Magnetic response of soils and vegetation to heavy metal pollution--a case study

Geochemical fingerprinting and magnetic susceptibility to unravel the heterogeneous composition of urban soils

The typically high heterogeneity of urban soil properties challenges their characterization and interpretation. The objective of this study was to investigate if proximally sensed volume-specific magnetic susceptibility and/or geochemical soil properties can uncover differences in anthropogenic, lithogenic and pedological contributions in, and between, urban soils. We also tested if volume-specific magnetic susceptibility can predict heavy metal enrichment. Data on 29 soil properties of 103 soil horizons from 16 soils from Ghent, Belgium, were analyzed by factor analysis. A correlation analysis, and in-depth analysis of five contrasting urban soils supplemented insights gained from the factor analysis. The factor analysis extracted four factors: 29.2 % of the soil property variability was attributed to fossil fuel combustion and industrial processes, with high (>0.80) loadings for S, organic carbon, magnetic susceptibility, and Zn. Furthermore, 26.0 % of the variability was linked to parent material differences, with high loadings (>0.80) for K, Rb and Ti. In absence of geogenic carbonates, increased soil alkalinity due to anthropogenic input of CaCO₃ explained 17.0 % of the variability. Lastly, 4.7 % of the variability resulted from variable Zr contents by local geology. Elemental analysis by XRF, possibly combined with magnetic susceptibility measurements, helped to explain lateral or vertical differences related to (1) the nature of anthropogenic influence, for instance burning (e.g., by the S and Zn content) or the incorporation of building rubble (e.g., by the Ca content); (2) the particle size distribution (e.g., by the K, Rb or Ti content); (3) lithology (e.g., by the Zr content); or (4) pedology, such as organic matter build-up (e.g., by the S content) or leaching of alkalis (e.g., by the Ca content). Even though artifacts and soil translocation were common in the studied soils, volume-specific soil magnetic susceptibility measured on fine earth predicted the total heavy metal pollution loading index well (Pearson correlation = 0.85).

Advanced mineral magnetic and geochemical investigations of road dusts for assessment of pollution in urban areas near the largest copper smelter in SE Europe

This study aims to evaluate the urban pollution by combined magnetometric and geochemical analyses on road dusts from three towns in the vicinity of Cu-smelter and ore mining. A collection of 117 road dust samples was investigated for their magnetic characteristics (magnetic susceptibility (χ), frequency dependent susceptibility, anhysteretic and isothermal (IRM) remanences), IRM step-wise acquisition and thermal demagnetization. Coarse grained magnetite and hematite were identified as major iron oxides in the emissions from ore spills and smelter, while traffic-related magnetic minerals were finer magnetite grains. Degree of pollution is assessed by geo-accumulation index, enrichment factor and Pollution Load Index (PLI) for a set of potentially toxic elements (PTEs). Using the geochemical data, we evaluate the carcinogenic and non-carcinogenic health risks for the population. Our results show that dust emissions from the industrial facilities likely pose significant health hazard for adults and children caused largely by Arsenic pollution in "hot spots". Based on the strong correlation between χ and most of the PTEs, detailed variations in pollution degree inside the urban areas are inferred. Strong linear regression between χ and PLI allows designating limit susceptibility values, corresponding to the PLI categories. This approach can be successfully applied for monitoring and mapping purposes at high spatial and temporal resolution.

Comparison of heavy metal bioaccessibility between street dust and beach sediment: Particle size effect and environmental magnetism response

Direct ingestion of urban sediment particles represents an important pathway of human exposure to heavy metals. The effect of particle sizes on metal bioaccessibilities in human digestive system has not been fully understood. In this study, an in-vitro simulation experiment (PBET), along with environmental magnetic measurements, is conducted on two urban sediments (street dusts and beach sediments) with different particle sizes (Φ31.1 ± 7.36 μm for street dusts and Φ134 ± 21.1 μm for beach sediments) for the purposes of assessing the particle size effect on metal bioaccessibilities in simulated gastric and intestinal tracts, and exploring the environmental magnetism response to different digestion processes. For street dusts, the bioaccessibilities of heavy metals decrease significantly from gastric (12.1 (Cu) ~ 39.9% (Pb)) to intestinal phase (0.41 (Pb) ~ 2.08% (Cd)) due to an increase in digestive juice pH. However, for beach sediments, the metal bioaccessibilities in the intestinal phase is similar to, or even higher than, those in the gastric phase. These demonstrate that clay minerals and Fe/Mn oxides concentrated in fine particles play an important role in adsorbing and fixating heavy metals in neutral intestinal tract. Compared with those of the original samples, the χ_fd% values of the PBET treated street dusts decrease significantly, and the decreasing extents (Δχ_fd%) are positively correlated with the concentrations of the PBET extracted Fe (p < 0.05). However, a reverse trend is observed for the beach sediment samples. These findings suggest that the magnetic minerals formed during the digestion process might affect the metal bioaccessibilities in gastrointestinal tract.

Technogenic magnetic particles from steel metallurgy and iron mining in topsoil: Indicative characteristic by magnetic parameters and Mössbauer spectra

Technogenic magnetic particles (TMPs), produced during various industrial processes, are released into the atmosphere as dust and get deposited on the surrounding topsoil. The mineralogical and structural differences of TMPs produced in different technological processes should be reflected in their magnetic properties and therefore should be indicative for industrial pollution sources. The goal of this study was to characterize the TMPs by novel methodological approach, based on combination of magnetic methods and Mössbauer spectroscopy to indicate parameters that are discriminative enough to be used as environmental indicators for iron metallurgy, steel production, and iron mining. We collected the topsoil samples in the vicinity of 4 European iron- and steelworks, located in three different countries (Poland, Norway, and Czech Republic) and operating for minimum 40 years. We sampled also topsoil close to the opencast iron mine, iron ore dressing plant, and over strongly magnetic natural background. Analysis of the hyperfine parameters of the Mössbauer spectra revealed that TMPs are "magnetite-like" minerals with low stoichiometry. It is indicated by ratio of iron ions contributions in B sites (octahedral) and A sites (tetrahedral) in magnetite spinel structure, which is much lower than 2.0 (theoretical value for stoichiometric magnetite). The characteristic feature of TMPs collected from the vicinity of old metallurgical plants (>180 years) was the high contribution of surface components probably related to the surface oxidation/maghemitization. We found that, TMPs can be easily differentiated from geogenic magnetite based on their magnetic parameters. The TMP produced by the iron and steel metallurgy had relatively narrow ranges of magnetic parameters (saturation ratio Mrs/Ms, <0.15, coercivity ratio Bcr/Bc 2.5-6.0 and saturation to susceptibility ratio Mrs/χ 3.5-15). These magnetic parameters may be indicative for TMPs emitted by these pollution sources and helpful in the study of historical pollution sources in topsoil in urban and post-industrial areas.

A multi-proxy magnetic approach for monitoring large-scale airborne pollution impact

The interpretive utility of environmental magnetic proxies for investigating airborne particulate matter (PM) pollution impact is restricted by differences in soil composition, land cover and land use. For soil magnetic applications, land use strongly influences magnetic particle distribution down the soil profile, even in homogeneous soil environments. Here, an adaptive approach is engineered to provide accurate magnetic proxy information for pollution monitoring across different land use types. In an 81-km² area between two industrial harbours, the irregular distribution of forests, arable lands, pasture and residential areas prevented robustly relating topsoil magnetic susceptibility data to known pollution impacts. Although normalized topsoil susceptibility values showed improved potential for deriving airborne pollution impacts, optimal results were obtained by depth-integrating magnetic susceptibility logs, revealing long-term impacts of both active and decommissioned industrial facilities. Complementing soil magnetic observations, active and passive (bio)magnetic monitoring allowed discriminating short-term pollution patterns and evaluating changes in PM impact across the study area. Hereby, active PM receptors (strawberry leaves and plastic coated cardboards (PCCs)) provided promising results, yet passive receptors allowed estimating pollution impacts more efficiently. For the latter, species-independent grass leaf sampling reflected airborne PM depositional patterns most accurately, whereas wiped anthropogenic surfaces proved too sensitive to wash-off.

Evergreen Needle Magnetization as a Proxy for Particulate Matter Pollution in Urban Environments

We test the use of magnetic measurements of evergreen needles as a proxy for particulate matter pollution in Salt Lake City, Utah. Measurements of saturation isothermal remanent magnetization indicate needle magnetization increases with increased air pollution. Needle magnetization shows a high degree of spatial variability with the largest increases in magnetization near roadways. Results from our magnetic measurements are corroborated by scanning electron microscopy of needle surfaces and by inductively coupled plasma mass spectrometry of metal concentrations in residues collected from sampled needles. Low-temperature magnetic analysis suggests the presence of small (<20 nm) partially oxidized magnetite particles on needles collected adjacent to a major roadway. Magnetization may be a low-cost proxy for certain metal concentrations (including lead) during periods of increased particulate pollution. The spatial resolution of our method appears capable of resolving changes in ambient particulate matter pollution on the scale of tens to hundreds of meters. Questions remain regarding the timescales over which evergreen needles retain particulate matter accumulated during atmospheric inversion events in Salt Lake City. Results presented here corroborate previous studies that found needle magnetization is a fast, cost-effective measure of particulate matter pollution. This method has the potential to provide high spatial resolution maps of biomagnetically monitored particulate matter in polluted urban environments year-round.

Magnetic mineral constraint on lead isotope variations of coal fly ash and its implications for source discrimination

Coal fly ash in the atmosphere affects air quality and potentially influences the global climate by promoting oceanic productivity. Although accurately tracing the sources of fly ashes is vital for emission control, it remains a challenging task. Stable lead (Pb) isotope analysis is a useful tool for tracing atmospheric pollution but it fails to accurately address coal combustion emissions due to the broad range of Pb isotopic composition of coal. Environmental magnetic parameters can be used as a rapid and economical proxy for tracing atmospheric pollutants (including coal fly ashes) and have the potential for discriminating emission sources. In this study, we combined magnetic parameters with Pb isotopic signatures in order to better discriminate the sources of coal fly ash. Both magnetic particles and Pb are highly concentrated in the fly ashes compared with the feed coals. Most of the fly ashes exhibit higher ²⁰⁶Pb/²⁰⁷Pb and lower ²⁰⁸Pb/²⁰⁶Pb ratios than those of the feed coals. Furthermore, the Pb isotopic compositions of the fly ashes are highly correlated (p < 0.01) with the concentrations of magnetic particles (especially hematite), suggesting that the variation of Pb isotopes in the fly ashes is controlled by the adsorption of Pb on magnetic minerals. Based on the established relationship between magnetic minerals and Pb isotopes within coal fly ashes, we re-analyzed previously reported magnetic and Pb isotopic data from atmospheric dust and demonstrated the effectiveness of the combined method in discriminating coal fly ash in the atmosphere.

Elemental and magnetic analyses, source identification, and oxidative potential of airborne, passive, and street dust particles in Asaluyeh County, Iran

One of the most important environmental issues in arid and semi-arid regions is deposition of dust particles. In this study, airborne, passive, and street dust samples were collected in Asaluyeh County, in August 2017, September 2017, and February 2018. The PM_2.5 and PM₁₀ concentrations for the sampling period ranged between 19.7 and 76.0 μg/m³ and 47.16-348 μg/m³ with an average of 46.4 μg/m³ and 143 μg/m³, respectively. Monthly dust deposition rates ranged from 5.2 to 26.1 g/m² with an average of 17.85 g/m². Positive Matrix Factorization (PMF) applied to the dust compositional data indicated that Sb, Zn, Pb, Mo, Cu, and As come from anthropogenic sources while Al, Fe, Ti, Mn, Ni, Cr, and Co originate mostly from geogenic sources. The PMF results indicated that the geogenic material was the major source of passive and airborne dust samples. Elemental compositions were similar for passive dust and local surface soil. Frequency-dependent magnetic susceptibility (χ_If and χ_fd%) showed that the local soil is entisol. Isothermal remanent magnetization (IRM_-100mT/IRM_1T) versus saturation IRM (SIRM) demonstrated that the background sample contains ferrimagnetic minerals, but with increasing SIRM, the concentration of soft magnetic magnetite-like phases increases and the magnetic particles are larger. Mrs./Ms. versus Bcr/Bc indicated that the magnetic particles sizes were probably between 120 and 1000 nm. Eu values and the mean Eu/Eu* and La/Al values clearly show that the airborne dust is most affected by oil industries, while passive dust samples primarily originated from local surface soils. These assumptions were confirmed by Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model results. The samples display a moderate level of oxidation towards ascorbic acid (OP_AA) and glutathione (OP_GSH). Regarding the passive and airborne dust samples, backward Generalized Estimating Equations (GEE) modeling results display a significant positive relationship between geogenic material and oxidative potential (OP). It includes many redox-active transition metals. Alternatively, the street dust OP is strongly related to geogenic and industrial sources and OP_AA is marginally related to urban sources. It was shown that measured magnetic parameters can be used for OP estimation.

Tracking the magnetic carriers of heavy metals in contaminated soils based on X-ray microprobe techniques and wavelet transformation

Technogenic magnetic particles (TMPs) from industrial activities are major contamination sources of soils and dusts because they usually carry large amounts of heavy metals. The understanding of the association between TMPs and heavy metals in contaminated soils helps to trace the polluting sources and probing into the mechanism of magnetic phases enriched with heavy metals. In this study, we tracked the magnetic carries of heavy metals from different emission sources in steel industrial regions by using the synchrotron-based probe techniques and multiscale analytical methods. The μ-XRF mapping showed that TMPs contained various heavy metals, depending on their sources. The Fe K-edge μ-XANES revealed that the ferroalloy, pyrrhotite and TMPs in steel slag and coal ash were major magnetic phases in contaminated soils. Their relative content varied differently at the microscale. The multiscale analysis revealed that the heavy metals associated with magnetic phases exhibited pronounced scale dependence, depending on the size, type, and assemblage of different magnetic phases. Multiscale source apportionment revealed that the contamination sources varied differently at multiple scales. Heatmap analysis revealed that at 8-μm scale, Co, Cr, Cu and Mn were mainly derived from ferroalloy, while Ti, Zn and As from both ferroalloy and TMPs from coal ash.

Evaluating the potential of topsoil magnetic pollution mapping across different land use classes

Soil magnetic measurements are used increasingly to estimate the impact of airborne, combustion-related particulate matter (PM) pollution in dense measurement grids. Although many studies have proven the potential of topsoil magnetic measurements in environmental monitoring, their application is not straightforward when factors such as parent material or land use have to be accounted for. Often, the influence of land use on the soil magnetic signal is circumvented by targeting forest soils, where deposited magnetic particles are best preserved in the topsoil. However, when large forests are absent, e.g. in densely populated areas or environments with more heterogeneous land use, this approach often impedes reliable and comprehensive spatial sampling. We evaluated if topsoil magnetic pollution mapping across different land use classes, against a homogeneous geological environment of sandy soils, could help increase the spatial reliability of results in regional scale surveys. Although detailed magnetic property analysis and evaluation of trace metal concentrations in soils on arable land, forest and pasture showed the impact of atmospheric pollution, topsoil susceptibility measurements did not allow delineating the magnetic footprint of PM pollution. Land use strongly influenced the distribution of magnetic particles through soil, and the evaluation of anomalous magnetic topsoil enhancement required the integration of downhole susceptibility soundings. We conclude that topsoil susceptibility mapping remains a useful tool to evaluate PM pollution impact, yet its application potential across land use classes is limited.

Use of magnetic susceptibility to assess metals concentration in soils developed on a range of parent materials

This research was conducted to evaluate the utilization of magnetic susceptibility measurements in the assessment of metal concentrations in soils developed on a range of parent materials in northwestern Iran. Eighty surface soil samples were collected from eight parent rocks including ultrabasic rocks, basalt, andesite, granite, marl, limestone, Qom formation, and shale. The collected samples were assessed to determine magnetic susceptibility at low frequency (χlf) and concentrations of some metals comprising chromium (Cr), iron (Fe), copper (Cu), nickel (Ni), zinc (Zn), cobalt (Co), and manganese (Mn). The results showed that the highest levels of metals and χlf were observed in basic and ultrabasic soils. Strong positive correlations (P < 0.01) detected between χlf and Fe (0.87), Mn (0.78), Zn (0.74), Ni (0.90), Co (0.78), and Cr (0.90) in all samples indicated a potential for using magnetic susceptibility in semi-quantitative estimation of metal concentrations in soils of natural ecosystems. Multiple linear regression between metal contents and χ_lf showed that Ni, Zn, Mn, and Co could explain 77% of the total variance in χ_lf in the study area. K-means cluster analysis categorized the studied soils into three groups based on metals and χ_lf variability. Clustering of soils based on their parent rocks and use of further magnetic measures, i.e., saturation isothermal remanent magnetization (SIRM), isothermal remanent magnetization (IRM100mT) and natural remanent magnetization (NRM) are expected to improve the accuracy of metal concentration predictions in natural soils of the study area.

Responses of magnetic properties to heavy metal pollution recorded by lacustrine sediments from the Lugu Lake, Southwest China

Environmental magnetism, which is rapid, sensitive, economical, and non-destructive, has been used to assess heavy metal pollution in lake sediments based on the relationships between magnetic properties and heavy metal concentrations. We conducted a systematic environmental magnetic and heavy metal study of the sediments of the core LGS from Lugu Lake in Southwest China. The results show that the concentration-related magnetic parameters (χ, χ_ARM, and SIRM) in the core LGS showed an increasing trend from bottom to top. The results of rock magnetism indicated that the dominant magnetic particles were magnetite. Two sources of magnetic minerals can be distinguished by the correlations of χ vs. χ_fd% and χ vs. χ_ARM/χ: the surrounding catchment and anthropogenic activities. In addition, Pearson correlation analysis and principal component analysis showed that the concentration-dependent magnetic parameters have significant correlations with heavy metal (Al, Ti, Fe, Cr, Ni, Cu, Zn, and Cd) concentrations as well as the Tomlinson pollution load index (PLI), indicating that there are essential linkages of sources, deposition, and migration between magnetic particles and heavy metals. Based on previously reported ¹³⁷Cs and ²¹⁰Pb data, the historical trends of heavy metal pollution in Lugu Lake were successfully reconstructed, and the causes of heavy metal pollution were mainly agricultural practices and atmospheric metal depositions from anthropogenic sources. The significant correlations between magnetic parameters, heavy metals, and the PLI indicate that magnetic parameters can potentially be used as an index of heavy metal pollution in lacustrine deposits.

Superparamagnetic iron oxides nanoparticles from municipal solid waste incinerators

During their production, management, and landfilling, bottom (BA) and fly (FA) ashes from municipal solid waste incineration may liberate Fe-bearing, ultrafine particles and easily enter different environmental sinks of the biosphere. We aim to explore a collection of BA and FA samples from Italian incinerators to probe magnetic mineralogy and the fraction of harmful superparamagnetic (SP) nanoparticles (d<30nm). X-ray diffraction, electron microscopy observation, temperature- and frequency-dependent magnetometry, and Mossbauer analysis are performed. The integration of information from our rock magnetic and non-magnetic techniques leads us to conclude that the dominant magnetic carrier in our samples is magnetite and its intermediate/impure forms, while sulphides (i.e., monoclinic pyrrhotite) are important ancillary magnetic phases. The SP fraction fluxing from the BA and FA outputs of a single incinerator is detected and estimated in 10³tons/year. This work stresses the need to calibrate the current technologies towards a safer management of combustion ashes and certainly to inform the environmental impact assessment by using a combination of different methods.

Magnetic susceptibility of spider webs as a proxy of airborne metal pollution

The purpose of this pilot study was to test spider webs as a fast tool for magnetic biomonitoring of air pollution. The study involved the investigation of webs made by four types of spiders: Pholcus phalangioides (Pholcidae), Eratigena atrica and Agelena labirynthica (Agelenidae) and Linyphia triangularis (Linyphiidae). These webs were obtained from outdoor and indoor study sites. Compared to the clean reference webs, an increase was observed in the values of magnetic susceptibility in the webs sampled from both indoor and outdoor sites, which indicates contamination by anthropogenically produced pollution particles that contain ferrimagnetic iron minerals. This pilot study has demonstrated that spider webs are able to capture particulate matter in a manner that is equivalent to flora-based bioindicators applied to date (such as mosses, lichens, leaves). They also have additional advantages; for example, they can be generated in isolated clean habitats, and exposure can be monitored in indoor and outdoor locations, at any height and for any period of time. Moreover, webs are ubiquitous in an anthropogenic, heavily polluted environment, and they can be exposed throughout the year. As spider webs accumulate pollutants to which humans are exposed, they become a reliable source of information about the quality of the environment. Therefore, spider webs are recommended for magnetic biomonitoring of airborne pollution and for the assessment of the environment because they are non-destructive, low-cost, sensitive and efficient.

Response of magnetic properties to metal deposition on urban green in Nanjing, China

Environmental magnetism is a simple and fast method that can be used to assess heavy metal pollution in urban areas from the relationships between magnetic properties and heavy metal concentrations. Leaves of Osmanthus fragrans, one of the most widely distributed evergreen trees in Nanjing, China, were collected from four different district types, i.e., residential, educational, traffic, and industrial. The magnetic properties and heavy metal concentrations were measured both for unwashed (dust-loaded) and washed leaves. Scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed that unwashed leaves accumulated much dust due to atmospheric deposition. The value of magnetic properties and heavy metal concentrations in unwashed leaves was significantly higher than those of washed leaves, indicating that these characteristics were mainly derived from atmospheric particulate matter. Saturation isothermal remanent magnetization (SIRM) values obtained from unwashed and washed leaves ranged from 209.14 × 10^-6 to 877.85 × 10^-6 Am² kg^-1 and from 69.50 × 10^-6 to 501.28 × 10^-6 Am² kg^-1, respectively. High concentrations of heavy metals, such as Pb and Fe, the Tomlinson pollution load index, and the SIRM of unwashed leaves occurred in the traffic and industrial districts. A preliminary principal component analysis identified the source categories and suggested that industrial activities may be more related to the release of particulate matter rich in Fe. The heavy metal concentrations and pollution load index showed significant positive correlations with the low-frequency magnetic susceptibility and SIRM of unwashed leaves, indicating that these properties can be used to semi-quantify atmospheric heavy metal pollution. Our study suggests that it is possible to employ magnetic measurements as a useful tool for the monitoring and assessment of atmospheric heavy metal pollution.

Trace metals and magnetic particles in PM2.5: Magnetic identification and its implications

Magnetic measurement was combined with geochemical analysis to investigate the trace metal pollution of PM_2.5. The study was carried out in Nanjing, China, where the average PM_2.5 concentrations in summer and winter in 2013–2014 were 66.37 and 96.92 μg/m³, respectively. The dominant magnetic mineral in PM_2.5 had a low-coercivity pseudo-single domain and consisted of magnetite and hematite. Iron-oxide magnetic particles comprised spherical as well as angular particles. Stable Pb isotopic ratio determinations showed that Pb in summer samples derived from coal emissions while the main sources of winter samples were smelting industry and coal emissions. The magnetic properties of the particles correlated strongly with trace metals derived from anthropogenic activities, such as industrial emission, coal combustion, and traffic vehicle activities, but poorly with those derived from natural sources. In the multiple linear regression analysis, Cr and Fe had higher correlation coefficients (training R > 0.7) in contrast to the low training R of As, Cd, Ni, Sr, and Ti (<0.5) determined using the PM_2.5 concentrations and magnetic parameter values as the decision variables. Our results support the use of environmental magnetism determinations as a simple and fast method to assess trace metals in urban particulate matter.

Magnetic signature, geochemistry, and oral bioaccessibility of "technogenic" metals in contaminated industrial soils from Sindos Industrial Area, Northern Greece

The objective of this study was to assess the contamination level of potentially harmful elements (PHEs) in industrial soils and how this relates to environmental magnetism. Moreover, emphasis was given to the determination of the potential mobile fractions of typically "technogenic" metals. Therefore, magnetic and geochemical parameters were determined in topsoils (0-20 cm) collected around a chemical industry in Sindos Industrial Area, Thessaloniki, Greece. Soil samples were presented significantly enriched in "technogenic" metals such Cd, Pb, and Zn, while cases of severe soil contamination were observed in sampling sites north-west of the industrial unit. Contents of Cd, Cr, Cu, Ni, Pb, Mo, Sb, Sn, and Zn in soils and pollution load index (PLI) were highly correlated with mass specific magnetic susceptibility (χ _lf). Similarly, enrichment factor (EF) and geoaccumulation index (I _geo) for "technogenic" Pb and Zn exhibited high positive correlation factors with χ _lf. Principal component analysis (PCA) classified PHEs along with the magnetic variable (χ _lf) into a common group indicating anthropogenic influence. The water extractable concentrations were substantially low, while the descending order of UBM (Unified BARGE Method) extractable concentrations in the gastric phase was Zn > Pb > As > Cd, yet Cd showed the highest bioaccessibility (almost 95%).

Magnetic Properties as a Proxy for Predicting Fine-Particle-Bound Heavy Metals in a Support Vector Machine Approach

The development of a reasonable statistical method of predicting the concentrations of fine-particle-bound heavy metals remains challenging. In this study, daily PM_2.5 samples were collected within four different seasons from a Chinese mega-city. The annual average PM_2.5 concentrations determined in industrial, city center, and suburban areas were 90, 81, and 85 μg m^-3, respectively. Environmental magnetic measurements, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, hysteresis loops, and thermomagnetism, indicated that the main magnetic mineral of PM_2.5 is low-coercivity pseudosingle domain (PSD) magnetite. Using a support vector machine (SVM), both the volume- and mass-related concentrations of heavy metals were predicted by the PM_2.5 mass concentrations and meteorological factors, with or without magnetic properties as input variables. The inclusion of magnetic variables significantly improved the prediction results for most heavy metals. Predictions based on models that included the magnetic properties of the metals Al, Fe, Mn, Ni, and Ti were promising, with R values of >0.8 in both the training and the test stages as well as relatively low errors. Our results demonstrate that the inclusion of environmental magnetism in a SVM approach aids in the effective monitoring and assessment of airborne heavy-metal contamination in cities.

Magnetic- and particle-based techniques to investigate metal deposition on urban green

Urban green works as a recorder of atmospheric PM. This paper reports on the utility of combining magnetic- and particle-based techniques to investigate PM leaf deposition as a bio-indicator of metal pollution. Ivy (Hedera helix) leaves were collected from five different land use classes, i.e. forest, rural, roadside, industrial, train. Leaf magnetic measurements were done in terms of saturation isothermal remanent magnetization (leaf SIRM), while ca. 40,000 leaf-deposited particles were analyzed through SEM/EDX to estimate the elemental composition. The influence of the different land use classes was registered both magnetically and in terms of metal content. Leaf area-normalized SIRM values ranged from 19.9 to 444.0μA, in the following order forest<rural<roadside<industrial<train. Leaf SIRM showed to be significantly correlated (p<0.01) with the content in Fe, Zn, and Pb, followed by Mn and Cd (p<0.05), while no significant correlation was found with the metals Cr and Cu. Although presenting a similar metal content, roadside and train were magnetically very distinct. By exhibiting a very high content in Pb, and with an Fe content being comparable to the one observed at the forest and rural land uses, the industrial leaf-deposited particles showed to be mainly due to industrial activity. While SEM/EDX is a suitable approach for detailed particle analysis, leaf SIRM of ivy can be used as a rapid discriminatory tool for metal pollution. Their complementary use delivers further knowledge on land use classes reflecting different PM conditions and/or sources.

Granulometric and magnetic properties of deposited particles in the Beijing subway and the implications for air quality management

The subway system is an important traffic facility in Beijing and its internal air quality is an environmental issue that could potentially affect millions of people every day. Due to the intrinsic nature of rail abrasion in subway tunnels, iron-containing particles can be generated and become suspended in the subway environment. While some studies (e.g. Li et al., 2006) have monitored the in-train levels of PM2.5 (particles<2.5μm), there is a lack of systematic assessment of the concentration and characteristics of iron-containing particles in the Beijing subway system. Here we report results of a study on the granulometric and magnetic properties of deposited particle samples collected at different localities of the Beijing subway system. Our results show that the subway samples are characterized by the presence of fine particles. Volume proportions of 6.1±1.3% for particles<2.5μm and 27.5±6.1% for particles<10μm are found in the bulk subway samples. These samples exhibit a strong magnetic signal, which is approximately two orders of magnitude higher than that in naturally deposited particles collected in Beijing. Fine grained ferromagnetic and ferrimagnetic minerals (e.g. iron and magnetite, respectively) are identified from mineral magnetic measurements and scanning electric microscopy. The samples collected from the Beijing stations with platform screen doors are found to be magnetically stronger and finer than those without them, suggesting that platform screen doors have failed to block the fine iron-containing particles released from the rail tunnel. Given the potential health consequences of fine suspended iron-containing particles, our results have important implications for air quality management in the Beijing subway system.

Framework for using deciduous tree leaves as biomonitors for intraurban particulate air pollution in exposure assessment

Fine particulate matter (PM2.5) air pollution, varying in concentration and composition, has been shown to cause or exacerbate adverse effects on both human and ecological health. The concept of biomonitoring using deciduous tree leaves as a proxy for intraurban PM air pollution in different areas has previously been explored using a variety of study designs (e.g., systematic coverage of an area, source-specific focus), deciduous tree species, sampling strategies (e.g., single day, multi-season), and analytical methods (e.g., chemical, magnetic) across multiple geographies and climates. Biomonitoring is a low-cost sampling method and may potentially fill an important gap in current air monitoring methods by providing low-cost, longer-term urban air pollution measures. As such, better understanding of the range of methods, and their corresponding strengths and limitations, is critical for employing the use of tree leaves as biomonitors for pollution to improve spatially resolved exposure assessments for epidemiological studies and urban planning strategies.

Study of road dust magnetic phases as the main carrier of potentially harmful trace elements

Mineralogical and morphological characteristics and heavy metal content of different fractions (bulk, non-magnetic fraction-NMF and magnetic fraction-MF) of road dusts from the city of Thessaloniki (Northern Greece) were investigated. Main emphasis was given on the magnetic phases extracted from these dusts. High magnetic susceptibility values were presented, whereas the MFs content of road dust samples ranged in 2.2-14.7 wt.%. Thermomagnetic analyses indicated that the dominating magnetic carrier in all road dust samples was magnetite, while the presence of hematite and iron sulphides in the investigated samples cannot be excluded. SEM/EDX analyses identified two groups of ferrimagnetic particles: spherules with various surface morphologies and textures and angular/aggregate particles with elevated heavy metal contents, especially Cr. The road dusts (bulk samples) were dominated by calcium, while the mean concentrations of trace elements decreased in the order Zn > Mn > Cu > Pb > Cr > Ni > V > Sn > As > Sb > Co > Mo > W > Cd. MFs exhibited significantly higher concentrations of trace elements compared to NMFs indicating that these potentially harmful elements (PHEs) are preferentially enriched in the MFs and highly associated with the ferrimagnetic particles. Hazard Index (HI) obtained for both adults and children through exposure to bulk dust samples were lower or close to the safe level (=1). On the contrary, the HIs for the magnetic phases indicated that both children and adults are experiencing potential health risk since HI for Cr was significantly higher than safe level. Cancer risk due to road dust exposure is low.

Trace metal contamination in surface sediments of intertidal zone from Qinhuangdao, China, revealed by geochemical and magnetic approaches: Distribution, sources, and health risk assessment

Based on geochemical and magnetic approaches, the distribution, sources, and health risk of trace metals in surface sediments from a seashore tourist city were investigated. A significant correlation was found between magnetic susceptibility (χ) and trace metals, which suggested that levels of trace metals in the sediments can be effectively depicted by the magnetic approach. The spatial distribution of χ and trace metals matched well with the city layout with relatively higher values being found in the port and busy tourist areas. This result, together with enrichment factors (EFs) and Tomlinson pollution load index (PLI) of metals, suggested that the influence of human activities on the coastal environment was noticeable. Principal component analysis (PCA) indicated that trace metals in the sediments were derived from both anthropogenic and natural sources. Noncarcinogenic risk assessment showed that there was no potential health risk of exposure to metals by means of ingestion or inhalation.

Magnetic particulate matters in the ashes of few commonly used Indian cigarettes

Physical aspects of tobacco samples, used in some commonly available Indian brands of cigarettes, with emphasis on their magnetic characterization before and after they get burnt into ashes, are described. The present work highlights the ultrafine nature of the cigarette ashes and provides a compositional insight of their constituent particulate matters as revealed by the XRD and SEM studies. Based on the EDX spectra, elemental distributions of different tobacco samples, before and after they get burnt, are presented. In this work, magnetic measurements of the un-burnt tobacco samples are reported. An attempt is made to shed light on the origin of magnetism observed in these samples.

Combination of magnetic parameters and heavy metals to discriminate soil-contamination sources in Yinchuan--a typical oasis city of Northwestern China

Various industrial processes and vehicular traffic result in harmful emissions containing both magnetic minerals and heavy metals. In this study, we investigated the levels of magnetic and heavy metal contamination of topsoils from Yinchuan city in northwestern China. The results demonstrate that magnetic mineral assemblages in the topsoil are dominated by pseudo-single domain (PSD) and multi-domain (MD) magnetite. The concentrations of anthropogenic heavy metals (Cr, Cu, Pb and Zn) and the magnetic properties of χlf, SIRM, χARM, and 'SOFT' and 'HARD' remanence are significantly correlated, suggesting that the magnetic minerals and heavy metals have common sources. Combined use of principal components and fuzzy cluster analysis of the magnetic and chemical data set indicates that the magnetic and geochemical properties of the particulates emitted from different sources vary significantly. Samples from university campus and residential areas are mainly affected by crustal material, with low concentrations of magnetic minerals and heavy metals, while industrial pollution sources are characterized by high concentrations of coarse magnetite and Cr, Cu, Pb and Zn. Traffic pollution is characterized by Pb and Zn, and magnetite. Magnetic measurements of soils are capable of differentiating sources of magnetic minerals and heavy metals from industrial processes, vehicle fleets and soil parent material.

The influence of weather and climate on the reliability of magnetic properties of tree leaves as proxies for air pollution monitoring

Monthly monitoring of magnetic properties of Platanus hispanica tree leaves was used to assess atmospheric pollution in Madrid (Spain) and its suburban town of Pozuelo de Alarcón. Magnetic susceptibility, isothermal remanent magnetisation and metal concentrations were analysed to study the sources of atmospheric pollutants and their spatial and temporal evolution. In addition to urban dust, our results indicated that lithogenic dust and incorporation of trace metals in the leaf tissue also control the magnetic susceptibility of tree leaves. Global comparisons with cities of different climatic regimes suggest that air humidity is the key factor controlling the relative influence of pollutants, lithogenic dust and biological effects on the magnetic properties of tree leaves. Interaction of the atmosphere and tree leaves depends not only on local meteorology but also on climate. Climate, especially air humidity, and meteorology need to be considered when interpreting the magnetic properties of tree leaves as an atmospheric pollution tool.

Response of magnetic properties to heavy metal pollution in dust from three industrial cities in China

Magnetic method is a reliable and powerful technique for identification of the relative contribution of industrial pollutants. However, it has not been fully applied in urban area impacted by non-ferrous metal (NFM) smelting/processing activities. The aim of this study is to explore the applicability of magnetic methods for detecting heavy metal contamination in dust from three NFM smelting/processing industrial cities (Ezhou, Zhuzhou, and Hezhang) in China. The enhancements of magnetic susceptibility (MS) and saturation isothermal remanent magnetization (SIRM) together with heavy metals were significant in the studied areas in comparison with the background values. Scanning electron microscope (SEM) analysis revealed that magnetic particles in dust from Ezhou were dominated by spherules, while those from Zhuzhou and Hezhang were mainly consisted of irregular-shaped particles. κ-T curves and X-ray diffraction (XRD) analyses indicated that the magnetic particles from Ezhou were dominated by magnetite and metallic iron, whereas those from Zhuzhou and Hezhang were consisted of magnetite and hematite. Our study indicates that magnetic properties of the dust are sensitive to the NFM smelting/processing related heavy metal pollutants. However, the relationship between magnetic parameters and heavy metals was influenced by the presence of metallic iron particles and multi-sources of metal pollutants.

Biomonitors of urban air pollution: Magnetic studies and SEM observations of corticolous foliose and microfoliose lichens and their suitability for magnetic monitoring

This study explored the suitability of available lichen species as air pollution biomonitors and assessed their potential for magnetic monitoring in cities. Several lichens on tree bark were collected in urban and industrial sites from Tandil city, as well as control sites. The results showed that magnetite-like minerals were the main magnetic carriers in all sites and samples. However, the concentration varied between clean and polluted sites. In addition, magnetic-grain size-distribution showed clear differences between sites. Observations by scanning electron microscopy showed different particles in a variety of shapes and grain sizes; moreover, the presence of iron oxides and several toxic elements was detected by energy dispersive spectroscopy analysis. Although eleven lichen species were identified that appeared suitable for use as air-pollution monitors, three of them, Parmotrema pilosum, Punctelia hipoleucites and Dirinaria picta, occurred more frequently in the area, thus constituting appropriate species for future monitoring in the study area.

Using magnetic and chemical measurements to detect atmospherically-derived metal pollution in artificial soils and metal uptake in plants

Quantification of potential effects of ambient atmospheric pollution on magnetic and chemical properties of soils and plants requires precise experimental studies. A controlled growth experiment assessing magnetic and chemical parameters was conducted within (controls) and outside (exposed) a greenhouse setting. Magnetic susceptibility (MS) measurements showed that while initial MS values were similar for the sample sets, the overall MS value of exposed soil was significantly greater than in controls, suggesting an additional input of Fe-containing particles. Scanning electron microscope images of the exposed soils revealed numerous angular magnetic particles and magnetic spherules typical of vehicular exhaust and combustion processes, respectively. Similarly, chemical analysis of plant roots showed that plants grown in the exposed soil had higher concentrations of Fe and heavy (toxic) metals than controls. This evidence suggests that atmospheric deposition contributed to the MS increase in exposed soils and increased metal uptake by plants grown in this soil.

The relationship between magnetic parameters and heavy metal contents of indoor dust in e-waste recycling impacted area, Southeast China

Environmental contamination due to uncontrolled e-waste recycling is an emerging global problem. The aim of this study is to test the applicability of magnetic methods for detecting the metal pollutants emitted from e-waste recycling activities. Dust samples collected from a typical e-waste recycling region in Guiyu, Guangdong Province, China, were investigated using magnetic, geochemical, micro-morphological and mineralogical analysis. The values of mass-specific susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) in dusts from e-waste recycling impacted areas ranged from 101 to 636×10(-8) m(3) kg(-1) and from 10.5 to 85.2×10(-3) Am(2) kg(-1), respectively. There was a significant correlation between SIRM and χ (r(2)=0.747, p<0.001), indicating that ferrimagnetic minerals were dominating χ in the dust samples. The values of χ(fd)% varied from 2.6 to 4.6% with a mean of 3.4%, which suggested that magnetic carriers in the dusts are predominately coarse-grained particles. Two shapes of magnetic particles, spherule (10-150 μm) and angular-shaped particles (30-300 μm), were identified by scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX) analyses. κ-T curves, magnetic hysteresis loops and X-ray diffraction (XRD) analysis indicated that these magnetic particles were magnetite and goethite. There were significant correlations between SIRM and heavy metals (especially Cd, Co, Fe, Ni and Zn) as well as the Tomlinson pollution load index (PLI) of the dust, indicating that SIRM can be used as an efficient proxy for metal pollution in the e-waste recycling impacted area.

Assessment of heavy metal pollution from a Fe-smelting plant in urban river sediments using environmental magnetic and geochemical methods

Environmental magnetic proxies provide a rapid means of assessing the degree of industrial heavy metal pollution in soils and sediments. To test the efficiency of magnetic methods for detecting contaminates from a Fe-smelting plant in Loudi City, Hunan Province (China) we investigated river sediments from Lianshui River. Both magnetic and non-magnetic (microscopic, chemical and statistical) methods were used to characterize these sediments. Anthropogenic heavy metals coexist with coarse-grained magnetic spherules. It can be demonstrated that the Pollution Load Index of industrial heavy metals (Fe, V, Cr, Mo, Zn, Pb, Cd, Cu) and the logarithm of saturation isothermal remanent magnetization, a proxy for magnetic concentration, are significantly correlated. The distribution heavy metal pollution in the Lianshui River is controlled by surface water transport and deposition. Our findings demonstrate that magnetic methods have a useful and practical application for detecting and mapping pollution in and around modern industrial cities.

Evaluation of environmental magnetic pollution screening in soils of basaltic origin: results from Nashik Thermal Power Station, Maharashtra, India

BACKGROUND, AIM, AND SCOPE

Soils of basaltic origin cause difficulties in environmental magnetic screening for heavy metal pollution due to their natural high background values. Magnetic parameters and heavy metal content of highly magnetic topsoils from the Deccan Trap basalts are investigated to assess their potential for use in environmental magnetic pollution screening. This work extends the fast and cost-effective magnetic pollution screening techniques into soils with high natural magnetic signals.

MATERIALS AND METHODS

Fifty-five topsoil samples from N-S and W-E transects were collected and subdivided according to grain size using wet sieving technique. Magnetic susceptibility, soft isothermal remanent magnetization (Soft IRM), thermomagnetic analysis, scanning electron microscopy (SEM), and heavy metal analysis were performed on the samples.

RESULTS

Magnetic analyses reveal a significant input of anthropogenic magnetic particulate matter within 6 km of the power plant and the adjacent ash pond. Results depend strongly on the stage of soil development and vary spatially. While results in the W, E, and S directions are easily interpretable, in the N direction, the contribution of the anthropogenic magnetic matter is difficult to assess due to high magnetic background values, less developed soils, and a more limited contribution from the fly ash sources. Prevailing winds towards directions with more enhanced values seem to have a certain effect on particulate matter accumulation in the topsoil. Thermomagnetic measurements show Verwey transition and Hopkinson peak, thus proving the presence of ferrimagnetic mineral phases close to the pollution source. A quantitative decrease of the anthropogenic ferrimagnetic mineral concentration with increased distance is evident in Soft IRM measurements. SEM investigations of quantitatively extracted magnetic particles confirm the fly ash distribution pattern obtained from the magnetic and heavy metal analyses. Evaluation of magnetic and chemical data in concert with the Pollution Load IndiceS (PLIS) of Pb, Zn, and Cu reveals a good relationship between magnetic susceptibility and the metal content.

CONCLUSIONS

Integrated approaches in data acquisition of magnetic and chemical parameters enable the application of magnetic screening methods in highly magnetic soils. Combined data evaluation allows identification of sampling sites that are affected by human activity, through the deviation of the magnetic and chemical data from the general trend. It is shown that integrative analysis of magnetic parameters and a limited metal concentration dataset can enhance the quality of the output of environmental magnetic pollution screening significantly.

Onset of industrial pollution recorded in Mumbai mudflat sediments, using integrated magnetic, chemical, 210Pb dating, and microscopic methods

The onset and rise of urban and industrial pollution in the Mumbai region was reconstructed from an anthropogenically contaminated mudflat sediment profile from the adjacent Thane creek using magnetic parameters, polycyclic aromatic hydrocarbon (PAH) data, metal contents, and the (210)Pb dating technique. The 1.8 m vertical section at Airoli (Navi Mumbai) reveals an increase of magnetic susceptibility (χ) from background values of (20-50) to (75-100) × 10(-8) [m(3) kg(-1)] in the anthropogenically affected zone above ∼93 cm. A sharp rise of χ from (75-100) to (130-215) × 10(-8) [m(3) kg(-1)] subdivides the anthropogenically affected zone at a depth of ∼63 cm. Characterization with rock magnetic parameters (SIRM, Soft IRM, and S-ratio) reveals a significant contribution of ferri(o)magnetic phases in the upper zone. Based on the magnetic classification sampling intervals for cost-intensive PAH and metal analyses were determined. Steadily increasing contents of PAH and metals of anthropogenic origin are observed above the boundary depth at ∼93 cm. A sediment accumulation rate of 1.2 ± 0.3 cm/yr provided by (210)Pb dating dates the ∼63 cm boundary to 1951. Increasing industrial activity, including the establishment of a coal-fired power plant in 1956, and refineries between 1955 and 1960, correlates well with the substantial increase of χ, PAH, and metal contents. Scanning electron microscopy (SEM) investigation on magnetic extracts from the contaminated zone reveals the presence of magnetic spherules derived from industrial high-temperature processes.

Biomonitoring of atmospheric particulate matter using magnetic properties of Salix matsudana tree ring cores

Magnetic properties of atmospheric particulate matter collected by both natural and artificial dust receptors are increasingly being used as proxy parameters for environmental analyses. This study reports the first investigation of the relationship between smelting factory activity and the impact on the environment as recorded by the magnetic signature in Salix matsudana tree rings. Magnetic techniques including low-temperature experiments, successive acquisition of isothermal remanent magnetisation (IRM), hysteresis loops and measurements of saturated IRM (SIRM) indicated that magnetic particles were omnipresent in tree bark and trunk wood, and that these particles were predominantly magnetite with multidomain properties. The magnetic properties of tree trunk and branch cores sampled from different directions and heights implied that the acquisition of magnetic particles by a tree depends on both orientation and height. The differences of SIRM values of tree ring cores indicated that pollution source-facing tree trunk wood contained significantly more magnetic particles than other faces. The results indicated that magnetic particles are most likely to be intercepted and collected by tree bark and then enter into tree xylem tissues during the growing season to become finally enclosed into the tree ring by lignification. There was a significant correlation between time-dependent SIRM values of tree ring cores and the annual iron production of the smelting factory. From the dependence of magnetic properties with sampling direction and height, it is argued that magnetic particles in the xylem cannot move between tree rings. Accordingly, the SIRM of tree ring cores from the source-facing side can contribute to historic studies of atmospheric particulate matter produced by heavy metal smelting activities.

Management of hazardous road derived respirable particulates using magnetic properties of tree leaves

The magnetic properties of tree leaves along with their ecological, economical and aesthetic importance can be used to control road derived respirable particulates. Isothermal remanent magnetization (IRM(300) mT) of three different tree leaves viz. Mango (Mangifera indica), Sisso (Dalbergia sisso) and Banyan (Ficus benghalensis) were determined and IRM(300) mT normalized for the leaf area. The normalized 2-D magnetization of leaves as shown by results is dominantly controlled by leaf morphology and traffic density. F. benghalensis (Banyan) leaf has highest 2-D magnetization and D. sisso (Sisso) leaf having least 2-D magnetization suggesting greater ability of F. benghalensis (Banyan) tree leaves to reduce magnetic particulates. The particle size of the magnetic grains falls in the category of PM2.5, a particle size hazardous to human health due to its capacity to be inhaled deeply into the lungs.

Magnetic mapping of fly-ash pollution and heavy metals from soil samples around a point source in a dry tropical environment

The Singrauli region in the southeastern part of Uttar Pradesh, India is one of the most polluted industrial sites of Asia. It encompasses 11 open cast coal mines and six thermal power stations that generate about 7,500 MW (about 10% of India's installed generation capacity) electricity. Thermal power plants represent the main source of pollution in this region, emitting six million tonnes of fly-ash per annum. Fly-ash is deposited on soils over a large area surrounding thermal power plants. Fly-ashes have high surface concentrations of several toxic elements (heavy metals) and high atmospheric mobility. Fly ash is produced through high-temperature combustion of fossil fuel rich in ferromagnetic minerals. These contaminants can be identified using rock-magnetic methods. Magnetic susceptibility is directly linked to the concentration of ferromagnetic minerals, primarily high values of magnetite. In this study, magnetic susceptibility of top soil samples collected from surrounding areas of a bituminous-coal-fired power plant were measured to identify areas of high emission levels and to chart the spatial distribution of airborne solid particles. Sites close to the power plant have shown higher values of susceptibility that decreases with increasing distance from the source. A significant correlation between magnetic susceptibility and heavy metal content in soils is found. A comparison of the spatial distribution of magnetic susceptibility with heavy-metal concentrations in soil samples suggests that magnetic measurements can be used as a rapid and inexpensive method for proxy mapping of air borne pollution due to industrial activity.

Magnetic approach to normalizing heavy metal concentrations for particle size effects in intertidal sediments in the Yangtze Estuary, China

In this study, mineral magnetic, particle size and geochemical analyses were conducted on intertidal sediments from the Yangtze Estuary to examine the feasibility of heavy metal concentrations normalization using magnetic techniques. Susceptibility of Anhysteretic Remanent Magnetization (chiARM), the ratio of chiARM to SIRM (Saturation Isothermal Remanent Magnetization) and susceptibility (chiARM/SIRM and chiARM/chi, respectively), and to a lesser degree, frequency dependent susceptibility (chifd), displayed significant correlations with the fine sediment fraction (<16 microm). The strong relationships between chiARM and heavy metals can be explained by the role of particle size and iron oxides in controlling metal concentrations. This study demonstrates that chiARM can be used to normalize for particle size effects as efficiently as common reference elements such as Al. Furthermore, the rapid and non-destructive nature of mineral magnetic measurement technique means that chiARM has a considerable application value in environmental quality monitoring and related studies.