Availability of Cu and Zn in an acidic sludge-amended soil as affected by zeolite application and liming

Purpose  

Acidic soils exhibit high trace element availability compared to neutral pH soils, and thus, when trace metals are added (e.g. due to sewage sludge application), measures should be taken to reduce their mobility. In this experiment, we tested two such methods, liming and zeolite addition. The aim was to measure the availability, in ryegrass (Lolium perenne L.), of heavy metals (Cu and Zn) added to soil with sewage sludge in both acidic and limed soil.     

Distribution of heavy metals in soils of the Yellow River Delta: concentrations in different soil horizons and source identification

Purpose

The Yellow River Delta, an active land-ocean interaction area, will develop into a large eco-economic region in East China during the coming decade. It is necessary to assess the geochemical features of heavy metals in the soils. The objectives of this research were to evaluate the concentrations and distribution of heavy metals (Cr, Ni, Cu, Zn, Pb, and Cd) in soil profiles of the area and to identify their sources.

Materials and methods

Horizon samples were collected based on pedogenic features from bottom to top in each profile to a depth of 120 cm and a total of 92 samples were collected. The sampling sites were grouped into four lines from inland to coastal area with three land use types (cotton field, cereal field, and wetland). The concentrations of Cr, Ni, Cu, Zn, Pb, and Cd were measured by inductively coupled plasma-mass spectrometry. Iron oxide fractions in the soil were extracted by oxalate-oxalic acid and dithionite-citrate-bicarbonate. X-ray diffraction (XRD) was used to determine the mineral composition of the soils. Multivariate statistical analysis and historical data were employed to identify the possible sources of these heavy metals.

Results and discussion

The mean concentrations of heavy metals were elevated along the Yellow River region and in the southern part of the delta; however, they were generally lower than the Chinese guideline values. As for the depth distribution of heavy metals in soil profiles, the maximum values of Cr, Ni, Cu, Zn, and Cd in middle horizon of cotton field were almost twice than those in surface horizon. The iron oxides and XRD analysis indicated that the trace elements accumulation appeared to be related with the contents of crystalline iron oxide and layer silicates. Historical data from suspended sediments of the Yellow River and principal component analysis (PCA) implied that most of the metals (Cr, Ni, Cu, and Zn) were sourced from natural alluviation and sedimentation.

Conclusions

The Yellow River Delta soils were slightly polluted by heavy metals the Yellow River Delta. The special pedogenic horizon characterized by higher iron oxides and layered silicates minerals in the middle and lower part of the soil profile was found with heavy metals enrichment, which required to be studied further. Suspended sediments transported by the Yellow River were suggested to be one of the major sources for the heavy metals accumulation in the basal soils of this region.     

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu,Cr, Ni,and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

Purpose

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT).

Materials and methods

Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha^?1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals.

Results and discussion

The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvín, this increase peaked at an application rate of 90 Mg ha^?1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha^?1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C _E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil.

Conclusions

The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C _E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C _E for soil Cu was not related to plant Cu for all soils studied.     

Transfer of Cd, Pb, and Zn to water spinach from a polluted soil amended with lime and organic materials

Purpose

The transfer of heavy metals from soil to crops comprises several steps, including soil-to-root and subsequent root-to-shoot tranfer. The purpose of this study was to investigate the different steps of soil-to-crop transfer of Cd, Pb, and Zn.

Materials and methods

This study was carried out with a greenhouse pot experiment using a soil polluted with Cd, Pb, and Zn which was amended with rice straw, pig manure, sheep dung, or peat, with and without lime. Water spinach (Ipomoea aquatica) was used as the test crop and was grown after a season of rice cultivation.

Results and discussion

The results showed that all the amendments promoted the root-to-shoot transfer of Cd, Pb, and Zn. The soil-to-root transfer factors (TFs) of Pb and Zn tended to increase with increasing available Pb and Zn in the soils, while no clear relationship between the TF of Cd and available soil Cd was observed. The root-to-shoot TF of Cd, Pb, and Zn tended to decrease with increasing available amounts in the soils and were negatively correlated with the concentrations of the metals in the roots (r _Cd?=?0.820, r _Pb?=?0.789, r _Zn?=?0.769).

Conclusions

The soil-to-root transfer of Cd, Pb, and Zn was significantly different from the root-to-shoot transfer. The soil-to-root transfer was mainly influenced by the amount of available metal in soil, whereas the root-to-shoot transfer was mainly controlled by the concentrations of the metals in the root.     

Effects of bacteria on metal bioavailability,speciation, and mobility in different metal mine soils: a column study

Purpose  

Successful phytoremediation depends mainly on the bioavailability of heavy metals in the soil. Recently, soil microbes possess several mechanisms that are able to change metal bioavailability in the soil, which provides a new strategy for investigating biogeochemical cycling of metals in contaminated soils. Three metal mines soils with elevated concentrations of Cd, Pb, and Zn from China were applied in this column study to (1) evaluate the effects of metal tolerant bacterial inoculation (Burkholderia cepacia, accession number: AB051408) on metal release, (2) monitor the migration of metals in the rhizospheric horizon (0–20 cm), and (3) investigate metal speciation and sequential fractions in soil.     

Lability and sorption of heavy metals as related to chemical,physical, and mineralogical characteristics of highly weathered soils

Purpose  

Heavy metal lability, probably, is the most important isolated factor to cause toxicity in plants and organisms in soils. Sorption of heavy metals, in turn, affects directly the amount of their labile forms in soils. Therefore, to assess sorption and quantify labile forms of Cd, Cu, Ni, Pb, and Zn, adsorption and incubation studies were carried out.     

Mixed chelators of EDTA,GLDA, and citric acid as washing agent effectively remove Cd,Zn, Pb,and Cu from soils

Purpose

Soil washing with chelators is a viable treatment alternative for remediating multi-contaminated soils. The aim of this study was to investigate the removal efficiencies of Cd, Zn, Pb, and Cu in alkaline and acid multi-metal-contaminated soils by washing with the mixed chelators (MC).

Materials and methods

The batch experiments were carried out to evaluate the removal efficiencies of heavy metals in contaminated soils by the MC with different molar ratios of EDTA, GLDA, and citric acid, and evaluated the washing factors, including contact time, pH, MC concentration, and single and multiple washings at the same MC dose, on the removal efficiencies.

Results and discussion

Results showed that the removal efficiencies for Cd, Zn, Pb, and Cu by the MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) were as much as those of the only EDTA washing from both soil at the same application dose of total chelators; moreover, the application dose of EDTA decreased by 80%. For the alkaline-contaminated soil, the removal efficiencies of Cd, Zn, Pb, and Cu decreased with the increasing of the solution pH, which was opposite to acid-contaminated soil. This was attributed to that the metal-ligand complex could be obviously re-adsorbed on the soil surface sites, particularly in low pH values. The removal efficiencies of Cd, Zn, Pb, and Cu depended on MC concentration. A higher MC concentration led to a more effective removal of Cd, Zn, Pb, and Cu in alkaline-contaminated soil; however, their changes were slightly increased in acid-contaminated soil. At the same dose of MC, single washing with higher MC concentration might be favorable to remove heavy metals, moreover, with much less wastewater generation.

Conclusions

The MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) may be a useful, environmentally friendly, and cost-effective chelators to remediate heavily multi-metal-contaminated soil.

     

Trace metals in sediments and aquatic plants from the Xiangjiang River, China

Purpose

The metal concentrations and Pb isotopic composition in sediments and plants from the Xiangjiang River, China, were investigated to understand the contamination and potential toxicity of metals in sediments; to determine the accumulation and distribution of metals in plant tissues; and to trace the possible pollution source of Pb in sediments and plants.

Materials and methods

Sediments and plants were collected from 43 sampling sites in the study region. After sediments were air-dried and passed through a 63-??m sieve, they were acid-digested and DTPA-extracted for determination of total and bioavailable metals. The plants were separated into roots, leaves, and stems; dried; cut into pieces; and digested with HNO₃?CH₂O₂. Metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) and Pb isotopic composition were analyzed by inductively coupled plasma-mass spectrometry.

Results and discussion

Maximum As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in sediments were 47.18, 55.81, 129.5, 161.6, 160.4, 430.7, and 1,098.8?mg?kg^?1, respectively. The bioavailable fractions of As, Cd, Cu, Pb, and Zn had significant linear relationship with their corresponding total contents in sediments while no significant relationship was observed between bioavailable and total contents of Cr and Ni. In general, plant tissues showed higher As, Cd, Cu, Pb, and Zn concentrations and lower Cr and Ni concentrations compared with sediments. The ²⁰⁶Pb/²⁰⁷Pb ratios decreased in the order of total > bioavailable > stems ?? leaves > roots. A strong linear correlation was observed between the ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁶Pb/²⁰⁷Pb ratios of the plant tissues, sediments, and the possible pollution sources of Pb in the Xiangjiang River.

Conclusions

As, Cd, Cu, Pb, and Zn demonstrated higher contamination levels in sediments and plants compared with Cr and Ni. Cd had highest potential ecological risk. The Pb from anthropogenic sources with low ²⁰⁶Pb/²⁰⁷Pb ratios was preferentially associated with the bioavailable fractions in sediments and accumulated in roots. The Pb in plant tissues is mainly derived from the Pb in sediment and is taken up through the sediment-to-root pathway.     

Forms of Cu (II), Zn (II), and Pb (II) compounds in technogenically transformed soils adjacent to the Karabashmed copper smelter

Purpose

The aim was to study Cu (II), Zn (II), and Pb (II) forms in technogenically transformed soils adjacent to the Karabashmed copper smelter.

Materials and methods

Studies were performed in the plume zone of the Karabash smelter and in the floodplains of Ryzhii Brook and Sak-Egla River. Geomorphological and geochemical migration processes prevail in technogenic landscapes. The differentiation of landscape-geochemical conditions plays the dominant role, which determines the localization of metals. The total Mn, Cr, Ni, Cu, Zn, Pb, Cd, and As contents and the macroelement compositions of soils were determined by X-ray fluorescence. The composition of Cu, Pb, and Zn compounds in soils was determined by the Tessier sequential fractionation. The determination of the geochemical fractions of heavy metals in soils is a key issue in the study of their mobility. The metals were fractionated into the following five fractions: exchangeable, bound to carbonates, bound to Fe and Mn oxides, bound to organic matter, and residual fractions.

Results and discussion

It is shown that the total Zn and As contents in the 0- to 5-cm layer of soils on monitoring plots exceed their lithosphere clarks in hundreds of times, and the total Cu, Pb, and Cr contents exceed their lithosphere clarks in tens of times. Factors and processes controlling the distribution and transport of Cu, Pb, and Zn forms in soils were determined. According to landscape-geochemical differentiation, the eluvial (automorphic) catena (plot T4) takes the main technogenic load of dust fallouts from the Karabash copper smelter. The accumulation of material brought from above and the geochemical precipitation of discharges from tailings dumps occur in superaqual catenas (plots T1, T2, and T3). In the technogenically transformed soils, the basic stabilizers of the mobility of Cu is organic matter, for Pb it is Fe-Mn (hydro) oxides, and for Zn - it is clay minerals.

Conclusions

The distributions of Cu, Zn, and Pb forms in the studied technogenically transformed soils are due to a number of factors: First, these are the composition of technogenic pollutants contaminating ecosystems and the time during which the contamination occurred, and second, this is the combination of physicochemical properties controlling the buffer properties of the polydisperse system of soils and parent materials.

     

Geochemical studies on the contamination and dispersion of trace metals in intertidal sediments around a military air weapons shooting range

Purpose  

A number of publications have raised trace metal contamination of soils and sediments within and around shooting ranges used for sport or military training. To our knowledge, however, there is no publication on the contamination of sediments derived from military shooting ranges in a marine environment. Therefore, this work was purposed to assess the dispersion and fractionation of ammunition- and bomb-derived trace metals in intertidal sediment.     

Rhizosphere effects of <Emphasis Type="Italic">Populus euramericana</Emphasis> Dorskamp on the mobility of Zn,Pb and Cd in contaminated technosols

Purpose

This study aimed at investigating the rhizosphere effects of Populus euramericana Dorskamp on the mobility of Zn, Pb and Cd in contaminated technosols from a former smelting site.

Materials and methods

A rhizobox experiment was conducted with poplars, where the plant stem cuttings were grown in contaminated technosols for 2 months under glasshouse conditions. After plant growth, rhizosphere and bulk soil pore water (SPW) were sampled together. SPW properties such as pH, dissolved organic carbon (DOC) and total dissolved concentrations of Zn, Pb and Cd were determined. The concentrations of Zn, Pb and Cd in plant organs were also determined.

Results and discussion

Rhizosphere SPW pH increased for all studied soils by 0.3 to 0.6 units compared to bulk soils. A significant increase was also observed for DOC concentrations regardless of the soil type or total metal concentrations, which might be attributed to the plant root activity. For all studied soils, the rhizosphere SPW metal concentrations decreased significantly after plant growth compared to bulk soils which might be attributed to the increase in pH and effects of root exudates. Zn, Pb and Cd accumulated in plant organs and the higher metal concentrations were found in plant roots compared to plant shoots.

Conclusions

The restricted transfer of the studied metals to the plant shoots confirms the potential role of this species in the immobilization of these metals. Thus, P. euramericana Dorskamp can be used for phytostabilization of technosols.

     

Contaminated sediments as a potential source of Zn, Pb, and Cd for a river system in the historical metalliferous ore mining and smelting industry area of South Poland

Background, aim, and scope  Elevated levels of heavy metals in the aquatic and soil systems can be caused by the weathering of mineralized rocks. This enrichment is often considerably enlarged by historical and current mining and smelting activities. In Poland, the most contaminated river systems are those in the Silesia region. The metalliferous ore mining and smelting industries have been the main sources of heavy metal pollutions over the last 100–170 years. The previous and present studies have shown very high concentrations of heavy metals in the bottom sediments of the Mala Panew River, the most polluted tributary of the Oder River. The main objective of this work was to study temporary changes of selected metal (Zn, Pb, and Cd) concentrations in upper layer of bottom sediments at the measuring point near the outlet of the Mala Panew River into the Oder River, and to determine the vertical distribution of the metals in the sediment cores from the most polluted middle part of this river. The mobility of the metals and their potential bioavailability were assessed based on metal partitioning in the sediments and metal concentrations in pore waters. The presented data were compared with metal concentrations in aquatic sediments from similar historical mining and smelting sites in Poland and other countries. Methods  The upper layer of bottom sediment samples from the same Mala Panew River measuring point were collected six times in the period 1997–2005, while five sediment cores were collected once from the middle course of Mala Panew River in 2006. Abiotic parameters such as pH and Eh have been determined in situ. Metal contents were determined in the <20 and <63 μm size fractions of sediments after digestion in a microwave oven with aqua regia or concentrated nitric acid. Metal mobility was assessed in the selected sediment cores by the chemical forms of metals (sequential extraction method) and their concentrations in pore waters were investigated. Results  The concentrations of Cd, Pb, and Zn in the upper layer of sediments varied, depending on both the season and the year of sampling. Their mean concentrations (from six samplings) are [mg/kg]: Zn 1,846, Pb 229 and Cd 73. The metal concentrations in the sediment cores varied with the depth in the range of [mg/kg]: 0.18–559 for Cd, 26.2–3,309 for Pb and 126–11,153 for Zn, although the highest accumulations generally could be observed in the deeper layers. The most mobile metal fractions, i.e., exchangeable, carbonate and easily reducible fractions, are typical of Zn and Cd. Cadmium was found to be the most mobile metal and its relative contribution ranges from 84 to 96%, while in the case of Zn it ranged from 45 to 94%. Lead is mainly associated with the moderately reducible fraction (30–60%). Relative contributions of metal chemical forms slightly vary with the depth in the sediment profile. The results obtained for the pore water samples show very high concentrations of the metals studied, especially in the case of Cd (31–960 μg/dm³) and Zn (300–4,400 μg/dm³). Discussion  Accumulation of Cd, Pb, and Zn in the upper layer of the bottom sediments and in the sediment core samples from the Mala Panew River is very high, considerably exceeding the local geochemical background. High contributions of mobile Cd and Zn and the toxicity of cadmium can cause environmental risk. Our measurements also suggest that mobile metals can migrate into groundwater, whereas the groundwater itself can leach some chemicals from river sediments, because of a relatively high water table in the study area, especially during rainfall periods. Comparison of the results obtained with the literature data from the last decade shows that the concentrations of Cd and Zn in the sediments from the Mala Panew River are the highest among other submersed sediments in Poland and other regions (e.g., the Mulde River, Germany). Conclusions  The Mala Panew River is one of the most polluted rivers when compared with similar historical mining and smelting areas in Poland and elsewhere. The sediments studied are strongly polluted with the metals analyzed. In the upper layer of the bottom sediments there has been no reduction of Zn and Cd amounts over the last decade, which could suggests a long-term migration and a secondary contamination. Considerably higher accumulations of metals in overbank sediment cores and in the deeper core section could result from strong contamination in previous decades and translocation of Cd and Zn (secondary pollutants). The relatively high concentrations of the two metals in pore waters support these findings. Cadmium is crucial in the environmental risk assessment because of its high mobility and toxicity. These data are important for water/sediment management in the transboundary Oder River catchment, situated in Poland, Germany and the Czech Republic. Recommendations and perspectives  It is important to assess mobility phase and pore water in the contaminated historical aquatic sediments. Such studies may help explain the changes, which take place in the sediment layers as well as at the water–sediment interface. Obtained results should be used for the risk assessment of the historical contaminated sediments at the local river-basin scale. The treatment of contaminated sediments, e.g., dragging activity, should be considered as very important in management strategies in order to avoid remobilization of metals.     

Removal of trace and major metals by soil washing with Na<Subscript>2</Subscript>EDTA and oxalate

Background, aim, and scope  

Various metals such as cationic metals (Cu, Pb, Zn) and anionic metals (As, Cr) often coexist in real soils, and normal soil washing techniques for the removal of cationic metals with a single-washing reagent make it rather difficult to simultaneously remove all of them. Oxalate could effectively remove anionic As and EDTA could effectively remove the cationic metals, so it was possible to remove all coexisting cationic and anionic metals by washing with the combination of Na₂EDTA and oxalate. The objective of this study was to (1) discuss the possibility of removing five metals, As, Cd, Cu, Pb, and Zn, effectively from the soil by washing with Na₂EDTA-combined oxalate; (2) optimized through the consecutive washing.     

Speciation of heavy metals in garden soils: evidences from selective and sequential chemical leaching

Purpose  

Gardening (especially food growing) in urban areas is becoming popular, but urban soils are often very contaminated for historical reasons. There is lack of sufficient information as to the bioavailability of soil heavy metals to plants and human in urban environments. This study examines the relative leachability of Cr, Ni, As, Cd, Zn, and Pb for soils with varying characteristics. The speciation and mobility of these metals can be qualitatively inferred from the leaching experiments. The goal is to use the data to shed some light on their bioavailability to plant and human, as well as the basis for soil remediation.     

Metal contamination of soils, sediments and dusts in the vicinity of marine leisure boat maintenance facilities

Purpose

Metal contamination arising from boat maintenance is a growing environmental concern. In this study, metals currently or historically employed in boat paints (Ba, Cu, Pb, Sn and Zn) have been determined in geosolids sampled from within and in the vicinity of two leisure boat maintenance facilities in south west England.

Materials and methods

Samples of dusts, sediments and soils from two boatyards and from various urban control sites were fractionated through 63 μm before being digested in boiling aqua regia. Metal concentrations were determined in sample digests by inductively coupled plasma spectrometry.

Results and discussion

Metal concentrations were highly variable in each medium but were greatest in boatyard dusts which, pre-fractionation, often contained visible particles of paint. Metal concentrations in sediments and soils were higher than concentrations in respective control samples and, in many cases, exceeded environmental quality standards or predicted effect concentrations. Observations are attributed to the heterogeneous contamination of geosolids by fine particulates of antifouling paint generated during boat maintenance and repair; specifically, particulates contaminate sediment via boatyard runoff (with rainfall and washdown water), while soil is contaminated through the deposition of fine, airborne paint dusts.

Conclusions

This study demonstrates that boat paint particles enriched in a variety of metals contaminate both coastal and terrestrial environments. Contamination arises from the removal and dispersion of dusts during boat maintenance. Stricter measures for the containment and disposal of wastes generated by boat repair and repainting are, therefore, recommended.     

Heavy metal pollution of the world largest antimony mine-affected agricultural soils in Hunan province (China)

Purpose  

The present work concerns the distribution of ten heavy metals (Sb, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn) in the surrounding agricultural soils of the world largest antimony (Sb) mine in China. The objective is to explore the degree and spatial distribution of heavy metal pollution of the Sb mine-affected agricultural soils. The presented data were compared with metal concentrations in soils from mining and smelting sites in China and other countries.     

Using humic products as amendments to restore Zn and Pb polluted soil: a case study using rapid screening phytotest endpoint

Purpose

Heavy metal contamination is a priority issue affecting millions of hectares of soil throughout the world. One of the most promising, environmentally friendly, and cost-effective approaches to restore polluted soils could be applying organic amendments. We investigated the remediation potential of three types of humic products with regard to their effect on the bioavailability of Pb and Zn, content of nutrients, and the ability to mitigate acute phytotoxicity in contaminated soil.

Materials and methods

Spodosol samples were spiked with Pb (550 mg kg^?1) and Zn (880 mg kg^?1). Then, two different commercial humic products (from peat and lignosulfonate) and natural humic acids (from brown oxidized coal) were added in two doses to reach an equal content of carbon: a 10% increment and a 30% increment of the initial total organic carbon in the soil. After 30 days, the content of metals and nutrients (S, K, Na, Ca, Mn, P) was determined by the sequential extraction (i?H₂O, ii?NH₄COOH pH 4.8, iii–CH₃COOH). The effect of humic products on heavy metals bioavailability was evaluated using the calculated partition indexes. Seed germination and root elongation of Sinapis alba were also determined. Chemical and biochemical variables were aggregated by the principal component analysis.

Results and discussion

Humic products reduced the amount of bioavailable fractions of Pb and Zn in soils. The partition index, which quantitatively describes bioavailable fractions of the Zn and Pb in the soil, was 28–49% lower than in the spiked (Pb+Zn) control. The inhibition of root elongation and seed germination of mustard by Zn and Pb was significantly mitigated by humic products; in the soil test, the root length and seed germination were up to 36–87% higher than those of the Pb+Zn control and did not differ from those in the non-amended treatments. This effect may have been associated with the structural differences (H/C and O/C ratio) and content of nutrients (Na and K) in humic products.

Conclusions

Commercial humic products used in poor multi-contaminated soils can maintain plant growth by improving nutrient status due to heavy metals immobilization and can be a promising approach to remediate the soil contaminated with heavy metals at extremely high concentrations.

     

Toxicity assessment using <Emphasis Type="Italic">Lactuca sativa</Emphasis> L. bioassay of the metal(loid)s As,Cu, Mn,Pb and Zn in soluble-in-water saturated soil extracts from an abandoned mining site

Purpose  

We used the different soluble-in-water concentrations of As, Cu, Mn, Pb and Zn from contaminated soils in an abandoned mining area (anthropogenic origin) to assess the phytotoxicity of the abandoned site using the results obtained with a Lactuca sativa L. bioassay.     

Distribution of As, Cd, Pb, and Zn in redox features of mine-waste impacted wetland soils

Purpose

Wetland soils of the Coeur d??Alene (CdA) River Basin of northern Idaho, USA are contaminated with toxic elements released during mining activities. In this paper, we report results from a multi-scale investigation of total As, Cd, Pb, and Zn distributions along a transect of these contaminated soils.

Materials and methods

Four sites along an 80-m transect were established at the Black Rock Slough wetland in CdA River Basin. The elevation difference between the upslope and lowland site was 1.1?m. Soils were sampled from three depths, down to 45?cm. Redoximorphic features were isolated from the soils and categorized into five types of cemented particles, and Fe-enriched and depleted soil masses. Soils and isolated soil separates were analyzed for total elemental concentration.

Results and discussion

Within soil profiles, contaminants are enriched in surface horizons as compared to the original depositional profiles. Enrichment was more dramatic in the upland sites than the lowland sites. Fe-enriched masses that ranged in size from a few millimeters to several centimeters were also enriched in As, Pb, and Zn. At the smallest scale investigated, five different soil aggregate types ranging in size from 1 to 2?mm in diameter had distinct contaminant associations: Fe-cemented aggregates were elevated in As and Zn; Mn-cemented aggregates had more than five times as much Pb as the bulk soil; root channels were elevated in As; and charcoal particles were elevated in all contaminants, particularly Pb and Cd.

Conclusions

Results show that in wetland soils pedogenic processes differentially distribute contaminants amongst the redoximorphic features. The distribution is affected by landscape position and water table influence. At the pedon scale, there is an enrichment of As, Cd, Pb, and Zn in surface horizons, suggesting that upward flux of contaminants is occurring. This contaminant redistribution should be considered in design of management and remediation strategies.     

Application of the Weng’s ratio for the identification of Zn, Cu, and Pb contamination in soils and sediments

Purpose

This work explores the application of the use of Zn, Cu, and Pb relative contents as a new type of normalization method for geochemical properties of soils and sediments in an Atlantic Basin (Anllóns River, NW Spain). The method is based on the conservative behavior of these elements, which exhibit a certain concentration ratio that remains stable as long as there are no human disturbances.

Materials and methods

The average relative contents of Zn, Cu, and Pb were calculated by dividing the concentration of each metal in soils or sediments, in the <63-μm fraction, by the sum of Zn, Cu, and Pb, expressed as a percentage. The evaluation of the sum of the average relative concentrations of Zn, Cu, and Pb (Ri), together with three standard deviations for each element, namely, Ri ± 3Si, allows a hexagon to be constructed, represented in ternary diagrams of Zn:Cu:Pb. Following the method proposed by Weng et al. (Environ Geol 45:79–85, 2003), those samples falling outside the hexagon must be considered outliers.

Results and discussion

Results obtained confimed the conservative behavior between the relative contents of Zn, Cu, and Pb in surficial samples (soils, bed, and suspended sediments). Only sediment cores displayed nonconservative behavior, showing a marked Pb enrichment, with respect to the surficial samples. When Zn, Cu, and Pb relative contents were plotted in ternary diagrams, outliers were best classified when the hexagon was drawn with standard deviations of samples from the study area. The hexagon drawn with an international database of soils and sediments showed a poorer classification of outliers.

Conclusions

The results showed that total Zn, Cu, and Pb relative contents may be employed to investigate anthropogenic disturbances of these elements in soils and sediments of the Anllóns River Basin, thus corroborating that this type of normalization may be employed as a tool to assess outliers in a contaminated area.