitrogen application did not change significantly the uptake of heavy metals. Lime application reduced the Ni²⁺ uptake of plants considerably, especially in sandy soil. In case of a calcium carbonate addition the dry-matter production of the plant was not affected by nickel. In chernozem soil the effect of lime application – i.e., the reduction of nickel uptake – was of a lesser degree. The significantly lesser Cr³⁺ uptake was further limited by a calcium carbonate application for both soils studied. A graphic presentation of these effects is given.     

Comparison of chromium and nickel uptake of plants grown in different soils

The chromium and nickel uptake of ryegrass has been examined in pot experiments in extremely different soils, poor sandy and fertile black chernozem. The effect of calcium carbonate doses and nitrogen supply on heavy metal uptake of the plant has been studied for chromium and nickel loadings (0–100 mg/kg Cr³⁺ or Ni²⁺) applied as inorganic salts. The ability to uptake Cr³⁺ and Ni²⁺ differs significantly and is highly affected by the characteristics of soils, and depends on the metal investigated. The heavy metal uptake of the plant differs significantly in acid, colloid deficient sandy soils; while artificial chromium contamination did not modify the dry-matter production in the pots in either soil, a large quantity of nickel reduced the yields significantly. Nitrogen application did not change significantly the uptake of heavy metals. Lime application reduced the Ni²⁺ uptake of plants considerably, especially in sandy soil. In case of a calcium carbonate addition the dry-matter production of the plant was not affected by nickel. In chernozem soil the effect of lime application – i.e., the reduction of nickel uptake – was of a lesser degree. The significantly lesser Cr³⁺ uptake was further limited by a calcium carbonate application for both soils studied. A graphic presentation of these effects is given.     

Dynamics of Heavy Metals in Soils of a Reed Bed System

Abstract

Heavy metal balances of a reed bed system (soil pH > 7, carbonate content about 30%) continuously flooded with sewage during 5 years indicate that only Pb, Zn, Cd and Cu were partly stored in the soil. Strong reductive conditions, high sewage percolation and metal complexation with soluble organic compounds caused a considerable leaching of Fe, Mn, Ni and Cr from the soil and formation of amorphous iron oxides. The results indicate that continously flooded reed bed systems with high percolation rates are not suitable for the elimination of heavy metals. Conversely, it should be possible to purify metal contaminated soils through percolation of sewage with low metal content.     

New Sediment and Soil CRMs for Extractable Trace Metal Content

Abstract

The lack of uniformity in leaching procedures used to measure broadly defined forms of heavy metals does not allow the results to be compared world-wide nor the methods to be validated since the results obtained are “operationally defined”. An attempt was made to certify several mineral soils CRMs for single extraction by using acetic acid, EDTA and DTPA for Cd, Cr, Cu, Ni, Pb and Zn. Recently, to complete the series of soil CRMs, an organically enriched soil was prepared SO25. For sediments a CRM 601 was produced and certified for metals extractable by using the BCR three step sequential extraction. Not all the trace elements were certified and only indicative values were given for some of them due to poor reproducibility. We performed a systematic study of the effect of the variables identified as potential sources of uncertainty in the use of this scheme. With this study the sources of uncertainty were revealed and an optimised version of the protocol was proposed. With this new version it was possible to certify all the trace elements studied. New sediment material S33 is now proposed for certification and additional data are given for the sediment CRM 601. This modified procedure was also applied to a soil CRM 483 and good results were obtained. This procedure may thus be applied to polluted soils.     

Chemical Characterization of Silage Effluents and their Influence on Soil Bound Heavy Metals

Abstract

Silage effluents, generated during silaging of various crops, are produced in high amounts in cattle breeding farms. Due to their acidity and high content of dissolved organic matter, they are causing disposal problems. On the other hand, their ability to mobilise soil bound trace elements (i.e. heavy metals) might be useful for the decontamination of polluted soils.

With an aim to perform metal leaching studies, silage effluents from various ensiled crops (maize, rape, grass, clover, sugar-beet leaves) were collected from Bavarian farms and analysed for their main inorganic and organic constituents. Important TOC sources (TOC concentrations from 13.9 to 53.6 gl^?1) are short chain aliphatic acids (concentrations between 235 and 638 mM·D1^?1; predominant compound: lactic acid), amino acids (ranging from 22.8 to 151 mM·D1^?1) and polypeptides (concentrations from 3.8 to 20.0 g·D1^?1).

The release of heavy metals from two adsorbents (bentonite and peat) and from a polluted soil under the influence of silage effluents was studied in batch tests. The leaching efficiencies for the soil bound metals increase following the order: sugar-beet leaves < clover < maize < rape < grass. The extraction rates obtained with grass silage juice are: Cd 74.7%, Zn 55.7%, Cu 53.5%, Ni 38.9%, Cr 12.7% and Pb 8.9%. After neutralisation the leaching rates dropped, with the exception of copper.     

Radioactive contamination of the environment as a result of uranium production: a case study at the abandoned Lincang uranium mine,Yunnan Province,China

The distribution of radioactive pollutants, such as²²²Rn, U, Th and²²⁶Ra in the air, surface waters, soils and crops around the Lincang uranium mine, Yunnan Province, China, is studied. The mechanical, geochemical and biogeochemical processes responsible for the transport and fate of the radioactive elements are discussed based on the monitoring data. The pollutants concentrations of effluents from the mine tunnels were dependent on pH and which were controlled by biochemical oxidation of sulfide in the ore/host rocks. Radon anomalies in air reached 4 km from the tailings pile depending on radon release from the site, topography and climate.²³⁸U and²²⁶Ra abnormities in stream sediments and soil were 40—90 cm deep and 790—800 m away downstream. Anomalies of radioactive contaminants of surface watercourses extended 7.5—13 km from the discharge of effluents of the site mainly depending on mechanical and chemical processes. There were about 2.86 ha rice fields and 1.59 km stream sediments contaminated. Erosion of tailings and mining debris with little or no containment or control accelerated the contamination processes.

     

Effects of RAMEB on Bioremediation of Different Soils Contaminated with Hydrocarbons

The limiting factor of soil remediation is often the low accessibility of the pollutants.Laboratory experiments have been carried out to investigate the effect of the randomlymethylated cyclodextrin (RAMEB) on bioremediation of various types of soils spikedwith Diesel and transformer oil and also on actual site soils contaminated with poorlydegradable mazout. The contaminated soil in the aerobic solid phase microcosm-experiments was amended with nutrients and supplemented with different amounts of RAMEB. An integrated chemical-biological-ecotoxicological methodology was applied to follow the bioremediation. The laboratory study proved the bioremediation enhancing effect of RAMEB both on artificially contaminated soils and on actual site mazout contaminated soils. RAMEB activated soil microbes by improving the bioavailability of the contaminants and accelerating biodegradation. Efficacy of RAMEB was influenced both by contaminantand environment related factors, such as the type and concentration of the pollutinghydrocarbons and characteristics of the soil.     

Sequential Extraction of Copper and Zinc from Sewage Sludges. Use of Organic Solvents

Abstract

Sequential extraction procedures were used to evaluate the bioavailability of metals from two sewage sludges after application in soils. Organic solvents were used prior to sequential extraction to evaluate the influence of oil and waxes on heavy metals extractability.

The preliminary results showed that a extraction of oil and waxes present in the sewage sludges by n-hexane followed by acetone increased the accessibility of Cu and Zn and did not remove substantial metal amounts.