Seasonal and time variability of heavy metal content and of its chemical forms in sewage sludges from different wastewater treatment plants

Sewage sludges obtained from seven wastewater treatment plants from the province of Salamanca, Spain, were periodically sampled to determine seasonal and time variation of their elemental composition over 2000 to 2002. The aim of this paper was to provide additional insight to evaluate the potential environmental impact following soil incorporation of these materials as amendments. Aqua regia extractable metals (pseudo total content) of Cd, Cr, Cu, Ni, Pb and Zn were determined and furthermore, the main chemical forms of metals within the sludge were evaluated using a five-step fractionation procedure. All the studied sludges displayed high fertility properties due to their richness of OC, P and K. Total mean concentrations of Cd, Cr, Cu, Ni, Pb and Zn in the sludges were within the regulation of the Spanish legislation. Using an multifactor analysis of variance, significant differences between Cr, Cu, Ni, Pb and Zn pseudo total contents (p<0.01) of sludges at different sites were found while the Cd content was statistically similar. Also significant differences were found between these pseudo total contents of heavy metals in samples collected along the time after three years (0.001相似文献   

Effects of sewage sludge on pH and plant availability of metals in oxidising sulphide mine tailings

A field study was conducted adjacent to the tailings deposit of the Aitik copper mine in the north of Sweden to investigate the effects of sewage sludge on pH and plant availability of Al, Mn, Cu, Zn, Ni, Pb, As, Cr and Cd in the oxidising sulphide tailings. One treatment was supplied with sewage sludge, while the control received NPK-fertiliser. The tailings samples were collected at the beginning and the end of the growing season and extracted by NH(4)NO(3), NH(4)Ac-EDTA and HNO(3). Plant tissue concentrations of the elements were determined in the above-ground parts of barley (Hordeum vulgare) and red fescue (Festuca rubra). The application of sewage sludge resulted in higher crop yields compared to the control, although the buffering capacity and the metal immobilising effect of the sludge were limited. The pH decreased from 6.6 to 4.3 in the control and from 6.4 to 4.8 in the sludge-treated tailings during the growing season, probably due to sulphide oxidation in the tailings. This resulted in increased levels of soluble elements in all treatments studied. Application of sewage sludge resulted in elevated levels of soluble Zn and lower values of soluble As and Cd in the unaltered tailings but increased levels of specifically adsorbed Cu, Ni and As in the oxidised tailings. This was partly reflected in the plants, as the application of sewage sludge resulted in 67 mg Zn kg(-1) in barley grains and 60 mg Zn kg(-1) in red fescue shoots, both values twice as high as the corresponding values in the control, but lower As contents in both straw (0.3 mg kg(-1)) and grain (0.06 mg kg(-1)) of barley compared to the control (0.6 and 0.2 mg kg(-1), respectively). In addition, red fescue grown in sludge-treated plots contained significantly higher levels of Al, Cu, Pb, As and Cr compared to the control. The levels of several metals in barley and red fescue grown in both treatments exceeded background values found in the literature. The Cu content in barley straw exceeded 100 mg kg(-1) in both treatments and might be toxic to grazing animals. Thus, this study suggests that adding sewage sludge to the mine tailings at Aitik would not counteract the effects of the sulphide oxidation in the tailings. Furthermore, using a sequential extraction technique proved preferable to using total metal analysis in order to predict plant uptake of the elements in the tailings.     

Heavy metal pollution of soils affected by the Guadiamar toxic flood

Total heavy metal concentrations were determined in soil samples of seven selected areas along the Guadiamar river valley affected by the toxic flood, after removal of the deposited sludge. Mean total concentrations of nine elements (As, Au, Bi, Cd, Cu, Pb, Sb, Tl and Zn) out of the 23 (As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, In, Mn, Mo, Ni, Pb, Sb, Sc, Sn, Th, Tl, U, V, Y and Zn) analysed were higher in sludge-covered soils than in unaffected soils. Mean values of total As, Au, Pb, Sb, Tl and Zn in sludge-affected soils were higher than the upper limits for normal soils world-wide. Mean concentrations of Bi, Cd and Cu were within these ranges, although some individual values exceeded the upper limits. In all sampling areas, severe heavy metal pollution was observed in the superficial layers (0-20 cm) of most of the affected soils, which decreased downward in the soil profile. Generally, in soils with more than 25% of clay, concentration of heavy metals below the 20-cm depth decreased to values close to those of the background level of the Guadiamar valley soils, while in coarser soils, heavy metal pollution penetrated below this depth, being noticeable down to a depth of at least 50-80 cm.     

Baseline values for heavy metals in agricultural soils in an European Mediterranean region

Baseline values for heavy metals were proposed in Alicante (Spain), a representative agricultural area of the European Mediterranean region, as a basis to identify and assess soil contamination processes at regional level. Fifty-four agricultural plots were sampled and heavy metals concentrations were analysed for nine elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) by atomic absorption spectrometry (AAS) after acid digestion with HNO(3) and HCl in a microwave oven. Heavy metal concentrations obtained in the study area were similar to concentrations analysed by other authors within the European Mediterranean region. However, some agricultural plots with a high heavy metal content were identified by statistical treatment (boxplots) as outliers and, therefore, were not considered for establishing baseline values. Baseline values in Alicante were proposed by taking into account the statistical approach extensively used elsewhere, which refers to the increase in the mean plus twice the standard deviation. The baseline values were: 0.7 mg/kg for Cd, 11 mg/kg for Co, 36 mg/kg for Cr, 28 mg/kg for Cu, 19,822 mg/kg for Fe, 402 mg/kg for Mn, 31 mg/kg for Ni, 28 mg/kg for Pb and 83 mg/kg for Zn. The experience gained in this work further suggests that baseline values for heavy metals should be proposed in other areas. This is necessary to facilitate the identification of soil contamination processes over the whole European Mediterranean region as a basis to undertaking appropriate action to protect soil resource quality.     

Heavy metal distribution in some French forest soils: evidence for atmospheric contamination

This study is one of very few dealing with the distribution and the origin of heavy metals in French soils from a priori non-polluted forest areas. The abundance of heavy metals measured in these soils decreases as follows: Cr>Zn>Pb>Ni>Cu>Co>Cd. Total concentrations of Pb, Cr and Ni in some soils exceed the European thresholds for non-polluted soils and even the French association of normalization critical values for sludge spreading. The lowest heavy metal contents are observed in acid soils while the highest concentrations are in the calcaric cambisol and in the mollic andosol, which is rather scarce as compared with the other French forest soils. With the exception of the podzol, Cr and Ni concentrations increase with depth in all soil profiles. The distribution pattern of Co, Cu, Zn depends on the soil characteristics. In some acid soils, however, Cu and Zn decrease with depth. Pb and Cd are accumulated in the upper soil horizons. Heavy metals accumulate in deep soil horizons in relation to important clay content in the dystric planosol and stagnic luvisol. The concentration of each heavy metal is always controlled by different parameters (soil pH, iron and aluminum oxide content, clay content, organic matter and cation exchange capacity), which are heavy metal specific. This study highlights the metal-trapping character of andosol and calcaric soil, the weak heavy metal retention in acid soils, the leaching and trapping character in leached clayed soils, and the migration of heavy metals in the podzol. Pb and Cr concentrations indicate a significant enrichment in surface horizons from various soils in areas which receive significant acid atmospheric pollution. Particularly, the highest Pb content is observed in a soil located in the N-NE part of France. Lead isotope ratios measured in the cambic podzol and the calcaric cambisol, exhibit the importance of the anthropogenic sources and particularly the influence of global atmospheric inputs from leaded gasoline compared to regional and local industrial emissions. The anthropogenic Pb contribution is estimated to 83, 30 and 11%, respectively, for surface, intermediate and deep horizons of the cambic podzol located in the northern part of France, and to 68% in surface horizon of the calcaric cambisol located in the Alps.     

Heavy metal behaviour during the activated sludge process I. Extent of soluble and insoluble metal removal

The extent of removal of Ag, Bi, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Tl and Zn and their distribution between the soluble and insoluble phases in the influent, and effluent of the activated sludge process has been studied using a pilot-scale plant operated at sludge ages of 3, 6, 9 and 12 days. Molybdenum, Tl, Co, Mn and Ni were >50% soluble in the influent settled sewage. The mean removals of the former two metals were <3% and the latter three were 35 and 50%. Silver, Bi, Cd, Cr, Cu, Pb and Zn were all <35% soluble in the influent and had substantial removals of >75%. Solubilities were greater in the effluent than the influent with the exception of Mn. The observed overall removals of Ag, Bi, Co, Ni, Pb, Tl and Zn were almost entirely due to insoluble metal removal; Cd, Cr and Cu removals had a significant contribution from soluble metal removal. Overall Mn removal appeared to be solely due to soluble metal removal.     

Adsorption of heavy metals on Na-montmorillonite. Effect of pH and organic substances

Clays (especially montmorillonite and bentonite) are widely used as barriers in landfills to prevent contamination of subsoil and groundwater by leachates containing heavy metals. For this reason it is important to study the adsorption of metals by these clays. The sorption of seven metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) on Na-montmorillonite was studied as a function of pH and in the presence of ligands, forming complexes of different stabilities with the metals of interest. The continuous column method was used as it better simulates natural conditions. The total capacity of Na-montmorillonite towards these metals was determined. The pH variations influence to a higher extent the concentrations of Cu, Pb and Cd in the effluent. Moreover the results suggest that complex formation hinders the sorption of the metals on the clay, with an increasing influence in the order: Mn < or = Pb < or = Cd < or = Zn < Ni < Cu < Cr. The evaluation of the total capacity of Na-montmorillonite shows that this clay is a good sorbent towards all examined metals.     

An inventory of heavy metals inputs to agricultural soils in England and Wales

An inventory of heavy metal inputs (Zn, Cu, Ni, Pb, Cd, Cr, As and Hg) to agricultural soils in England and Wales in 2000 is presented, accounting for major sources including atmospheric deposition, sewage sludge, livestock manures, inorganic fertilisers and lime, agrochemicals, irrigation water, industrial by-product 'wastes' and composts. Across the whole agricultural land area, atmospheric deposition was the main source of most metals, ranging from 25 to 85% of total inputs. Livestock manures and sewage sludge were also important sources, responsible for an estimated 37-40 and 8-17% of total Zn and Cu inputs, respectively. However, at the individual field scale sewage sludge, livestock manures and industrial wastes could be the major source of many metals where these materials are applied. This work will assist in developing strategies for reducing heavy metal inputs to agricultural land and effectively targeting policies to protect soils from long-term heavy metal accumulation.     

Reproducibility of the BCR sequential extraction procedure in a long-term study of the association of heavy metals with soil components in an upland catchment in Scotland

Humic iron podzol soils from three different plots at the Glensaugh Research Station, Aberdeenshire have been sampled on an annual basis since 1990 and analysed using both total digestion and the original BCR sequential extraction procedure. Particular care was required during the oxidation of these organic soils to prevent loss of material. The residue from the sequential extraction was analysed so that the values for total concentration derived from the total digestion and from the sum of the concentrations in the fractions of the extraction procedure could be compared. The comparison was good for all three soils indicating that not only did the sequential extraction give good recovery but that this was reproducible over a period of several years. The proportion of metals extractable at each step remained relatively constant thereby demonstrating the reproducibility of the procedure and the stability of the metals in the soils over the time scale of the sampling used. Whereas the total concentrations of Cr, Cu and Ni were highest in the soil from a roadside plot, this was not the case for Cd, Pb and Zn. In the case of Pb, concentrations in soils (0-25-cm depth) well away from the road were over 100 mg/kg and well above the expected background level. The distribution of metals between each of the extracted fractions varied not only between each metal but also between each of the three soils indicating that both metal and soil influenced the measured distribution. The distribution of Pb in the roadside soil was different from those in the other two soils and over 10% was extracted in the first, acetic acid soluble, fraction.     

Short-term effects of biosolid and municipal solid waste applications on heavy metals distribution in a degraded soil under a semi-arid environment

Digested biosolid (SS) and municipal solid waste (MSW) were surface-applied to a degraded carbonated soil, under semi-arid environment, at rates of 0 and 80 Mg/ha, to determine the changes in organic matter and in the distribution of heavy metals in the topsoil, 1 year after its application. Waste application slightly increased the organic matter content and improved the composition of humic fractions in the treated soils, mainly in the MSW amended plots. A sequential extraction method (Tessier et al., 1979) was used to determine the distribution of Cd, Cr, Cu, Ni, Pb and Zn in both the waste and the amended.soils. Waste application had little effect on the total concentration of Ni and Cr in the treated soils as a consequence of the low availability of these metals in the wastes. A considerable increase of Cd, Cu, Pb and Zn was observed as a consequence of the high content and/or high availability of these metals in the wastes. The more labile fraction (exchangeable fraction) of all metals studied increased slightly (< 1.5 mg/kg) when SS and MSW were added. However, a remarkable increase in the Fe/Mn oxide fraction of Cd, Cu and Pb and in the organic fraction of Zn were noted in treated plots, this increase being higher in the MSW treated soils.     

电渗析法去除未脱水污泥中重金属的试验研究

为了降低城镇生活污泥中重金属含量,采用三槽型电解槽研究了反应时间和NaClO预处理对未脱水污泥中重金属Zn、Cu、Cr和Ni去除率的影响。试验结果表明,延长反应时间可以提高未脱水污泥中重金属去除率。电渗析反应时间为14 h时,污泥中Zn、Cu、Cr和Ni的去除效果较好,去除率分别为52. 08%、27. 24%、31. 66%和46. 42%。污泥中重金属的初始非稳定态比例越大,电渗析反应后的去除率越高。NaClO/HNO_3组合预处理的污泥中重金属去除率最高,对Zn、Cu、Cr和Ni的去除率分别达到70. 32%、35. 39%、36. 80%和56. 78%。     

Quantities and associations of lead, zinc, cadmium, manganese, chromium, nickel, vanadium, and copper in fresh Mississippi delta alluvium and New Orleans alluvial soils

The topic of this study is the effect of anthropogenic metals on the geochemical quality of urban soils. This is accomplished by comparing the metal contents and associations between two alluvial soils of the lower Mississippi River Delta, freshly deposited alluvial parent materials and alluvial soils collected from a nearby urban environment. Fresh alluvium samples (n = 97) were collected from the Bonnet Carré Spillway. The urban alluvial soil samples (n = 4026) were collected from New Orleans and stratified by census tracts (n = 286). The Spillway samples tend to have less Pb and Zn than generally noted for the baseline of natural soils. Except for Mn and V, Spillway alluvium contains significantly less metal than urban soils. For Spillway samples, the median metal content (in microg g(-1)) is 4.7 Pb, 11.1 Zn, 0.7 Cd, 164 Mn, 0.8 Cr, 3.9 Ni, 3.2 V, and 3.9 Cu. For urban soils, the median metal content (in microg g(-1)) is 120 Pb, 130 Zn, 3.2 Cd, 138 Mn, 2.1 Cr, 9.8 Ni, 3.8 V, and 12.7 Cu. Metal associations also differ between Spillway alluvium and urban alluvial soils. Fresh alluvium correlation coefficients between individual metals vary from 0.87 to 0.99 (P < 10(-13)) except for Cr which ranges from 0.57 to 0.68 (P < 10(-7)). The urban soil correlation coefficients for metals and the index value are 0.40-0.98. In urban soils, Pb, Zn, Cr, and Cu are dominant metals and highly associated, with a correlation coefficient ranging from 0.83 to 0.98 (P < 10(-25)). Their strong association justifies the use of GIS to map the integrated soil metal index (sum of the medians of metals by census tract) of New Orleans. Although also positively correlated (0.40-0.68, P < 10(-10)), Cd, Mn, Ni and V differ in their distribution in the city compared to Pb, Zn, Cr and Cu. Overall, significantly higher metal values occur in the inner city and lower values occur in outlying areas. The human health impact of the mixture of metals is not well understood. This study provides empirical data about the mixture and distribution of metals in New Orleans alluvial soils. Given common technical development, especially of traffic flows in cities, similar patterns of soil metals are expected for all US cities and probably international cities as well. Primary prevention of urban metal accumulations is necessary to enhance and sustain the development of urban culture.     

Heavy metal and micronutrient uptake in soybeans as influenced by sewage sludge amendment

Soybean (Glycine max (L.) Merr.) uptake of the elements, Cd, Ni, Pb, Cu, Zn and Mn, from a sewage sludge-amended Mecklenburg soil was conducted in the greenhouse. “Bragg” soybeans were grown in pots for five weeks at which time the tops and roots were sampled separately for elemental analysis. Soil samples from each pot were extracted with DTPA (diethylenetriaminepentaacetic acid) and the concentration of extractable elements correlated with the elemental content in the soybean plant. There was a significant increase in dry matter production with sludge treatment. Concentrations of Cd, Ni and Pb in the soybean shoots and roots increased from sludge-amended soil as compared to the control. The metal concentration in the soybean tissue increased with increasing levels of sludge amendment. Uptake of the heavy metals was greater by the roots than by the shoots indicating some barrier to movement of the metals from roots to shoots. The DTPA extractable Cd in sludge-amended soil increased significantly, and showed correlation to the soybean tissue metal concentrations. As for the micronutrients, Cu increased in the soybean shoot as the extractable Cu increased. There was no significant relationship between soybean tissue Zn and Mn and extractable Zn and Mn.     

Relationships among total recoverable and reactive metals and metalloid in St. Lawrence River sediment: bioaccumulation by chironomids and implications for ecological risk assessment

The availability and bioaccumulation of metals and metalloids, and the geochemical interactions among them, are essential to developing an ecological risk assessment (ERA) framework and determining threshold concentrations for these elements. The purpose of this study was to explore the relationships among total recoverable and reactive metals and metalloid in sediment and their bioaccumulation by chironomids. In the fall of 2004 and 2005, 58 stations located in the three fluvial lakes of the St. Lawrence River and its largest harbour area in Montreal, Canada, were sampled. Nine total recoverable and reactive metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and one metalloid (As) were measured in whole sediment using two extraction methods: HCl/HNO(3) and HCl 1N, respectively. The bioaccumulation of six metals (Cd, Cr, Cu, Ni, Pb and Zn) and As by chironomids was evaluated in a subset of 22 stations. Strong collinearities were observed between some total recoverable or reactive metal concentrations in sediment; two principal clusters, including collinear metals, were obtained. The first one included metals of mainly geological origin (Al, Cr, Fe, Mn, Ni), while the second one included As, Cd, Cu, Pb and Zn, which likely derive mainly from point sources of anthropogenic contamination. Each element also showed strong collinearity between their total recoverable and reactive forms (0.65< or =r < or =0.97). We can conclude that both chemical forms are equivalent for use in statistical models needed to explain biological responses and also in screening risk assessment. However, these relationships are not always proportional. Lower availability percentages were observed for Cd, Cu and Zn in the highly mixed-contaminated area of the Montreal Harbour, even though concentrations in sediment were higher. We observed a significant correlation (0.50< or =r < or =0.56) between concentrations in chironomids and concentrations of both total recoverable and reactive Cr and Pb in sediment. Arsenic was an exception, with accumulation by chironomids being highly related to reactive sediment concentrations. Finally, we observed variable influences of explanatory factors (e.g. sediment grain size, Al, Fe, Mn, S, TOC), depending on which metal or metalloid was being predicted in chironomids. In this context, it is difficult to choose a universal predictive method to explain the bioaccumulation of specific metals, and more research is still needed into normalization procedures that consider a combination of explanatory factors.     

Partitioning of trace metals before and after biological removal of metals from sediments

Metal removal by biological solubilization in three strongly contaminated sediments was carried out in a two-liter stirred bioreactor. Biological treatment yielded metal removal efficiencies in the range of 11-30%, 43-57%, 60-79%, 61-90%, 18-21%, 0-10% for Pb, Cu, Zn, Cd, Ni and Cr, respectively. The treated sediments were then rinsed with a NaCl solution (0.5 M), resulting in an increase by nearly 47% in Pb removal for the three sediments, while for other metals (Cu, Zn, Cd, Ni, Cr), the NaCl rinse did not seem to allow any significant increase in metal solubilization. A standard procedure of sequential selective extraction (SSE) was applied to the sediments before and after each treatment. With regard to Pb, Zn and Cd, the carbonate bound fractions (2/3 sediments) represented 18-42% of metals prior to treatment, while the iron and manganese oxides bound fraction constituted 39-60% of metals for the three sediments. Between 90 and 100% of Pb, Zn and Cd removed by the process came from the fractions bound to carbonates and from those bound to Fe and Mn oxides. The organic matter and sulfide bound fractions contained 65-72% of total Cu present before treatment and the process removed, on average, 63% Cu present in this fraction. In contrast, Ni and Cr were found mainly in the residual fractions (50-80%). Finally, this biological treatment did not solubilize Cr appreciably, while removal of Ni mostly originated from the carbonate and Fe/Mn oxides fractions (70-80%).     

兰州某铝厂旧址周围土壤重金属污染及分布特征

研究了兰州某铝厂旧址周围土壤重金属形态特征,找出了该土壤中重金属元素的形态分布及变化规律,分析了引起7种重金属元素形态变化的主要因子。结果表明,该铝厂周围土壤重金属Cu、Mn、Ni、Pb、Zn、Cr、Cd污染严重。各重金属元素的含量随样品采集半径的增加而减少,7种重金属的形态分析结果表明,重金属污染主要以残渣态为主,Cd、Mn和Cr的弱酸态占有较大的比例,其中Cd的生态风险性最高。同时对重金属的环境效应和生态风险作出一定的评价,为治理和改善该地区土壤环境质量积累科学数据。     

Modeling heavy metal uptake by sludge particulates in the presence of dissolved organic matter

The uptake of the seven heavy metal ions Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) by sludge particulates in single-metal systems was investigated. Results showed that under acidic and neutral pH conditions, the uptake of all heavy metals by sludge particulates increases with the increase of pH. However, in the alkaline pH region, the uptake of Cu(II), Ni(II), and Co(II) decreases with the increase of pH, primarily due to the high dissolved organic matter (DOM) concentration in high pH conditions. Based on chemical reactions among heavy metal, sludge solids, and DOM, a mathematical model describing metal uptake as functions of DOM and pH was developed. The stability constants of metal–sludge and metal–DOM complexes can be determined using this model in conjunction with experimental metal uptake data. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on March 1997, the stability constants of Cu(II)–sludge complex (log K_S) and Cu(II)–DOM complex (log K_L) are 5.3±0.2 and 4.7±0.3, respectively; for Ni(II), they are 4.0±0.2 and 3.9±0.2, respectively. Results also showed that under neutral and low pH conditions (pH<8), the DOM effects on metal uptake for all heavy metals are insignificant. Therefore, the DOM term in the model can be ignored. Results showed that, for the secondary sludge sample collected from Baltimore Back River Wastewater Treatment plant on December 1996, the estimated log K_S values of metal–sludge complexes for Cd(II), Co(II), Cr(III), Cu(II), Ni(II), Pb(II), and Zn(II) are, respectively, 3.6±0.2, 3.0±0.1, 5.5±0.1, 4.8±0.1, 3.1±0.1, 5.1±0.1, and 4.4±0.3.     

Total metal concentrations and partitioning of Cd, Cr, Cu, Fe, Ni and Zn in sewage sludge

Application of the BCR three-step sequential extraction procedure to sewage sludge samples collected at an urban wastewater treatment plant (Dom ale, Slovenia) is reported. The total concentrations of Cd, Cr, Cu, Fe, Ni and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS) under optimised measurement conditions. Total acid digestion including hydrofluoric acid (HF) treatment and aqua regia extraction were compared in order to estimate the efficiency of aqua regia extraction for determination of total metal concentrations in sewage sludge. It was found experimentally that aqua regia quantitatively leached these heavy metals from the sewage sludge and could therefore be applied in analysis of total heavy metal concentrations. The total concentrations of 856 mg kg⁻¹ Cr, 621 mg kg⁻¹ Ni and 2032 mg kg⁻¹ Zn were higher than those set by Slovenian legislation for sludge to be used in agriculture. Total concentrations of 2.78 mg kg⁻¹ Cd, 433 mg kg⁻¹ Cu and 126 mg kg⁻¹ Pb were below those permitted in the relevant legislation. CRM 146R reference material was used to follow the quality of the analytical process. The results of the BCR three-step sequential extraction procedure indicate high Ni and Zn mobility in the sludge analysed. The other heavy metals were primarily in sparingly soluble fractions and hence poorly mobile. Due to the high total Ni concentration and its high mobility the investigated sewage sludge could not be used in agriculture.     

Long-term effects of the Aznalcóllar mine spill-heavy metal content and mobility in soils and sediments of the Guadiamar river valley (SW Spain)

In 1998, a toxic spill from a pyrite mine (Aznalcóllar, SW Spain) contaminated some 40 km2 of the Agrio and Guadiamar river valley with heavy metal-enriched tailings sludge and acidic mine water. The aim of this study is to describe the long-term effects of heavy metal migration particularly with respect to the extent of vertical redistribution of As, Cd, Cu, Fe, Pb, S, Sb and Zn in soils and sediments of the river Guadiamar 4 years after the accident. For an assessment of the mobility behaviour, chemical associations of Cu, Pb, Sb and Zn in depth profiles polluted by tailings were determined by using sequential extraction procedures. In 2002, residues of toxic tailings were found in several places along the river Guadiamar. Heavy weathering has accelerated heavy metal displacement and contamination of the surrounding soil. Two element groups of contrary mobility can be distinguished: Cd and Zn are highly mobile and show strong displacements in acidic surroundings. Accumulation zones for Cd and Zn develop in less acidic soil layers due to the occurrence of Fe oxides, which constitute retaining fractions for these elements. The immobile elements Pb and Sb represent the second group. Highest concentrations of Pb and Sb are found in the tailings sludge. Cu and As show a variable distribution pattern. As a consequence of the heavy metal migration, an accumulation zone has formed up to 30 cm into the underlying soil at the time of investigation. In the future, there may be further penetration of heavy metals to greater depths.     

Concentrations of selected metals in honey consumed in Nigeria

The concentration of metals, cadmium (Cd), lead (Pb), nickel (Ni), chromium (Cr), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), and zinc (Zn) was measured in selected samples of honey in Nigeria with a view to providing information on the regional concentration profile of metals in these honeys. The honey samples were digested with a mixture of acids and analysed for metal concentrations using atomic absorption spectrophotometry. The concentrations of metals (mg kg^?1) in these honeys ranged from < 0.3 for Cd,<0.50–39.75 for Pb,<0.25–6.98 for Ni,<0.25–55.25 for Cr,<0.25–71.25 for Cu,<0.25–3.50 for Co,<5.0–163.15 for Fe,<11.0–31.75 for Mn and 1.0–31.0 for Zn. The concentrations of metals were relatively high but lower than their respective permissible limits in food except for Pb and Cu in some samples. The regional distribution patterns of metals indicated that honey samples from the Niger Delta region of Nigeria had higher mean concentrations of Ni, Cr, Co, Fe and Zn than honey samples from other regions. The honey samples from the northern region had higher mean concentrations of Pb and Cu.