Magnetic Concentration Parameters Research Articles

The use of environmental magnetic properties, elemental analysis and geostatistical tools for soil pollution assessment, a lesson from Takum, Nigeria

The study is aimed at investigating the pollution status of Takum town, Nigeria using environmental magnetism, geochemistry and geostatistics. A total of 79 topsoil (0–10 cm) samples were collected and used for the measurement of various environmental magnetic parameters and some heavy metals (Ti, Cr, Mn, Fe, Ni, Cu, Zn, Hg and Pb). Magnetic susceptibility (χ), saturation and anhysteric remanent magnetizations were highly variable having values that ranged from 32.11 to 1118.57 × 10−8 m3kg−1, 95.03–1206.59 × 10−8 m3kg−1 and 199.87–16002 × 10−5 Am2kg−1 respectively. These values reflect top soil enhancement due to the dominance of secondary ferrimagnetic minerals which is revealed by thermomagnetic runs to be mainly magnetite. The frequency dependent susceptibility χfd% had an average value of 10.63% implying that the samples are dominated by pedogenic superparamagnetic grains. However, the presence of multi-domains grains from vehicular sources are also evident. The mean concentration of the measured heavy metals decreased in the order: Fe > Ti > Mn > Zn > Pb > Cu > Ni > Hg. Based on various indices, Hg and Pb have been identified as the elements constituting the greatest risk to the area. Significant positive correlations (r = 0.402, P < 0.01 – r = 0.751, P < 0.001) were obtained between magnetic concentration parameters and Cr, Fe, Zn, Pb and Pollution Load Index, supporting the use of environmental magnetic properties for quick assessment and monitoring of pollution levels in the Takum soils. The sources of heavy metal pollution have been identified to originate from vehicular, agricultural, pedogenic and weathering activities. Different degrees of significant correlation were obtained between magnetic parameters, heavy metals and particle size classes, indicating the possibility of using magnetic techniques as proxy for textural parameters.

Magnetic Mineralogy of Speleothems From Tropical-Subtropical Sites of South America

Fe-bearing minerals are a tiny fraction of the composition of speleothems. They have their origin in the karst system or are transported from the drainage basin into the cave. Recent studies on the magnetism of speleothems focused on the variations of their magnetic mineralogy in specific time intervals and are usually limited to a single sample. In this study, we describe a database of environmental magnetism parameters built from 22 stalagmites from different caves located in Brazil (South America) at different latitudes, comprising different climates and biomes. The magnetic signal observed in these stalagmites is dominated by low-coercivity minerals (∼20 mT) whose magnetic properties resemble those of the magnetite formed in pedogenic environments. Also, a comparison with few samples from soils and the carbonate from cave’s walls shows a good agreement of the magnetic properties of speleothems with those of soil samples, reinforcing previous suggestions that in (sub-)tropical regimes, the dominant magnetic phase in speleothems is associated with the soil above the cave. Spearman’s rank correlation points to a positive strong correlation between magnetic concentration parameters (mass-normalized magnetic susceptibility, natural remanent magnetization, anhysteretic remanent magnetization, and isothermal remanent magnetization). This implies that ultrafine ferrimagnetic minerals are the dominant phase in these (sub-)tropical karst systems, which extend across a diverse range of biomes. Although the samples are concentrated in the savannah biome (Cerrado) (∼70%), comparison with other biomes shows a higher concentration of magnetic minerals in speleothem underlying savannahs and lower concentration in those underlying moist broadleaf forests (Atlantic and Amazon biome) and dry forests (Caatinga). Thus, rainfall, biome, and epikarst dynamics play an important role in the concentration of magnetic minerals in speleothems in (sub-)tropical sites and indicate they can be an important target for paleoenvironmental research in cave systems.

A Pedogenic Model for the Magnetic Enhancement of Late Miocene Fluvial‐Lacustrine Sediments From the Xining Basin, NE Tibetan Plateau

AbstractContinuous sequences of Cenozoic fluvial‐lacustrine sediments are well preserved in the northeastern edge of the Tibetan Plateau (TP), and they provide a good opportunity to improve our understanding of the tectonic uplift and paleoenvironmental evolution of the NE TP. To date, however, the factors controlling the variations in the magnetic properties of these fluvial‐lacustrine sediments remain complex and ambiguous. Here we systematically assess the contribution of pedogenesis to the magnetic enhancement of late Miocene fluvial‐lacustrine sediments in the Xining Basin, using a combination of rock magnetic, diffuse reflectance spectroscopy, and geochemical methods. Our results demonstrate that the magnetic concentration parameters show a long‐term increasing trend since the late Miocene, with two dramatic increases at ~11 and 9 Ma. Based on the examination of several factors that may affect the magnetic properties of fluvial‐lacustrine sediments in the NE TP, we argue that an accelerated drying process in waterlogged environments, induced by late Miocene global cooling or/and tectonic uplift, may have caused the changes from anaerobic to aerobic conditions and resulted in the observed stepwise increases in pedogenic intensity. The two dramatic increases in magnetic parameters are closely related to intensified aridification and tectonic activity in the NE TP at ~11 and 9 Ma, respectively. These observations suggest that the pedogenic magnetic enhancement model, caused by the disappearance of a waterlogged and reducing pedogenic environment since the late Miocene, should be reconsidered as a possible factor explaining the magnetic properties of fluvial‐lacustrine sediments in the NE TP.

Source apportionment of soil-contamination in Baotou City (North China) based on a combined magnetic and geochemical approach

We studied the magnetic properties and trace element concentrations (Cr, Cu, Fe, Mn, Pb, Ti, V, Zn) of urban topsoils from 111 urban sites in a large REE-Nb-Fe mining and smelting city, Baotou, Inner Mongolia, China. The results show that pseudo-single domain and multi-domain magnetite dominates the magnetic properties of the soil samples, and the magnetic concentration parameters show a large positive anomaly near the Baotou iron and steel works. The average contents of all trace metals exceeded their background level in soils in Inner Mongolia, except for Pb. The spatial distribution and correlation analysis show that magnetic parameters related to the magnetite concentration and Cr, Fe, Mn, Ti, V and Zn show similar trends of variation. In addition, the results of PCA show that Fe, Ti, and V are highly correlated with the magnetic particles derived from the Baotou iron and steel works, tailing dam, chromium plant, and cement plant. In contrast, Cr, Mn, Pb and Zn are derived from both the steel plant and traffic pollution. Using a PMF model, three potential pollution sources are identified: industrial pollution, including the steel works, tailing dam, cement plant and chromium plant, are reflected by χlf, χARM, SIRM and SOFT, and they account for 71.2%; traffic pollution is reflected by Pb and Zn and accounts for 9.0%; and natural sources, reflected by χfd%, χARM/χ, χARM/SIRM, HARD%, S−300, S−100 and Ti, contribute 19.8%. The results are potentially useful for developing control measures for reducing trace metal contamination in soils in Baotou city, and in addition we conclude that a combined magnetic approach and geochemical approach is an effective means for qualitative and quantitative sources apportionment of urban surface soil pollution.

Magnetic Response of Heavy Metal Pollution in Playground Dust of an Industrial Area

The use of mineral magnetic measurements as a potential pollution proxy is explored as an alternative means of monitoring heavy metal pollution in playground dust in industrial areas. Dust samples were collected from playgrounds in an industrial area in Nanjing. The magnetic properties of the samples were analyzed, and the total and acid-extractable concentrations of heavy metals were measured.Mineral magnetic concentration parameters[mean magnetic susceptibility (χlf) 939.31×10-8 m3·kg-1 and saturation isothermal remanent magnetization (SIRM) 16618.74×10-5 A·m2·kg-1] indicate that the dust samples contain high concentrations of magnetic minerals when compared to the non-industrial zone of the city. High and stable S-ratio values (mean 0.97, standard deviation 0.01) indicate the prominence of ferromagnetic minerals. Low values of anhysteretic remanent magnetization (χARM)/χlf(2.35) and χARM/SIRM (0.12×10-3 m·A-1) indicate predominantly coarse pseudo single domain (PSD) and multi-domain (MD) magnetic grain size assemblages. The playground dust is considered moderately to highly polluted, and the enrichment factor values for Cd, Zn, Cu, and Pb indicate extremely high contamination levels in the playground dust. Mineral magnetic parameters[χlf, SIRM, hard isothermal remanent magnetization (HIRM), χARM, and χARM/SIRM] reveal significant correlations with total and acid-extractable concentrations of the trace metals, and the correlations with total concentrations are stronger. The most significant correlations were found with mineral magnetic concentrations (χARM and SIRM) and total concentrations of the elements Mn, Ni, and Cr and the Tomlinson pollution load index (PLI) (0.69 ≤ r ≤ 0.86, P<0.01). Consistent spatial characteristics between them were also found, showing that the total concentrations of heavy metals and magnetic parameter values are higher in the playgrounds near and downwind of the power plant. Results of a principal component analysis indicate that anthropogenic activities (mainly from coal consumption by power plants) are the main sources for both heavy metals and magnetic minerals. In summary, significant correlations and consistent spatial characteristics between heavy metal contents and magnetic parameters and the same anthropogenic source for heavy metals and magnetic minerals confirm that magnetic parameters could be considered as efficient indicators for heavy metal contamination in the playground dust in industrial areas.

Offshore sediments record the history of onshore iron ore mining in Goa State, India

Environmental magnetic and geochemical analyses combined with 210Pb dating were carried out on a sediment core off Goa from Arabian Sea to reconstruct the sedimentation history of last three and a half centuries and to investigate the impact of onshore iron ore mining on the offshore sedimentation. A drastic increase in sedimentation rate and mineral magnetic concentration parameters divides the core into two units (1 & 2) at a depth of 41cm (1982CE). The high magnetic susceptibility values in Unit 1 sediments are coeval with increased iron ore production on land and illustrate the role of terrestrial mining on the increased offshore sedimentation. The early diagenetic signals were observed in Unit 2 of the core with low concentration parameters, coarse magnetic grain size and magnetically hard mineralogy. The geochemical data of the core also record the Little Ice Age (LIA) climatic events of Dalton and Maunder solar minima.

Investigation of the pollution in the street dust at Xuzhou, China, using magnetic, micro-morphological and Mössbauer spectra analyses

This study reports a detailed examination of the magnetic mineralogy of street dust samples collected in Xuzhou, a heavily industrial city in China. Several different approaches have been utilized in the characterization, from standard mineral magnetic techniques such as magnetic hysteresis and microscopy to non-standard techniques such as Mossbauer spectroscopy. Magnetic properties and the concentrations of four metals including Cu, Zn, Ba and Pb were reported for each sample. The primary magnetic mineral was found to be multidomain magnetite-like material. Scanning electron microscope analyses of street dust revealed: spherule-shaped iron oxides and angular particles with complex chemical composition. The concentrations of Cu, Zn, Pb and Ba were 3, 4.8, 2.8 and 1.3 times higher, respectively, than the soil background values of this study area. Both Cu and Ba showed significant correlations with the magnetic concentration parameters χARM (susceptibility of anhysteretic remanent magnetization) and saturation isothermal remanent magnetization. The combination of the various methods offers a powerful analytical technique in the study of magnetic properties of street dust.

Heavy metal monitoring of beach sands through environmental magnetism technique: a case study from Vengurla and Aravali beaches of Sindhudurg district, Maharashtra, India

Mineral magnetic, geochemical and statistical analyses were carried on surface sediments collected from Vengurla and Aravali beach, along west coast of India, premonsoon (PreM), monsoon(M) and postmonsoon (PM). Magnetic concentration parameters (χlf, ARM, SIRM and HIRM) are strongly correlated within them PreM during M and PM. Thermomagnetic analysis identifies titanomagnetite, magnetite, maghemite and hematite as the dominant magnetic mineralogy of the sediments. Strong correlation was deciphered between magnetic parameters and heavy metal (Cu, Cr, Zn and Ni) PreM and PM which obliterated in M. This shows influx of magnetic minerals and heavy metals is more in M than PreM and PM. The monsoonal influx is more haphazard and random in M because of enhanced weathering resulting in weak correlation between different mineralogical and geochemical entities. This finding outlines the efficacy of simple, rapid and non-destructive magnetic measurement which can be used as an indicator for heavy metal contamination. It can act as a proxy for measuring of heavy metal content in the coastal and beach environment.

Detecting the sensitivity of magnetic response on different pollution sources – A case study from typical mining cities in northwestern China

Rapid monitoring and discriminating different anthropogenic pollution is a key scientific issue. To detect the applicability and sensitivity of magnetic measurements for evaluating different industrial pollution in urban environment, characteristics of topsoil from three typical fast developing industrial cities (Jinchang, Baiyin and Jiayuguan in Gansu province, northwestern China) were studied by magnetic and geochemical analyses. The results showed that magnetic susceptibility was enhanced near industrial areas, and PSD-MD magnetite dominated the magnetic properties. Magnetic concentration parameters (χlf, SIRM, and χARM) showed different correlations with heavy metals and PLI in the three cities, indicating significantly different magnetic response to different pollution sources. Principal component analysis showed that ferrimagnetic minerals coexist with heavy metals of Fe, As, Cu, Pb, and Zn in Baiyin and Fe, V, Cu, Mn, Pb, and Cr in Jiayuguan. Fuzzy cluster analysis and regression analysis further indicated that the sensitivity of magnetic monitoring to fuel dust is higher than that to mineral dust near non-ferrous metal smelters, and fossil fuel consumption is an important factor for increasing magnetite content. In all the three cities, the sensitivity of magnetic monitoring to pollutants from steel plants is much higher than that from non-ferrous metal plants. Therefore, magnetic proxies provide a rapid means for detecting heavy metal contamination caused by multi-anthropogenic pollution sources in a large scale area, however, the sensitivity was controlled by pollution sources.

Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

A high-resolution rock magnetic study was carried out in Integrated Ocean Drilling Program (IODP) Expedition 316 Hole C0008A located in the Megasplay Fault Zone of the Nankai Trough, SW offshore Japan, in order to document changes in magnetic properties throughout gas hydrate-bearing horizons. A total of 169 Pleistocene discrete samples were collected from ~110 to 153 m core depth below sea floor (CSF), and their magnetic minerals concentration, grain size, composition, and rock magnetic parameters were estimated. Results showed the presence of iron oxides ((titano)-magnetite), iron sulfides (greigite and pyrrhotite), and their mixture, among which single-domain greigite is the most major magnetic mineral present in the samples. Two horizons containing ferrimagnetic iron sulfides (114.5–127.5 and 129.5–150 m CSF) covering almost the entire studied interval were identified, both associated with slight local pore water anomalies, suggesting occurrence of gas hydrates and anoxic conditions. These results are different from the neighboring Hole C0008C (215 m away from Hole C0008A) where four pore water anomalies and six iron sulfide-rich intervals were identified for the same time slice. Comparison of the lithology, physical properties, and geochemical data of the two boreholes at Site C0008 suggests that a combination of processes (e.g., availability of reactive iron, microbial activity) is responsible for such laterally varying distribution of the ferrimagnetic iron sulfides.

Atmospheric pollution history at Linfen (China) uncovered by magnetic and chemical parameters of sediments from a water reservoir

We studied magnetic and chemical parameters of sediments from sediments of a water reservoir at Linfen (China) in order to quantitatively reconstruct the atmospheric pollution history in this region. The results show that the main magnetic phases are magnetite and maghemite originating from the surrounding catchment and from anthropogenic activities, and there is a significant positive relationship between magnetic concentration parameters and heavy metals concentrations, indicating that magnetic proxies can be used to monitor the anthropogenic pollution. In order to uncover the atmospheric pollution history, we combined the known events of environmental improvement with variations of magnetic susceptibility (χ) and heavy metals along the cores to obtain a detailed chronological framework. In addition, air comprehensive pollution index (ACPI) was reconstructed from regression equation among magnetic and chemical parameters as well as atmospheric monitoring data. Based on these results, the atmospheric pollution history was successfully reconstructed.

An Eocene–Miocene continuous rock magnetic record from the sediments in the Xining Basin, NW China: indication for Cenozoic persistent drying driven by global cooling and Tibetan Plateau uplift

Tibetan Plateau uplift and global cooling have generally been thought to have caused the drying of the Asian inland, but how and when these factors drove the aridification is unknown. The Xining Basin at the NE Tibetan Plateau received continuous Eocene-Miocene fine-grained sediments, providing an excellent opportunity to address this question. Here we present detailed rock magnetic and diffuse reflectance spectroscopy (DRS) analyses for a well-dated Cenozoic sedimentary record from the Xiejia section in the basin. Magnetic susceptibility (chi), saturation magnetization (Ms) and saturation isothermal remanent magnetization (SIRM) in this section show a long-term decreasing trend from similar to 52 to similar to 25 Ma, well coinciding with global cooling and drying in the region, and an increasing trend since similar to 25 Ma, which is in contrast to the further progressing aridification of the basin. Thermomagnetic results and DRS-determined hematite contents suggest that the relative content of magnetite and hematite is the main control on the chi, Ms and SIRM values. We argue that the long-term Eocene-Oligocene global cooling increased the drying of the Asian inland, lowering the lake level and exposing a larger area to low temperature oxidation for longer times, thus producing more hematite and leading to the decreasing trend of magnetic concentration parameters from similar to 52 to similar to 25 Ma. An intensive uplift of the NE Tibetan Plateau since similar to 25 Ma, associated with a change in the sedimentary source, might be responsible for the increase of chi, Ms and SIRM after 25 Ma.

Heavy metals in Xuzhou urban roadside topsoils (China): magnetic characterization and enrichment mechanism

Heavy metal contamination is prevalent in urban areas where soil represents a significant sink. Urban topsoil samples were collected and metal concentrations including Pb, Zn, Cu, Cd, Ni and Co were measured by inductively coupled plasma mass spectrometry. All analyzed metals showed elevated concentrations compared to local background concentrations with the exception of Co. Cadmium was the metal most enriched in the analyzed area, presenting enrichment factor, on average, of 16.5. Mineral magnetic concentration parameters (χlf and SIRM) exhibited significant relationships with Pb, Zn, Cu and Cd, respectively. Zinc, Co and Ni exhibited a substantial build-up in the finest particles (<28 μm). Enrichment was positively correlated with carbonate complexation constants (but not bulk solubility products) and suggests that the dominant mechanism controlling metal enrichment in these samples is a precipitation of carbonate surfaces that subsequently adsorb metals.

A dynamic approach to urban road deposited sediment pollution monitoring (Marylebone Road, London, UK)

The use of mineral magnetic measurements (χLF, χARM and SIRM) as a potential pollution proxy using road deposited sediment (RDS) is explored as an alternative means of monitoring pollution on a busy city road. Comparison of sediment-related analytical data by correlation analysis between mineral magnetic, particle size and geochemical properties is reported. Mineral magnetic concentration parameters (χLF, χARM and SIRM) reveal significant (p < 0.001; n = 61) associations with PM1.0, PM2.5 and PM10. Significant associations were also found with mineral magnetic concentrations (χLF and SIRM) and specific concentrations of the elements Fe, Ni, Cu, Zn and Mn (p < 0.001; n = 61). Inter-geochemical correlation analysis found strong associations (p < 0.001; n = 61) between Fe, Ni, Cu, Zn and Mn and suggest anthropogenic enrichment influences. Low χFD% measurements imply an influence of multi-domain mineralogy, indicative of anthropogenic combustion processes. SEM micrographs also support this, as all samples contain Fe spherules indicative of vehicular combustion processes. This study advocates rapid and simple initial assessment of urban pollution episodes using mineral magnetic measurements as a dynamic explorative technology.

Potential linkages between mineral magnetic measurements and urban roadside soil pollution (part 2)

Use of mineral magnetic concentration parameters (χLF, χARM and SIRM) as a potential pollution proxy for soil samples collected from Wolverhampton (UK) is explored. Comparison of soil-related analytical data by correlation analyses between each magnetic parameter and individual geochemical classes (i.e. Fe, Pb, Ni, Zn, Cd), are reported. χLF, χARM and SIRM parameters reveal significant (p < 0.001 n = 60), strong (r = 0.632-0.797), associations with Fe, Cu, Zn and Pb. Inter-geochemical correlations suggest anthropogenic influences, which is supported by low χFD% measurements that infer an influence of multi-domain mineralogy are indicative of anthropogenic combustion processes. Results indicate mineral magnetic measurements could potentially be used as a geochemical indicator for soils in certain environments and/or specific settings that are appropriate for monitoring techniques. The mineral magnetic technique offers a simple, reliable, rapid, sensitive, inexpensive and non-destructive approach that could be a valuable pollution proxy for soil contamination studies.

Mineral magnetic measurements as a particle size proxy for urban roadside soil pollution (part 1)

The use of mineral magnetic concentration parameters (χLF, χARM and SIRM) as a potential particle size proxy for soil samples collected from Wolverhampton (UK) is explored as an alternative means of normalizing particle size effects. Comparison of soil-related analytical data by correlation analyses between each magnetic parameter and individual particle size classes (i.e. sand, silt and clay), more discrete intervals within classes (e.g. fine sand or medium silt) and cumulative size fractions (e.g. clay + fine silt) are reported. χLF, χARM and SIRM parameters reveal significant (p < 0.05; p < 0.001 n = 60), moderate negative (rs = -0.3 to -0.557) associations with clay, silt and sand content. Contrary to earlier research findings which found positive relationships, this indicates that magnetic measurements cannot always provide a predictable particle size proxy and it is only certain environments and/or specific settings that are appropriate for granulometric normalization by this technique. However, if future researchers working in other soil settings can identify a formal predictable relationship, the technique is known to offer a simple, reliable, rapid, sensitive, inexpensive and non-destructive approach that could be a valuable proxy for normalizing particle size effects in soil contamination studies.

Oligocene–Miocene relative (geomagnetic) paleointensity correlated from the equatorial Pacific (IODP Site U1334 and ODP Site 1218) to the South Atlantic (ODP Site 1090)

Late Oligocene to Early Miocene relative paleointensity (RPI) proxies can be correlated from the equatorial Pacific (IODP Site U1334 and ODP Site 1218) to the South Atlantic (ODP Site 1090). Age models are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale. The RPI records do not contain significant power at specific (orbital) frequencies, and hence there is no significant coherency between RPI proxies and the normalizers used to construct the proxies, although orbital power is present in some normalizers. There is no obvious control on RPI proxies from mean sedimentation rate within polarity chrons, magnetic grain size proxies or magnetic concentration parameters. The salient test is whether the equatorial Pacific records can be correlated one to another, and to the records from the South Atlantic. All records are dominated by RPI minima at polarity reversals, as expected, although the comparison within polarity chrons is compelling enough to conclude that the intensity of the Earthʼs axial dipole is being recorded. This is supported by the fit of RPI data from Sites U1334 and 1218 after correlation of the two sites using diverse core-scanning data, rather than polarity reversals alone. We do not see a consistent relationship between polarity-chron duration and mean RPI, and no consistent skewness (“saw-tooth” pattern) for RPI within polarity chrons. Stacks of RPI records for 17.5–26.5 Ma include long-term changes in RPI on Myr timescales that are superimposed on RPI minima associated with polarity reversals, and shorter-term variations in RPI with an apparent pacing of ∼50 kyr. The equatorial Pacific to South Atlantic correlations indicate that RPI can be used as a (global) stratigraphic tool in pre-Quaternary sediments with typical pelagic sedimentation rates of a few cm/kyr.

Magnetic properties and heavy metal pollution of soils in the vicinity of a cement plant, Xuzhou (China)

Abstract This study characterized the magnetic property and levels of heavy metals of the topsoils near a cement plant. The concentrations of five selected heavy metals (Pb, Cu, Zn and Cd) were measured on 32 topsoil samples (0–20 cm) collected near a cement plant via inductively coupled plasma/mass spectroscopy (ICP-MS). The orders of enrichment factors (EF), on average, were Cd (7.3) > Cu (3) > Zn (2.9) > Pb (2.1), respectively. A self-organizing map (SOM) was applied to the concentrations of heavy metals for “correlation hunting”. Mineral magnetic concentration parameters, such as the specific magnetic susceptibility (χ), susceptibility of anhysteretic remanent magnetization (χ ARM ), saturation isothermal remanent magnetization (SIRM), together with interparametric ratios (such as IRM − 100mT /SIRM, SIRM/χ, χ ARM /SIRM) show that ferrimagnetic, superparamagnetic (SP) and multi-domain (MD) minerals dominated the soils. The results of correlation analysis indicate that copper showed a significant correlation with χ, χ ARM and SIRM but such a relationship with χ, χ ARM and SIRM was only weakly identified for Zn, Cd and Pb.

Environmental magnetic studies on surface sediments: a proxy for metal and hydrocarbon contamination

Visakhapatnam is one of the major port cities, and it is developed into a hub of many large- and medium-scale industries. Due to growing industrialization and urbanization, coast is vulnerable to both organic and inorganic micro-pollutants. Twenty-five surface sediments were collected along the Visakhapatnam coast for the measurement of texture size, petroleum hydrocarbons, trace metals and environmental magnetic parameters. The percentage of coarser particles was more in the northern region, whereas the percentage of fine particles was increased toward south. Elevated levels of petroleum hydrocarbons and trace metals were attributed due to marine and land-based sources, in particular, those were due to shipping activities, treated and partially treated sewage and industrial wastes. The concentrations of trace metals, petroleum hydrocarbons and magnetic minerals were decreased from nearshore to seaward. Our results revealed that the magnetic mineralogy is dominated by magnetite with a small proportion of hematite, and the grain size of magnetic minerals was in the range of pseudo-single domain to multidomain nature with detrital origin. From the principal component analysis, the magnetic concentration and mineralogy-dependent parameters co-vary with the heavy metal and PHC concentrations, suggesting that the inputs of magnetic minerals, petroleum hydrocarbons and heavy metals in the Visakhapatnam shelf sediments were derived from the same anthropogenic sources. Thus, the large magnetic dataset can be used to reduce the number of chemical analysis; hence, environmental magnetic parameters were used as a proxy for both organic and inorganic micro-pollutants.

Magnetic properties of river sediments and their relationship with heavy metals and organic matter in the urban area in Lanzhou, China

As the largest industrial city locating in the Northwestern China, Lanzhou has become one of the most seriously polluted cities in the world. In this study, investigations were performed on the magnetic properties, heavy metals and organic matter contents of a total of 23 sediment samples collected from eight selected rivers in the Lanzhou urban area. The results of the study indicate that the magnetic properties of the sediment samples are predominated by low-coercivity magnetite. The river sediments are classified into three types, i.e., downstream polluted, upstream polluted, and less affected, based on the contribution from anthropogenic activities in different segments of the river as indicated by the variation of magnetic mineral concentration parameters. Moreover, a strong linear positive correlation exists among some of the magnetic parameters and organic matter content, heavy metals (Cr, Ni, Pb, Zn, Fe) and total enrichment factor (R) of the bulk deposit samples, which indicates that environmental magnetic technology may be an effective method for distinguishing source apportionment and monitoring river sediment pollution in urban areas.