Fractionation of potentially toxic elements in urban soils from five European cities by means of a harmonised sequential extraction procedure

Assessment of Microplastics and Potentially Toxic Elements in Surface Sediments of the River Kelvin, Central Scotland, United Kingdom

Contamination of the environment by microplastics (MPs), polymer particles of <5 mm in diameter, is an emerging concern globally due to their ubiquitous nature, interactions with pollutants, and adverse effects on aquatic organisms. The majority of studies have focused on marine environments, with freshwater systems only recently attracting attention. The current study investigated the presence, abundance, and distribution of MPs and potentially toxic elements (PTEs) in sediments of the River Kelvin, Scotland, UK. Sediment samples were collected from eight sampling points along the river and were extracted by density separation with NaCl solution. Extracted microplastics were characterised for shape and colour, and the polymer types were determined through attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Pollution status and ecological risks were assessed for both the microplastics and PTEs. Abundance of MPs generally increased from the most upstream location (Queenzieburn, 50.0 ± 17.3 particles/kg) to the most downstream sampling point (Kelvingrove Museum, 244 ± 19.2 particles/kg). Fibres were most abundant at all sampling locations, with red, blue, and black being the predominant colours found. Larger polymer fragments were identified as polypropylene and polyethylene. Concentrations of Cr, Cu, Ni, Pb and Zn exceeded Scottish background soil values at some locations. Principal component and Pearson's correlation analyses suggest that As, Cr, Pb and Zn emanated from the same anthropogenic sources. Potential ecological risk assessment indicates that Cd presents a moderate risk to organisms at one location. This study constitutes the first co-investigation of MPs and PTEs in a river system in Scotland.

Assessment of anthropogenic pollution in Guanabara Bay (SE Brazil) through biogeochemical data and stable isotope mixing models

This work intends to identify pollution sources along the margins of Guanabara Bay (GB; SE Brazil) through a multiproxy approach and Bayesian stable isotopic mixture model (BSIMM). For this purpose, 33 surface sediment samples were collected and analyzed for granulometry, geochemistry (heavy metals, total organic carbon-TOC, stable isotopes of carbon and nitrogen-δ13C and δ15N, Rock-Eval pyrolysis parameters-REPP), and physicochemical parameters. Metal concentrations (E) dissolved in water (EW), adsorbed by organic matter (EOM) and by Mn hydroxides (EMn), and total extracted concentrations (ET) were analyzed. Sampling was conducted in 2018 after an oil spill from Reduc Oil Refinery. Potential Ecological risk index (PERI), based on metals, classified 85% of the analyzed stations as having moderate to considerable ecological risk. The metals with the potential to cause the highest ecological risk were CdW, CdOM, PbOM, and HgOM. The combination of BSIMM and REPP data was an effective proxy for oil spill detection by indicating the presence of polycyclic aromatic hydrocarbons (PAHs). Relatively high TOC contents suggested that the analyzed stations are eutrophicated environments. BSIMM discriminated three groups of stations with different sources of organic matter (OM), endorsing the result previously shown by the cluster analysis: (A) Niterói region, Botafogo marina, Glória marina, Fiscal and Fundão islands with diffuse sources of OM, including marine phytoplankton and material of continental origin from highly polluted rivers and domestic sewage; (B) region near Fundão and Governador islands and Mangue Channel outlet with OM (≃70%) supplied by highly polluted streams and a small contribution of PAHs; (C) Duque de Caxias and Botafogo-Urca inlet with significant contributions of PAHs, materials from C-3 plants and rivers polluted by urban sewage. Results of linear regressions in conjunction with BSIMM indicate that HgMn and PbOM mainly affect Group A's stations. Although the eastern margin of GB (Niterói; Group A) showed greater oceanic interaction than the other groups, it presented substantial concentrations of metals, potentially harmful (i.e., Hg and Pb) to marine biota and human health.

Environmental bioavailability of arsenic, nickel and chromium in soils impacted by high geogenic and anthropogenic background contents

High arsenic, chromium and nickel in soils can pose a hazard to the ecosystem and/or human health. Large areas can be affected by elevated potentially toxic elements (PTE) background contents, entailing a significant effort for managing the potential risk. Assessing the environmental hazard associated to PTE-contaminated soils requires the determination of soil PTE environmental bioavailability, which reflects the capacity of these elements to be transferred to living organisms. Here we assess the environmental bioavailability of As, Cr and Ni in topsoils from the Liège basin and Belgian Lorraine, two areas in Wallonia, Belgium, affected by elevated As, Cr and Ni background contents. The source of soil As, Cr and Ni differs in Liège and Lorraine: anthropogenic in the former location and geogenic in the latter. The environmental bioavailability of PTE was determined using two complementary approaches: (1) by chemical fractionation with the Community Bureau of Reference (BCR) three-step sequential extraction protocol and (2) by estimating the phytoavailability using a plant-based biotest (Lolium multiflorum as plant model). The results show that total As (6-130 mg·kg-1), Cr (15-268 mg·kg-1), and Ni (8-140 mg·kg-1) contents in the Liège and Lorraine soils frequently exceed the soil clean-up standards. However, no positive correlation was found between the total contents and BCR extraction results or rye-grass contents, except for As in Liège soils. Total As, Cr or Ni contents surpassing soil standards do not necessarily result in elevated mobile, potentially mobilizable and phytoavailable contents. In general, environmental bioavailability of As, Cr and Ni is higher in soils from Liège basin compared to those sampled in Belgian Lorraine. The mobile and potentially mobilizable fractions of As, Cr and Ni account for <30 % of their total contents following the BCR extractions. Our study provides valuable information for sustainable management at the regional scale of soils containing high PTE contents.

Characterization and chemical fractionation of potentially toxic elements in soils of a pre-mining mineralized area; an evaluation of mobility and environmental risk

The environmental geochemical characterization of mineralized areas prior to mining does not receive adequate attention. This study shows trace element distribution in soils of two unexploited porphyry copper deposits located in Darreh-Zereshk and Ali-Abad in central Iran. The study was carried out using a compositional data analysis (CoDa) approach and combination of multivariate statistics and clustering techniques, which made it possible to identify the geochemical associations representing the different areas of the mineral deposits. The results of the chemical analyses, performed by ICP-MS, revealed high concentrations of those elements typically associated with porphyry deposits (As, Co, Cu, Mo, Ni, Pb, and Zn). The typical zonal pattern with an anomaly of Cu in central parts of the system and the prevalence of epithermal elements (Ag, Cd, Pb, and Zn) toward the peripheral propylitic alteration zone were recognized. The XRD analysis of selected soil samples allowed us to determine the distribution of elements within the different carrier minerals. Afterward, geochemical speciation patterns were investigated by a four-step sequential extraction procedure based on BCR protocol. The residual fraction consisting of primary resistant minerals was found to be the main host for As (73-93.4%), Cr (65.1-79.6%), Cu (54.3-81.4%), Ni (58.9-80.6%), V (75.9-88%), and Zn (56.5-60.5%) in the studied soils. Even though these elements are not readily leachable, their behavior and distribution could be largely affected by the mining operation and consequent changes in the physicochemical properties of the soil. The soluble-exchangeable phase was only less than 15% of the total extractions for all elements, except for Cd. With respect to the mobility factor (MF), Cd was the most mobile element followed by Sb and Pb. The measured risk assessment code (RAC) presented the following risk order: Cd > Sb > Ni > Co > Pb > Cr > As > Zn > Cu > V. This study reveals that the acquisition of pre-mining geo-environmental data of trace elements is very important to establish pre-mining backgrounds and baselines for evaluating post-mining or post-reclamation geochemical signatures.

Toxicity evaluation of polycyclic aromatic hydrocarbons (PAHs) in soils of coal chemical industry areas, North China

Objectives of this study were to investigate the concentrations, distributions, toxicities, and risk assessment of 16 polycyclic aromatic hydrocarbons in surface soils surrounding a coal chemical industrial zone in the southeast of Shanxi province, China. A total of 52 topsoil samples were collected from different land-use areas: cereal agriculture, roadsides, and parkland. Results show that the total PAHs (∑₁₆PAHs) ranged from 3.87 × 10³ to 116 × 10³ µg kg^-1 and that the total carcinogenicity PAHs (∑BPAHs) ranged from 3.11 × 10³ to 94.2 × 10³ µg kg^-1, with the highest concentration of ∑₁₆PAHs noted in the RS samples, followed by PS and AS. The entire risk quotient of all PAH maximum permissible concentrations (RQ∑PAH_MPCi) was greater than 1.0, and the minimum concentration entire risk quotient (RQ∑PAH_NCi) of 84.3% of all samples was higher than 800. The value of the total toxicity equivalent concentration of PAH (PAHBapeq) for areas surrounding the coal chemical industrial zone was higher than the value of the standard level, and the incremental lifetime cancer risk (ILCR) far exceeds the U.S. EPA's risk standard. The toxic properties of PAHs indicated that the soils in the survey areas have a high risk to human health and the environment.

The significance of applying different factors for the evaluation of sediment contamination by toxic elements and estimation of the ecological risk

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conducted to determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasina watershed. The sequential extraction results, which enable the evaluation of mobility of the studied elements, have indicated that Zn, Ni, Cu, Cr, and As can be considered slightly mobile, whereas Pb, Mn, Cd, and Co were regarded as possibly mobile elements. Lead was dominantly bounded (specifically adsorbed or co-precipitated) to iron and manganese oxides (up to 80%) and may be released by reduction. Since the content of the exchangeable fraction (F1) is an indicator for anthropogenic impact on the aquatic environment, a low percentage (0-8%) of studied toxic elements in this fraction indicated that these elements have lithogenic origin in most sampling locations in the area of study. Except for Pb, the substantial positive correlations between Al and other elements showed that studied elements came primarily from terrigenous sources. Although the values obtained for the risk assessment code (RAC) indicated a slightly increased mobility of some elements (up to 22.44%), the values of the modified risk assessment code (mRAC), which include toxic effects on the environment, showed there is no danger of pollution by studied elements (all values were < 1%). Our recommendation is to use mRAC instead of RAC in ecochemical studies and assessment of the degree of sediment and soil pollution, because mRAC includes toxic effects of elements. Based on ATI values, river sediments show no toxic to a low toxic degree. Even though obtained results indicate that there was no considerable risk for river water contamination, the ecological risk for Fe and Pb should be monitored in the future.

Pollution Characteristics and Spatial Distribution of Heavy Metals in Coal-Bearing Sandstone Soil: A Case Study of Coal Mine Area in Southwest China

Soil pollution in coal mining areas is a serious environmental problem in China and elsewhere. In this study, surface and vertical profile soil samples were collected from a coal mine area in Dazhu, Southwestern China. Microscopic observation, concentrations, chemical speciation, statistical analysis, spatial distribution, and risk assessment were used to assess heavy metal pollution. The results show that the weathering of coal-bearing sandstone and mining activities substantially contributed to soil pollution. The concentrations of Fe, Ni, Cu, Zn, Mn, Cd, Hg, and Pb exceeded their background values. Cd caused the most intense pollution and was associated with heavily-extremely contaminated soils. The residual fraction was dominant for most metals, except Cd and Mn, for which the reducible fraction was dominant (Cd: 55.17%; Mn: 81.16%). Zn, Ni, Cd, and Cu presented similar distribution patterns, and Hg and As also shared similar distribution characteristics. Factor 1 represented anthropogenic and lithologic sources, which were affected by mining activities; Factor 2 represented anthropogenic sources, e.g., fertilizers and traffic pollution; and Factor 3 represented the contribution of metals from soil-forming parent material. More than half of the study area had high pollution risk and was not suitable for vegetable cultivation.

Potentially Toxic Elements in Urban Soils from Public-Access Areas in the Rapidly Growing Megacity of Lagos, Nigeria

Rapid urbanization can lead to significant environmental contamination with potentially toxic elements (PTEs). This is of concern because PTEs are accumulative, persistent, and can have detrimental effects on human health. Urban soil samples were obtained from parks, ornamental gardens, roadsides, railway terminals and locations close to industrial estates and dumpsites within the Lagos metropolis. Chromium, Cu, Fe, Mn, Ni, Pb and Zn concentrations were determined using inductively coupled plasma mass spectrometry following sample digestion with aqua regia and application of the BCR sequential extraction procedure. A wide range of analyte concentrations was found—Cr, 19−1830 mg/kg; Cu, 8−11,700 mg/kg; Fe, 7460−166,000 mg/kg; Mn, 135−6100 mg/kg; Ni, 4−1050 mg/kg; Pb, 10−4340 mg/kg; and Zn, 61−5620 mg/kg—with high levels in areas close to industrial plants and dumpsites. The proportions of analytes released in the first three steps of the sequential extraction were Fe (16%) < Cr (30%) < Ni (46%) < Mn (63%) < Cu (78%) < Zn (80%) < Pb (84%), indicating that there is considerable scope for PTE (re)mobilization. Human health risk assessment indicated non-carcinogenic risk for children and carcinogenic risk for both children and adults. Further monitoring of PTE in the Lagos urban environment is therefore recommended.

Fractionation of Metal(loid)s in Three European Mine Wastes by Sequential Extraction

Mine waste can constitute an environmental hazard, especially when poorly managed. Environmental assessment is essential for estimating potential threats and optimizing mine waste management. This study evaluated the potential environmental risk of sulfidic mine waste samples originating from the Neves Corvo Mine, Portugal, and the closed Freiberg mining district, Germany. Metal(loid)s in the waste samples were partitioned into seven operationally defined fractions using the Zeien and Brummer sequential extraction scheme. The results showed similar partitioning patterns for the elements in the waste rock and tailing samples from Neves Corvo Mine; most metal(loid)s showed lower mobility, as they were mainly residual-bound. On the contrary, the Freiberg tailing sample had considerably elevated (24–37%) mobile fractions of Zn, Co, Cd, and Mn. The majority of Fe (83–96%) in all samples was retained in the residual fractions, while Ca was highly mobile. Overall, Pb was the most mobile toxic element in the three samples. A large portion of Pb (32–57%) was predominantly found in the most mobilizable fractions of the studied waste samples. This study revealed that the three mine wastes have contamination potential for Pb and Zn, which can be easily released into the environment from these waste sources.

Assessment of natural and anthropogenic factors on the distribution of chemical elements in soil from the Skopje region, North Macedonia

The main objective of this study is to present the distribution of different chemical elements in soil samples from the Skopje region, North Macedonia. To determine the level of presence of chemical elements, soil samples are collected from a total of 60 locations. From each location, from an area of 5 × 5 km² samples of soil are collected: topsoil (0-5 cm) and subsoil (20-30 cm). The soil samples were analyzed for 69 elements by using two instrumental methods: inductively coupled plasma-atomic emission spectrometry (ICP-AES) for macro-elements and inductively coupled plasma-mass spectrometry (ICP-MS) for trace elements. A factor analysis was applied to analyze the factors affecting the linear combination variables grouped at the same factor. Spatial distribution maps of each factor as well as distribution maps for the analyzed elements were prepared by universal kriging interpolation. It was found that the distribution of most elements follows the lithology of the examined area, except for some elements (Cd, Cu, Fe, Hg, Mn, Pb, and Zn) whose higher contents are found in the area of the city of Skopje as a result of urban and industrial activities (traffic, metal processing, fossil fuel combustion for heating).

Chemical Fractionation, Environmental, and Human Health Risk Assessment of Potentially Toxic Elements in Soil of Industrialised Urban Areas in Serbia

The primary focus of this research was the chemical fractionation of potentially toxic elements (PTEs) and their presence in several industrialised cities in Serbia. Furthermore, their origin, contamination levels, and environmental and human health risks were assessed. The results indicated that the examined soils were characterised by slightly higher Cu, Ni, Pb, and Zn levels than those set by European and national regulations. These elevated Cu, Pb, and Zn concentrations were caused by intensive traffic and proximity to industry, whereas the higher Ni levels were a result of the specific geological substrate of the soil in the study area. The environmental risk was found to be low and there was no enrichment/contamination of the soil with these elements, except in the case of Pb, for which moderate to significant enrichment was found. Lead also poses a potential non-carcinogenic risk to children through ingestion and requires special attention due to the fact that a significant proportion of this element was present in the tested soil samples in a potentially available form. Analysis of the health risks showed that children are more at risk than adults from contaminants and that ingestion is the riskiest exposure route. The carcinogenic risk was within the acceptable limits.

Optimization and assessment of a sequential extraction procedure for calcium carbonate rocks

Sequential extraction analyses are widely used for the determination of element speciation in sediments and soils. Typical sequential extraction protocols were developed to extract from low-carbonate samples and therefore are not necessarily suitable for high-carbonate samples. In this study, we tested increased reagent to sample ratios to adjust an existing sequential extraction procedure to analyze high-CaCO₃ samples with concentrations ranging from 70 to above 90 %. Complete dissolution of the CaCO₃ phase, and a higher extraction efficiency of manganese associated with the carbonate phase, was achieved when using four times the original reagent to sample ratio in the 2nd extraction step. This increase of reagent did not compromise the extraction of subsequent phases as shown by unaffected Fe concentrations in a low-carbonate sample. Hence, an essential outcome was that increasing the solution to sample ratio did not lead to the dissolution of other sedimentary phases, such as hydrous and crystalline iron oxides or sulfides. Thus, compared to other extraction protocols that use a lower reagent to sample ratio in the carbonate dissolution step, the new protocol allowed the complete extraction of oxide and sulfide phases in the following extraction steps. Furthermore, the study demonstrated the benefit of replacing Na-acetate with NH₄-acetate to extract exchangeable ions and carbonates. We observed increased intensities for several analytes, i.e., trace metals such as Mo and As, due to less suppression of the analyte signal by NH₄-acetate than by Na-acetate during analysis by inductively coupled plasma optical emission spectrometry (ICP-OES).

Contamination of children's sandboxes with potentially toxic elements in historically polluted industrial city

When playing in sandboxes, children are particularly vulnerable to poisoning with potentially toxic elements (PTE) due to their hand-to-mouth behaviour. In Slovenia, the city of Celje is heavily contaminated due to zinc ore smelting and iron industry. In some sandboxes, sand from Mežica Pb-Zn mine waste was used. Granulometric and XRF analysis showed that all samples contain larger percentage of fine-sized particles and some have higher As, Ba, Cd, Pb and Zn contents than allowed. By XRD and SEM/EDS analysis we identified carries of PTE, and confirmed three possible sources of contamination: the waste material from the Pb-Zn mine, the emissions from local industry and from the old Zn-smelting stockpile used as a landfill. The total health risk (ΣHI) exceeds critical value in one sandbox. The bioaccessibility of PTEs is alarming due to presence of highly soluble metal-bearing particles. Study revealed importance of combining results of health risk evaluation with bioaccessibility of elements, which is a function of the carriers of PTE. This knowledge is essential for undertaking remedial measures. Improper use of waste material could result in introducing hazardous material in the environment. We propose frequent replacement of sand and stricter legislation regulating status and usage of waste materials.

Fractionation of Potentially Toxic Elements (PTEs) in Urban Soils from Salzburg, Thessaloniki and Belgrade: An Insight into Source Identification and Human Health Risk Assessment

Concentrations of potentially toxic elements (PTEs) (Al, As, Cd, Cr, Cu, Ni, Pb, and Zn) were measured in topsoil samples collected from parks in the cities of Salzburg (Austria), Thessaloniki (Greece), and Belgrade (Serbia) in order to assess the distribution of PTEs in the urban environment, discriminate natural (lithogenic) and anthropogenic contributions, identify possible sources of pollution, and compare levels of pollution between the cities. An assessment of the health risks caused by exposure to PTEs through different pathways was also conducted. The study revealed that, with the exception of Pb in Salzburg, levels of PTEs in the soils in polluted urban parks were higher than in unpolluted ones, but still lower than those recorded in other European soils. Results of sequential analyses showed that Al, Cr, and Ni were found in residual phases, proving their predominantly lithogenic origin and their low mobility. In contrast, the influence of anthropogenic factors on Cu, Pb, and Zn was evident. Site-dependent variations showed that the highest concentrations of As, Cu, Pb, and Zn of anthropogenic origin were recorded in Salzburg, while the highest levels of Al, Cr, and Ni of lithogenic origin were recorded in Belgrade and Thessaloniki, which reflects the specificity of the geological substrates. Results obtained for the health risk assessment showed that no human health risk was found for either children or adults.

Profiles and species of Mn, Fe and trace metals in soils near a ferromanganese plant in Bagnolo Mella (Brescia, IT)

For the last forty-five years (from 1974 to present) ferroalloy production in Bagnolo Mella, Northern Italy, has generated particulate emissions enriched in potentially toxic metals and metalloids including arsenic (As), lead (Pb) and manganese (Mn). Of these, Mn is unique in that it has a significant background concentration and is seldom studied as a contaminant but is potentially a significant toxin derived from dusts regionally. Here we examine the distribution, redistribution, speciation and bioavailability of the Mn-contaminated top soils affected by atmospheric emissions adjacent to the ferroalloy plant. Four sites, variably located in the study area in terms of both distance and direction from the plant, were considered as representative of increasing levels of industrial influence. Soil profiles showed that metal concentrations (measured by X-ray fluorescence) varied considerably by location, i.e. higher in the sites closer to the plant and also at the surface level, although distributed throughout the top 15 cm, suggesting appreciable redistribution possibly due to soil mixing or infiltration. Most metal concentrations were correlated, except Mn which was independent and more variable across the sites than the other elements. Sequential chemical extractions indicated that Pb was primarily associated with Mn oxides, while As was most significantly associated with iron oxides. When Mn concentration significantly exceeded background levels, it was present in phases that were resistant to acid dissolution, very different from typical uncontaminated soils. X-ray Absorption Near Edge Spectroscopy (XANES) analyses suggested this recalcitrant Mn phase is likely a Mn-bearing spinel such as magnetite, that can be particularly toxic if ingested or inhaled. These first results highlight the legacy of ferroalloy production on surrounding soils, as well as the importance of Mn speciation for soil apportionment evaluation and human exposure estimation.

Comparison of two non-specific flow-through sequential extraction approaches to identify the physico-chemical partitioning of potentially harmful elements in a certified reference material

Two non-specific sequential extraction methods utilising chemometric data processing (chemometric identification of substrates and element distribution, CISED) have been developed and used to determine the physico-chemical partitioning of potentially harmful elements (PHE) in certified reference material BCR CRM 701 (lake sediment). A miniaturized centrifugation method in which the sample was extracted on a filter insert in a polypropylene centrifuging tube, and a quasi-flow through method in which the sample was supported on a TX40 filter in a 47 mm in-line polycarbonate filter holder, gave similar results. The CISED data processing identified nine components. Seven of these were of geochemical origin - two carbonate components, an Al/Fe oxide/hydroxide component, three Fe-dominated components and one Si-dominated component - while the others represented the TX40 filter blank. The overall extraction capabilities of the methods were similar to that of the well-established BCR sequential extraction (Σsteps 1-3). However, whilst the BCR extraction is operationally defined, the CISED provides information on associations between PHE and the geochemical components identified. The flow through CISED procedure has potential applications in investigating the chemical speciation of PHE associated with urban airborne particular matter.

Distribution of chemical forms of mercury in sediments from abandoned ponds created during former gold mining operations in Colombia

Total mercury (THg) and methylmercury (MeHg) were studied in sediments from 27 abandoned gold mining ponds (AGMPs) through small-scale artisanal gold mining in the district of San Juan in Chocó region of Colombia. The AGMPs were abandoned in the last century (1997) and were grouped into three distinct groups (2-6; 7-12; 13-20 years). Overall concentration (in ng g^-1) pattern of THg in sediments varied from 39.06 to 1271.32 (avg. 209.57) with 174.81 (13-20 years), 205.56 (7-12 years) and 248.33 (2-6 years) respectively. MeHg concentrations accounted for 3.3-10.9% (avg. 6.5%) of THg and were significantly correlated with THg during all periods. Correlations between organic matter (OM) vs MeHg and THg were negative in the oldest pools, signifying a "dilution effect" or "natural burial" of THg and MeHg. Results for sequential extraction indicate that the fraction of elemental Hg (Hg-e) and organo chelated Hg (Hg-o) represent the main chemical forms of Hg in the sediments, regardless of the abandonment period, whereas the bioavailable fraction was only 0.12-1.65% of THg. The significant statistical relationship between MeHg, THg and OM suggests that these parameters control the distribution, mobility, toxicity and bioavailability of Hg in the sediments of these abandoned ponds. Evaluation of THg with sediment quality guidelines indicates that the values are on the higher side for Threshold effect concentration and Upper continental crust. Comparing of MeHg with many other regions outside Colombia is a worrying factor and needs immediate attention to protect the human health.

Spatial distribution and pollution assessment of heavy metals in soil from the Republic of North Macedonia

The purpose of the study was to determine the spatial distribution and pollution assessment of 39 chemical elements in soil from the Republic of North Macedonia. From the whole territory of the country top soil samples (0-30 cm) were collected from 995 locations with a grid of 5 × 5 km distance between the sampling locations. Two analytical techniques were used for the analysis of soil samples: inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry. Based on a comparison of statistical parameters, spatial distribution of particular elements and results of cluster and factor analysis, four mаin geochemical associations were identified: (1) association connected with the Neogene and Quaternary volcanism (Ba, Be, Ce, Hf, K, La, Rb, Th, Tl, U and Zr); (2) association of siderophile elements (Co, Cu, Fe, Mn, Sc, Ti and V); (3) association connected with ophiolites and Mesozoic ultrabasic magmatic rocks of Vardar zone (Cr and Ni) and (4) chalcophile (sulphide) elements (As, Bi, Cd, Pb, Sb, Sn and Zn). The regional distribution was prepared according to the eight statistical regions in Macedonia, distribution according to 15 most common geological formation and distribution according to 13 pedological units.

Winter chemical partitioning of metals bound to atmospheric fine particles in Dongguan, China, and its health risk assessment

To analyze the relationship between nanoparticles and the chemical forms in an urban atmospheric environment, metallic particles with different diameters were collected using a nanoparticle sampling system and analyzed for chemical and morphological characteristics, bioactivity, and the risk of carcinogenic and non-carcinogenic effects. The source of the atmospheric particles was analyzed based on the enrichment factor method, and the carcinogenicity of the atmospheric particles was analyzed using the health risk model. The partition contents of metals extractable by a weak acid, including As, Ca, Cd, Cs, Pb, Sr, and Zn, were in a range of 32.17-71.4%, with an average value of 47.07%. The content of oxides and reducible metals of all of the elements was generally low. Potassium was distributed mainly in the residual and weak-acid-extractable fractions. Barium had a high proportion of the oxidation state. Each fraction of Zn was basically the same, while the content of the weak-acid-extractable fraction was slightly higher. We found bio-access potential to be positively correlated with a high proportion of the weak acid extracts such as Mg, Sr, and Zn. We also found there to be a large weak-acid-extractable fraction (F1) and residual fraction (F4) and relatively enriched elements and strongly enriched elements, which means F1 and F4 may be the cause of enrichment. The hazard index (HI) and the total cancer risk (TCR) were far beyond the safety threshold when the diameter of the particle was in the range of 0.1-0.5 μm, indicating that the residents in Dongguan city were experiencing obvious non-carcinogenic and carcinogenic risks.

Measuring Copper, Lead and Zinc Concentrations and Oral Bioaccessibility as Part of the Soils in Scottish Schools Project

Determination of potentially toxic elements in soils with which children have regular contact can provide valuable information to support health risk assessment. It is also important to engage schoolchildren with soil science so that they become well-informed citizens. The Soils in Scottish Schools project involved pupils across Scotland in the collection of soil from school grounds for determination of copper, lead and zinc. Samples were subjected to microwave-assisted aqua-regia digestion to determine pseudototal analyte concentrations. The simplified bioaccessibility extraction test was applied to estimate bioaccessibility. Analysis was performed by inductively coupled plasma mass spectrometry. Pseudototal analyte concentrations varied widely: Cu 15.6–220 mg∙kg−1; Pb 24.6–479 mg∙kg−1 and Zn 52.5–860 mg∙kg−1. Higher concentrations were measured in urban areas, which were historically home to heavy manufacturing industries, with lower concentrations in soils from more rural schools. Bioaccessible analyte concentrations also varied widely (Cu 3.94–126 mg∙kg−1; Pb 6.29–216 mg∙kg−1 and Zn 4.38–549 mg∙kg−1) and followed similar trends to pseudototal concentrations. None of the elements studied posed a significant health risk to children through accidental soil ingestion whilst at play during breaks in the school day, although the relatively high bioaccessible levels of lead at some locations are worthy of further investigation.

Cobalt speciation and phytoavailability in fluvo-aquic soil under treatments of spent mushroom substrate from Pleurotus ostreatus

Cobalt (Co) is a nutrient for soil microorganisms and crops, as well as a worldwide industrial pollutant. When the level of Co exceeds the acceptable limit, this heavy metal can lead to devastating consequences for soil environments. There is considerable attention and concern about elevated levels of Co contaminating soil and crops. Spent mushroom substrate (SMS) is a potential amendment for the adsorption of pollutants, which has potential for resolving Co-polluted soil that spans the world. To investigate the environmental behavior and risks associated with Co in fluvo-aquic soil under specific treatments of SMS from Pleurotus ostreatus, a lab-scale pot experiment was conducted. SMS and exogenous Co were added to soil, which was retained for approximately 30 days. Pakchois (Brassica chinensis L.) were planted in the treated soil for 28 days until harvest. The Co speciation in soil (modified BCR sequential extraction) and Co accumulation in pakchoi tissue were studied. When the SMS concentration was within a range of 0 to 9 g kg^-1 (total amount = 0 to 2.7 g), Co in the acid-soluble fraction was transformed to the oxidizable fraction in soil, resulting from the mesh structure on the surface of SMS, as well as the amide and carboxyl in the SMS molecular structure. In this situation, the Co accumulation levels in the pakchois decreased significantly (P < 0.05), indicating the efficacy of SMS for reducing Co phytoavailability. However, when the SMS concentration reached 12 g kg^-1, the phytoavailability increased again (P < 0.05). When the SMS concentration ranged from 8.86 to 9.51 g kg^-1, the Co phytoavailability in soil reached a minimum, while the biomass of pakchoi reached a maximum. Conclusively, SMS from Pleurotus ostreatus are effective for reducing the Co phytoavailability, as well as for reducing the chance of Co transferring into a human's body through crops (i.e., food consumption). In order to achieve the optimum efficacy, the SMS concentration in soil should be maintained at a range of 8.86 to 9.51 g kg^-1.

Effect heating dwell time has on the retention of heavy metals in the structure of lightweight aggregates manufactured from wastes

The main objective of this paper was to study how effective thermal treatment is in the retention of different heavy metals (HMs) within the structure of artificial lightweight aggregates (LWAs). These LWAs were manufactured by washing aggregate sludge and sewage sludge. The consequence of increasing the heating dwell time whilst manufacturing these LWAs was also determined. Partitioning of the HMs (Cr, Ni, Cu, Zn, Cd and Pb) was studied by means of the optimized BCR sequential extraction procedure. Then, the leaching ratio (LRx,y) was calculated. Thermal treatment was totally effective for immobilizing most of the elements studied except for a part of the non-residual Zn and Cd fraction which could volatilize, and the fractions of Pb which were water- and acid-soluble, weakly adsorbed, exchangeable, and oxidable. These were more highly concentrated in the LWAs than in the initial waste mixture. The effect of increasing heating dwell time on the retention of heavy metals in the LWAs depended on both the chemical element studied and the heating dwell time. This study is very important since certain rises in the heating dwell time caused a decrease in retention of some specific heavy metals in the LWAs.

ABBREVIATIONS

BCR-SEP: optimized BCR sequential extraction procedure; b.d.l: below the detection limit; F1: weakly adsorbed, exchangeable and water- and acid- soluble fraction; F2: reducible fraction; F3: oxidable fraction; F4: residual fraction; HM: heavy metal; ICP-MS: inductively coupled plasma-mass spectroscopy; LOI: loss on ignition; LWA: lightweight aggregate; LWA-5: lightweight aggregate sintered for 5 min; LWA-10: lightweight aggregate sintered for 10 min; LWA-20: lightweight aggregate sintered for 20 min; LWA-30: lightweight aggregate sintered for 30 min; LR_x,y: leaching ratio of the element x in the fraction y; n.e: not established; S: compressive strength; SS: sewage sludge; WA_24h: water absorption after 24 hours; WAS: washing aggregate sludge; W75S25: mixture of 75% (wt) of the dried washing aggregate sludge and 25% (wt) of the dried sewage sludge; ρ_b: loose bulk density; ρ_d: dry particle density; ∑1 + 2 + 3: non-residual fraction; ∑1 + 2 + 3 + 4: total concentration; ∑2 + 3: reducible and oxidable fractions.

Fractionation, Mobility, and Contamination Assessment of Potentially Toxic Metals in Urban Soils in Four Industrial Serbian Cities

The main soil properties, concentrations of selected elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn), and the chemical speciation of each element were determined in urban soil samples taken from urban parks in four Serbian cities (Belgrade, Pančevo, Obrenovac, and Smederevo) exposed to different sources of pollution. Pollution indices (PI, PI_N) and factors (MF, ICF, GCF) also were evaluated. The study revealed As and Cd concentrations below the detection limit, whereas the content of Cr, Cu, Fe, Mn, Ni, Pb, and Zn at some sites exceeded the limits established by local regulations, as well as the background values, which may represent an environmental threat. Sequential extraction results show that Fe, Cr, Cu, and Ni were predominantly in the residual fraction at most sites; however, Ni from Pančevo and Smederevo also was bound to the reducible fraction. The presence of Pb at all sites and Zn in Smederevo and Belgrade was mainly associated with the reducible and residual fractions. The highest Mn content was found in the reducible fraction, followed by the acid soluble/exchangeable and residual fractions. Based on the obtained indices and factors, the overall soil status at the selected sampling sites was found to range from the warning limit to slightly polluted, whereby Smederevo had the highest risk, and Pančevo and the control site the lowest risk of contamination by toxic metals.

Impact of Land Use on Concentrations of Potentially Toxic Elements in Urban Soils of Lagos, Nigeria

BACKGROUND

Among soil contaminants, potentially toxic elements (PTE) are of major significance because they are ubiquitous, toxic and persistent. Chronic exposure of humans to these elements has been linked with developmental delay, cancer, atherosclerosis and kidney damage, stomach ailments, respiratory problems, heart disease and cancer.

OBJECTIVES

The present study aims to investigate current PTE concentrations in urban soils of Lagos, an example of a rapidly urbanizing megacity in a developing country. The variation in PTE (chromium (Cr), copper (Cu), iron (Fe), magnesium (Mn), nickel (Ni), lead (Pb) and zinc (Zn)) levels across different land use types was examined. Information from this study will be useful in the ranking of contaminated sites, environmental quality management, guidance for remediation, redevelopment of contaminated sites and will provide crucial information for general urban planning decisions.

METHODS

Five areas spread across four local government areas were selected, representing different socio-economic areas of Lagos (Victoria Island, Lagos mainland, Ikeja, Ifako-Ijaiye and Makoko). Sampling locations within the study areas were comprised of school playgrounds, roadsides, ornamental gardens, open spaces, train stations, industrial estates and dump sites. A total of 126 samples were collected.

RESULTS

The overall mean levels of PTE concentrations in this study were comparable to those found in large European cities where main pollution sources include traffic and current or former heavy manufacturing industries.

CONCLUSIONS

Regulation and legislation on environmental issues, including effective solid waste management strategies and enforcement of emission standards should be emphasized in order to reduce the impact of PTE pollution on the inhabitants of urban areas in developing countries.

COMPETING INTERESTS

The authors declare no competing financial interests.

Geochemical properties of topsoil around the coal mine and thermoelectric power plant

The results of the systematic study of the spatial distribution of trace metals in surface soil over the Bitola region, Republic of Macedonia, known for its coal mine and thermo-electrical power plant activities are reported. The investigated region (3200 km²) is covered by a sparse sampling grid of 5 × 5 km, but in the urban zone and around the thermoelectric power plant the sampling grid is denser (1 × 1 km). In total, 229 soil samples from 149 locations were collected including top-soil (0-5 cm) and bottom-soil samples (20-30 cm and 0-30 cm). Inductively coupled plasma - atomic emission spectrometry (ICP-AES) was applied for the determinations of 21 elements (Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, Sr, V and Zn). Based on the results of factor analyses, three geogenic associations of elements have been defined: F1 (Fe, Ni, V, Co, Cr, Mn and Li), F2 (Zn, B, Cu, Cd, Na and K) and F3 (Ca, Sr, Mg, Ba and Al). Even typical trace metals such as As, Cd, Cu, Ni, P, Pb and Zn are not isolated into anthropogenic geochemical associations by multivariate statistical methods still show some trends of local anthropogenic enrichment. The distribution maps for each analyzed element is showing the higher content of these elements in soil samples collected around the thermoelectric power plants than their average content for the soil samples collected from the whole Bitola Region. It was found that this enrichment is a result of the pollution by fly ash from coal burning which deposited near the plant having a high content of these elements.

Use of magnetic biochars for the immobilization of heavy metals in a multi-contaminated soil

Modified biochars, including magnetic biochars, have been tested in water for the removal of inorganic pollutants. However, at present it is unknown if they possess benefits over conventional biochar materials in relation to land remediation. A paddy soil was collected near Liantang village in Lechang Pb-Zn mine area in Guangdong Province (China). The soil was polluted with Cd, Cu, Zn and Pb, with total contents of 1.4mg/kg, 80mg/kg, 1638mg/kg and 2463mg/kg, respectively. We prepared magnetic and conventional biochar from two feedstocks (poultry litter and Eucalyptus) at a temperature of 300 and 500°C. A sequential extraction procedure for the speciation of heavy metals and a phytotoxicity test using rice were performed. Acid-soluble Cd in soils amended with PLB was 8 to 10% lower than in the control polluted soil. This figure was 27 to 29% for acid-soluble Zn and 59 to 63% for acid-soluble Cu. In some cases, differences were found between the heavy metal fractionation in samples amended with magnetic and conventional biochars. Plant biomass was unaffected by most treatments, but increased by 32% in the treatments containing magnetic poultry litter biochar. Our study shows that a careful choice of feedstock is of utmost importance for successful containment of heavy metals in a multi-contaminated mining area soil. An appropriate choice of feedstock (in the case of this study poultry litter vs. eucalyptus) was more determinant with respect to the mobility of pollutants than altering pyrolysis temperature or modifying surface properties through magnetization. However, surface modification through magnetization can have a significant impact on plant yield and offer comparative advantages in the management of some degraded landscapes.

Application of a combined approach including contamination indexes, geographic information system and multivariate statistical models in levels, distribution and sources study of metals in soils in Northern China

The purpose of this study is to recognize the contamination characteristics of trace metals in soils and apportion their potential sources in Northern China to provide a scientific basis for basic of soil environment management and pollution control. The data set of metals for 12 elements in surface soil samples was collected. The enrichment factor and geoaccumulation index were used to identify the general geochemical characteristics of trace metals in soils. The UNMIX and positive matrix factorizations (PMF) models were comparatively applied to apportion their potential sources. Furthermore, geostatistical tools were used to study the spatial distribution of pollution characteristics and to identify the affected regions of sources that were derived from apportionment models. The soils were contaminated by Cd, Hg, Pb and Zn to varying degree. Industrial activities, agricultural activities and natural sources were identified as the potential sources determining the contents of trace metals in soils with contributions of 24.8%-24.9%, 33.3%-37.2% and 38.0%-41.8%, respectively. The slightly different results obtained from UNMIX and PMF might be caused by the estimations of uncertainty and different algorithms within the models.

Modeling of phytoextraction efficiency of microbially stimulated Salix dasyclados L. in the soils with different speciation of heavy metals

Bioaugmentation of soils with selected microorganisms during phytoextraction can be the key solution for successful bioremediation and should be accurately calculated for different physicochemical soil properties and heavy metal availability to guarantee the universality of this method. Equally important is the development of an accurate prediction tool to manage phytoremediation process. The main objective of this study was to evaluate the role of three metallotolerant siderophore-producing Streptomyces sp. B1-B3 strains in the phytoremediation of heavy metals with the use of S. dasyclados L. growing in four metalliferrous soils as well as modeling the efficiency of this process based on physicochemical and microbiological properties of the soils using artificial neural network (ANN) analysis. The bacterial inoculation of plants significantly stimulated plant biomass and reduced oxidative stress. Moreover, the bacteria affected the speciation of heavy metals and finally their mobility, thereby enhancing the uptake and bioaccumulation of Zn, Cd, and Pb in the biomass. The best capacity for phytoextraction was noted for strain B1, which had the highest siderophore secretion ability. Finally, ANN model permitted to predict efficiency of phytoextraction based on both the physicochemical properties of the soils and the activity of the soil microbiota with high precision.

Characterization and origin of organic and inorganic pollution in urban soils in Pisa (Tuscany, Italy)

We assessed the quality of 31 urban soils in Pisa by analyzing total petroleum hydrocarbons (TPHs), Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn, and the platinum group elements (PGEs). The risk was evaluated by the geological accumulation index (I _geo) and the enrichment factor (EF). Results were compared with those obtained from a non-urban site and with the quantitative limits fixed by Italian legislation. In nearly all the monitored sites, the legal limit for TPH of 60 mg/kg in residential areas was exceeded, indicating widespread and intense pollution throughout the entire city area. The I _geo indicated no Cd, Cu, Mn, Ni, and Zn pollution and minimal Pb and Cr pollution due to anthropogenic enrichment. Legal Hg and Zn limits of 1 and 150 mg/kg, respectively, were exceeded in about 20% of sites; Cd (2 mg/kg), Cr (150 mg/kg), and Cu (120 mg/kg) in only one site; and the Ni legal limit of 120 mg/kg was never exceeded. Some urban soils showed a higher Hg level than the more restrictive legal limit of 5 mg/kg concerning areas for industrial use. Based on the soluble, exchangeable, and carbonate-bound fractions, Mn and Zn showed the highest mobility, suggesting a more potential risk of soil contamination than the other metals. The TPH and both Cr and Hg amounts were not correlated with any of the other monitored metals. The total contents of Cd, Pb, Zn, and Cu in soils were positively correlated with each other, suggesting a common origin from vehicular traffic. The PGE values (Pt and Pd) were below the detection limits in 75%-90% of the monitored areas, suggesting that their accumulation is at an early stage.

Distribution of potentially toxic elements (PTEs) in tailings, soils, and plants around Gol-E-Gohar iron mine, a case study in Iran

This study investigated the concentration of potentially toxic elements (PTEs) including Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, V, and Zn in 102 soils (in the Near and Far areas of the mine), 7 tailings, and 60 plant samples (shoots and roots of Artemisia sieberi and Zygophylum species) collected at the Gol-E-Gohar iron ore mine in Iran. The elemental concentrations in tailings and soil samples (in Near and Far areas) varied between 7.4 and 35.8 mg kg^-1 for As (with a mean of 25.39 mg kg^-1 for tailings), 7.9 and 261.5 mg kg^-1 (mean 189.83 mg kg^-1 for tailings) for Co, 17.7 and 885.03 mg kg^-1 (mean 472.77 mg kg^-1 for tailings) for Cu, 12,500 and 400,000 mg kg^-1 (mean 120,642.86 mg kg^-1 for tailings) for Fe, and 28.1 and 278.1 mg kg^-1 (mean 150.29 mg kg^-1 for tailings) for Ni. A number of physicochemical parameters and pollution index for soils were determined around the mine. Sequential extractions of tailings and soil samples indicated that Fe, Cr, and Co were the least mobile and that Mn, Zn, Cu, and As were potentially available for plants uptake. Similar to soil, the concentration of Al, As, Co, Cr, Cu, Fe, Mn, Mo, Ni, and Zn in plant samples decreased with the distance from the mining/processing areas. Data on plants showed that metal concentrations in shoots usually exceeded those in roots and varied significantly between the two investigated species (Artemisia sieberi > Zygophylum). All the reported results suggest that the soil and plants near the iron ore mine are contaminated with PTEs and that they can be potentially dispersed in the environment via aerosol transport and deposition.

Use of Agricultural Wastes for the Immobilization of Metals in Polluted Soils in Lagos State, Nigeria

BACKGROUND

An increase in human and industrial activities has led to an increase in the pollution of soils by metals. If these metals become bioavailable, there is potential for human exposure, leading to possible health effects. Remediation of soils is important to ensure that soil is suitable for agricultural purposes.

OBJECTIVES

To explore the use of sawdust and cow dung to remediate contaminated soil by reducing the bioavailability of metals.

METHODS

Soil samples were collected from Oke Afa dumpsite and Owode Onirin metallic store and total metal concentrations were determined by digesting with aqua regia and analyzed using flame atomic absorption spectrophotometry. The effect of varied dosages (1-5 g) of cow dung and sawdust on the immobilization of the selected metals was investigated, and results were compared with disodium hydrogen phosphate (DSHP) amendments. A single reagent leaching test was carried out with 0.1 M calcium chloride to determine the bioavailability of metals before and after amendment.

RESULTS

Before amendment, the amount of bioavailable metal in the soil sample from Oke Afa dumpsite was 57.5 mg/kg, 194 mg/kg and 17.5 mg/kg for copper (Cu), lead (Pb) and zinc (Zn), respectively, while in the second soil sample, from Owode Onirin metallic store, the amount of bioavailable Cu, Pb and Zn was observed to be 19.9 mg/kg, 36.4 mg/kg and 11.1 mg/kg, respectively. Up to 73.4% of mobile Zn was immobilized using DSHP, while cow dung and saw dust were effective in the immobilization of Cu and Pb, but not Zn.

CONCLUSIONS

Cow dung and sawdust reduced the bioavailability of copper and lead, while Zn can be effectively immobilized with the use of DSHP. It was generally observed that the bioavailability of heavy metals decreased with increasing dosage of the amendments.

Use of the Physiologically Based Extraction Test for the Assessment of Bioaccessibility of Toxic Metals in Vegetables Grown on Contaminated Soils

BACKGROUND

An important concern for human health is the uptake of toxic metals by vegetables from soils and their consumption by humans.

OBJECTIVES

To assess the oral bioaccessibility of metals in vegetables (spinach, pumpkin, celosia, okro leaves and waterleaf) grown on contaminated soils collected from five different sites in Lagos, Nigeria.

METHODS

The soil and vegetables were acid digested and the total metal concentrations (copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb) and zinc (Zn)) were determined using a flame atomic absorption spectrophotometer. A bioaccessibility study of the edible parts of the vegetables was estimated using the modified in vitro physiologically based extraction test (PBET).

RESULTS

The results for total concentration showed that individual vegetable types differed in their levels of metal uptake. The values were in the range of 0.5-13.5 mg/kg for Cd, 2.0-221 mg/kg for Cu, 2.5-37.7 mg/kg for Cr, 10-250 mg/kg for Zn. Pb was below the detection limit. The transfer factor from soil to vegetable followed the order of Cd >Zn > Cu > Cr >Pb.

DISCUSSION

For the PBET study, metals were solubilized mostly in the gastric phase, and the results varied in the range of 0.4-114.4 mg/kg for Cu, 0.1-2.4 mg/kg for Cd, and 0.8-137 mg/kg for Zn, but there was little or no bioaccessibility in the intestinal phase. Cr and Pb were non-detectable in either the gastric or intestinal phase.

CONCLUSIONS

Although the level of metals (Cd, Cu and Zn) available for absorption in the gastric phase were found to be low in most of the vegetables studied, the experiment revealed that metals are likely released in the human gut after intake of vegetables grown on contaminated soil.

Geochemistry of mercury in tropical swamps impacted by gold mining

Artisanal and small-scale gold mining (ASGM) poses a serious threat to the local environment. Colombia has very active ASGM activities, where mercury (Hg) ends in piles of mining waste, soils, and waterways. In this study, we assessed Hg speciation and bioavailability in sediments of two tropical swamps, impacted by ASGM. In Ayapel swamp, total Hg (T-Hg) concentrations in sediments ranged between 145 and 313 ng g(-1) dry weight (dw) (mean: 235 ± 49 ng g(-1) dw), whereas Grande Achi swamp levels are 3-fold higher (range: 543-1021 ng g(-1) dw; mean: 722 ± 145 ng g(-1) dw). Even though lower levels of Hg were found in Ayapel, methylation was found to be significantly higher than in Grande Achi, and it is significantly higher in the dry than in the rainy season for both swamps. This increased methylation is linked to the statistically significant correlation between T-Hg, MeHg and organic matter in the Ayapel swamp. In fact, Hg content in both swamps is mainly associated to the organic fraction (Hg-o), with a higher statistically significant difference in Ayapel (43 ± 5%) compared to Grande Achi (33 ± 5%). On the other hand, a significant percentage (30 ± 6%) of elemental Hg fraction (Hg-e) was found in Grande Achi, directly related with Hg released during the gold recovery process from upstream ASGM sites. The percentage of the bioavailable fraction (Hg-w and Hg-h) is elevated (up to 15%), indicating a potential risk to the aquatic environment and human health because these labile Hg species could enter the water column and bioaccumulate in biota.

Effect of Miscanthus cultivation on metal fractionation and human bioaccessibility in metal-contaminated soils: comparison between greenhouse and field experiments

The in situ stabilization of metals in soils using plants with great biomass value is a promising, cost-effective, and ecologically friendly alternative to manage metal-polluted sites. The goal of phytostabilization is to reduce the bioavailable concentrations of metals in polluted soil and thus reduce the risk to the environment and human health. In this context, this study aimed at evaluating Miscanthus × giganteus efficiency in phytostabilizing metals on three contaminated agricultural sites after short-term exposure under greenhouse conditions and after long-term exposure under field conditions. Particular attention was paid to the influence of Miscanthus cultivation on (i) Cd, Pb, and Zn fractionation using sequential extractions and (ii) metal bioaccessibility using an in vitro gastrointestinal digestion test. Data gave evidence of (i) different behaviors between the greenhouse and the field; (ii) metal redistribution in soils induced by Miscanthus culture, more specifically under field conditions; (iii) higher environmental availability for Cd than for Pb and Zn was found in both conditions; and (iv) overall, a higher bioaccessible fraction for Pb (about 80 %) and Cd (65-77 %) than for Zn (36-52 %) was recorded in the gastric phase, with a sharp decrease in the intestinal phase (18-35 % for Cd, 5-30 % for Pb, and 36-52 % for Zn). Compared to soils without culture, the results showed that phytostabilization using Miscanthus culture provided evidence for substantial effects on oral bioaccessibility of Cd, Pb, and Zn.

Combine the soil water assessment tool (SWAT) with sediment geochemistry to evaluate diffuse heavy metal loadings at watershed scale

Assessing the diffuse pollutant loadings at watershed scale has become increasingly important when formulating effective watershed water management strategies, but the process was seldom achieved for heavy metals. In this study, the overall temporal-spatial variability of particulate Pb, Cu, Cr and Ni losses within an agricultural watershed was quantitatively evaluated by combining SWAT with sediment geochemistry. Results showed that the watershed particulate heavy metal loadings displayed strong variability in the simulation period 1981-2010, with an obvious increasing trend in recent years. The simulated annual average loadings were 20.21 g/ha, 21.75 g/ha, 47.35 g/ha and 21.27 g/ha for Pb, Cu, Cr and Ni, respectively. By comparison, these annual average values generally matched the estimated particulate heavy metal loadings at field scale. With spatial interpolation of field loadings, it was found that the diffuse heavy metal pollution mainly came from the sub-basins dominated with cultivated lands, accounting for over 70% of total watershed loadings. The watershed distribution of particulate heavy metal losses was very similar to that of soil loss but contrary to that of heavy metal concentrations in soil, highlighting the important role of sediment yield in controlling the diffuse heavy metal loadings.

Metal content and distribution in surface sediments in an industrial region

The present study aimed to evaluate Cu, Cr, Ni, Zn, Pb, Mn, Al, and Fe contents, as well as their geochemical partitioning in Sinos River basin sediments in southern Brazil. This basin is a densely populated area with a substantial number of industries, especially metallurgy, electroplating works, steel mills, petrochemicals, and tanneries. The total metal concentrations were determined by X-ray fluorescence and the sediment phase concentrations were determined by applying the BCR-701 sequential extraction method proposed by the Community Bureau of Reference of the European Community, using ICP/OES. The contents extracted by a solution of 0.5 mol/L HCl were also considered. Metal contents were evaluated in the sediment fraction <63 µm. Results in the industrialized and densely populated region showed an increase in the total concentrations of Cu, Cr, Zn, and Pb, and in the potentially mobile fractions for Cu, Cr, Zn and Ni sequentially extracted. Cr stood out particularly in the Portão stream, showing 1,286 mg/kg as a result of the total concentration, considering the tannery region influence.

Geochemical variability of heavy metals in soil after land use conversions in Northeast China and its environmental applications

The long-term agricultural reclamation since the 1950s has resulted in significant land use change from natural landscape to cultivated land in the Sanjiang Plain of Northeast China, which has had important consequences for many soil physical, chemical and biological processes. To understand the impact of land use conversions on heavy metal geochemistry, soil samples were collected from natural wetland, natural forestland, paddy land and dry farmland in a case study area and analyzed for total concentrations and chemical fractions of six heavy metals. Results showed that the natural wetland reclamation for the paddy land has caused obvious losses of Cd, Cu and Zn from the soils. In addition, a significant decrease in the Zn concentration was found after the land conversion from natural forestland to dry farmland. Because all the analyzed heavy metals predominated in the stable residual fraction regardless of the land use type, the response of metal mobility to the land use conversions was generally weak. Consequently, soil erosion was identified as the major factor that enhances heavy metal losses in the cultivated lands, especially in the paddy land. The close link between heavy metal loss and the reduction of clay and organic matter contents after land reclamation suggested that the diffuse heavy metal pollution occurred mainly in small erosion events. Considering the continuous paddy land expansion, special attention should be paid to the bioaccumulation of Pb in the paddy rice. Overall, these findings can help to improve the sustainability and safety of intensive agricultural activities in Northeast China as well as other similar areas.

Release of cadmium, copper and lead from urban soils of Copenhagen

We studied the bonding and release kinetics of Cd, Cu and Pb from different soils in the older metropolitan area of Copenhagen. Total Cd, Cu and Pb concentrations were elevated 5-27 times in the urban soils compared to an agricultural reference soil, with Cd and Pb in mainly mobilisable pools and Cu in strongly bound pools. The soils were subjected to accelerated leaching studies in Ca(NO3)2 or HNO3 solutions resulting in release up to 78, 18 and 15% of total Cd, Cu and Pb soil concentrations over a period of 15 weeks. The relative initial Cd and Pb release rates increased 10 fold when pH decreased 2 and 3 units, respectively, while increases in Cu release rates were only seen at pH below 4. The total leachable Cu and Pb pools were higher in urban soils compared the agricultural reference soil but not for Cd.

Source identification and health risk assessment of metals in urban soils around the Tanggu chemical industrial district, Tianjin, China

We conducted an investigation to identify the sources of metals in urban surface soils, and to assess the associated human health risks, around the Tanggu chemical industrial district, Tianjin, China. The metal concentrations and spatial distributions in 70 soil samples from the study area were determined. Pollution sources were identified using multivariate statistical analysis. They mainly attributed Cu, Pb, and Zn pollution to vehicular traffic and industrial discharges, Cd pollution to industrial activities and anthropogenic waste including industrial discharges, sewage sludge, and municipal solid waste, As and Hg pollution to coal combustion and point source emissions from the chemical industry, and Cr and Ni pollution to the soil parent material. Soil properties, particularly the organic matter content, were found to be important factors in the distribution and composition of metals. A health risk assessment showed that samples from the northwestern and southeastern parts of the study area may pose significant health risks to the population.

Risk assessment for Cd, Cu, Pb and Zn in urban soils: chemical availability as the central concept

To assess the geochemical reactivity and oral bioaccessibility of Cd, Cu, Pb and Zn in urban soils from the Porto area, four extractions were performed including Aqua Regia (AR; pseudototal), 0.43 M HNO3 (reactive), 0.01 M CaCl2 (available), and 0.4 M glycine at pH = 1.5, SBET method (oral bioaccessible pool). Oral bioaccessibility in urban soils was higher than in samples from rural, industrial and mining areas which is most likely related to sources of metals and parent materials of corresponding soils. The availability and reactivity were described well by non-linear Freundlich-type equations when considering differences in soil properties. The resulting empirical models are able to predict availability and reactivity and can be used to improve the accuracy of risk assessment. Furthermore, a close 1:1 relationship exists between results from the 0.43 M HNO3 method and the SBET method which substantially facilitates risk assessment procedures and reduces analytical costs.

Availability of geogenic heavy metals in soils of Thiva town (central Greece)

Potentially toxic metals in the urban chemical environment impose risks to both ecosystem and human health. Here, we evaluate the labile pools and availabilities of non-anthropogenic Ni, Cr, Co and Mn in soil samples from Thiva town (central Greece) and investigate their associations with common soil properties and geochemical data obtained by the aqua regia and single selective dissolutions. Experimental work included the initial application of the sequential extraction protocol proposed by the European Community Bureau of Reference and chemical extractions with ethylenediamine tetraacetic acid solution and a modified physiologically based extraction test with the aim to obtain the operationally defined fractions of plant availability and human bioaccessibility, respectively. The leachate results demonstrated that despite the significant contribution of residual metal species especially for Ni and Cr, the studied serpentine soils provide chemically labile pools for all the considered elements. Nickel was found to be the most available metal with the order being Ni > Cr ∼ Co ∼ Mn for plant uptake and Ni > Cr > Co ∼ Mn for human bioaccessibility. The aqua regia extractable concentrations are not predictors of elemental availabilities except for Ni bioaccessible data interpreting however only a moderate percentage of the total variance. The incorporation of basic soil properties (mostly total organic carbon), geochemical data for the major elements Ca, Mg and Fe and ammonium oxalate extractable Cr significantly improved the estimations for individual elements entailing the strong influence of the chemistry and mineralogy of soil materials to the release of focus metals from the soil matrix. This study provides for the first time bioaccessible data for serpentine-derived soils that are more realistic for evaluating potential adverse effects on the human health.

Distribution, speciation, and risk assessment of selected metals in the gold and iron mine soils of the catchment area of Miyun Reservoir, Beijing, China

In order to investigate the metal distribution, speciation, correlation and origin, risk assessment, 86 surface soil samples from the catchment area around the Miyun Reservoir, Beijing, including samples from gold and iron mine areas, were monitored for fractions of heavy metal and total contents. Most of the metal concentrations in the gold and iron mine soil samples exceeded the metal background levels in Beijing. The contents of most elements in the gold mine tailings were noticeably higher than those in the iron mine tailings. Geochemical speciation data of the metals showed that the residual fraction dominated most of the heavy metals in both mines. In both mine areas, Mn had the greatest the acid-soluble fraction (F1) per portion. The high secondary-phase fraction portion of Cd in gold mine samples indicated that there was a direct potential hazard to organisms in the tested areas. Multivariate analysis coupled with the contents of selected metals, showed that Hg, Pb, Cr, and Ni in gold mine areas represented anthropogenic sources; Cd, Pb, and Cr in iron mine areas represented industrial sources. There was moderate to high contamination of a few metals in the gold and iron soil samples, the contamination levels were relatively higher in gold mine than in iron mine soils.

Lability of potentially toxic elements in soils affected by smelting activities

Determination of total concentration of potentially toxic elements (PTEs) in soil is not a reliable tool for evaluating potential exposure risk for humans. PTE lability (EDTA, SBET and solution extraction) and chemical speciation (BCR sequential extraction) were investigated for Pb, Cd, Cu, and Zn, as well as how these could be affected by flooding in soils polluted by smelting activities. The flooding experiment was performed in pots from which soil solution was extracted at different time intervals using Rhizon Moisture Samplers. After experiments, the soil was again subjected to the previous extractions (EDTA, SBET, and BCR) in order to reveal the changes which occurred during anoxia. From the results we can conclude that PTE lability is very high and flooding caused the increase in their mobility up to 100% (for bioaccessible Pb). The experiment demonstrated that temporary reducing conditions can increase the risk of contaminants passing to other environmental compartments and the food chain.

Major inputs and mobility of potentially toxic elements contamination in urban areas

Soil quality in urban areas is affected by anthropogenic activities, posing a risk to human health and ecosystems. Since the pseudo-total concentrations of potentially toxic elements may not reflect their potential risks, the study of element mobility is very important on a risk assessment basis. This study aims at characterising the distribution and major sources of 34 elements in two Portuguese urban areas (Lisbon and Viseu), with different geological characteristics, industrial and urban development processes. Furthermore, the potential availability of As, Co, Cr, Cu, Ni, Pb and Zn was assessed, by measuring the fraction easily mobilised. Lisbon is enriched in elements of geogenic and anthropogenic origin, whereas in the smaller city, the high levels observed are mainly related to a geogenic origin. Background values can be more relevant than the dimension of the city, even when anthropogenic components may be present, and this parameter should be considered when comparing results from different cities. Regarding the potential available fraction, a high variability of results was observed for elements and for sampling sites with an influence of the soil's general characteristics. Elements showing very high concentrations due to geological reasons presented, in general, a low mobility and it was not dependent on the degree of contamination. For elements with major anthropogenic origin, only Zn was dependent on the pseudo-total content. Yet, the highest available fractions of some elements, both with major geogenic and anthropogenic origin, were observed in specific contaminated samples. Therefore, a site-specific evaluation in urban soils is important due to the high spatial variability and heterogeneity.

Distribution of heavy elements in urban and rural surface soils: the Novi Sad city and the surrounding settlements, Serbia

Concentrations of ten heavy elements (Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn), as well as the pH values, organic matter contents, and electrical conductivities were measured in the surface soil samples collected from 21 sites of urban areas in the city of Novi Sad, the second largest city in Serbia, its suburban settlement and the nearby villages. Range of the heavy element concentrations was from 0.16 mg/kg (for Hg) to 18,994 mg/kg (for Fe). Significantly higher Hg and Mn concentrations were observed in subgroups with rural and market garden samples in comparison to the subgroups with urban and grassland samples, respectively, while the contents of Pb found in the grasslands subgroup were significantly higher than in the subgroup with market garden soils. Only one sample of urban soil exceeded the maximum permissible value for Zn set by the relevant Serbian legislation. According to the Dutch soil quality standard, the Cd and Co concentrations in majority of the examined soils were higher than the target values for unpolluted soil. The content of Hg was above the target value in 52% of the samples, most of them belonging to the subgroup of market garden soils. The results for the Novi Sad city area were compared to the relevant data available for other cities in the Western Balkan Countries. Principal component analysis of data revealed seven outlying samples, while the rest of the analyzed samples were grouped together indicating similar heavy element patterns most probably due to mixed emission sources.

Chemical partitioning in lightweight aggregates manufactured from washing aggregate sludge, fly ash and used motor oil

The optimized BCR sequential extraction procedure was applied to washing aggregate sludge and fly ash, the raw materials used to produce artificial lightweight aggregates (LWAs) in a previous study. The mixtures of the raw materials and the two types of LWAs obtained have also undergone this procedure. As a result, it has been possible to evaluate the effects of the heating process on the extraction behaviour of twenty-eight elements. The thermal process reduces the availability of all the studied heavy metals, with the exception of Mo. The availability of the other elements is also reduced, with the exceptions of As and Sb, which increase in the non-residual fractions.

Mercury fractionation in the sediments of Vembanad wetland, west coast of India

Transformations among different mercury species associated with sediments can have a major effect on the metal's mobility and potential for methylation and hence bioaccumulation. In the present study, various fractions of mercury in the sediments of Vembanad wetland system analysed. Total mercury (THg) concentration in the surface sediment varied from 16.3 to 4,230 ng/g. The results of sequential extraction showed that the major portion of mercury in these sediments existed as elemental form followed by organo-chelated form. The least portion observed was the residual fraction (mercury of natural origin). Even though the percentage of mercury observed in the easily available fractions is relatively small, absolute values of these mobile Hg fractions are quite high due to the very high total mercury values. The fractionation of mercury in the sediment was controlled by the organic matter, sulphur complexes and concentration of THg. The results showed that the bioavailability of mercury is high as the amount of mercury found in the initial three fractions is high, which can also enhance the methylation potential of the Vembanad wetland sediments. The fractionation pattern of mercury also revealed the presence of anthropogenic mercury content in the Vembanad wetland sediments.

Effects of grinding and shaking on Cd, Pb and Zn distribution in anthropogenically impacted soils

The effects of grinding size and shaking process on the results of Cd (cadmium), Pb (lead) and Zn (zinc) distribution measurements three agricultural and three kitchen garden soils highly contaminated by past atmospheric fallout of two lead and zinc smelters in northern France were studied. The physico-chemical parameters and pseudo-total concentration of metals within these soils were determined. The fractionation of metals was performed in triplicate, using the procedure recommended by the Standards, Measurements and Testing program (SM&T), on each air-dried soil sample, ground to pass through 2-mm, 0.315-mm and 0.250-mm sieves and using a reciprocating or rotary shaker. The samples were analysed by flame or electrothermal absorption atomic spectrometry using a self-reversal background system. For both shaking processes, the grinding size had no effect on the fractionation of metals in contaminated agricultural soils. In contrast, using a reciprocating shaker, the fractionation of metals in the kitchen garden samples sieved at <2mm was so different that in the samples prepared to pass through the 0.315-mm and 0.250-mm sieves. Therefore changes (use of a 50 mL graduated polypropylene centrifuge tube, evaporation of the solution to a fixed volume in step 3 and the use of an automatic shaking heating bath) were made to the initial procedure and a rotary shaker was used to improve the suspension of the soil samples during extraction. For all grinding sizes, the fractionation of the three metals contained in the contaminated kitchen garden soil samples was successfully achieved. Nevertheless, some discrepancies from samples sieved at <2mm were obtained. On the other hand, it is worth noting that the effect of the type of shaker on the distribution of metal depended on the soil and the grinding size. From an analytical point of view, precision and trueness were improved after optimisation of the procedure for all sequential extraction procedure steps. The best results were obtained for samples sieved at <0.250 mm. Similar trends were obtained using the CRM BCR(®)-701 certified material. All the results showed that optimisation of the sequential extraction procedure could be adopted for the Cd-, Pb- and Zn-partitioning in contaminated kitchen garden soils with high-level anthropogenic sources.

Trace metal contamination in urban soils of China

The contamination of urban soils can affect the health of people living in urban areas, and the surrounding ecosystems. Urbanization in China has taken place at an unprecedented pace in the last three decades. This paper provides an overview of studies on the quality of urban soils in China with special reference to trace metal contamination. It summarizes the characteristics of accumulation, spatial and temporal distribution, and major sources of various toxic or potentially toxic trace metals in urban soils as reported in recent literature. Levels of pollution in urban soil and road dust were discussed using the concentrations, enrichment factors, pollution indexes, and chemical fractionation of trace metals in major cities of China, and compared with other countries. In future studies, more pollutants in urban environments need to be included in multi-compartmental environmental surveillance for potential risk assessments. In addition to routine urban soil surveys by a harmonized methodology, a comprehensive assessment of soil quality is needed for the control and management of many urban brownfield sites. Taking into consideration pathways of exposure and site characteristics, risk assessment frameworks for major pollutants in urban soils, which integrate land use type and environmental availability, may be developed in the future.