Geochemistry Of Heavy Metals Research Articles

Geochemical Modeling and Quality Assessment of the Surface Waters from the Mouhoun River System, Burkina Faso: Implications of Water–Rock Interactions and Anthropogenic Activities

Major ion and heavy metal geochemistry was used to investigate the factors that control the Mouhoun River water quality in western Burkina Faso. Major cation concentrations was in the following decreasing order: Ca2+> Na+> K+> Mg2+, reflecting silicate weathering. However, relatively high HCO3- and SO42- concentrations could be related to dissolution of calcite and sulfide minerals, respectively. The average heavy metal concentrations in the riverine system were in the following order: FeT>Ag>Mn>Zn>Pb>Cu>Ni>AsT>Cr>Hg>Co>Cd with FeT and Ag exceeding the World Health Organization permissible limits. Concentrations of all heavy metals, except Cr, were higher in the Mouhoun system compared to the average world river concentrations. Adsorption and speciation models showed that Zn, Ag, Cd, Co, Cr and Ni are likely to remain in their free ionic forms, and thus posing serious threats to aquatic life and human health. Ag-Hg-Ni-Cd association around Poura and Tenado on the principal component plot suggested that the widespread artisanal gold mining in these areas may have contributed to these metals’ loading. In contrast, NH4+, Pb, Cu, Cr, AsT and Zn were clustered around a densely populated and industrialized Kou watershed, pointing to agricultural and industrial sources of these pollutants. Furthermore, the Kou River had the highest metal index followed by Tenado, Samendeni, Poura and Boromo. Hence, the chemistry of the Mouhoun River and its tributary appears to be mainly controlled by population density and various anthropogenic activities taking place in their drainage basins. The findings could provide avenues for sound and sustainable water resource management in a water scarce semi-arid environment.

Heavy metal geochemistry and toxicity assessment of water environment from Ib valley coalfield, India: Implications to contaminant source apportionment and human health risks

The present study aims to investigate the hydrogeochemical evolution of heavy metals and assesses impacts of mining activities on the groundwater resources and potential human health risks in the coal mining areas of Ib valley coalfield. In this perspective, a total of one hundred and two mine water and groundwater samples were collected from different locations. The water samples were analysed for some selected heavy metals i.e. Mn, Cu, Pb, Zn, Ni, Co, As, Se, Al, Sr, Ba, Cd, Cr, V and Fe using ICP-MS. In addition, pH and SO42− concentration were also measured following APHA procedure. The water pH in the Ib valley coalfields ranged from 3.26 to 8.18 for mine water and 5.23 to 8.52 for groundwater, indicating acidic to alkaline nature of water. Mn in mine water and Zn in groundwater environment were observed as the most dominant metals. The water hazard index (WHI) reflects that around 80% of mine water are non-toxic (WHI<5), 5% slightly toxic (5<WHI>10) and 15% extremely toxic (WHI>15). Relatively high pH and low concentration of dissolved metals and SO42− in groundwater as compared to mine water indicate lesser impact of mining activities. The calculated drinking water quality index (DWQI) suggests that Mn, Al, Ni and Fe in mine water and Mn, Fe, Ni and Pb in groundwater were the major objectionable metals which caused the water quality deterioration for drinking uses. Further, the non-carcinogenic health risk assessment for adult male, female and child populations identifies Co, Mn, Ni as the key elements making the water hazardous for human health. Comparatively higher ratio of ingestion rate and body weight in child population might be causing higher health risks in child population as compared to adult male and adult female population.

Urban geochemistry of heavy metals in road dust from Cairo megacity, Egypt: enrichment, sources, contamination, and health risks

Traffic emissions, overpopulation, and poor urban planning have degraded the environmental quality of the Greater Cairo megacity. As road dust is considered the main sink of pollutants in urban environments, thirty road dust samples from six major roads were collected. ICP-OES was used to analyze the samples in order to determine the contamination grade using the pollution indices, decipher metal sources and geochemical associations using multivariate analysis, and evaluate the ecological and human health risks. The average contents of heavy metals were arranged in decreasing order: Fe (1181.12), Zn (201.36), Pb (66.10), Ni (32.42), Cu (26.07), Cr (26.00), Co (14.78), As (2.76), and Hg (0.93) mg/kg. The spatial pattern showed that new urban communities exhibited lower contamination levels compared to unplanned old districts, especially for traffic elements (Pb, Zn, and Cu). The highest Igeo mean value was observed for Hg (3.34) followed by Zn (1.34), Pb (1.24), Ni (0.10), As (− 0.19), Co (− 0.24), Cu (− 0.73), and Cr (− 1.05). Additionally, CF values indicated very high contamination levels for Pb and Zn, whereas the highest PLI value was observed at Ramses Street. All EF values were higher than 1.5, indicating the anthropogenic enrichment of metals. RI values classified Cairo as a region with considerable ecological risk, observing that Hg was the main contributor. Correlation analysis and PCA showed that Pb and Zn originated from vehicle exhaust, Hg, Cu, and As from domestic and industrial activities, and Fe and Co from natural origin. Cr and Ni exhibited potential carcinogenic risks for children through ingestion; conversely, the non-carcinogenic risks were within safe levels. As a result, the use of clean energy is recommended to mitigate the accumulation of heavy metals in road dust and to improve the quality of life.

Clay mineralogy and heavy metal geochemistry of the Tigris River sediments in selected area of northern Iraq

Thirteen samples of sediment were collected from the Tigris River between Hammam Al-Aleel and Fat'ha area, northern Iraq to determine the texture of these sediments, clay mineral assemblages and concentrations of some heavy metals. The grain size analysis of the samples revealed that the silt fraction is the most dominant type in the studied samples, and the size decreases down-stream in accordance with the river's morphology and gradient. The clay fraction was examined by employing XRD to recognize the clay mineral types. It was found that montimorillonite is the most dominant mineral, in addition to illite, palygoriskite, kaolinite and chlorite. The heavy metal elements were determined by Atomic Adsorption Spectrum (AAS) instrument and they included Zinc (Zn), Copper (Cu), Cobalt (Co), Cadmium (Cd) and Lead (Pb) in the clay fraction. However, due to human activities like fertilization of soil and industrial water, such elements as Pb (163 ppm), Zn (121 ppm), Co (33 ppm) were higher than the normal concentration, while the concentration of Cu (42 ppm) was lower than the normal.

Heavy metal content and potential ecological risk assessment of sediments from Khnifiss Lagoon National Park (Morocco)

Coastal lagoons are important but sensitive environments, being transitional zones between land and sea. The Khnifiss lagoon is the most important desert wetland in Morocco, but little data have been produced concerning heavy metal geochemistry and enrichments in the sediments. Therefore, 26 surface sediments (15 intertidal and 11 subtidal) and 2 sediment cores were collected in 2016 and analyzed for a selection of heavy metals. The data were processed to assess the degree of contamination and the corresponding potential ecological risk, using several accumulation/enrichment indices, and the singular and multi-metal risk indices. Mean concentrations in the bottom layers of the two cores, dating from a pre-industrial age according to geochronological analysis, were used as the local geochemical background. The resulting values were on the whole lower than those reported for other areas of the northeastern coast of Morocco. Multivariate statistics were also applied to better understand relationships among variables (metals and other geochemical parameters) and to reveal similarities among sample groups. The results showed that, although the lagoon is not yet affected by significant anthropogenic influences, small enrichments can be recognized, especially for Ni and Cd. The cause may be related to the proximity to the main national highway, the vehicles and machinery used in the saltworks located in the area, and the small harbors used principally for fishing. In addition, industrial emissions from the Atlantic coast of Morocco and adjacent countries can be reasonably attributed as additional contributors to the enrichments. In terms of potential ecological risk, Cd shows the greatest impact compared to the other metals investigated.

Environmental geochemistry of heavy metals in coral reefs and sediments of Chabahar Bay

The amount of heavy metals in coral reefs and sediments and their impact on the marine environment is of great importance. The present study aimed to determine the quantity and quality, distribution, and origin of the elements introduced into the reefs and sediments of Chabahar Bay. In this research, specimens of coral reefs and sediments were collected from six stations in coral regions of Chabahar Bay. Then, standard grain size analysis was performed on the sediment sample. An ICP-MS analysis was done to identify heavy metals. The results indicate that the sediment type of coral regions of Chabahar Bay is gravelly sand, gravelly muddy sand, and muddy gravelly sand. Moreover, sediments have two clastic and biochemical origins, and their formation environment is a carbonate environment consisting of small and single reefs, often coral reefs. On the other hand, the concentrations of cadmium and lead in sediments as well as the concentrations of cadmium and cobalt in the coral reefs of Chabahar Bay are higher than concentrations of them in the earth's crust and global marine sediments. The highest contamination is associated with cadmium and lead, followed by aluminum and nickel (moderate contamination rate) and then, other elements (low contamination rate). Because of a significant/high correlation, the nickel and vanadium elements are the sources of oil pollution. Considering the maximum distribution of heavy metals, the breakwater and basin of Shahid Beheshti Port and the Great Sea are considered as the extremely contaminated places in the coral regions of Chabahar Bay, confirming the organic and human-induced origins of contaminations.

A time-series of heavy metal geochemistry in sediments of Galveston Bay estuary, Texas, 2017-2019

Galveston Bay is an anthropogenic-influenced estuary where industrial runoff, wastewater, and shipping vessel discharges enter the bay alongside natural freshwaters. Here, heavy metal concentrations in Galveston Bay surface sediment (2-year quarterly time-series) and a single sediment core are presented to explore the anthropogenic and geochemical controls on the spatiotemporal distributions, fluxes, sources, and potential toxicity of metals within this estuary. Samples were leached to distinguish authigenic sediment coatings from geogenic crystalline material. Spatial differences dominate the observed concentration variability, with higher metal concentrations in eastern vs. western bay sediments, as the eastern bay is where metals are flocculated from the dissolved phase and/or sediments are hydrodynamically trapped. Temporal variations are a secondary controlling factor, with sediment metal concentrations positively correlated with Trinity River discharge. Core data indicate stable Fe, Pb Ni, Cd and Hg levels during the 20th century but increasing Cu and Zn levels in recent years. Galveston Bay sediments are potentially toxic for As, Cd, Cr, Cu, Ni, Sb, Zn and Hg, based on federal toxicity standards. Enrichment factors and statistical analyses suggest that Ni and Cr originate from natural sources, while anthropogenic sources dominate supply of As, Cd, Hg, Ni, Pb, Sb, and Zn. This unique time-series shows that major flooding events, such as Hurricane Harvey in 2017, affect surface sediment metal distributions in Galveston Bay, but not any more than the natural geochemical controls on spatiotemporal distributions of metals in anthropogenic-influenced estuaries.

Sequential Extraction and Geochemistry of Heavy Metals in Ayetoro Coastal Sediments, Southwestern Nigeria

Previous geochemical investigation of Ayetoro area discovered that its coastal sediments are enriched with sulphide mineralization. However, in order to determine the geochemical phases of the heavy metals in the coastal sediments, random sampling method was utilized across 10 locations, at a depth of 40cm using Van grab sampler at a sampling density of 200m interval. Atomic Absorption Spectrophotometer (AAS) Buck Scientific Model 205A was used to analyze nine (9) heavy metal concentrations namely Ni, Zn, Co, Mn, Fe, Pb, Cr, Cd and Cu in the coastal sediments, followed by sequential extraction of the metals, using five fractional phases. The results revealed that the geochemical concentration of the heavy metals as follows: Ni (5.89ppm - 16.82ppm), Zn (2.59ppm - 115.65ppm.), Co (1.22ppm - 22.77ppm), Mn (30.95ppm - 186.49ppm), Fe (6.632ppm - 1925.96ppm), Pb (5.17ppm - 55.96ppm), Cr (0.26ppm - 28.06ppm), Cd (0.13ppm -22.23ppm), and Cu (2.26ppm - 41.94ppm) and showed the concentration order as Residual&gt;Reducible&gt;Organic&gt;Exchangeable&gt;Carbonate. Most of the heavy metals in carbonate and exchangeable phase have low concentration except for Cd. This implied that Cd is of low mobility and bioavailability which is very dangerous as its intake by man leads to kidney diseases and causes bones to become weaker. Also, Mobility factor of Cd stood out because of its high concentration in the exchangeable phase compared to other four non-residual phases. The mobility and bioavailability of the heavy metals are in this order: Cd&gt;Co&gt;Ni&gt;Pb&gt;Cr&gt;Mn&gt;Cu&gt;Zn&gt;Fe respectively. The analysis of variance (ANOVA) revealed that the heavy metals are significantly different in all the phases based on their accumulation index in the sediments while majority of the heavy metals lacked the ability to remobilize but can be released into the environment under reducing and oxidizing conditions.

Discussion on Key Issues of Geochemical Monitoring of Soil Heavy Metal in Xiong'an New District

To build a soil environmental quality monitoring network and collect the systematic soil geochemical data of heavy metals before and after the construction of Xiong'an New District(XND), long-term variations in soil heavy metal levels during the XND construction were monitored based on the land quality geochemical survey monitoring data and the geochemical distribution of heavy metals. Parameters such as sampling density, sampling quantity, and sampling period were estimated to construct the geochemical monitoring network, which provides a reference for the future long-term monitoring of soil heavy metal geochemistry in XND. The results indicate that variations in the amount of heavy metals As, Cd, Cu, Hg, and Pb are greater than 36%, while the nugget coefficients of Cd, Cu, and Pb are greater than 75% because of the superposition of manmade sources on the high natural background levels. At the 95% and 90% confidence levels, while the allowable error Δ of the sample mean value is 5%, 10%, and 15% and heavy metals as As, Cd, Cu, Hg,Ni, Pb and Zn is monitored in soil environmental quality monitoring network, the proper numbers in the study area are 1077, 270, 120 and 767, 192, 86, respectively. The minimum detectable change(MDC)of each heavy metal species is between 0.0025 and 2.54 mg ·kg-1. Soil heavy metal monitoring requires different revisit intervals under different annual change rates, but in the study area, revisit intervals of soil monitoring are approximately two years under the current conditions of constant annual change rates.

Effect of Land Use Conversion on Surface Soil Heavy Metal Contamination in a Typical Karst Plateau Lakeshore Wetland of Southwest China.

Land use conversion could directly or indirectly influence heavy metal geochemistry by changing soil properties. The aim of this study was to explore the effect of land use conversion on surface soil heavy metal contamination in the karst plateau lakeshore wetlands of Southwest China. Based on this, a total of 120 soil samples were collected from 30 sites from different types of land uses (farmlands, grasslands and woodlands) around a lake in Suohuangcang National Wetland Park in August 2017. Contents of As, Cd, Cu, Cr, Hg, Pb and Zn were analyzed, and soil heavy metal contamination was assessed in all three land use types. Results showed that land use transformation from farmland to grassland or woodland was not conducive to the release of soil heavy metal. Surface soil of all three land use types have been moderately polluted by As, Cr, Pb, and Zn, and grassland and woodland also had moderate Cd contamination. The pollution load index (PLI) results revealed low heavy metal contamination in grassland and woodland but no contamination in farmland. Although the integrated contamination in the studied region did not pose a serious potential ecological risk (RI < 150), it might affect human health through the water supply and food chain. Therefore, it is necessary to monitor and control As, Cd, Cr, Pb, and Zn concentrations of surface soil through controlling pollutants, improving waste treatment, as well as strengthening supervision and management in the vicinity of the Suohuangcang National Wetland Park.

Environmental geochemistry of heavy metals in the groundwater of coal mining areas: A case study in Dingji coal mine, Huainan Coalfield, China

To elucidate the environmental geochemistry characteristics of groundwater in Huainan Coalfield, the largest coalfield in southern China, 59 groundwater samples from 12 locations were collected and measured for 18 heavy metals (Li, V, Cu, Pb, Zn, Cd, Ni, Mn, Co, Cr, Fe, Ba, Al, Be, Ti, Sr, Mo, and As), pH, and 7 ions (K+, Na+, Ca2+, Mg2+, Cl–, SO42–, and HCO3–). The Fe and Mn contents of most water samples were within class III of the People’s Republic of China Quality Standard for Groundwater. The Pb, Zn, Cd, Cr, Co, and Ba contents were assessed by the fuzzy mathematical method, and their levels in the groundwater were within class II. pH was negatively correlated with 11 heavy metals (Li, V, Cu, Pb, Zn, Cd, Ni, Mn, Cr, Ba, and Sr) and positively correlated with Al, Ti, and Co. The ranking of uptake rates affected by pH was Al > Ba > Ti > Si > Li > Mn. The Li content was correlated with six ions (Na+, Ca2+, Mg2+, Cl–, SO42–, and HCO3–), Sr was correlated with the first five ions, and Ba was correlated with the first four ions. Principal component analysis of V, As, Mn, Pb, Cd, Ni, Cr, Li, and Zn in the groundwater indicated that they derived from lixiviation of soil and rocks, precipitation, surface runoff, and surface pollution by heavy metals.

Heavy Metal Geochemistry of Soils in Selected Industrial and Farmlands of Enugu State: A Preliminary Investigation

Heavy Metal Geochemistry of Soils in Selected Industrial and Farmlands of Enugu State: A Preliminary Investigation

Major ion and dissolved heavy metal geochemistry, distribution, and relationship in the overlying water of Dongting Lake, China.

Deteriorating lake water quality has become a serious environmental issue around the globe. Heavy metals dissolved in the overlying water of lakes are notably more toxic than those found in lake sediment. Given this, we sought to better understand the characteristics of particular major ion and dissolved heavy metal in Dongting Lake-the second largest freshwater lake in China. Overlying water samples were collected from Dongting Lake to investigate the major ion geochemistry and to examine the relationship between the major ions and dissolved heavy metals. Chemical analysis of the overlying water showed that the average cation concentration was the highest for Ca2+, followed by Mg2+, Na+, and K+. Similarly, the highest anion concentration was SO42-, followed by Cl-, NO3-, and HCO3-. Total dissolved solids in the overlying water of Dongting Lake ranged from 66.19 to 159.20mg/L, with an average value of 93.13mg/L. The predominant hydrochemical type was Ca-SO4. The mean concentrations of dissolved heavy metal in both surface and deep waters decreased in the following order: Zn > Cr > Ni > Cu > Pb > Cd. Importantly, all of the selected heavy metals tested in the overlying water were lower than the corresponding toxicity reference values. Co-occurrence network analyses were performed and compared the correlations between all measured major ions and heavy metals. Results of the subsequent principal component analyses revealed that heavy metal levels in the aquatic environment primarily originated from natural processes and were enhanced by anthropogenic activities.

Spatial distribution and geochemistry of heavy metals in soils: A case study from the NE area of Vaslui county, Romania

This study reports the concentrations and sources of heavy metal pollution (As, Cd, Co, Cr, Cu, Ni, Pb, and Zn) in 193 soil samples from the northeast part of Vaslui county. Spatial distribution patterns, principal component analysis (PCA), and hierarchical clustering analysis (HCA) were used to assess the distribution of elements in the area and to identify the sources of elements and to classify them as geogenic or anthropogenic. PCA and HCA results suggest that As, Ni, and Co were consistently from natural sources; Pb, Zn, and Cu were consistently from anthropogenic sources; and Cr and Cd may be affected by both lithogenic and anthropogenic sources. A spatial interpolation allowed for the identification of agricultural activities as the main source of Cu pollution. Some places in the north of the area show high values of Zn and Pb, probably due to anthropogenic pollution caused by traffic or human activities. Maps of the heavy metal distribution were constructed for the whole area.

Intra-annual variability in the heavy metal geochemistry of ground waters from the Deccan basaltic aquifers of India

Geochemical baseline (geogenic+anthropogenic) and background (geogenic) levels of heavy metals in the ground waters from basaltic aquifers of Deccan Volcanic Province of India depicted intra-annual variability on spatial scale. Classified into ‘Group I’ (Fe > Mn > Zn > Pb) and ‘Group II’ (Mo > Ni > Cr > Cu), metals depicted contrasting enrichment and depletion patterns seasonally, attributable to geologic controls and water table fluctuations. While, fortification in Mo–Ni in post-monsoon (high water table) is on account of combined lithogenic+anthropogenic contributions, pre-monsoon augmentation in Fe–Mn (low water table) is entirely lithogenic. Positive values of Normalised Difference Dispersal Index, replicates the dominant role of soil/vadose zone as a chief supplier of metals to the groundwater during post-monsoon, while negative figures recommend host rock as a primary source of accretion of metals in pre-monsoon. Higher Ni/Cr ratios for wells in alluvial aquifer (fertile agriculture plain) than the basaltic and dyke aquifers, further suggest enhanced input of the elements (Mo, Ni > Cu) from soil and agriculture land use in post-monsoon season. Values of Ni/Cr ratio above unity for majority of the wells in post-monsoon and nearly 50 % wells in pre-monsoon suggest privileged weathering of olivine, followed by pyroxene > plagioclase feldspar (Ni/Cr <1) as a major cause of heavy metal load to the groundwater. Pearson correlation coefficients authenticate these inferences by means of elemental associations. The study unveils multi-source derivation of heavy metals related to seasonal fluctuation in the water table conditions leading to range of heavy metals in the groundwater from the study area. The target hazard quotient (THQ) values of heavy metals closer to unity and above unity highlight the possible health risk hazard associated with the consumption of metal contaminated groundwater. The study thus highlights the importance of baseline geochemical mapping to assess the state of near surface environment as heavy metals are closely linked to human health.

Effects of pH and Salinity on Adsorption of Hypersaline Photosynthetic Microbial Mat Exopolymers to Goethite: A Study Using a Quartz Crystal Microbalance and Fluorescence Spectroscopy

ABSTRACTSalinity and pH are two water chemical factors that vary drastically—seasonally or daily—in a variety of aquatic environments. Drastic change of salinity and pH may have a significant impact on adsorption of microbial extracellular polymers (EPS) to sediment minerals and thus influence many other important elemental geochemical processes. However, how salinity and pH changes affect EPS adsorption to minerals is poorly known. In the present study, adsorption of EPS from a hypersaline microbial mat to goethite at different pH values (4, 7 and 10) and salinity (0.15‰, 35‰ and 70‰) was monitored online using a quartz crystal microbalance (QCM) with EEM fluorescence spectroscopy as a complementary method. The adsorption kinetics were well described by an exponential function. The adsorption capacity of EPS to goethite significantly increased as the pH and salinity increased. The pH and salinity dependence of EPS adsorption to goethite is of great importance for understanding the environmental geochemistry of heavy metals in aquatic environments. In inland lakes and estuary zones, the seasonal or daily pulse of hydrological events will drastically alter water salinity and pH and consequently exert significant influences on the mobility, chemical species and ecotoxicity of heavy metals through the EPS pathway. It is necessary to systematically investigate the geochemical behavior of EPS in such dynamic aquatic environments and their potential effects on other geochemical processes.

Heavy metal geochemistry and mineral magnetic characterization of urban soil in Xuzhou, China

In the present study, the enrichment, availability, speciation of heavy metals including Pb, Zn, Cu, Cd, Ni and Sb and magnetic properties of urban soils of Xuzhou (China) were investigated. All analyzed metals showed elevated concentrations compared to local background concentrations. Cadmium and Sb are the metals most enriched in the analyzed area, presenting enrichment factor, on average, of 16.5 and 8.3, respectively. By self-organizing map in combination with diagnostic ratios, the source of Sb, Cd, Cu and Pb in soils might be mainly from traffic emissions. Sequential extractions indicate that metals were primarily associated with the reducible fraction with the exception of Ni. The order of extraction efficiency of various metals was SBET (simplified physiologically based extraction test) > DTPA (diethylenetriaminepentaacetic acid) > CaCl2. The magnetic results show that soil samples were dominated by a strong ferrimagnetic mineral component with multi- and single-domain magnetic grains. Only CaCl2 extractable Sb was found to show significant correlations with χlf and SIRM. For both DTPA and SBET extractions, all metals investigated showed significant associations with both χlf and SIRM (saturation isothermal remanent magnetization).

Concentration and fractionation of trace metals in surface sediments of intertidal Bohai Bay, China

Surface sediments from intertidal Bohai Bay were sampled for the geochemical and environmental assessment of six trace metals (Cd, Cr, Cu, Ni, Pb and Zn). Results indicate that sediment grain size plays an important role in controlling the distribution and fractionation of them. Metal concentrations in clayey silt sediments are all clearly higher than in sand and silty sand ones. Cd and Pb in clayey silt sediments are more mobile than in sand and silty sand ones. Two sediment quality guidelines and two geochemical normalization methods (index of geoaccumulation and enrichment factor) were used to judge the potential risk and accumulation of metals. According to the mean probable effects level quotient, the combination of studied metals may have a 21% probability of being toxic. The sediments with high fraction of clay and silt have been contaminated by trace metals to various degrees, among which Cr contributes the most to contamination.

Geochemical behavior assessment and apportionment of heavy metal contaminants in the bottom sediments of lower reach of Changjiang River

Heavy metal contamination of bottom sediments of the Changjiang River is widely reported, however, the potential source and methods of transportation of these heavy metals in the contaminated sediments is poorly defined. This paper examines the correlation between heavy metals and geochemical indices, including Fe 2 O 3 , Al 2 O 3 , total organic carbon (TOC) and black carbon (BC), as well as magnetic susceptibility (MS). Using these indices we investigate the contamination characteristics of heavy metals in the sediments by with Principal Component Analysis (PCA). Results from 83 sediment samples collected in the lower reach of Changjiang River (from Nanjing to Shanghai) show that the first principal component accounts for 52.23% of the total variance, corresponding to the heavy metals, Co, Cr, Cu, Ni and Zn, and conservative components of Fe 2 O 3 , Al 2 O 3 and TOC. This result indicates that heavy metal distributions are controlled by the transportation and sedimentation of fine particles which is also confirmed by particle size analysis. The second principal component explains 24.81% of the variance and is dominated by Cd, Pb and MS, which, collectively, result chiefly from industrial and transportation activities and, for MS, fly ash production. The third principal component accounts for 7.91% of the variance and corresponds solely to Hg. Principal component analysis/multiple linear regression (PCA/MLR) was used to estimate the contribution of the three principal components to each heavy metal. PCA/MLR results suggest that more than 50% of Co, Cr, Cu, Ni and Zn were influenced by the particle size effect. Particle size effect and fly ash account for 37.1% and 27.7% of As. Cd and Pb were mainly explained by fly ash. 98.9% of Hg was related to PC3, which represented black carbon (BC). Our study indicates that the combination of geochemical and multivariable statistical methods clearly characterizes the geochemistry of heavy metals in sediment of the lower reaches of the Changjiang River and suggests that power plants are the main source of heavy metal pollution. ► PCA/MLR indicated that the particle size influenced distributions of Co, Cr, Cu, Ni and Zn by over 50%. ► Fly ash production should be a main carrier of heavy metals, especially for Cd and Pb. ► Black carbon (BC) showed good correlation with Hg.

Application of SEM/EDS to environmental geochemistry of heavy metals

Heavy metals represent a ubiquitous constituent of the near-surface environment, present in widely varying concentrations that typically have little impact on human behaviour and health. However, the mining of metals and use of these metals in industrial processes has produced significant anthropogenic inputs of metals to both local and global environments. As such, a rigorous overview of the current accumulation of heavy metals and knowledge of mineralogy of heavy metal-bearing phases is important for understanding their stability, solubility, mobility, bioavailability and toxicity. These data are of fundamental importance for environmental risk assessment and evaluation of future scenarios. Since conventional geochemical analyses provide limited information, other analytical methods have to be utilized for the characterisation of heavy metal-bearing phases. Significant analytical method for identification and characterisation of heavy metals in environmental media is a scanning electron microscope coupled with energy dispersive X-ray spectrometer (SEM/EDS), an apparatus for qualitative and semi-quantitative chemical analysis at microne level, newly introduced to Geological Survey of Slovenia. Use of SEM/EDS was already introduced to environmental studies world-wide. In Slovenia, SEM/EDS analyses of environmental media were firstly carried out on the Meža River stream sediments and snow deposits from Ljubljana urban area. Heavy metal-bearing phases in the Meža River stream sediments were apportioned to three source areas: Mežica mining/smelting area (geogenic-technogenic origin), Ravne ironworks area (technogenic origin) and the Meža River catchment area (geogenic origin), which corresponds to data obtained by conventional geochemical and multivariate statistical methods. Airborne particles, identified in urban snow deposits, were interpreted as geogenic particles, represented by fragments of heavy metal-bearing minerals, and technogenic particles that originate from combustion of solid and liquid fuels, iron and steel melting processes and road traffic emissions. SEM/EDS proved to be a very useful analytical method for the study of heavy metal-bearing phases and characterisation according to their sources and genesis.