Heavy metal speciation and mobility assessment of arid soils in the vicinity of Al Ain landfill, United Arab Emirates

Sixty-four surface soil samples taken in the vicinity of Al Ain landfill were analysed for cadmium, chromium, copper, nickel, lead and zinc by inductively coupled plasma spectroscopy. Extraction techniques were used to establish the association of the total concentrations of the six metals in the soil samples with their contents in the exchangeable, carbonate, iron/manganese oxides, and residual fractions. In the investigated soils, the recorded concentrations were as follows: 0.043 mg kg^-1 for cadmium, 19.1 mg kg^-1 for chromium, 53.3 mg kg^-1 for copper, 60 mg kg^-1 for nickel, 13.7 mg kg^-1 for lead, and 117 mg kg^-1 for zinc. Cadmium, chromium, nickel, lead and zinc concentrations in the investigated soil samples reflect the natural background values in shale, whereas copper is slightly enriched. I-geo (geoaccumulation index) values of the metals in the soils under study indicate that they are uncontaminated with cadmium, chromium, nickel, lead and zinc, but contaminated to moderately contaminated with copper. Heavy metal contents in the sediments were found to be significantly influenced by different physico-chemical parameters. The effect of these parameters can be arranged in the following order: clay fraction > carbonate fraction > silt fraction > organic matter fractions. A sequential extraction procedure showed that the total concentrations of the heavy metals are largely bound to the residual phase (retained 71.4% of cadmium, 77.8% of chromium, 75% of copper, 47% of nickel, 62.8% of lead, and 75.8% of zinc). A likely sequence of mobility in the investigated soils is as follows: chromium > lead > nickel > cadmium > zinc > copper.     

Metal distributions in soil receiving urban pavement runoff and snowmelt.

Wet and dry deposition of anthropogenic metals and particulates generated from urban and traffic activities can result in contamination of urban-land-use soils. These particulate residuals encompass a wide size gradation, from 1 to greater than 10 000 microm. This study hypothesized that such contamination of surficial soils can be analyzed and explained as a function of the soil/residual granulometry. This study analyzed the gradation-based physical characteristics for 10 urban transportation land-use sites with soil/residual complexes (SRCs) located throughout metropolitan Cincinnati, Ohio, and an urban residential reference site. Particle density (rho(s)) of SRCs ranged from 2.8 to 2.1 g/cm3, with the lower particle density associated with particles less than 100 microm. For each site, specific surface area generally increased with decreasing particle size, while the predominance of total surface area was associated with the coarser size fractions, except for the clayey glacial till reference site not influenced by traffic. Cumulative analysis for lead, copper, cadmium, and zinc associated with SRCs indicated that more than 50% of the metal mass was associated with particles greater than 250 microm, with more than 80% associated with particles greater than 106 microm. Study results are similar to rainfall-runoff and snowmelt distributions. Results provide guidance when considering potential fate and control of metals transported by urban drainage and are distributed across the SRC size gradation.     

Anthropogenic lead distribution in soils under arable land and permanent grassland estimated by Pb isotopic compositions

The role of land use on fate of metals in soils is poorly understood. In this work, we studied the incorporation of lead in two neighboring soils with comparable pedogenesis but under long-term different agricultural management. Distributions of anthropogenic Pb were assessed from concentrations and isotopic compositions determined on bulk horizon samples, systematical 5-10 cm increment samples, and on 24-h EDTA extracts. Minor amounts of anthropogenic lead were detected until 1-m depth under permanent grassland, linked to high earthworm activity. In arable land, exogenous Pb predominantly accumulated at depths <60 cm. Although the proximity between the two sites ensured comparable exposition regarding atmospheric Pb deposition, the isotopic compositions clearly showed the influence of an unidentified component for the cultivated soil. This work highlights the need for exhaustive information on historical human activities in such anthropized agrosystems when fate of metal pollution is considered.     

Atmospheric heavy metal deposition accumulated in rural forest soils of southern Scandinavia

Thirty-three years of measurements of atmospheric heavy metal (HM) deposition (bulk precipitation) in Denmark combined with European emission inventories form the basis for calculating a 50-year accumulated atmospheric input to a remote forest plantation on the island of Laesoe. Soil samples taken in two depths, 0-10cm and 10-20cm, at eight forest sites at the island were used to determine the increase in HM content in the eolian deposited top soils of the plantation. Concentrations of lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), vanadium (V), nickel (Ni) and arsenic (As) were determined in atmospheric deposition and in soils. The accumulated atmospheric deposition is of the same magnitude as the increase of these metals in the top soil.     

Influence of initial pH on bioleaching of heavy metals from contaminated soil employing indigenous Acidithiobacillus thiooxidans

Bioleaching of heavy metals from contaminated soil was carried out employing indigenous sulfur oxidizing bacterium Acidithiobacillus thiooxidans. Experiments were carried out to assess the influence of initial pH of the system on bioleaching of chromium, zinc, copper, lead and cadmium from metal contaminated soil. pH at the end of four weeks of bioleaching at different initial pH of 3-7 was between 0.9 and 1.3, ORP between 567 and 617mV and sulfate production was in the range of 6090-8418mgl(-1). Chromium, zinc, copper, lead and cadmium solubilization ranged from "59% to 98%" at different initial pH. A. thiooxidans was not affected by the increasing pH of the bioleaching system towards neutral and it was able to utilize elemental sulfur. The results of the present study are encouraging to develop the bioleaching process for decontamination of heavy metal contaminated soil.     

Effects of pH on the toxicity of cadmium, copper, lead and zinc to Folsomia candida Willem, 1902 (Collembola) in a standard laboratory test system

EC₅₀s for cadmium, copper, lead and zinc were determined for juvenile production of Folsomia candida at pH6.0, 5.0 and 4.5 in a standard laboratory test system. In contrast to most previous studies where metal toxicity was increased at low pHs, in our experiments there was no clear relationship between soil acidity and EC_{50-reproduction} in this species. The EC_{50-reproduction} values (μg g⁻¹) for cadmium and zinc were similar at all three pHs (pH6.0: Cd 590, Zn 900; pH5.0: Cd 780, Zn 600; pH4.5: Cd 480, Zn 590). In contaminated field sites adjacent to primary zinc smelters, zinc is invariably present in soils at concentrations of at least 50 times that of cadmium Thus deleterious effects of mixtures of these metals on populations of Collembola in such sites can be attributed to zinc rather than cadmium.     

Mobility of heavy metals as related to soil chemical and mineralogical characteristics of Brazilian soils

In order to better understand the relationship between soil characteristics and mobility of some heavy metals, correlation studies were conducted in samples of unlimed and limed A, B and C horizons of three Brazilian soils, representative of the majority of the tropical soils. A number of chemical and mineralogical characteristics of one Oxisol and two Ultisols were related to the retardation factors (Rf) for zinc (Zn), cadmium (Cd), copper (Cu) and lead (Pb). The retardation factors, obtained in leaching column experiments, were used as an estimate of solute movement in the profile. Soil types and soil horizons were found to influence metal retardation factors which, in turn, correlated better with the chemical than the mineralogical soil characteristics. For the unlimed soil samples, the soil characteristics that significantly correlated with Zn-Rf and Cd-Rf were the sum of exchangeable bases (SB), and soil exchangeable (Ca-KCl) and non-exchangeable (Ca-HCl) calcium contents. These results showed the strong influence of the cation exchange phenomenon on the retention and mobility of these two metals. For Cu and Pb, not only SB, cation exchange capacity (CEC) and Ca-KCl and Ca-HCl but also the organic matter correlated well with the Rf, showing that complex or chelate formation may play an important role in the movement of these elements. The important soil chemical characteristics related to the retardation factors in the limed soil samples were SB for Cd, and Ca-HCl for Cu and Pb, suggesting that precipitation may also influence the mobility and retention of the latter two heavy metals in these soil samples. Soil pH influenced the heavy metals adsorption and movement as shown by the significant correlation with the retardation factors when the combined data for the unlimed and limed soil samples was considered.     

Distribution of chromium, cadmium, nickel and lead in agricultural soils collected from Kazanli-Mersin, Turkey

This study reports total levels of chromium, cadmium, nickel and lead in the agricultural land adjacent a factory producing chromate compounds in Kazanli-Mersin. Surface soil samples were collected from fields around the factory as well as from fields farther away to measure contamination due to aerial transportation and deposition of dust produced in the industrial process. Heavy metals in soil were extracted using wet digestion, and concentrations were measured by atomic absorption spectrophotometry. The concentrations were compared with Turkish maximum allowable concentration values. The metal concentrations averaged 80, 0.14, 228 and 431mg1kg^-1 for chromium, cadmium, nickel and lead, respectively. Soil samples contaminated with chromium were mainly found 500–20001m from the factory and decreased with increasing distance from the factory. Elevated chromium and nickel concentrations were determined in the soils around the factory, especially to the northwest (prevailing wind) and west. Lead concentrations exceeded the limit in only roadside soils (4000 and 50001m to the west), but tended to increase in the vicinity of industrial activity (especially in the west, the northwest and the north). The cadmium concentration did not exceed the limit and was within the normal range for soils.     

Cadmium exposure from the cement dust emissions: a field study in a rural residence

The cement dust is one of the causes of pollution in the environment. In the present study, the cadmium concentrations of soil and plant specimens taken from a rural area exposed to cement factory emissions were determined and also the blood concentrations and sensitivity conditions in humans residing in this rural area were investigated. The 108 soil (36 for control) and plant specimens were collected from eight different directions of the cement plant located in Cukurhisar town in Eski?ehir city. Blood samples of the individuals residing in this area were taken from 258 subjects (258 for control) following a physical examination, and patch tests were also applied. The results show that the cadmium concentrations of the soil and plant specimens taken from different places in different directions of the factory were higher than in the control areas. The physical examination of subjects did not reveal results different from those of the control group except for the diagnosis of contact dermatitis. The analysis of venous blood samples showed that cadmium concentrations were found to be within the reference values given for both groups, but higher in the subjects (p<0.001). According to the results of patch tests, sensitivity to cadmium was found to be more frequent for the subject group than the control group (p<0.05). Those results show that, although clinical tools revealed no toxic effects for the subject, except contact dermatitis, the cement plant increases cadmium pollution on the surrounding environment.     

Efficiency of lipopeptide biosurfactants in removal of petroleum hydrocarbons and heavy metals from contaminated soil

This study describes the potential application of lipopeptide biosurfactants in removal of petroleum hydrocarbons and heavy metals from the soil samples collected from industrial dumping site. High concentrations of heavy metals (like iron, lead, nickel, cadmium, copper, cobalt and zinc) and petroleum hydrocarbons were present in the contaminated soil samples. Lipopeptide biosurfactant, consisting of surfactin and fengycin was obtained from Bacillus subtilis A21. Soil washing with biosurfactant solution removed significant amount of petroleum hydrocarbon (64.5 %) and metals namely cadmium (44.2 %), cobalt (35.4 %), lead (40.3 %), nickel (32.2 %), copper (26.2 %) and zinc (32.07 %). Parameters like surfactant concentration, temperature, agitation condition and pH of the washing solution influenced the pollutant removing ability of biosurfactant mixture. Biosurfactant exhibited substantial hydrocarbon solubility above its critical micelle concentration. During washing, 50 % of biosurfactant was sorbed to the soil particles decreasing effective concentration during washing process. Biosurfactant washed soil exhibited 100 % mustard seed germination contradictory to water washed soil where no germination was observed. The results indicate that the soil washing with mixture of lipopeptide biosurfactants at concentrations above its critical micelle concentration can be an efficient and environment friendly approach for removing pollutants (petroleum hydrocarbon and heavy metals) from contaminated soil.     

Investigation of heavy metal accumulation in Polygonum thunbergii for phytoextraction

In this study, cadmium (II), lead (II), copper (II) and zinc (II) were determined in Polygonum thunbergii and soil from the Mankyung River watershed, Korea. Soil samples contained detectable lead (<17.5 g g(-1)), copper (<8.4 g g(-1)) and zinc (<24.5 g g(-1)), whereas cadmium was undetectable. Whole plants of P. thunbergii contained detectable lead (<320.8 g g(-1)), copper (<863.2 g g(-1)) and zinc (<2427.3 g g(-1)), whereas cadmium was detectable only in the stem (<7.4 g g(-1)) and root (<10.1 g g(-1)). Whole plant concentrations were very different for each metal, particularly in the case of zinc. The mean content of heavy metal in the whole plants increased in the order of cadmium (8.5 g g(-1))相似文献   

Tidal salt marsh sediment in California, USA. Part 2: occurrence and anthropogenic input of trace metals

Surface sediment samples (0–5 cm) from 5 tidal salt marshes along the coast in California, USA were analyzed to investigate the occurrence and anthropogenic input of trace metals. Among study areas, Stege Marsh located in the central San Francisco Bay was the most contaminated marsh. Concentrations of metals in Stege Marsh sediments were higher than San Francisco Bay ambient levels. Zinc (55.3–744 μg g⁻¹) was the most abundant trace metal and was followed by lead (26.6–273 μg g⁻¹). Aluminum normalized enrichment factors revealed that lead was the most anthropogenically impacted metal in all marshes. Enrichment factors of lead in Stege Marsh ranged from 8 to 49 (median = 16). Sediments from reference marshes also had high enrichment factors (2–8) for lead, indicating that lead contamination is ubiquitous, possibly due to continuous input from atmospherically transported lead that was previously used as a gasoline additive. Copper, silver, and zinc in Stege Marsh were also enriched by anthropogenic input. Though nickel concentrations in Stege Marsh and reference marshes exceeded sediment quality guidelines, enrichment factors indicated nickel from anthropogenic input was negligible. Presence of nickel-rich source rock such as serpentinite in the San Francisco Bay watershed can explain high levels of nickel in this area. Coefficients of variation were significantly different between anthropogenically impacted and non-impacted metals and might be used as a less conservative indicator for anthropogenic input of metals when enrichment factors are not available.     

Palygorskite as a feasible amendment to stabilize heavy metal polluted soils

The sorption behaviour of palygorskite has been studied with respect to lead, copper, zinc and cadmium in order to consider its application to remediate soils polluted with these metals. The Langmuir model was found to describe well the sorption processes offering maximum sorption values of 37.2 mg/g for lead, 17.4 mg/g for copper, 7.11 mg/g for zinc and 5.83 mg/g for cadmium at pH 5-6. In addition the effect of palygorskite amendment in a highly polluted mining soil has been studied by means batch extractions and leaching column studies. The soluble metal concentrations as well as the readily-extractable metal concentrations were substantially decreased at any concentration of palygorskite applied to soil (1, 2, 4%), although the highest decrease is obtained at the 4% dose. The column studies also showed a high reduction in the metal leaching (50% for lead, 59% for copper, 52% for zinc and 66% for cadmium) when a palygorskite dose of 4% was applied.     

Performance evaluation of intermediate cover soil barrier for removal of heavy metals in landfill leachate

This pilot-scale study evaluated the use of intermediate cover soil barriers for removing heavy metals in leachate generated from test cells for co-disposed fly ash from municipal solid waste incinerators, ash melting plants, and shredder residue. Cover soil barriers were mixtures of Andisol (volcanic ash soil), waste iron powder, (grinder dust waste from iron foundries), and slag fragments. The cover soil barriers were installed in the test cells' bottom layer. Sorption/desorption is an important process in cover soil bottom barrier for removal of heavy metals in landfill leachate. Salt concentrations such as those of Na, K, and Ca in leachate were extremely high (often greater than 30 gL(-1)) because of high salt content in fly ash from ash melting plants. Concentrations of all heavy metals (nickel, manganese, copper, zinc, lead, and cadmium) in test cell leachates with a cover soil barrier were lower than those of the test cell without a cover soil barrier and were mostly below the discharge limit, probably because of dilution caused by the amount of leachate and heavy metal removal by the cover soil barrier. The cover soil barriers' heavy metal removal efficiency was calculated. About 50% of copper, nickel, and manganese were removed. About 20% of the zinc and boron were removed, but lead and cadmium were removed only slightly. Based on results of calculation of the Langelier saturation index and analyses of core samples, the reactivity of the cover soil barrier apparently decreases because of calcium carbonate precipitation on the cover soil barriers' surfaces.     

Effect of soil pH on availability to crops of metals in sewage sludge-treated soils. II. Cadmium uptake by crops and implications for human dietary intake

Appropriate pH-related permissible soil-limit concentrations for cadmium in sewage sludge-treated agricultural soils were estimated from the proportional changes in concentrations of cadmium in potatoes, oats and ryegrass grown on two sludge-amended soils and at different pH values. Implications for potential human dietary intake of cadmium were also assessed. Yields of crops increased with increasing soil pH, probably in response to decreasing uptake of zinc as soil pH value was raised. In general, cadmium concentrations in peeled potato tubers, potato peelings, oat straw and ryegrass decreased as simple linear functions of increasing soil pH over the range of pH values measured (pH 3.9-7.6). Cadmium concentrations in potato peel were particularly sensitive to changing pH conditions, whereas cadmium levels in oat grain were independent of soil pH. On the basis that a highly precautionary approach is adopted in setting soil standards for heavy metals, appropriate permissible concentrations of cadmium in sludge-treated agricultural soil which protect the human food chain were determined as 2.0 and 2.5 mg Cd Kg(-1) for banded pH ranges of 5.0-5.5 and 5.5-6.0, respectively.     

An explanation for the apparent losses of metals in a long-term field experiment with sewage sludge

Large losses of metals applied to soil in metal-contaminated sewage sludge have been reported. The potential pathways of loss, including lateral movement from treated plot areas, have not been examined. A field experiment, which started in 1942, was investigated to determine the amount of lateral movement of zinc, cadmium, copper, nickel, chromium and lead due to conventional cultivation processes. A two-dimensional 'dispersion' model (i.e. movement of soil due to cultivation) fitted well to the observed movement of metals, and gave coefficients for movement of 0.24 and 0.13 m(2) per tillage operation in dimensions parallel or perpendicular to the direction of ploughing, respectively. For testing purposes, the model was used to predict the concentrations of metals in specific areas of a plot or average concentrations for whole plots at different points in time. The concentrations measured in soil samples agreed well with the predicted values. Finally, the model was also used to estimate the proportion of the metal load applied between 1942 and 1961 that remained in the 0-27 cm cultivated layer in 1985. About 80% was accounted for: this large recovery is of great relevance to the long-term disposal of metal-contaminated wastes to land. Detailed analyses of soil profile samples showed that approximately 1% of the metals applied had moved 3.5 cm below the plough layer or less, but there was no evidence of accumulation of metals in deeper horizons down to 46 cm. These results are discussed in relation to the other potential losses of metals in the experiment.     

Isotopic characterisation of lead in contaminated soils from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria

Soil samples from the vicinity of a non-ferrous metal smelter near Plovdiv, Bulgaria contained very high concentrations of cadmium, lead and zinc (up to 140, 4900 and 5900 mg kg(-1), respectively). A roadside soil in a relatively uncontaminated area also contained high concentrations of the same metals (24, 1550 and 1870 mg kg(-1), respectively) indicating that the transport of ores could be a source of contamination. Even though the lead isotope ratios in all the samples fell within a very narrow range (for example, 1.186-1.195 for (206)Pb/(207)Pb), the samples could be differentiated into three distinct groups: ores ((206)Pb/(207)Pb and (208)Pb/(207)Pb ratios of 1.1874-1.1884 and 2.4755-2.4807, respectively), current deposition (1.1864 and 2.4704-2.4711, respectively) and local background (1.1927-1.1951 and 2.4772-2.4809, respectively). Although most of the current deposition has its origin in the ores used at the smelter, up to 12% could be from other sources such as petrol lead.     

Mobility of arsenic, cadmium and zinc in a multi-element contaminated soil profile assessed by in-situ soil pore water sampling, column leaching and sequential extraction

Three methods for predicting element mobility in soils have been applied to an iron-rich soil, contaminated with arsenic, cadmium and zinc. Soils were collected from 0 to 30 cm, 30 to 70 cm and 70 to 100 cm depths in the field and soil pore water was collected at different depths from an adjacent 100 cm deep trench. Sequential extraction and a column leaching test in the laboratory were compared to element concentrations in pore water sampled directly from the field. Arsenic showed low extractability, low leachability and occurred at low concentrations in pore water samples. Cadmium and zinc were more labile and present in higher concentrations in pore water, increasing with soil depth. Pore water sampling gave the best indication of short term element mobility when field conditions were taken into account, but further extraction and leaching procedures produced a fuller picture of element dynamics, revealing highly labile Cd deep in the soil profile.     

Difference of lead,copper and zinc concentrations between interiors and exteriors of peds in some contaminated soils

Solute transport of elements in soils depends on the soil structural and hydraulic properties, and it is controlled by sorption and diffusion, which both limit the mobility and distribution of elements in soils. This study was conducted to compare lead (Pb), copper (Cu) and zinc (Zn) concentrations between ped exteriors and interiors of some contaminated soils. The results show that the differences of the heavy metals between exteriors and interiors decreased in the order clayey soil, clayey loam soil, loam soil. For same soils, the differences decreased from Pb to Cu to Zn. The differences in readily extractable concentrations of the three metals between ped exteriors and interiors were much larger than the differences in their total metals, this may indicate that extractable metals were more recently deposited. The higher Pb and Cu concentrations in the ped exteriors than interiors may additionally be explained by anthropogenic input, movement and downward through preferential flow.     

Characterization and spatial distribution of heavy metals in sediment from Cedar and Ortega rivers subbasin

The Cedar and Ortega rivers subbasin is a complex environment where both natural and anthropogenic processes influence the characteristics and distributions of sediments and contaminants, which in turn is of importance for maintenance, dredging and pollution control. This study investigated the characteristics and spatial distribution of heavy metals, including lead (Pb), copper (Cu), zinc (Zn) and cadmium (Cd), from sediments in the subbasin using field measurements and three-dimensional kriging estimates. Sediment samples collected from three sampling depth intervals (i.e., 0-0.10, 0.11-0.56 and 0.57-1.88 m) in 58 locations showed that concentrations of Pb ranged from 4.47 to 420.00 mg/kg dry weight, Cu from 2.30 to 107.00 mg/kg dry weight, Zn from 9.75 to 2,050.00 mg/kg dry weight and Cd from 0.07 to 3.83 mg/kg dry weight. Kriging estimates showed that Pb, Cu and Cd concentrations decreased significantly from the sediment depth of 0.10 to 1.5 m, whereas Zn concentrations were still enriched at 1.5 m. It further revealed that the Cedar River area was a potential source area since it was more contaminated than the rest of the subbasin. Comparison of aluminum (Al)-normalized metal concentrations indicated that most of the metals within the top two intervals (0-0.56 m) had concentrations exceeding the background levels by factors of 2-10. A three-dimensional view of the metal contamination plumes showed that all of the heavy metals, with concentrations exceeding the threshold effect level (TEL) that could pose a threat to the health of aquatic organisms, were primarily located above the sediment depth of 1.5 m.