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1.
Sequential core sediments from northwestern Taihu Lake in China were analyzed for grain size, organic carbon and heavy metal content. The sediments are composed of organic-poor clayey-fine silts. The chemical speciations of Cu, Fe, Mn, Ni, Pb, and Zn were also analyzed using the BCR sequential extraction procedure. Cu, Fe, Ni, and Zn are mainly associated with the residue fraction; Mn is concentrated mainly in exchangeable/carbonate fraction and residue fraction; and Pb mainly in Fe/Mn oxide fraction and organic/sulfide fraction. The exchangeable/carbonate fractions of Cu, Fe, Ni, Zn and Pb are lower. The fractions of Ni, Pb and Zn bound to the Fe/Mn oxide have significant correlations with reducible Mn; the organic/sulfide fractions of Cu, Mn, Ni, Pb, and Zn have significant correlations with TOC. The extractable fractions of Cu, Mn, Ni, Pb, and Zn are high at the top 4 cm of the core sediments as compared to those in the deeper layers, showing the anthropogenic input of heavy metals is due to rapid industrial development. The heavy metal pollution history of the sediments has been recorded since the late 1970s, determined by the result of ^137Cs dating.  相似文献   

2.
恬矿库周围土壤中重金属存在形态特征研究   总被引：48，自引：4，他引：44  
通过对大冶铜绿山铜铁矿尾矿库周围土壤中重金属形态分析实验,研究了重金属各种形态在土壤中的分布特征。由对比实验可知,尾矿库周围土壤中Ｃｕ、Ｐｂ、Ｚｎ、Ｃｄ等重金属含量都显著地高于对照样品,书经受到重金属的严重污染。土壤中重金属形态分布征为：ｗ（Ｃｒ、Ｚｎ、Ｆｅ）;可变换态〈碳酸盐态〈有机态〈铁锰氧化态〈残渣态;ｗ（Ｃｕ、Ｐｂ）：可变换态〈碳酸盐态〈有机态〈残渣态〈铁锰氧化态;ｗ（Ｃｄ）：残渣态,有机  相似文献   

3.
Coastal reclamation has been carried out along the coastal areas near Shenzhen, China in a large scale since 1980s by dumping fill materials over the marine mud at the sea bottom. Usually the area to be reclaimed is drained first and some of the mud is air-dried for a few weeks before it is buried by fill. After reclamation, the terrestrial groundwater, which is relatively acidic and with high dissolved oxygen, gradually displaces the seawater, which is alkaline with high salinity. The changes in the burial conditions of mud and the properties of the pore water in the mud may induce the release of some heavy metals into the mud. Field survey confirms that the pH and salinity of the groundwater in the reclamation site are much lower than the seawater. Chemical analyses of mud and groundwater samples collected from the reclamation sites reclaimed in different years indicate that most of the heavy metals in the mud decrease gradually with time, but the heavy metals in the groundwater are increased. The release of heavy metals into pore water due to reactivation of heavy metals in the mud is of environmental concern. To understand why some of the heavy metals can be released from the mud more easily than others, a sequential extraction method was used to study the operationally determined chemical forms of five heavy metals (Cu, Ni, Pb, Zn, and Cd) in the mud samples. Heavy metals can be presented in five chemical forms: exchangeable, carbonate, Fe–Mn oxide, organic, and residual. Ni and Pb were mainly associated with the Fe–Mn oxide fraction and carbonate fraction; Zn was mainly associated with organic fraction and Fe–Mn oxide fraction, while Cu and Cd were associated with organic fraction and carbonate fraction, respectively. If the residual fraction can be considered as an inert phase of the metal that cannot be mobilized, it is the other four forms of heavy metal that cause the noticeable changes in the concentration of heavy metals in the mud. On the basis of the speciation of heavy metals, the mobility of metals have the following order: Pb (36.63%) > Cu (31.11%) > Zn (20.49%) > Ni (18.37%) > Cd (13.46%). The measured metal mobility fits reasonably well with the degree of concentration reduction of the metals with time of burial observed in the reclamation site.  相似文献   

4.
太湖MS岩芯重金属元素地球化学形态研究   总被引：21，自引：4，他引：17  
采用BCR三步提取法对太湖MS岩芯沉积物中Cu、Fe、Mn、Ni、Pb和Zn等6种重金属元素的化学形态进行了研究.结果表明,有效结合态的Cu、Ni和Pb主要以有机物及硫化物结合态、Fe-Mn氧化物结合态存在,Fe和Zn主要以Fe-Mn氧化物结合态存在,Mn主要以可交换态及碳酸盐结合态存在;Fe-Mn氧化物结合态的Ni、Pb和Zn与可还原态的Mn有较好的正相关关系,有机物及硫化物结合态的Cu、Mn、Ni、Pb和Zn与有机碳含量有较好的正相关关系;重金属形态分布体现了重金属元素地球化学性质的差异,以及重金属形态含量与沉积物理化性质的关系.沉积岩芯重金属元素形态垂向变化规律及次生相富集系数表明,Cu、Mn、Ni、Pb和Zn在沉积岩芯13～4 cm有效结合态含量较稳定,为自然沉积;4～0 cm有效结合态含量明显升高,存在一定程度的人为污染.根据137Cs测年结果判断,沉积岩芯Cu、Mn、Ni、Pb和Zn等重金属污染开始于20世纪70年代末期,主要污染元素及污染历史与太湖流域污染工业类型及经济发展阶段相吻合.  相似文献   

5.
The Tessier sequential extraction scheme (SES) was applied to sediments from the Odiel river catchment (Iberian Pyritic Belt, SW of Spain), one of the most acid rivers on Earth, to assess the chemical association (exchangeable, carbonatic, bound to manganese and iron oxides, bound to organic matter and residual mineral) of heavy metals (Zn, Cd, Pb, Cu, Cr, Mn, Ni, Fe, and Hg). Sediments are very heterogeneous in their textural characteristics, showing different grain size. Twenty-seven samples were studied from from areas along the Odiel River, from the source to the mouth, with special interest in the Odiel Marshes Natural Park due to its ecological significance. Samples were classified as sandy (especially at the river mouth with low iron oxide and organic matter content) and clay-silty (in the middle of the river catchment with high iron oxide content). The numerous sandy samples with low pH values explain the low levels of metals upstream, although potential metals contributions arise from mining and ore. However, the presence of sulfate in the mining area and carbonate at the mouth may explain the high presence of lead and iron in these sandy zones. Some percentage of mobile Ni, Cu, and Zn were detected in the mining area, but the elevated relative percentage of exchangeable Cd in the estuary is even more remarkable. The percentage of Zn bound to carbonate is considerable in the catchment but especially in the estuary. However, Cu is only detected in the carbonate phase downstream, in spite of the low concentration of carbonate, which represents a drawback in the application of the Tessier SES to these types of samples. Finally, relatively high percentages of residual, non-mobile, Hg and Pb were observed, in the estuarine and mining areas, respectively. Sand, lime, and clay fractions of representative samples from Areas I, II, and III were used in a metal speciation study. Mainly, the elements analyzed had accumulated in the non-residual fractions. In the mining area of the Pyrite Belt, the elements analyzed are mainly bound to Fe–Mn oxides (Fe + Mn + Cu + Cr + Pb + Mn ± Zn) and the organic matter/sulfide fraction (Ni + Zn + Hg ± Cd), independent of sediment grain size. In conclusion, we show that the results of the study of chemical speciation in sediments from acid rivers are independent of the sediment grain size considered.  相似文献   

6.
Soils from historical Pb mining and smelting areas in Derbyshire, England have been analysed by a 5-step sequential extraction procedure, with multielement determination on extraction solutions at each step by ICP-AES. Each of the chemical fractions is operationally defined as: (i) exchangeable; (ii) bound to carbonates or specifically adsorbed; (iii) bound to Fe–Mn oxides; (iv) bound to organic matter and sulphides; (v) residual. The precision was estimated to be about 5%, and the overall recovery rates were between 85 and 110%. The carbonate/specifically adsorbed and Fe–Mn oxide phases are the largest fractions for Pb in soils contaminated by both mining and smelting. Most of the Zn is associated with Fe–Mn oxide and the residual fractions. Cadmium is concentrated in the first 3 extraction steps, particularly in the exchangeable phase. The most marked difference found between soils from the mining and smelting sites is the much higher concentrations and proportions of metals in the exchangeable fraction at the latter sites. This indicates greater mobility and potential bioavailability of Pb, Zn and Cd in soils at the smelting sites than in those in the mining area. The most important fraction for Fe and Al is the residual phase, followed by the Fe–Mn oxide forms. In contrast, the Fe–Mn oxide fraction is the dominant phase for Mn in these soils. In the mining area, most of the Ca is in the carbonate fraction (CaCO3), while the exchangeable and residual phases are the main fractions for Ca at the smelting sites. Phosphorus is mainly in the residual and organic fractions in both areas. The exchangeable fractions of Pb, Zn and Cd in soils were found to be significantly related to the concentrations of these metals in pasture herbage.  相似文献   

7.
Different plant communities have established spontaneously on Sanmen Pb/Zn mine tailing. The site was inspected and four different plant communities were identified according to their species composition. To understand the effects of different communities on mine tailing physico-chemical properties, a community survey was carried out in Sanmen Pb/Zn mine tailing, and the physico-chemical properties and heavy metal (Cu, Pb, Cd and Zn) distribution of mine tailings were determined. Results showed that there were four types of communities (I, II, III and IV) in Sanmen Pb/Zn mine tailing. From community I to IV, the number of plant species and community characteristics (aboveground biomass, underground biomass, coverage and height) consistently increased. Moreover, the nutrient pool and physico-chemical properties of mine tailing consistently reestablished from community I to IV, while the total heavy metal content consistently decreased. The contents of residual fractions, Fe–Mn oxide fractions for Pb, Zn, Cu and Cd and exchangeable fractions for Pb and Zn also consistently decreased. However, the contents of organically bound fraction had no obvious change from community I to IV. Moreover, the contents of Cu organically bound fraction reversely increased. Results demonstrate that communities I, II, III and IV should be a progressive community succession. Moreover, along with the progressive community succession, phytostabilization and phytoextraction of mine tailings are more and more effective.  相似文献   

8.
The species of Cu, Pb, Zn, Cd and Cr in sediments of the Taihu Lake, China, have been analyzed using the sequential chemical extraction method. Variations in the chemical fractions of these metals and their geographic distributions have also been studied. For all five metals, the residual fraction is highest but the exchangeable fraction is lowest among all the fractions. Compared to other metals, Cd has the highest percentage in the exchangeable fraction, and Cr is associated mainly with the residual fraction. Cu in the organic fraction and Pb in the Fe-Mn fraction are the important species, whereas the lowest percentages are found for Cd in the organic fraction, Cu in the Fe-Mn oxide fraction and Pb in the carbonate fraction. With respect to spatial differences, the total contents in the non-residual fractions of the metals in bay sediments are found to be higher than those in other sediments. The fractions of Cd, Cu and Cr showed significant variations in different regions. The fractions of Pb and Zn, however, did not show significant variations in spatial distribution, suggesting different amounts and different paths of anthropogenic input for the metals. Comparisons of the metal speciation indicated that Cd might be the most bioavailable metal, followed by Pb.  相似文献   

9.
The heavy metal contents of Mn, Ni, Cu, Zn, Cr, Co, Pb, Cd, Fe, and V in the surface sediments from five selected sites of El Temsah Lake was determined by graphite furnace atomic absorption spectrophotometer. Geochemical forms of elements were investigated using four-step sequential chemical extraction procedure in order to identify and evaluate the mobility and the availability of trace metals on lake sediments, in comparison with the total element content. The operationally defined host fractions were: (1) exchangeable/bound to carbonate, (2) bound to Fe/Mn oxide, (3) bound to organic matter/sulfides, and (4) acid-soluble residue. The speciation data reveals that metals Zn, Cd, Pb, Ni, Mn, Cu, Cr, Fe, and V are sink primarily in organic and Fe–Mn oxyhydroxides phases. Co is mainly concentrated in the active phase. This is alarming because the element is enriched in Al Sayadin Lagoon which is still the main site of open fishing in Ismailia. Average concentration of the elements is mostly above the geochemical background and pristine values of the present study. There is a difference on the elemental composition of the sediment collected at the western lagoon (Al Sayadin Lagoon), junction, the shoreline shipyard workshops, and eastern beach of the lake. Depending upon the nature of elements and local pollution source, high concentration of Zn, Pb, and Cu are emitted by industrial wastewater flow (shoreline workshops), while sanitary and agricultural wastewater (El Bahtini and El Mahsama Drains) emit Co and Cd in Al Sayadin Lagoon. On the other hand, there is a marked decrease in potentially toxic heavy metal concentrations in the sediments at the most eastern side of the lake, probably due to the successive sediment dredging and improvements in water purification systems for navigation objective. These result show that El Temsah receives concentrations in anthropogenic metals that risk provoking more or less important disruptions, which are harmful and irreversible on the fauna and flora of this lake and on the whole ecobiological equilibrium.  相似文献   

10.
The seasonal variation in the trace metals’ concentrations (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were investigated in surface sediments of the Pandoh Lake. The horizontal distribution of TC, TN, and TP reflects spatial and temporal differences in sedimentary organic production. The chemical sequential extraction of heavy metals was carried out by seven-step fractionation scheme (Leleyter and Probst in Int J Environ Chem 73:109–128, 1999). The significant concentrations of Ni and Cd were associated with “water soluble (Eua)” fraction in the monsoon and winter, respectively, while “exchangeable (Exch)” and “carbonate-bound (Carb)” fractions for Ni and Cd were abundant in winter and summer. The Cd, Cu, and Pb associated with “Exch” fraction in the summer season support their availability on exchange sites due to oxidized nature of surface sediments. Enrichment of Co, Fe, Mn, and Zn in “AFeO” fraction showed poor bioavailability, while Cd, Cu, and Mn in the monsoon, Co in the winter and summer, and Zn in the winter season showed significant “organically bound (Org)” fraction. The ANOVA was significant for chemical fractions of trace elements except “Carb” fraction of Pb and Zn and “CFeO” fraction of Pb. Factor analysis revealed that the “Eua”, “Exch”, and “Carb” fractions together control the metal enrichment of “MnO”, “AFeO”, and “CFeO” fractions in the summer season.  相似文献   

11.
A field study was conducted to clarify the effect of rhizosphere processes on the accumulation and partitioning of heavy metals (Pb, Zn, Cu, Cr, Cd and Ni) in mangrove sediments. Metals were fractionated by a sequential extraction procedure into three chemically distinct fractions: water soluble, exchangeable and carbonate bound (B1), Fe–Mn oxide bound (B2), and organic and sulfide bound (B3). Results indicate that rhizosphere processes tend to increase the metal concentrations in the rhizosphere sediments. However, plant uptake may result in the decrease of the metal concentrations in the rhizosphere sediments when the metal concentrations are relatively low in the bulk sediments. Compared with the bulk sediments, the rhizosphere sediments have low concentrations of heavy metals in the B1 and B2 fractions and high concentrations in the B3 fraction. Either an increase or decrease in the residual fraction of heavy metals in the rhizosphere sediments may appear, depending on whether the formation of the refractory metal-organic compounds or the activation of the residual fractions dominates. Results also indicate that mangrove plants absorb and store non-essential metals in the perennial tissues, thus reducing the export of non-essential metals via leaf litter transport. Mangrove plants are excellent candidates for phytostabilization of heavy metals in intertidal substrates.  相似文献   

12.
太湖沉积物中重金属的地球化学形态及特征分析   总被引：24，自引：2，他引：22  
用连续提取法分析了太湖沉积物5种重金属的地球化学形态,对地球化学形态的组成和地理特征进行了分析研究.重金属地球化学形态配分的共同特点是可交换态最低,残渣态最高.两种形态中Cd的可交换态最高,Cr的残渣态最高,可交换态最低.Cd的碳酸盐态较高,Cr的最低;Pb、Cd的Fe-Mn氧化态较高,Cu的偏低;Cu的有机态最高,Cd的最低;Zn的地球化学形态比例大都处于中间.地域上变化较大的元素是Cd和Cu,变化不明显的元素有Pb和Zn.化学成分中Fe2O3、MnO与重金属地球化学形态的相关性最好,TOC与Cu的形态相关系数最高.综合对比分析表明,太湖沉积物重金属的生物有效性以Cd为最高,其次为Pb.  相似文献   

13.
Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO3–HClO4) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.  相似文献   

14.
The lakes of the Himalaya are degrading due to increase in toxic heavy metal loading. This study reports the last 50-year heavy metal pollution loading in the Rewalsar Lake, Himachal Pradesh, India. Sediment cores were recovered to study the pollution loading in the lake sediments. The 137Cs and 210Pb isotope-based sedimentation rate suggest rapid sedimentation in the lake during the last ~50 years. The concentrations of Mn, Cu, Zn, Cd, Pb, Co, Ni, Cr metals in the lake sediments owe its contributions both to the natural and anthropogenic sources. Prior to ca 1990 AD, metal loading was dominated by the lithogenic input, whereas post ca 1990 AD the metal loading was controlled by the anthropogenic factors. The Pb concentration in the lake gradually increased during 1990–2004 and then decreased significantly till present. The higher concentration of Pb seems to be derived from the fossil fuel burning, while the Cr concentration in the lake indicates the use of fertilizer in the catchment area. The lowest concentrations of elements around ca 1990 AD seem to have occurred due to channelization of the lake feeding system.  相似文献   

15.
Mine tailings may be remediated using metal tolerant microorganisms as they may solve the limiting conditions for healthy development of plants (i.e., low organic mater content and poor physical conditions). The aim of this study was to investigate the consequences of microbial colonization on the chemical speciation of trace metals. Surface samples from the Valenciana mine tailings (Guanajuato, Mexico) were used for long-term bioassays (BA), which consisted in the promotion of microorganisms, development on tailings material under stable laboratory conditions (humidity, temperature, and light exposure). A five-step sequential extraction method (exchangeable, carbonate/specifically adsorbed, Fe–Mn oxides, organic matter (OM)/sulfide, and residual fractions) was performed before and after BA. Extraction solutions and leachates were analyzed by inductively coupled plasma-mass spectrometry. OM content, cationic exchange capacity, and pH values were also assessed before and after BA. The results indicate that trace elements are generally present in nonresidual fractions, mainly in the Fe–Mn oxides fraction. The concentration of total Zn, As, Se, Pb, and exchangeable Cu and Pb is above the recommendable limits for soils. Despite the high bioavailability of the former elements, biofilms successfully colonized the tailing samples during the BA. Cyanobacteria and green algae, heterotrophic fungi, aerobic bacteria, and anaerobic bacteria composed the developed biofilms. Chemical controls of trace elements could be attributed to absorption onto inorganic complexes (carbonates, metal oxides), while biofilm occurrence seems to enhance complexation and immobilization of Cr, Ni, Cu, Zn, As, and Pb. The biofilm developed does not increase the bioavailable forms and the leaching of the trace elements, but significantly improves the OM contents (natural fertilization). The results suggest that biofilms are useful during the first steps of the mine tailings remediation.  相似文献   

16.
Core and surface sediment samples were collected from three sub-lakes ( Lake Nanyang, Lake Dushan and Lake Zhaoyang) in the Lake Nansi Basin, Shandong Province. In order to reveal the characteristics of spatial and historical distribution of heavy metals in different sublakes of the Upper Lake Nansi, heavy metal (As, Cr, Cu, Hg, K, Mn, Ni, Pb, Zn, Al, Fe, Ti and V) concentrations of sediment samples were investigated. Based on the activity of^137Cs in the sediments, the modem accumulation rate of Lake Nansi sediments is 3.5 mm/a. Our results show that the whole Upper Lake Nansi has been already polluted by heavy metals, among which Lake Nanyang has been polluted seriously by mercury, as well as by lead and arsenic, while Lake Dushan has been most seriously polluted by lead and arsenic. Historical variation of heavy metal (Cr, Cu, K, Ni, Zn, A1, Fe, Ti and V) concentrations shows an abrupt shift in 1962, resuiting in a division of two periods: from 1957 to 1962 when metal enrichment increased with time, and from 1962 to 2000 when it decreased with time, while that of some anthropogenic elements such as Hg, Pb and Mn tend to increase toward the surface. However, the variation trend of As in the sediments is different from that of Hg, Pb and Mn, with its maximum value appearing in 1982. Since 1982 the concentrations of As have decreased due to the forbidden use of arsenite pesticides. This variation trend revealed changes in manner of human activity (coal combustion, waste discharges from both industries and urban sewage ) within the catchment during different periods.  相似文献   

17.
Dianshan Lake is one of the important water supply sources for Shanghai City. The contents of heavy metals in the sediments are obviously higher than those in the overlying water body. The contents of Pb in the sediments vary seasonally; with increasing depth, the contents of Cd, Pb, Cu, Cr and Fe show no variation generally, but Mn varies in the peak pattern. Cd, Pb, Cu, Cr and Fe in the sediments are present predominantly in sludge phase, but iron and manganese oxide form of Pb and organic matter-sulfide form of Cu are their respective preferential combining forms. Manganese is present largely in exchangeable form, iron-manganese oxide combined form and sludge form. The contents of the various forms of Cd, Pb, Cu, Cr and Fe tend to vary with changing season and depth. The contents of exchangeable forms of Fe and Mn vary with depth in the peak-like pattern.  相似文献   

18.
A study of the San Pedro River (SPR), which is located in a semi-arid region in Sonora, Mexico, was conducted to evaluate the chemical, spatial and temporal (mobilization) trends of potentially harmful metals in its sediment in the rainy and dry seasons. High total concentrations of metals were detected in the following order: Fe > Cu > Mn > Zn > Pb > Cd. All studied metals except for Pb were increased during the dry season showing the effect of climate on the metal distribution in sediments. The results of sequential extraction indicated that the residual and Fe/Mn oxide fractions were the most important with regard to retaining potentially harmful metals in the sediments. In the exchangeable carbonate and Fe oxide fractions, high concentrations of metals were detected, representing high environmental risk. The geoaccumulation index shows slight to moderate contamination in most samples, and sampling point E4 (related to cattle activity) shows strong contamination for Cd, Cu, Pb and Zn. Enrichment factors (EFs) demonstrate anthropogenic origins for Pb (EF: 3–57), Cd (EF: 6–73) and Cu (EF: 1.5–224). This study shows that sediments are impacted by anthropogenic activities related to the mining industry, untreated wastewater discharges from the city of Cananea and cattle activities. Metal mobility in the SPR can disrupt the development of aquatic species in the river.  相似文献   

19.
 The distribution of Si, Al, Fe, Mn, Cu, Zn, Ni and Cr in different grain-size fractions and geochemical association of Fe, Mn, Cu and Zn with <63-μm size fraction of bed sediments of Damodar River has been studied. In general, concentrations of heavy metals tend to increase as the size fractions get finer. However at two sites, near mining areas, the coarser particles show similar or even higher heavy metal concentrations than finer ones. The higher residence time and/or presence of coarser particles from mining wastes are possibly responsible for higher metal content in the coarser size fractions. The chemical fractionation study shows that lithogenic is the major chemical phase for heavy metals. Fe and Mn are the major elements of the lithogenic lattice, constituting 34–63% and 22–59%, respectively, of total concentrations. Fe-Mn oxide and organic bound fractions are significant phases in the non-lithogenic fraction. The carbonate fraction is less significant for heavy metal scavenging in the present environment and shows the following order of abundance Zn>Cu>Mn>Fe. The exchangeable fraction of the Damodar sediments contains very low amounts of heavy metals suggesting poor bioavailability of metals. Received: 18 August 1998 · Accepted: 1 December 1998  相似文献   

20.
The Pliocene aquifer receives inflow of Miocene and Pleistocene aquifer waters in Wadi El Natrun depression. The aquifer also receives inflow from the agricultural activity and septic tanks. Nine sediment samples were collected from the Pliocene aquifer in Wadi E1 Natrun. Heavy metal (Cu, Sr, Zn, Mn, Fe, Al, Ba, Cr, Ni, V, Cd, Co, Mo, and Pb) concentrations of Pliocene aquifer sediments were investigated in bulk, sand, and mud fractions. The determination of extractable trace metals (Cu, Zn, Fe, Mn, and Pb) in Pliocene aquifer sediments using sequential extraction procedure (four steps) has been performed in order to study environmental pathways (e.g., mobility of metals, bounding states). These employ a series of successively stronger chemical leaching reagents which nominally target the different compositional fractions. By analyzing the liquid leachates and the residual solid components, it is possible to determine not only the type and concentration of metals retained in each phase but also their potential ecological significance. Cu, Sr, Zn, Mn, Fe, and Al concentrations are higher in finer sediments than in coarser sediments, while Ba, Cr, Ni, V, Cd, Co, Mo, and Pb are enriched in the coarser fraction. The differences in relative concentrations are attributed to intense anthropogenic inputs from different sources. Heavy metal concentrations are higher than global average concentrations in sandstone, USEPA guidelines, and other local and international aquifer sediments. The order of trace elements in the bulk Pliocene aquifer sediments, from high to low concentrations, is Fe?>?Al?>?Mn?>?Cr?>?Zn?>?Cu?>?Ni?>?V?>?Sr?>?Ba?>?Pb?>?Mo?>?Cd?>?Co. The Pliocene aquifer sediments are highly contaminated for most toxic metals, except Pb and Co which have moderate contamination. The active soluble (F0) and exchangeable (F1) phases are represented by high concentrations of Cu, Zn, Fe, and Mn and relatively higher concentrations of Pb and Cd. This may be due to the increase of silt and clay fractions (mud) in sediments, which act as an adsorbent, retaining metals through ion exchange and other processes. The order of mobility of heavy metals in this phase is found to be Pb?>?Cd?>?Zn?>?Cu?>?Fe?>?Mn. The values of the active phase of most heavy metals are relatively high, indicating that Pliocene sediments are potentially a major sink for heavy metals characterized by high mobility and bioavailability. Fe–Mn oxyhydroxide phase is the most important fraction among labile fractions and represents 22% for Cd, 20% for Fe, 11% for Zn, 8% for Cu, 5% for Pb, and 3% for Mn. The organic matter-bound fraction contains 80% of Mn, 72% of Cu, 68% of Zn, 60% of Fe, 35% of Pb, and 30% of Cd (as mean). Summarizing the sequential extraction, a very good immobilization of the heavy metals by the organic matter-bound fraction is followed by the carbonate-exchangeable-bound fraction. The mobility of the Cd metal in the active and Fe–Mn oxyhydroxide phases is the highest, while the Mn metal had the lowest mobility.  相似文献   

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