Frequency-dependent Magnetic Susceptibility Research Articles

Heavy metal contamination in soils of industrial estates of Tamil Nadu, India and source identification by magnetic susceptibility.

An increase in erratic industrial activity has been a major contributing factor to the significant contamination in environmental matrices. This study aimed to ascertain the level of heavy metal contamination in soils in major industrial estates of Tamil Nadu as well as the threats to human health and the environment that concomitant with it. This led to the use of the total reflection X-ray fluorescence (TXRF) spectroscopy technique to analyse 31 soil samples. Thus, the mean heavy metal concentrations were found to be in the ascending order: As < Ni < Pb < V < Cu < Zn < Cl < Mn < Sr < Cr < Al < Fe. Pb, Cr, Cu, As, and Zn have been identified as predominantcontaminants in the study area using the conventional pollution indices such as geo-accumulation index (Igeo), contamination factor (CF), and enrichment factor (EF). The magnetic susceptibility measurements indicates that the percentage of frequency dependence of magnetic susceptibility of the studied soil samples varied from 0.88 to 11.15 and that represents the presence of admixture ofsuperparamagnetic (SP) particles in the soil samples. From the results of multivariate statistical analyses, the sources ofidentified heavy metals were classified as anthropogenic sources(Cr, Cu, Pb, As, and Zn),natural sources(V, Mn, Fe, Ni, and Sr ),and intermediate sources (Al and Cl).

Exploring soil pedogenesis through frequency-dependent magnetic susceptibility in varied lithological environments

AbstractThe use of percent frequency-dependent magnetic susceptibility (χfd%) is well-established for detecting superparamagnetic (SP) components in fine-grained soils and sediments. This study employs χfd% as a direct indicator of pedogenetic processes in soils from the Moroccan Rif region. Three soil transects (T1, T2, and T3), each comprising four soil cores with depths reaching 100 to 120 cm, were sampled from distinct lithological formations within an area subject to moderate to intense erosion. A total of 272 soil samples were collected and analyzed using MS2 Bartington Instruments, providing values to calculate χfd% and identify ultrafine ferrimagnetic minerals (SP, &lt; 0.03 μm). In Quaternary fluvial terraces (T1) soils, approximately 60% of the samples indicate a mixture of SP, multidomain (MD), and Single Stable Domain (SSD) magnetic grains, while 30% contained coarser MD grains. Only 10% of the samples exhibit predominantly superparamagnetic (SP) grains. Soils on marly substrates (T2) showed 90% of samples with a combination of SP, MD, and SSD, and just 10% had SP grains. In contrast, soils from Villafranchian sandy deposits displayed χfd% values exceeding 10% in over 50% of samples, indicating that almost all iron components consist of SP grains. Physico-chemical analyses of the soils in profiles T1, T2, and T3 reveal distinct characteristics, including variations in clay content, organic matter, nutrient levels, and proportions of free and total iron. These results are important for understanding soil evolution and pedogenesis, with profiles T1 and T3 showing advanced development marked by high mineral iron, clay, and organic matter content. In contrast, profile T2 reflects a weak stage, influencing nutrient availability and contributing to overall soil dynamics in the respective profiles. The results of this study suggest that magnetic susceptibilities in these samples primarily originate from pedogenetic sources, revealing significantly advanced pedogenesis compared to T1 and T2 soils. The findings of this study align with previous research on soil erosion and degradation in the region, demonstrating that soils developed on terraces and marly substrates are more degraded and less stable than those on sandy substrates. This study underscores the utility of magnetic susceptibility as a rapid and effective indicator for initial soil assessment and gauging the degree of pedogenesis.

Middle - Late Eocene cold and wet climatic interval in East Asia: Evidence from lacustrine sediments of the lower Huoshaogou Formation in the Hexi Corridor, NE Tibetan Plateau

Knowledge of the climate of the Late Eocene is important for understanding the global climatic shift from a global Warmhouse to a Coolhouse. We obtained a climatic record for the interval of 38.10–36.33 Ma based on sedimentary facies analysis combined with measurements of color indices (CI) and magnetic susceptibility (MS) of the lower Huoshaogou Formation in the westernmost Hexi Corridor, Northeastern Tibetan Plateau. Our results reveal the following temporal sequence of sedimentary environments: delta plain, shore–shallow lake, deep lake, and braided river. The records of MS and CI co-vary with changes in sedimentary facies and color, respectively. The various proxy indicators indicate an overall warm and dry climate interrupted by a cold and wet interval in the middle part of the section during ~37.67–36.44 Ma, corresponding to a thick, greenish-colored lacustrine sedimentary layer with high values of lightness and low valuer of MS, frequency-dependent MS and redness. We suggest that this event was driven by the diversion of westerly winds due to the uplift of the southern Tibetan Plateau, together with the Tethys Sea retreat and the short-lived emergence or enhancement of the Asian monsoon.

Iron Age ceramics from Thracian rock-cut complexes from Bulgaria – Mineral magnetic relics of technological production and use

The Gluhite kamani Thracian rock-cut complex in the Eastern Rhodopes Mountain is famous with its more than 500 rock niches carved in the rock at heights up to 20 m. Continuous habitation starting from the final Chalcolithic (the second quarter of the 4th millenium BCE) until the Late Classical – Early Hellenistic period (late 5th – 4th century BCE) provides unique opportunity for studying diachronic changes in pottery production and use. In this contribution, systematic analysis of a collection of 135 ceramic sherds from five archaeological periods at the site was carried out using a combined mineral magnetic and geochemical approach. Magnetic susceptibility (χ), frequency-dependent magnetic susceptibility (χfd%) and firing temperature (Tfire), determined using the magnetic susceptibility method, were combined with data from elemental XRF analyses. Thermomagnetic measurements, employed for identification of magnetic minerals revealed the dominant presence of (titano)magnetite with low Ti-content and/or a fraction of single-domain magnetite and in few cases hematite. Although varying in a wide range, median χ values of ceramic sherds from the Early Iron Age (EIA) periods show similar distribution, while for Late Iron Age (LIA) with the introduction of the wheel-thrown pottery, χ values are higher, presumably due to decreased amount of silica-rich clastics in the clay. Concurrently, χfd% values decrease in ceramics from the LIA, indicating predominant presence of stable single-domain magnetite in the iron oxide composition of the ceramics. Firing temperatures (Tfire) estimations display a systematic pattern of two groups – higher (Tfire between 760 and 800 °C) and lower (Tfire ∼ 400–––600 °C). During the EIA periods both Tfire groups are present, characterized by systematic gradual decrease of the median value of the low Tfire when going from EIA1 towards the EIA2. Wheel-thrown pottery from the LIA show low Tfire ∼ 400 °C only. Based on the differences in thermomagnetic properties of ceramics, their magnetic parameters and Tfire estimates, two possible hypotheses are suggested to explain the observed changes in EIA ceramic characteristics: i) utilization of two differently sourced clay materials (illite-dominated and montmorillonite-dominated) for production of ceramics fired at higher and lower temperatures, respectively; and ii) utilization of one raw clay source, while using two firing regimes – firing at higher temperature for prolonged time, and fast firing to high temperature with successive stage of longer firing at lower temperature. Differences in thermomagnetic properties of wheel-thrown pottery from the LIA period leads to the assumption for utilization of diverse clay source for their production, as compared clay sources for the Early Iron Age periods.

Recent environmental and morphosedimentary evolution of the mining-impacted Nalón Estuary (Asturias, N Spain): Disentangling natural and anthropogenic processes

Distinguishing between natural and anthropogenic processes in sedimentary records from estuaries with legacy pollutants is an essential task, as it provides baselines to predict future environmental trajectories of coastal areas. Here, we have addressed the recent transformation history of the mining-impacted Nalón Estuary (Asturias, N Spain). Surface and core sediment records from marshes and tidal flats were examined through a broad multidisciplinary approach, involving micropaleontological (benthic foraminifera), sedimentological (grain-size), geochemical (trace metals, major element Al and total organic carbon), physical (magnetic susceptibility, frequency-dependent magnetic susceptibility and large microplastics) and radioisotopic (210Pb, 137Cs and 239+240Pu) proxies. Results suggest that the interplay between natural (high fluvial influence and extreme hydrological events) and anthropogenic (coal and mercury mining disposals) factors induced strong sedimentation-erosion processes, further shaping the recent evolution of the estuary. Short-time scale and intense sedimentation processes were revealed by overall high sediment accumulation rates, the dilution of some geological signatures and the rapid formation of a marsh in the lower estuary bay. The increasing mining fingerprints during the 20th century were shortly interrupted by the catastrophic riverine flooding of 1938. Conversely, current erosional processes by fluvial influence led to the remobilization of contaminated sedimentary materials and exposure of mining-legacy Hg levels in tidal flats from the middle sector. Fluvial activity, floodings and taphonomic biases exerted a major control on benthic foraminifera since the 19th century, although Hg ecotoxicological effects on modern assemblages at certain areas within the estuary cannot be discarded. These findings, along with the documented enhanced erosion of marshes with ‘trapped’ pollutants (Hg, coal microparticles and microplastics), highlight the importance of monitoring the environmental and geomorphic processes taking place in historically-contaminated estuaries.

Topsoil's magnetic and electrical properties in a volcanic and tropical region.

Environmental monitoring by measuring topsoil's magnetic and electrical properties is one practical, quick, and low-cost approach. This method has been used worldwide as a proxy for the presence of potentially toxic elements. However, additional research must be conducted on diverse soil types, geology, and climates. We determined the magnetic and electrical properties of urban and agricultural topsoils in a volcanic region and analyzed them as possible proxies of potentially toxic elements for environmental monitoring. To identify topsoil characteristics, we employed the measurements of magnetic susceptibility and hysteresis, electrical conductivity, total dissolved solids, power of hydrogen (pH), particle morphology, and element contents that were statistically analyzed to identify relevant properties. The result was able to differentiate volcanic soils from urban, industrial, and agricultural areas as well. The value of low-frequency magnetic susceptibility (χLF) in soils from urban areas is higher than 866.0±249.9 ×10-8 m3 kg-1, while the value of χLF in agricultural areas is 208.0±67.8 ×10-8 m3 kg-1. This is reinforced by the relationship between low-frequency and frequency-dependent magnetic susceptibility (χLF-χFD%) in samples from urban areas that fall within the same cluster dominated by coarse-grained magnetic minerals originating from anthropogenic processes. In contrast, the agricultural area forms a separate cluster primarily influenced by pedogenic processes from acid igneous rock minerals. Caution is required for interpreting the magnetic signal due to the high contents of lithogenic magnetic particles inherited from the parent materials of Andisols.

МАГНІТНО-МІНЕРАЛОГІЧНІ ВЛАСТИВОСТІ ҐРУНТІВ КИЇВЩИНИ, УРАЖЕНИХ ВІЙСЬКОВИМИ ДІЯМИ

Background. One of the dangerous effects on the environment caused by the military actions in Ukraine is the destruction of the soil. This includes its pollution, redistribution of genetic horizons, compaction, change of physical and chemical agronomic indicators, etc. Accumulated experience shows that most of these processes are reflected in the magnetic properties of soils. Methods. The applied magnetic method includes a full range of field and laboratory studies. More detailed magnetic mineralogical methods of measurements are described in. Results. On the basis of the diagram developed for the ratios of anhysteretic magnetic susceptibility to low-frequency magnetic susceptibility (χARM/χlf) and anhysteretic magnetic susceptibility to the frequency dependence of magnetic susceptibility (χARM/χfd), fine-grained magnetic particles of lithogenic and bacterial origin were detected in the soils of experimental areas of Kyiv region. For Stari Petrivtsi, only one group of samples was mainly identified. In Demydiv, we found two groups: a larger one, marked in green, and a smaller one, marked in red. Finally, two equivalent groups were identified in the Ozera study site. According to the results of the thermomagnetic analysis of magnetic susceptibility, an unusual "tail" for soils was identified after 600 °C, which indicates the content of metallic iron. The content of heavy metals in the magnetic extraction of soils from objects of military defeat depends on the composition of the alloys of the weapons striking a specific place. Conclusions. During the explosion of various types of ammunition, fragments of irregular shape are formed due to strong mechanical impact, and additional heating in the process leads to the formation of iron spherules. This complex physico-chemical process occurs as a result of the interaction of high-temperature gases, dust and molten metal. These objects are successfully identified by quick and cheap magnetic methods.

Temperature- and frequency-dependent magnetic susceptibility on archaeological ceramics of the Tlatilca culture (Mexico City): A pilot study towards an archaeointensity approach

Temperature-dependent susceptibility curves are commonly used in archaeointensity studies to identify changes in the magnetic mineralogy of archaeological ceramics. In this pilot study, we investigated the low- and high-temperature thermomagnetic behavior and frequency-dependent susceptibility of eight ceramics from a Tlatilca culture archaeological site in Mexico City, after heating them at five different temperatures (from 120 to 440 °C). Our objective is to establish a correlation between the thermomagnetic behavior and the parameters that determine the magnetic grain-size and magnetic domain in similar style of ceramics from different occupations of the site. Our findings show that superparamagnetic grains (SP) degrade with increasing reheating temperature in ceramics, and we conclude that this behavior is related to details in artifact processing, such as the use of pastillage to represent headdresses, and an important aspect to consider when working with samples for archaeointensity procedures.

The firing temperatures of burnt clay from the Chinese neolithic cultural relics and its paleoenvironmental imprints

The impact of human-induced fires on the surrounding environment has been particularly significant during the Anthropocene epoch. Neolithic burnt clay, which is widely distributed in the archaeological relics of ancient civilizations across the Eurasian continent, provides pivotal information about the ancient firing stories. However, understanding of the paleoenvironmental imprints of fire in burnt clay has been largely limited by the lack of sufficient analytical data on comprehensive knowledge of ancient firing conditions. In this study, a detailed magnetic analysis was conducted on burnt clay materials from a Neolithic site in Fujian, southeastern China, which presented a burnt clay-based record of the Neolithic firing temperature in relation to paleoenvironmental conditions. Based on magnetic analysis, the ancient firing temperature was determined to be approximately 620 °C, which is comparable with other records from Eurasian Neolithic sites. Frequency-dependent magnetic susceptibility provides alternative indicative information for ancient firing conditions in addition to conventional magnetic susceptibility. Furthermore, magnetic properties of burnt clay may decode the in-situ source characteristics with respect to geological background. In addition, a potential link between temporal variations in ancient firing temperatures in burnt clay and surrounding paleoenvironmental changes is tentatively interpreted by local environmental feedback of temperature-moisture conditions and anthropogenic activity. This study further confirms the archaeological potential of thermomagnetic properties as useful indicators in paleoenvironmental studies. More work combining paleoenvironmental and archaeological archives is critically essential to understand ancient firing history in the context of environmental conditions.

Frequency-Dependent Magnetic Susceptibility and Chemical Composition of Estuary Mangrove Sediment as Environmental Indicator of Ecosystem Degradation

Frequency-Dependent Magnetic Susceptibility and Chemical Composition of Estuary Mangrove Sediment as Environmental Indicator of Ecosystem Degradation

Identification of Sediment Formation Based on Magnetic Content and Element Composition of Mud Volcano in Sangiran Sediment using VSM and X-Ray Fluorescence

Based on trace geological history and several studies, the Sangiran mud volcano provides insight into the geology and hydrology of the region, aquifer system in the basin, groundwater flow patterns and characteristics, rock lithology, hydrogeology condition, and saltwater trap mapping. Related to these conditions, studies were conducted on the magnetic content and composition of the major oxide compounds in the Sangiran sediments. Sample analysis was based on geochemical methods. The methods consist of frequency dependent magnetic susceptibility and vibrating sample magnetometer (VSM) analysis. Geochemical analyses using x-ray fluorescence (XRF) analysis have been conducted and various elemental grades have been determined. VSM results confirm that the magnetic content of Sangiran sediments is partly dominated by Fe (17.66 percent) contained in hematite (Fe2O3). At the same time, the samples of Sangiran sediment were enriched by Si, Fe, Al, Ca, Cl, Ti, and K according to XRF measurements. The samples exhibited the highest Si and Fe concentrations in samples T1 (Si is 29.48 percent and Fe is 13.66 percent) and T7 (Si is 24.95 percent and Fe is 12.01 percent). Meanwhile, in the T4 sample, the highest concentrations were Si and Ca, 23.45 percent and 13.45 percent, respectively. Retrieved from the magnetic susceptibility measurement, this paper confirm that Fe content is one of the components of volcanic ash in the Sangiran sediment.DOI: 10.17977/um024v8i12023p009

Obliquity‐driven mountain permafrost‐related fluvial magnetic susceptibility cycles in the Quaternary mid‐latitude long‐term (2.5 Ma) fluvial Maros Fan in the Pannonian Basin

Magnetic susceptibility (MS) of the Quaternary long‐term mid‐latitude Maros fluvial fan (Pannonian Basin) was recorded to understand the stratigraphical features of source‐proximal fluvial depositional settings. Three fully cored 500‐m‐deep boreholes were sampled at 0.5‐m intervals; low‐field and frequency dependent MS were measured, and complementary hysteresis and SEM‐EDAX investigations were performed on selected samples. Logged susceptibility data were also used to log correlations established by a simultaneous comparison of wireline log and laboratory measurements. Time‐series analyses of the susceptibility records reveal a ~41‐ka and ~100‐ka cyclicity. Towards the source‐distal sections the intensity of the ~41‐ka cycles decreases, while that of the ~100‐ka cycles remains strong. Stratigraphical and spectral similarities were observed between the Maros fluvial fan and Chinese loess records; however, based on complementary magnetic data, the magnetic phase of the Maros Fan sections is related to the detrital magnetite that originates from the catchment during early postglacial permafrost degradations. The amplification of the ~41‐ka cycles can be attributed to the very high susceptibility values in source‐proximal settings and to the special stratigraphical feature of the distributive fluvial systems. This comprises the increased avulsion frequency on the fluvial fans in ‘glacial recession periods’, in concert with the ‘early postglacial’ occurrence of the permafrost‐related magnetite originating from the catchment. As a local phenomenon, this is significant since it records the obliquity‐driven variations in permafrost development in a catchment. However, fluvial and alluvial fans are widespread depositional landforms within the Eurasian mountain range and were possibly the same during the Quaternary deglaciations. Thus, obliquity‐driven magnetic susceptibility variations in source‐proximal fan deposits attached or adjacent to regions of loess deposition should also be considered when scanning for potential source material of aeolian deposits.

Hydrothermal alteration of surficial rocks at Los Humeros geothermal field, Mexico: a magnetic susceptibility approach

Utility of the geothermal surface manifestations (GSMs; thermal springs, geysers, fumaroles, and zones of hydrothermal alteration) in the studies related to the geothermal exploration is widely recognized. The identification of hydrothermally altered rocks and zones of alteration is very important because their presence indicates the type and size of the geothermal reservoir and existing thermal conditions. The use of traditional methods (i.e., geochemistry, mineralogy, and petrography) requires expensive equipment, time-consuming, and laborious sample preparation methods. Some of the rock magnetic parameters, like magnetic susceptibility (χlf) and percentage of frequency-dependent magnetic susceptibility (χfd%), are potential to become effective additional tools in identification of the hydrothermal rocks during the initial stages of geothermal exploration. Three chemical methods, Chemical Index of Alteration (CIA), loss-on-ignition (LOI), and the binary plot (CaO + Na2O + K2O) vs. (Fe2O3 + MnO + MgO), along with two rock magnetic methods, χlf and the binary plot (χlf vs. χfd%), are applied to nine intensively altered andesite reference rocks. All the five methods have correctly identified that 99 out of the total 350 studied rocks are altered. More altered rocks are distributed surrounding the several faults in the study area. Various faults (e.g., Los Humeros fault and the Loma Blanca fault) favor fluid flow and present strong hydrothermal alteration at the surface. However, there are no altered rocks on the surface region between the E-W trending Las Papas and Las Viboras faults. The presence of only the deeper fluid pathway toward the east in the surroundings of these two faults result into the almost absence of hydrothermal alteration along their strike at the surface. Consequently, there are not many altered rocks observed surroundings these two faults at the surface. These features suggest that the surface hydrothermal alteration at Los Humeros Geothermal Field (LHGF) is controlled by faults. χlf and χfd% are reliable, simple to measure, fast, cost-effective, and have the potential to become reliable additional tools for future exploration studies.

Magnetic susceptibilites of suspended sediment and microplastic abundance in a tropical volcanic estuary

Coastal and estuarine ecosystems are seriously threatened by pollutants, according to the literature. In the estuary, the zone that traps suspended particulate matter, namely, estuarine turbidity maxima (ETM), needs to be identified to prevent ecological threats, namely migration and species death. Magnetic measurements of sediments in volcanic rivers have also attracted attention because the sediment contains a high abundance of magnetic minerals. The method in this paper provides a low-cost, rapid, and nondestructive approach to environmental monitorings and assessments. However, the validity of magnetic measurements has not been investigated for their use in identifying the ETM zone in estuaries in volcanic regions. Therefore, this research aims to identify ETM zones in the estuaries of volcanic regions using magnetic properties to correlate the characteristics to microplastic abundance within suspended and surface sediments. The measurements consist of magnetic susceptibility at low frequency, magnetic susceptibility at high frequency, frequency-dependent magnetic susceptibility analyses, and acquisition of a hysteresis curve. Magnetic minerals were also identified using X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the values of magnetic susceptibility at low frequency significantly correlate with total dissolved solids and microplastics abundance in sediments. The frequency-dependent magnetic susceptibility values were significantly correlated with total dissolved solids, microplastics abundance, turbidity, and microorganism cells. This phenomenon indicates that the magnetic properties of suspended sediments can be used to identify an ETM zone in estuaries in tropical volcanic regions.

Holocene synchronous evolution of precipitation and soil moisture as evidenced by paleosol deposits in the Ili Basin, Central Asia

Assessing the impact of precipitation and temperature on soil moisture changes during the Holocene is essential to understanding the regional ecological environment change in the arid Central Asia core (CAC). However, this assessment is challenging due to the lack of reliable precipitation records. Here, we present Holocene paired precipitation and soil moisture records from the same paleosol deposits with well-constrained optically stimulated luminescence chronology in the Ili Basin, CAC. We selected dolomite content and the δ13C of organic matter to reflect precipitation change, and redness, frequency-dependent magnetic susceptibility, and total organic content to reflect soil moisture changes. The results show that precipitation and soil moisture records exhibit internal consistency, suggesting a synchronous evolution in both during the Holocene. We deduced that precipitation dominated Holocene soil moisture variations in the CAC. The increasing precipitation during the Holocene in the CAC may be attributed to the southward migration of the midlatitude westerlies and increasing penetration of water vapor from the Asian monsoon region.

Assessment of the impacts of land-use change and slope position on soil loss by magnetic susceptibility-based models

Soil loss is a global environmental problem resulting from the erosion process caused by many factors, including land use and slope position. Estimation of total soil loss from agricultural fields is useful for understanding the consequences of historical and current erosion. The main purposes of the current study are to explore the application of magnetic measurements in the mapping and measuring soil redistribution in cultivated (MZ13) and forested (MZ17) transects in a Moroccan subcatchment, to develop a methodological approach correlating magnetic susceptibility (MS, denoted χ) variation to soil erosion/aggradation, and to discriminate the effects of land-use change and slope position on the total cumulative soil loss, assessed using three recently established erosion models based on an MS parameter. MS measurements were done on several soil cores collected at different slope positions including the summit (SU), shoulder (SH), back slope (BS), foot slope (FS), toe slope (TS) for Transects MZ13 and MZ17. A tillage homogenization (T-H) model, simple correlation model (SCM), and simple proportional model (SPM) based on χlf (where lf indicates low frequency) were applied to estimate soil loss for each slope position in the two transects. The results show that the correlation between χlf and χfd (which is the frequency-dependent magnetic susceptibility percentage) is positive and high for the two transects (R2 = 0.95; p < 0.01). The results confirm that the χlf enhancement of soils selected in calcareous parent material is related to the pedogenic processes with the formation of superparamagnetic particles distributed along the slope positions. The current study proves that it is possible to trace and monitor soil erosion and deposition using magnetic parameters (χlf and χfd%) for different slope positions along cultivated and forested transects. The results confirm that the soil losses strongly depend on land use and slope position. Higher erosion depth (d) estimated using the three erosion models are comparable and were about d(T-H, BS17L) = −154.9 cm, d(SCM, BS17L) = −142.3 cm, and d(SPM, BS17L) = −143.6 cm for MZ17 Transect, and about d(T-H, FS13M) = −156.3 cm, d(SCM, TS13L) = −143.8 cm, d(SPM, FS13M) = −145.9 cm for MZ13 Transect. The applied models indicate that the strong losses take place in the upper and lower slopes of the cultivated transect, and in the middle and lower slopes of the forested transect.

Magnetic signatures of a creosote oil contaminated site: case study in São Paulo, Brazil

Soils and groundwater contamination modifies the physical–chemical conditions of the environment, altering natural biogeochemical processes of the ground. As a result, several mineral transformations occur, in which iron plays a decisive role. The presence of iron enables the study of magnetic properties, improving the understanding of the geophysical signatures of highly dynamic environments (e.g., biogeochemical hotspots and contamination plumes). In this work, we seek to identify creosote biodegradation related to the precipitation of magnetic minerals on sediments at a contaminated site in São Paulo, Brazil. Several rock magnetism analyses were carried out to provide the magnetic mineralogy of the samples in terms of their composition, size, and abundance. We conducted high-temperature thermomagnetic curves, frequency-dependent magnetic susceptibility, anesthetic remanent magnetization (ARM) and isothermal remanent magnetization (IRM) data, superparamagnetic concentration and dipole moment (SPCDM), and scanning electron microscopy (SEM) analyses. The magnetic signatures of the contaminated samples suggest an increase of superparamagnetic grains in the water table fluctuation zone if compared to the magnetic signatures of the uncontaminated samples. Thermomagnetic curves of contaminated samples showed a lower heterogeneity of the magnetic mineral phases than the uncontaminated ones. This work contributes to the advancement of the understanding of how natural biogeochemical processes are impacted by human actions, such as soil contamination, and even by climate change, which should affect soil redox conditions in periods of drought and flooding.

Assessing magnetic properties of biomonitors and road dust as a screening method for air pollution monitoring

Particulate matter (PM) pollution is one of the world's most serious environmental challenges. Among PM components, atmospheric heavy metals (HMs) are considered one of the main pollutants responsible for causing significant negative impacts on human health, and ecological quality. This study aimed to assess environmental magnetism as a simple and rapid method that can be used to evaluate heavy metal contamination in urban areas from the relationships between magnetic properties and heavy metal concentrations. For this purpose, road dust and leaf samples of two common evergreen species (Cupressus lusitanica/Casuarina equisetifolia) were sampled simultaneously for 2 years at sites with different levels of traffic pollution. The results found significant statistical correlations between the magnetic properties and the chemical substances of the plants studied, as Fe, Cr and V showed an r ≥ 0.9 and Cr and Zn r ≥ 0.7 with χlf in C. equisetifolia. The frequency-dependent magnetic susceptibility was found to be between 0% and 14% for plants, and 0% and 2% for road dust, suggesting a rather dissimilar particle size distribution for plants, and a less important contribution from the more hazardous ultrafine superparamagnetic magnetite for both. Confirming that magnetic analyses can be used to distinguish different degrees of urban air pollution.

The magnetic susceptibility of Pleistocene paleosols as a martian paleoenvironment analog

This work aims to introduce and test various semiquantitative field methods and environmental magnetic measurements to help prepare future planetary missions on Mars. For analog observations, paleosols of loess successions in various stages of soil development were investigated and were used as models to infer environmental change during environmental change on early Mars. Methods commonly used in terrestrial soils and sediment environments, such as soil development indices and low field and frequency-dependent magnetic susceptibility, are introduced and evaluated as potential proxies to constrain paleoenvironmental conditions and climate change on Mars billions of years ago. These methods include the following: 1) low field magnetic susceptibility, which may aid in the identification of weathered horizons (e.g., palaeosols) and provide insight into the degree of weathering intensity; 2) frequency-dependent magnetic susceptibility can constrain nanoscale magnetic contributions, including some with possible biogenic/bacterial origin, but its applicability to indicate the degree of pedogenesis is limited; and 3) the vertical distribution of low field magnetic susceptibility, i.e., the pattern of magnetic susceptibility curves, seems to work well in the indication of the balance between the sedimentary and pedogenic environment. Analysis of magnetic susceptibility curves may contribute to the identification of Martian paleosols, the characterization of the transition period between the soil-forming and subsequent sedimentary periods (Noachian-Hesperian and Hesperian-Amazonian transitions) and the identification of climate cycles; thus, these may be used as a frame of reference for evaluating paleoclimatic changes on Mars to e.g., the Noachian warm Mars and”Snowball Mars” periods.The results also suggest that the time dependence of the magnetic enhancement of paleosols seems to be nonlinear compared to the length of the pedogenic period itself, and magnetic susceptibility may work as a relative chronometric parameter, which can help to constrain the duration of pedogenic alteration and soil formation on Mars.

Nonlinear contributions to the dynamic magnetic susceptibility of magnetic fluids

• Higher order harmonic susceptibilities of magnetic fluids are obtained theoretically. • Mean spherical approximation is used with field strength expansion of magnetization. • Theoretical prediction is compared to the Langevin and Debye-Weiss limiting cases. • Field amplitude and frequency range of validity of the expanded MSA model is mapped. Based on our earlier analytical results for the magnetization of magnetic fluids with respect to the magnetic field strength, we propose an expansion method within the framework of mean spherical approximation (MSA) to obtain the coefficients of different nonlinear terms. Through a Fourier expansion of the frequency-dependent magnetic susceptibility the harmonic coefficients corresponding to the linear and nonlinear dynamic susceptibilities are calculated from the field expansion of magnetization. The frequency dependence of the higher order susceptibilities is determined on the basis of the Debye relaxation of magnetic dipoles. Our MSA based results are in line with the corresponding limiting case of the Debye-Weiss theory. We mapped the range of applicability of the expansion method concerning the field strength and frequencies. Our results show that under weak fields a 7th order expansion is sufficient to predict the magnitudes of the susceptibility components up to the 4th harmonic relevant for magnetic fluids.