Trace metal speciation and contamination in an intertidal estuary

An analysis of the geochemical distribution of selected trace metals among various geochemical phases of the sediments in the Tees estuary was carried out using a sequential extraction technique and Differential Stripping Voltammetry. The sediments of the estuary are mainly organic rich clay silts and metal concentrations exceed those in the water column. Speciation results show that contamination of the estuary is mainly from anthropogenic sources. Pb and Zn are associated with the reducible, residual and oxidisable fractions. The speciation pattern of Cd was similar to those of lead and zinc. However there were also some exchangeable and bound to carbonate fractions although these were less significant. Cu is largely associated with the oxidisable and residual fractions, with insignificant bound to carbonate, exchangeable and reducible fractions. The most bioavailable forms of the metals are the free inorganic ions. Total metal concentrations in the estuary display a downward trend since the 1970s.     

Metal speciation studies in the aquifer sediments of Semria Ojhapatti,Bhojpur District,Bihar

The pollution of aquifer sediments by heavy metals has assumed serious concern due to their toxicity and accumulative behavior. Changes in environmental conditions can strongly influence the behavior of both essential and toxic elements by altering the forms in which they occur and therefore quantification of the different forms of metal is more meaningful than total metal concentrations. In this study, fractionation of metal ions in aquifer sediments of Semria Ojhapatti area, Bhojpur district, Bihar has been studied to determine the ecotoxic potential of metal ions. The investigations suggest that iron, copper, and arsenic have a tendency to remain associated in the following order residual > reducible > acid-soluble > oxidizable; manganese and zinc have tendency to be associated as residual > acid-soluble > reducible > oxidizable. The risk assessment code reveals that manganese and zinc occur in significant concentration in acid-soluble fraction and therefore comes under the high risk category and can easily enter the food chain. Most of the iron, copper, and arsenic occur as immobile fraction (i.e. residual) followed by its presence in reducible fraction and would pose threat to the water quality due to changing redox conditions. The metal enrichment factor in the study area shows moderate to significant metal enrichment in the aquifer sediments which may pose a real threat in near future. The geo-accumulation index of metals also shows that the metals lie in the range of strongly contaminated (for iron at shallow depths) to moderately contaminated to uncontaminated values.     

Determination and speciation of heavy metals in sediments of the Juru River,Penang, Malaysia

The Juru River flows through largely urbanized areas and is grossly polluted by domestic wastes and discharges from pig farms. Other than carrying highly polluting organic materials, these wastes are also contaminated with heavy metals. To ascertain the extent of heavy metal pollution in the river, total and non-residual concentrations of Cu, Pb, Zn, Mn and Fe in sediment samples collected along the river were determined. The results indicate that both the total and non-residual metal concentrations in sediments can successfully be used to identify heavy metal pollution sources. The speciation of Zn, Mn and Fe in the sediment samples were investigated using a sequential leaching technique which identifies the elements among six operationally defined host fractions: (1) exchangeable, (2) carbonate and surface-associated, (3) easily reducible, (4) moderately reducible, (5) bound to organic matter and sulphides and (6) residual. The results indicate that Zn is mainly associated with the reducible fractions. Zn and Fe found in the moderately reducible fraction are significantly correlated, indicating that iron oxides is the preferred host phase by Zn.     

Chemical fractionation of heavy metals in urban soils of Guangzhou, China

Knowledge of the total concentration of heavy metals is not enough to fully assess the environmental impact of urban soils. For this reason, the determination of metal speciation is important to evaluate their environment and the mobilization capacity. Sequential extraction technique proposed by the former European Community Bureau of Reference (BCR) was used to speciate Cd, Cu, Fe, Mn, Ni, Pb, and Zn in urban soils from Guangzhou into four operationally defined fractions: HOAc extractable, reducible, oxidizable, and residual. The Cu, Fe, Ni, and Zn were predominately located in the residual fraction, Pb in the reducible fraction, and Cd and Mn within the HOAc extractable fraction. The order of Cd in each fraction was generally HOAc extractable > reducible > residual > oxidizable; Cu and Fe were residual > reducible > oxidizable > HOAc extractable; Mn was HOAc extractable > residual > reducible > oxidizable; Ni and Zn were residual > reducible > HOAc extractable > oxidizable; and Pb was reducible > residual > oxidizable > HOAc extractable. Cadmium was identified as being the most mobile of the elements, followed by Mn, Zn, Ni, Cu, Pb and Fe. Iron–Mn oxides can play an important role in binding Cd, Cu, Ni, Pb, and Zn and in decreasing their proportion associated with the residual fraction in the soils. With total concentrations of Cd, Cu, Ni, Pb, Zn, and Mn increase, these metals more easily release and may produce more negative effects on the urban environment.     

Speciation of metals in bed sediments and water of Qaraaoun Reservoir, Lebanon

Determination of only total element in sediments does not give an accurate estimate of the likely environmental impacts. Speciation study of metals in sediment provides information on the potential availability of metals (toxic) to biota under various environmental conditions. In water, the toxic metal specie is the free hydrated metal ion. The toxicity of metals depends especially on their chemical forms rather than their total metal content. The present study focuses on Qaraaoun Reservoir, Lebanon. Earlier studies focused only on total metal concentrations in sediment and water. The objective of this study was to determine metal speciation (Fe, Cr, Ni, Zn, Cu, Pb, Cd) in the (operationally defined) sediment chemical fractions and metal speciation in reservoir water. This would reflect on metal bioavailability and toxicity. Water samples and bed sediments were collected from nine sites during the dry season and a sequential chemical fraction scheme was applied to the <75-??m sieve sediment fraction. Metal content in each fraction was determined by the FAAS technique. The data showed that the highest percentages of total metal content in sediment fractions were for: Fe in residual followed by reducible, Cr and Ni in residual and in reducible, Cu in organic followed by exchangeable, Zn in residual and in organic, Pb in organic and carbonate, Cd was mainly in carbonate. Total metal content in water was determined by ICP-MS technique and aqueous metal speciation was predicted using AQUACHEM software interfaced to PHREEQC geochemical computer model. The water speciation data predicted that a high percentage of Pb and Ni were present as carbonate complex species and low percentages as free hydrated ions, highest percentage of Zn as carbonate complex species followed by free hydrated ion, highest percentage of Cd as free hydrated ion followed by carbonate complex species. The sensitivity attempt of free hydrated ion of Ni, Zn, Pb, and Cd in reservoir water revealed dependence of Zn and Cd on pH and alkalinity, while Ni and Pb were only dependent on pH.     

Small effects of a large sediment contamination with heavy metals on aquatic organisms in the vicinity of an abandoned lead and zinc mine

The effects of the long-term contamination of water reservoirs with mine effluents were investigated at an abandoned mine site in Upper Silesia, southern Poland. The studies covered metal content and mobility in bottom sediments as well as water chemistry in relation to the content of metals in selected macrophytes and their physiology and the composition of phyto- and zooplankton communities. Although it is 40 years since mining ceased, reservoir sediments are still heavily contaminated with cadmium, zinc and lead with concentrations (mg/kg), which vary roughly between 130–340, 10,000–50,000 and 4,000–12,000, respectively. About 50–80 % of these elements are associated with the reducible phase, and only a small percentage, <10 %, is present in the most mobile exchangeable phase. Despite the high total metal concentration in sediments, their content in the submerged plants Myriophyllum spicatum and the emerged plants Phragmites australis was low. The observed effects of heavy metal contamination on photosynthetic activity in the leaves of P. australis were negligible, whereas those in M. spicatum show up only as a difference in the distribution of photosynthetic activity in leaves of different ages, which seems to be related to the very good water quality and to the generally small concentrations of metals in pond water. The physicochemical properties of water also seem to control the presence of planktonic species more than does sediment contamination. However, a shift toward groups of species known to be more resistant to heavy metals (diatoms, green algae and Rotifera) indicates some adaptative changes related to the long-lasting contamination of ponds.     

Associations of cadmium, zinc, and lead in soils from a lead and zinc mining area as studied by single and sequential extractions

An exploratory study of the area surrounding a historical Pb?CZn mining and smelting area in Zawar, India, detected significant contamination of the terrestrial environment by heavy metals. Soils (n?=?87) were analyzed for pH, EC, total organic matter (TOM), Pb, Zn, Mn, and Cd levels. The statistical analysis indicated that the frequency distribution of the analyzed parameters for these soils was not normal. The median concentrations of metals in surface soils were: Pb 420.21 ?? g/g, Zn 870.25 ?? g/g, Mn 696.70 ?? g/g, and Cd 2.09 ?? g/g. Zn concentrations were significantly correlated with Cd (r?=?0.867), indicating that levels of Cd are dependent on Zn. However, pH, electrical conductivity and total organic matter were not correlated significantly with Cd, Pb, Zn, and Mn. To assess the potential mobility of Cd, Pb, and Zn in soils, single (EDTA) as well as sequential extraction scheme (modified BCR) were applied to representative (n?=?23) soil samples. The amount of Cd, Pb, and Zn extracted by EDTA and their total concentrations showed linear positive correlation, which are statistically significant (r values for Cd, Pb, and Zn being 0.901, 0.971, and 0.795, respectively, and P values being <0.001). The correlation coefficients indicate a strong relation between EDTA-extractable metal and total metal. These results appear to justify the use of ??total?? metal contents as a useful preliminary indicator of areas where the risks of metal excess or deficiency are high. The EDTA extractability was maximum for Cd followed by Pb and Zn in soils from all the locations. As indicated by single extraction, the apparent mobility and potential bioavailability of metals in soils followed the order: Cd ?? Pb >?> Zn. Soil samples were sequentially extracted (modified BCR) so that solid pools of Cd, Zn, and Pb could be partitioned into four operationally defined fractions viz. acid-soluble, reducible, oxidizable, and residual. Cadmium was present appreciably (39.41%) in the acid-soluble fraction and zinc was predominantly associated (32.42%) with residual fraction. Pb (66.86%) and Zn (30.44%) were present mainly in the reducible fraction. Assuming that the mobility and bioavailability are related to solubility of geochemical forms of metals and decrease in the order of extraction, the apparent mobility and potential metal bioavailability for these contaminated soil samples is Cd > Zn > Pb.     

Total concentrations, fractionation and mobility of heavy metals in soils of urban area of Guwahati, India

This work describes the results of assessment of the heavy metals, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in urban soil of Guwahati City, India from 31 sites of five different land use types covering residential, commercial, industrial, public utilities, and roadside. Sequential extraction procedure was used to evaluate the relative distribution of the eight metals in exchangeable, carbonate, reducible (Fe?CMn oxide), organic and sulfide, and residual fractions. Of the eight metals, Cd and Co occur in lower concentrations (Cd <?< Co) in all types of land, and concentration variation from one type of land use to another is not much significant for both the metals. Ni presence is more than Co, and the concentrations show some variation depending on land use status. Average Cr and Cu concentrations are ??100?mg/kg, but Cr has a significantly higher presence in industrial land use. The results are similar in case of Pb. The two metals, Mn and Zn have domination over the other metals, and the values are ??300?mg/kg. Industrial and roadside soil contains much more Mn, while commercial soil is most enriched with Zn. Of the metals, Ni has the largest proportion (~42%) bound to the exchangeable fraction and Co, Cr, and Pb also have appreciable proportion bound to the same fraction. A significant amount of Co is associated with carbonates. The reducible fraction has bound considerable quantity of Mn and Zn, while most of Cu is associated with the organic and sulfide fraction. Both Cd and Pb are dominantly associated with the residual fraction. Computation of the mobility factor of the metals indicates Mn to be the most mobile metal present in the soil samples.     

Distribution and speciation of selected metals in surface sediments, from the tropical Zuari estuary, central west coast of India

Estuarine sediments are major reservoirs for the metals. Distribution and mobility of metals within estuaries depends strongly on their specific chemical form. In the present study, surface sediments from Zuari estuary, Goa were analysed by a sequential procedure for Fe, Mn, Cu, Zn, Cr and Co to determine their distribution in five geochemical phases (Exchangeable, carbonate, Fe-Mn oxide (reducible) organic bound (oxidisable) and residual). The total metal content, sand, silt, clay and organic carbon were also determined of the surface sediments. The total metal contents were found to be greater than the background concentrations of average shale values as well as to that of earlier studies indicating enrichment probably due to the anthropogenic origin of metals. The results obtained from sequential procedure showed that among the studied elements, Mn and Co are potentially available in the bioavailable fractions (exchangeable, carbonate and Fe-Mn oxide bound fractions) indicating their importance in toxicity whereas rest of the metals viz. Fe, Cu, Zn and to some extent Cr are largely available in residual phase although they are available in other fractions. The main source of metals to the estuary is mining and its associated activities in the study area. Chemical speciation by sequential extraction procedure has helped in assessing the mobility, bioavailability, diagenesis and toxicity of metals and hence giving a better insight into the ultimate fate of pollutants, which are introduced into the estuarine environment. To understand the risk of the metals to the sediment dwelling organisms the data were compared with the Sediment Quality Values (SQV) using SQUIRT. Also, correlation and Factor analysis were carried out to understand the associations of metals in the different fractions with sand, silt, clay, organic carbon and with other metals.     

Heavy metal contamination of drinking water in Kamrup district, Assam, India

This study was undertaken to assess the heavy metal concentration of the drinking water with respect to zinc, copper, cadmium, manganese, lead and arsenic in Kamrup district of Assam, India. Ground water samples were collected from tube wells, deep tube wells and ring wells covering all the major hydrogeological environs. Heavy metals in groundwater are estimated by using Atomic Absorption Spectrometer, Perkin Elmer Analyst 200. Data were assessed statistically to find the distribution pattern and other related information for each metal. The study revealed that a good number of the drinking water sources were contaminated with cadmium, manganese and lead. Arsenic concentrations although did not exceeded WHO limits but was found to be slightly elevated. Copper and zinc concentrations were found to be within the prescribed WHO limits. An attempt has also been made to ascertain the possible source of origin of the metals. Positive and significant correlation existing between manganese with zinc and copper indicates towards their similar source of origin and mobility. In view of the present study and the level of heavy metal contamination, it could be suggested to test the potability of the water sources before using it for drinking purpose.     

Effects of leachant temperature and pH on leachability of metals from fly ash. A case study: Can thermal power plant, province of Canakkale, Turkey

Lignite powered electric generation plants result in increasing environmental problems associated with gaseous emissions and the disposal of ash residues. Especially, low quality coals with high ash content cause enormous quantities of both gaseous and solid fly ash emissions. The main problem is related to the disposal of fly ash, which, in many cases, contains heavy metals. It is known that toxic trace metals may leach when fly ash is in contact with water. In this study, fly ash samples obtained from the thermal power plant in the town of Can in Turkey were investigated for leachability of metals under different acidic and temperature conditions. The experimental results show that a decrease in pH of the leachant favors the extraction of metal ions from fly ash. A significant increase in the extraction of arsenic, cadmium, chromium, zinc, lead, mercury, and selenium ions from the ash is attributed to the instability of the mineral phases. These heavy metals concentrations increase with respect to increasing acidic conditions and temperature. Peak concentrations, in general, were found at around 30°C.     

Speciative distribution and bioavailability of metals in agricultural soils receiving industrial wastewater

In order to assess the metal pollution status of agricultural lands of Mandi Bahauuddin receiving industrial wastewater, 35 top soil samples were investigated for the determination of selected metal levels, i.e., Fe, Cu, Cd, Cr, Ca, Ni, and Pb by flame atomic absorption spectroscopy under optimum analytical conditions. The distribution of these metals in different operationally defined chemical fractions was also determined by using the sequential extraction technique. The highest mean total concentration was found for Fe while the least one was observed for Pb. All the studied metals were found to be present at levels much enhanced than national and international standards. Moreover, most of the metals were distributed principally in residual fraction with the exception of Ni which was found to be associated mainly with oxidizable fraction. The significant correlations were observed between Fe-Mn oxide-bound and residual fractions and exchangeable and oxidizable fractions for most of the metals. The highest mobility was exhibited by Ni that evidenced its enhanced bioavailability in the soil. The multivariate statistical analyses in terms of principal component analysis (PCA) and cluster analysis (CA) revealed multiple sources for various geochemical fractions of different metals. CA also revealed that the nonresidual fractions of most of the metals were very closely associated while PCA presented a distinctive behavior of Ca in the soil. It was therefore suggested that in order to avoid the metal contamination arising from industrial wastewater, appropriate remediation strategies must be adopted.     

Concentrations and bioaccessibility of metals in vegetation and dust near a mining haul road, Cape Krusenstern National Monument, Alaska

Vegetation, sub-surface peat, and road dust were sampled near the Delong Mountain Transportation System (DMTS) haul road in northwest Alaska in 2005-2006 to document aluminum, barium, cadmium, lead, and zinc concentrations, and to evaluate bioaccessibility of these metals. The DMTS haul road is the transport corridor between Red Dog Mine (a large-scale, lead-zinc mine and mill) and the coastal shipping port, and it traverses National Park Service lands. Compared to reference locations, total metal concentrations in four types of vegetation (birch, cranberry, and willow leaves, and cotton grass blades/stalks) collected 25 m from the haul road were enriched on average by factors of 3.5 for zinc, 8.0 for barium, 20 for cadmium, and 150 for lead. Triple rinsing of vegetation with a water/methanol mixture reduced metals concentrations by at most 50%, and cadmium and zinc concentrations were least affected by rinsing. Cadmium and zinc bioaccessibility was greater in vegetation (50% to 100%) than in dust (15% to 20%); whereas the opposite pattern was observed for lead bioaccessibility (<30% in vegetation; 50% in dust). Barium exhibited low-to-intermediate bioaccessibility in dust and vegetation (20% to 40%), whereas aluminum bioaccessibility was relatively low (<6%) in all sample types. Our reconnaissance-level study indicates that clean-up and improvements in lead/zinc concentrate transfer activities have been effective; however, as of 2006, metal dispersion from past and/or present releases of fugitive dusts along the DMTS road still may have been contributing to elevated metals in surface vegetation. Vegetation was most enriched in lead, but because bioaccessibility of cadmium was greater, any potential risks to animals that forage near the haul road might be equally important for both of these metals.     

Speciation of heavy metals in biosolids of wastewater treatment plants at Mysore,Karnataka, India

Urban wastewater treatment leads to the generation of large quantities of biosolids. Accumulation of biosolids is a problem of environmental relevance due to the existence of heavy metals in the biosolids. Determination of total metal in biosolid provides information relating pollution levels. Determination of their mobilization capacity and behaviour in the environment is an important task. An experimental approach commonly used for studying the mobility, transport and bioavailability of metal in biosolids is the use of selective sequential extraction procedure. In the present study an attempt has been made to study the heavy metal properties in biosolid samples collected from urban wastewater treatment plants located at Mysore, Karnataka. Few heavy metals selected for the present study are cadmium, chromium, copper, iron, nickel and zinc. The concentration of these metals in biosolids and their partition in different fractions are studied. The speciation of metals based on the sequential extraction scheme was carried out. The concentration of heavy metals is lower than that established by European legislation. The residual fraction has the maximum percentage of heavy metals whereas, only a small fraction of heavy metals (Fe, Zn and Cd) are extracted in the most soluble fractions, exchangeable and carbonate fractions.     

Biomonitoring in the Boulder River Watershed, Montana, USA: Metal Concentrations in Biofilm and Macroinvertebrates, and Relations with Macroinvertebrate Assemblage

Portions of the Boulder River watershed contain elevated concentrations of arsenic, cadmium, copper, lead, and zinc in water, sediment, and biota. We measured concentrations of As, Cd, Cu, Pb, and Zn in biofilm and macroinvertebrates, and assessed macroinvertebrate assemblage and aquatic habitat with the objective of monitoring planned remediation efforts. Concentrations of metals were generally higher in downstream sites compared with upstream or reference sites, and two sites contained metal concentrations in macroinvertebrates greater than values reported to reduce health and survival of resident trout. Macroinvertebrate assemblage was correlated with metal concentrations in biofilm and macroinvertebrates. However, macroinvertebrate metrics were significantly correlated with a greater number of biofilm metals (8) than metals in invertebrates (4). Lead concentrations in biofilm appeared to have the most significant impact on macroinvertebrate assemblage. Metal concentrations in macroinvertebrates were directly proportional to concentrations in biofilm, indicating biofilm as a potential surrogate for monitoring metal impacts in aquatic systems.     

Metal concentrations in water, sediment, and fish from sewage-fed aquaculture ponds of Kolkata, India

The concentrations of lead, cadmium, chromium, copper, and zinc were investigated in the sewage-fed pond water, sediment, and the various organs of Labeo rohita, Catla catla, Cirrhinus mrigala, Oreochromis mossambicus, and Cyprinus carpio cultured in sewage-fed ponds, Kolkata, India. Among the metals, cadmium, lead, and zinc were detected in water and, except lead, were below the water quality guideline levels for the protection of freshwater aquatic life proposed by CEQG (Canadian Environmental Quality Guidelines) and AENV (Alberta Environment). Therefore, lead could pose danger to aquatic organisms. All the five metals were detected in the sediment and, except cadmium and lead, were below the sediment quality guideline levels for aquatic life proposed by EPA (Environmental Protection Agency). Therefore, these two metals could be toxic to aquatic organisms. Significant (P > 0.05) differences were observed among the five fish species for all these metals accumulation. Also, significant (P > 0.05) differences were noticed among these metals accumulation in fish organs. Cadmium showed the least bioaccumulation, while zinc showed the highest bioaccumulation in all the fish species. Though the metal concentration in the different fish tissues was variable, the highest concentration was found in kidney and the lowest in the muscle. Concentrations of these metals in the muscle tissue of all the fish species were well below the consumption safety tolerance in fish set by WHO/FAO, and thus, so far as these metals are concerned, these sewage-fed cultured fishes are safe and suitable for human consumption.     

Fractionation and potential mobility of trace metals in Danube alluvial aquifer within an industrialized zone

Thirty-five alluvial sediments of the River Danube and 12 groundwater samples were taken within the Pan?evo Oil Refinery (Serbia). The results for groundwater samples exceed European primary drinking water standards for Fe (obtained results, >200 μg/l) and Mn (obtained results, >50 μg/l), while the levels of the trace metals are below the thresholds for drinking water quality. Sediments were treated by sequential extraction procedure with five different solutions, each having a higher extraction capacity than the previous one. We also wanted to determine the possible relationships among trace metals and between sediment properties and elemental concentrations. These solutions partitioned metals into CH₃COONH₄ extractable (F1); HCl carbonate extractable and NH₂OH·HCl easily reducible (F2); (NH₄)₂C₂O₄/H₂C₂O₄ moderately reducible (F3); H₂O₂–HNO₃ organic/sulfide extractable fractions (F4); and HCl acid-soluble residue (F5). The sum of trace metals Ni, Pb, Cu, and Zn associated with the first two fractions (exchangeable, carbonate, and easily reducible) is significant and extremely important because it represents the proportion of heavy metals that can be easily remobilized by changes in environmental conditions such as pH, redox potential, salinity, etc. Sediments located nearer the groundwater flow are exposed to stronger groundwater fluctuation and had a higher quantity of amorphous and less stable substrates of trace metals. Principal component analysis was used to understand and visualize the associations between the trace metals and certain geological forms within analyzed sediments. The observed association between Cr with total sulfur and Mn from the acid-soluble residue could indicate that Cr is in the form of reduced, less toxic Cr(III), which is from the ecochemical point of view very important.     

Consumption of heavy metal contaminated foods and associated risks in Bangladesh

This study investigated the magnitude of heavy metal contamination and determined the carcinogenic as well as non-carcinogenic risks associated with selected food consumption in Bangladesh. Commonly consumed varieties of rice, vegetables, and fish samples were analyzed to measure the concentrations of heavy metals such as cadmium, chromium, lead, arsenic, manganese, nickel, and zinc. These staple food items showed the greatest probabilities of heavy metal contamination in different phases of their production and marketing. Wide variations of metal concentrations were observed. Specifically, estimated daily intakes of arsenic and cadmium exceeded allowable daily intakes in all three food items. Toxicity scores of the metals were evaluated, and a comprehensive risk assessment was conducted to quantify the risks associated with the daily food consumption. Except for cadmium and lead in vegetables, all the contaminants present in each food item posed significant levels of carcinogenic risks up to 2.99?×?10^?3 compared to the EPA recommended carcinogenic risk level of 1.0?×?10^?6. Cadmium and arsenic intake due to rice consumption also posed unsafe levels of non-carcinogenic risks of 4.587 and 6.648, respectively, compared to the EPA recommended non-carcinogenic risk level of 1.0. Finally, a revised set of permissible limits was proposed for the heavy metals detected in the food items. Those permissible limits would ensure the risks associated with food consumption below the allowable carcinogenic and non-carcinogenic risk levels. Thus, this comprehensive approach would provide guidelines to formulate adequate control measures and regulatory limits of toxic metals in foods produced and marketed in Bangladesh.     

Transversal immission patterns and leachability of heavy metals in road side soils

Today there is consensus concerning the road traffic's role as a metal source. However, there are so far only a few studies which focus on the road side immission patterns regarding distance from roads, and especially in combination with the leachability of heavy metals down the soil profile. In this study, the aim was to analyse concentrations of traffic related metals in road side soils, at different depths and distances from roads, both to analyse the immission patterns as well as to explain the importance of the road construction design of the road side terrain. The BCR sequential extraction procedure was performed to be able to address the environmental risk in terms of metal mobility. Approximately 80 soil samples were analysed for seven metals; antimony (Sb), cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb), nickel (Ni) and zinc (Zn). The results showed that, depending on metal, the total metal concentrations in road side soils have increased 3-16 times compared to regional background during the last decades. Each metal had a limited dispersal distance from the roads as well as down in the soil profile and the road construction significantly affected the metal immission distance. Elevated metal concentrations were mostly found for top soils and down to 10 cm in the soil profiles. The labile fractions counted for more than 40% of the total concentrations for Cd, Cu, Ni, Pb and Zn, indicating a potential mobilization of the metals if the road side soils become disturbed. The present soil metal concentration levels are not alarming, but metals with a high accumulation rate might gradually be an upcoming problem if nothing is done to their emission sources.     

Use of sequential extraction to assess the influence of sewage sludge amendment on metal mobility in Chilean soils

In Chile, the increasing number of plants for the treatment of wastewater has brought about an increase in the generation of sludge. One way of sludge disposal is its application on land; this, however involves some problems, some of them being heavy metal accumulation and the increase in organic matter and other components from sewage sludge which may change the distribution and mobility of heavy metals. The purpose of the present study was to determine the effect of sewage sludge application on the distribution of Cr, Ni, Cu, Zn and Pb in agricultural soils in Chile. Three different soils, two Mollisols and one Alfisol, were sampled from an agricultural area in Central Chile. The soils were treated with sewage sludge at the rates of 0 and 30 ton ha(-1), and were incubated at 25 degrees C for 45 days. Before and after incubation, the soils were sequentially extracted to obtain labile (exchangeable and sodium acetate-soluble), potentially labile (soluble in moderately reducing conditions, K4P2O7-soluble and soluble in reducing conditions) and inert (soluble in strong acid oxidizing conditions) fractions. A two-level factored design was used to assess the effect of sludge application rate, incubation time and their interaction on the mobility of the elements under study. Among the metals determined in the sludge, zinc has the highest concentration. However, with the exception of Ni, the total content of metals was lower than the recommended limit values in sewage sludge as stated by Chilean regulations. Although 23% of zinc in sludge was in more mobile forms, the residual fraction of all metals was the predominant form in soils and sludge. The content of zinc only was significantly increased in two of the soils by sewage sludge application. On the other hand, with the exception of copper, the metals were redistributed in the first four fractions of amended soils. The effect of sludge application rate, incubation time and their interaction depended on the metal or soil type. In most cases an increase in more mobile forms of metals in soils was observed as the final effect.