Vertical Distribution Of Heavy Metals Research Articles

Two‐stage soil core sampler to collect a less‐compressed core from forested areas

AbstractA two‐stage sampler was designed to investigate the vertical distribution of heavy metals and trace elements that contaminate forest soils through atmospheric deposition. The hand‐corer consisted of two L‐shaped aluminum angles that were driven separately into the soil to reduce friction between the corer wall and the soil. This allowed for soil cores to be collected with less compression than with traditional corers. The corer is easily made, inexpensive, lightweight, and easy to carry. The degree of compression of soil cores collected at a depth of 20 cm from various montane forests in Japan was usually less than 10% (collected core length >18 cm); although, more compression occurred in soil with a higher air content. The degree of compression of soil cores collected from urban forests was lower than that in montane forests. When the two‐stage sampler was compared with a tube‐type sampler in a Japanese cedar (Cryptomeria japonica) forest, the compression degree of a soil core collected with the two‐stage sampler was a quarter that of the tube‐type sampler. The collection of less‐compressed soil cores will allow for reconstruction of a more accurate linear depth distribution of contaminants. To demonstrate this, we investigated the vertical distribution of Pb, Sb, and radioactive 137Cs in soil cores collected from conifer plantations on Mount Tsukuba, Japan, in April 2011. The migration centers of anthropogenic Pb, Sb, and 137Cs were positioned at 7.9, 7.5, and 3.3 cm from the ground surface, respectively. These distances probably reflect differences in the history of atmospheric pollution.

Variability of rare earth and heavy metal elements in a representative alluvial depositional system.

Heavy metals (Ni, Cr, W, Cd, and Pb) and rare earth elements (REE) were investigated in the flood plain sediments of an island of the lower Yangtze River near Nanjing to determine how the vertical distribution of heavy metals could be affected by natural sedimentation processes and anthropogenic contamination. Stratigraphic analyses of magnetic susceptibility and the mean grain size distribution of the deposits enabled us to identify layers associated with a relatively high influx of suspended sediments that resulted in sudden changes in the concentrations of heavy metals. The results show that layers associated with high sediment influx (0.8m depth) displayed low concentrations of Cr, Ni, W, and Cd that were mainly lithogenic in origin. The Post Archean Australian Shale (PAAS) normalized REE patterns in the flood plain cores were enrichment in Ce and Eu relative to PAAS, indicating that the sediments were most likely derived from a mixture of sediments and not from an anthropogenic source. Sharp increases in Y/Ho ratios, as well as heavy metal (Cd, Cr, Ni, and W) and Y concentrations were observed in the uppermost layer that could have been deposited from the rapid transport of sediment-laden, contaminated waters. The temporal (vertical) trends in Pb concentrations may be strongly influenced by coal burning. Elevated Pb concentrations (350ppm and 1000ppm) correlate with high magnetic susceptibility (> 200 m3 × kg-1) and the history of thermal power plant (1910-2002) activity. The anthropogenic inputs of Pb were, however, not diluted by high suspended sediment loads, which supports the argument that Pb was derived from fly ash.

Heavy Metals and Organic Carbon in the Bottom Sediments of Shallow Bights of the Peter the Great Bay

A noticeable feature of labile heavy metals is that they are highly prone to be to bioaccumulated and bioassimilated in natural environments. When in high concentrations, these metals are toxic to living organisms, as is particularly evident in the coastal shallow marine zones, which are most strongly affected by anthropogenic processes. This paper presents data on the contents of heavy metals, concentrations of organic carbon, and the granulometric composition of bottom-sediment cores in three shallow bights of the Peter the Great Bay, in two of which (Voevoda and Novgorodskaya bights), large bottom areas are overgrown with seagrass Zostera marina L. (sea zostera, ZM). Data on the vertical distribution of heavy metals and organic carbon in the cores showed that the highest concentrations of Zn and Cu (up to 204 and 91 mg/kg, respectively) occur in samples from Voevoda bight, and the highest concentrations of Mn and Pb (up to 344 and 45 mg/kg, respectively) were found in Novgorodskaya bight, where meadows of the seagrass grow. The highest Cr, Ni, and Co contents (up to 69, 31, and 13 mg/kg, respectively) were identified in Uglovoy bight, where sea grass is practically absent.

Main trends and results of 300-years anthropogenic impact on the geological environment and ecosystem of the Eastern Gulf of Finland

The seafloor of the eastern Gulf of Finland (the Baltic Sea), especially its easternmost part – Neva Bay – has experienced anthropogenic impacts since the beginning of the XVIII century. The aim of this paper is: i) to analyze results of different stages of anthropogenic impact on the geological environment and ecosystem, ii) to assess the influence of dredging, dumping, and aggregates (sand, gravel) and ferromanganese concretions extraction on bottom relief and sedimentation processes, and iii) to establish the major spatial and temporal trends of heavy metal accumulation in the soft bottom sediments. Since the establishment of St. Petersburg, and into the 1960s, there was a physical impact on the seabed through the construction of artificial islands, dredging, and dumping. From 1960s to the 1990s, these types of activity became even more intense, as nearshore submarine terraces were used for sand and gravel extraction, and sediment pollution (e.g., heavy metals) has become one of the main environmental problems of the region. Based on extensive geochemical data collected for the first time in the study area, we examined a vertical distribution of heavy metals in cores obtained from different sedimentary basins. Results demonstrate a trend of increasing concentration values from the 1940s to the 1990s. Background concentrations of heavy metals are based on the geochemistry of catchment areas, decreasing in concentrations from the northwest to the southeast, while the maximum concentrations of hazardous substances deposited from the 1970s to the 1990s were observed in the easternmost part of the gulf. Since the 1990s the heavy metal input to the Gulf of Finland has significantly decreased, so the concentration of these hazardous substances in the surface sediments dropped as well, demonstrating a spatial distribution corresponding more to background (natural, pre-industrial) values. On the other hand, big hydrotechnical projects, realized during the last 20 years – artificial territories and new harbors construction, accompanying with dredging and dumping, ferromanganese concretion extraction, etc. – led to resuspension and secondary pollution of water. The other problem is the expansion of anoxic areas, caused both by climate change and human-stimulated eutrophication. Near-bottom anoxic conditions stimulate heavy metal migration from bottom sediments into the water column. All these processes impacted benthic communities as our review of previously published studies reveals. Geological and geophysical research revealed that within some areas anthropogenic impact caused a complete change of the sedimentation processes such as direction and rates of transport, which led to the total transformation of bottom relief, surface sediment distribution, and the benthic communities.

136 Years of variation of sediment-associated metals in a subtropical reservoir in southern Brazil: Implications for the environmental change

Urban water supply reservoirs, their quality and quantity of water are affected by anthropogenic activities and environmental changes. They are aquatic ecosystems that respond to the dynamics of organic loads and nutrients, and episodes of eutrophication. Past disturbances in the watersheds and the water column can be noticed by the vertical distribution of heavy metals and trace metals in the sedimentary core. In this study, two sediment cores from the Passauna reservoir in Curitiba, Brazil were examined to assess the accumulation of heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), and nickel (Ni), and other major elements such as aluminum (Al), iron (Fe), manganese (Mn), potassium (K) and barium (Ba), and their association to pollution. Enrichment factor (EF) and geoaccumulation index (Igeo) were applied to the identified accumulation of metals as well as to the level of pollution. The decay of radionuclides, including 210Pb and 137Cs, were used to find the rate of sedimentation over 136 years. The results showed a spatial variation, with the highest concentration of metals found in the upstream part of the reservoir. The EF values of the following metals decreased: in core I, EF(Fe) > EF(Mn) > EF(Cd) > EF(Sb) > EF(Zn) > EF(Cu) > EF(Cr) > EF(Pb); and in core II, EF(Sb) > EF(Pb) > EF(Cd) > EF(Cr) > EF(Fe) > EF(V) > EF(Zn) > EF(Cu) > EF(Ni) > EF(Mn). The Igeo values of the metals decreased in core I Igeo(Fe) > Igeo(Sb) > Igeo(Al) > Igeo(Zn) > Igeo(Cd) > Igeo(Cd) > Igeo(Ni) > Igeo(Cr) > Igeo(Mn) > Igeo(Pb) > Igeo(V); and in core II, Igeo(Sb) > Igeo(Cd) > Igeo(Pb) > Igeo(Al) > Igeo(Cr) > Igeo(V) > Igeo(Fe) > Igeo(Cu) > Igeo(Ni) > Igeo(Zn) > Igeo(Mn). We used the Mn/Fe, Cu/Ni, and V(V + Ni) ratio to evidence changes in productivity and redox conditions in the water column over time.We observed that during the period 1930–1970 anthropogenic activities controlled the impacts on reservoir and water quality. The changes in the distribution of metals coincided with the expansion of agriculture and urban area. In addition, redox and productivity showed periods with different rates of productivity as well as alternate periods of trophic levels. In sum, this paper provides information on how the depositional environment affects the geochemical characteristics of sediment, explaining past environmental changes.

Magnetic Susceptibility as Proxy for Metal Concentrations and Their Risk Levels in Vaigai River Sediment, Tamilnadu, India: Horizontal and Vertical Approach

ABSTRACT Horizontal and vertical distributions of heavy metals (Al, Fe, Mg, Cd, Cr, Cu, Ni, Pb and Zn) and magnetic susceptibility of Vaigai river sediment have been assessed to know the heavy metal toxicity and magnetic behavior of the sediment. The present study intentionally shows the magnetic susceptibility as proxy for metal concentrations and their risk levels of sediment. Univariate statistical analysis is carried out to confirm the spatial distribution of the heavy metals. The metal concentrations in present sediment are compared with iportant toxic reference values such as TEL, PEL, ERL, ERM and TRV to predict the toxicity of metals. The result shows that the frequent biological effect can be possible due to Cd, Cr, Cu, Pb and Zn in all feet sediments. Some interesting pollution factors such as PLI, PER and mPEC-Q are calculated to know the pollution status of the river. High magnetic susceptibility values in S16, S18 and S25 indicate the presence of various magnetic minerals. Principal Component Analysis (PCA) is carried out to show magnetic susceptibility as proxy for measuring heavy metals and their risk levels. Since magnetic susceptibility is strongly associated with heavy metals and their risk levels, this may be proxy for determining heavy metals and their risk levels.

Distribution, risk assessment of heavy metals in sediments, and their potential risk on water supply safety of a drinking water reservoir, middle China.

Heavy metals in reservoir sediments were analyzed to assess the pollution level and to understand the potential risk on water supply safety. Heavy metals in sediments will enter the biological chain through bio-enrichment and bio-amplification in water and eventually pose a threat to the safety of drinking water supply. Analysis of eight sampling sites in JG (Jian gang) drinking water reservoir of the sediments showed that from Feb 2018 to Aug 2019 heavy metals including Pb, Ni, Cu, Zn, Mo, and Cr increased by 1.09-17.2%. Vertical distributions of heavy metals indicated that the concentrations increased gradually by 9.6-35.8%. Risk assessment code analysis indicated that Pb, Zn, and Mo were of high risk in the main reservoir area. What is more, enrichment factors of Ni and Mo were 2.76-3.81 and 5.86-9.41, respectively, showing the characteristics of exogenous input. The continuous monitoring results of the bottom water showed that the concentration of heavy metals in the bottom water exceeded the environmental quality standard value of surface water in China, and exceeded the standard by 1.76 times (Pb), 1.43 times (Zn), and 2.04 times (Mo), respectively. Heavy metals in the sediments of JG Reservoir, especially in the main reservoir area, have a potential risk of release from the sediment to the overlying water. Water supply reservoir as a source of drinking water, its quality is directly related to human health and production activities. Therefore, this first study on JG Reservoir is of great significance for the protection of drinking water safety and human health.

Vertical distribution, contamination status and ecological risk assessment of heavy metals in core sediments from a mangrove-dominated tropical river

Understanding the vertical distribution of heavy metals aids in tracing the contamination history, however, it is limited for mangrove-dominated river. Thus, this study aimed to assess the vertical distribution of nine heavy metals and their possible ecological risk in several layers of core sediments from a mangrove-dominated river inside the Sundarban mangrove forest (World heritage and Ramsar site), Bangladesh. 45 core samples from five stations were analyzed using Flame Atomic Absorption Spectrophotometer (FAAS). The findings showed that, with the exception of Fe, Ni, and Cu, which suggested increased metal release in recent times, higher metal levels were recorded in the surface layer (0–10 cm), followed by the middle layer (10–20 cm), and inner layer (20–30 cm) of sediment cores. When compared to non-industrial forest sediment, core sediment from industrial sites contained noticeably more metals (p < 0.05). Overall, the mean metal concentration (mg/kg) followed the increasing order of Cd < As < Pb < Cu < Cr < Zn < Ni < Mn < Fe. Among the studied metals, the levels of Cd and Ni exceeded the average shale value. Contamination indices such as enrichment factor (EF), contamination factor (CF), and geo-accumulation index (Igeo) showed that the studied sediments were only contaminated by Cd. Ecological risk assessed by ecological risk factor (Eri) and risk index (RI) suggested that the analyzed heavy metals, with the exception of Cd, posed no significant ecological threats. All of the heavy metals analyzed might have originated from similar anthropogenic sources, according to the correlation matrix, cluster analysis (CA), and principal component analysis (PCA).

Geochemical Characteristics of the Vertical Distribution of Heavy Metals in the Hummocky Peatlands of the Cryolithozone.

One of the main reservoirs depositing various classes of pollutants in high latitude regions are wetland ecosystems. Climate warming trends result in the degradation of permafrost in cryolitic peatlands, which exposes the hydrological network to risks of heavy metal (HM) ingress and its subsequent migration to the Arctic Ocean basin. The objectives included: (1) carrying out a quantitative analysis of the content of HMs and As across the profile of Histosols in background and technogenic landscapes of the Subarctic region, (2) evaluating the contribution of the anthropogenic impact to the accumulation of trace elements in the seasonally thawed layer (STL) of peat deposits, (3) discovering the effect of biogeochemical barriers on the vertical distribution of HMs and As. The analyses of elements were conducted by atom emission spectroscopy with inductively coupled plasma, atomic absorption spectroscopy and scanning electron microscopy with an energy-dispersive X-ray detecting. The study focused on the characteristics of the layer-by-layer accumulation of HMs and As in hummocky peatlands of the extreme northern taiga. It revealed the upper level of microelement accumulation to be associated with the STL as a result of aerogenic pollution. Specifically composed spheroidal microparticles found in the upper layer of peat may serve as indicators of the area polluted by power plants. The accumulation of water-soluble forms of most of the pollutants studied on the upper boundary of the permafrost layer (PL) is explained by the high mobility of elements in an acidic environment. In the STL, humic acids act as a significant sorption geochemical barrier for elements with a high stability constant value. In the PL, the accumulation of pollutants is associated with their sorption on aluminum-iron complexes and interaction with the sulfide barrier. A significant contribution of biogenic element accumulation was shown by statistical analysis.

Disclosing the ecological implications of heavy metal disturbance on the microbial N-transformation process in the ocean tidal flushing urban estuary

Anthropogenic source of heavy metals in the estuary-coastal sediment could cause serious environmental concerns. Thus, much needs to be concerned about the linkages between bacterial community, microbial nitrogen processes and heavy metals accumulation in the ocean tidal flush urban estuary where the river meet the sea. In this study, Illumina sequencing analysis and quantitative PCR (qPCR) were adopted to detect the effect of heavy metals on the bacterial community and nitrogen transformation genes from vertical sediment profiles in the four tidal flush estuaries. Results indicated that bacterial community and structure varied greatly from the vertical and spatial distribution. The vertical distribution of heavy metals varied greatly in the different groups. It was concluded that the accumulation of heavy metals mainly occurred in the medium layer of the depth from 40 cm to 70 cm. Heavy metals were found to pose a significant influence on the bacterial community and nitrogen transformation genes. The abundance of denitrification genes was highly associated with Cr, Zn, As and the abundance of amoA was vulnerable to the influence of Ni. Both denitrification and nitrification genes were greatly affected by C and N content, which indicated that the enhanced nitrogen transformation activities mainly occurred in the top layer sediment. Our results indicated that the bacterial community and nitrogen transformation functional genes were sensitive to the variation of heavy metals and nutrient content, which will provide new insight into the microbial N-cycling process influenced by pollutant and show a potential strategy for discharge management in the circumstances of estuary-coastal zones.

Vertical distribution of heavy metals in Karewa deposits of South Kashmir: environmental contamination and health risk assessment

Vertical distribution of heavy metals in Karewa deposits of South Kashmir: environmental contamination and health risk assessment

Vertical distribution of heavy metals in soil profile of peri-urban areas of Haryana

Soil serves as a sink for various heavy metals where they present long period of time in the soil and create a manyharmful effects on soil health. A survey was carried out in peri-urban areas of Mohindergarh and Narnaul city, Haryanairrigated by sewage and tube-well water. Study was conducted on vertical distribution of heavy metals in profile soilsamples. Soil samples were analyzed for initial properties of soil and DTPA extractable heavy metals (Zn, Cu, Cd,Cr, Pb, Ni and Co). The results revealed that the soluble heavy metals, viz. Zn, Cu, Cr, Cd, Pb and Co content in bothsewage and tube-well irrigated profile soil samples decreased with increased depth of soil in both Mohindergarh andNarnaul areas. But, the Ni content increased with depth in both areas of sewage and tube-well irrigated soils. It isconcluded that the profile soil samples were found below the permissible limit of soluble heavy metals concentration.

Retention and vertical distribution of heavy metals in mangrove sediments of the protected area swamp of Mallorquin, Colombian Caribbean

The accumulation, retention and vertical distribution of six heavy metals (Fe, Cu, Zn, Ni, Pb and Hg) in two contrasting sedimentary environments of the Swamp of Mallorquín Colombian Caribbean, one with mangrove plants (M) and another without plant covering (SM), were analyzed in order to establish the incidence that such plants may have on the distribution of those metals in their adjacent sediments. Total metal concentrations (μg g−1, Fe in %) in the sediment profile for the different sampling areas was: Fe (M: 3.4 ± 0.6; SM: 3.0 ± 1.2), Zn (M: 64.9 ± 3.7; SM: 60.7 ± 13.9), Cu (M: 42.6 ± 6.2; SM: 33.3 ± 8.9), Ni (M: 28.5 ± 3.6; SM: 24.3 ± 6.9), Pb (M: 3.5 ± 0.4; SM: 2.9 ± 0.7), Hg (M: 0.14 ± 0.03; SM: 0.11 ± 0.04). Correlation analysis suggest that distribution of Cu, Zn and Ni in the M zone would be dominated by the formation of iron sulfides and oxyhydroxides in sediments, while the organic matter would be influencing the distribution of Pb and Hg. On the other hand, SM showed correlation for most of the variables, making it difficult to establish the sedimentary phases influencing metal distribution, due to the codependency between the different diagenetic processes. Cu, Ni and Hg concentrations exceed prescribed sediment quality guidelines (SQGs) indicating potential adverse effect on biota. The results corroborate the suitability of mangrove sediments as metal sinks and the importance of mangrove ecosystem restoration and conservation in the Swamp of Mallorquín.

Vertical distribution of heavy metals in core sediments from Kelantan River off Tanah Merah, Kelantan, Malaysia

Core sediments from two sampling points namely TM 2 and TM3 which are located at the Kelantan Rive near to Tanah Merah district had been collected to determine the vertical profile of heavy metals contents. TM 2 and TM3 were located near to gold mining area and agriculture area, respectively. The heavy metals in Tanah Merah were analysed using Atomic Absorption Spectrophotometer (AAS) PinA Acle 900F model. The degree of pollution has been investigated using Geo-accumulation (Igeo) index. For the result, the average value of heavy metals in Tanah Merah are Cu (12.67 ± 5.38 mg/kg), Pb (44.57 ± 8.75 mg/kg), Cr (56.69. ± 10.38 mg/kg), Zn (157.89 ± 88.56 mg/kg), Fe (4.08 ± 0.82 %) and Al (7.84 ± 1.53 %). The vertical profile of Cu and Zn at the bottom layer showed the decreasing trend toward the bottom of sediment suggesting the additional anthropogenic input of both metals to the sediment. In addition, most of the concentration value of Zn at TM2 near to gold mining set were exceed the permissible limit set by WHO. Furthermore, the result from the Igeo index also supported sediments at TM 2 which is located near to mining area are extremely contaminated with Cu and Zn. As conclusion, the authorities should closely monitor the level of pollution at the Kelantan River especially near to mining area.

Vertical and Lateral Distribution of Heavy Metals in the Euphrates River Sediments between Heet and Fallujah, Western Iraq

In recent decades, significant attention has been paid to heavy metal contamination as a dangerous environmental problem because of the toxicity, abundance, persistence and bioaccumulation of these elements (Chen et al., 2016,) (Islam et al., 2017 and ) (Jin et al., 2019). In general, the contamination state of the environment is evaluated by the total concentration of heavy metals (Kanda et al., 2018). The riverine sediments are considered as the main basins for various pollutants following the largely uncontrolled discharge of contamination resulting from human activities and geogenic processes (Liu et al., 2018). The sediment contamination is an important indicator of environmental variation as a result of anthropogenic influence (Gao et al., 2019). River sediments serve as not only a major sink and carrier of heavy metals but also as potential sources of secondary pollution, which can reflect their contamination level (Tang et al., 2014 and ) (Hsu et al., 2016). The heavy metals are released into the aquatic environments from geogenic and anthropogenic sources. The geogenic sources include chemical leaching of bedrock, water drainage basins and runoff from banks (Raj et al., 2017). The anthropogenic sources of heavy metals pollution in aquatic systems include mining activities, industrial wastes disposal and pesticides use, (Chakravarty &amp; Patgiri, 2009). The heavy metals pollution of sediments is an indicator of the aquatic systems water quality (Zhao et al., 2012). The heavy metal distribution in sediments and pollution levels supplies a base for consideration of sediments treatment methods and evaluation of the potential releasing of heavy metals into water and transport downstream (Nawrot et al., 2020). The vertical and spatial distribution of heavy metals and pollution levels have been evaluated in sediments of many world rivers, such as the Yinma River, China (Guan et al., 2018), the Voghji River, Armenia (Gabrielyan et al., 2018), the Barigui River, Brazil (Machado et al., 2017), the Harazdan River, Armenia (Petrosyan et al., 2019), the Thames River, the UK (Vane et al., 2020), the Yang River, China (Tang et al., 2020), and the Lu Lu River, China (Ye et al., 2020). The spatial distribution of heavy metals in sediments of the Euphrates River in Iraq has been investigated by many authors (Issa &amp; Qanbar, 2016); (Al-Taher et al., 2020); and (Hussain &amp; Al-Jaberi, 2020). The spatial variation of heavy metal concentrations in sediments of the Euphrates River along the studied area between Heet and Ramadi Cities has been studied by (Al-Bassam &amp; Al-Mukhtar, 2008) and (Salah et al., 2012). The aim of the study is to investigate how heavy metals are laterally and vertically distributed in sediments of the given study area of Euphrates River between Heet and Fallujah Cities. This study represents the first attempt to investigate the vertical distribution of heavy metals in the Euphrates River sediments.

Interactions of heavy metal elements across sediment-water interface in Lake Jiaogang

Heavy metal pollution in lake systems has arisen plenty of threats for public health because of its high toxicity, persistence, and bioaccumulation. Whereas heavy metals are inextricably linked with bioavailability in pore water and overlying water. Lake Jiaogang is classified as an important water-carrying lake situated in the northern part of the Anhui Province China. In recent years, water quality in this lake declined due to increasing fishery aquaculture, livestock, and tourism. This study aims to bring insight into the interactions of heavy metal elements across sediment-water interface in Lake Jiaogang. Four representative regions were selected, more than ten heavy metals were chosen to quantify by the Community Bureau of Reference, diffusive gradient in thin-film (DGT), and high-resolution pore water equilibrators. The results showed that most heavy metals corresponded with the reducible fraction, acid-soluble fraction, and oxidizable fraction in the Eastern area (sample 3#) and aquaculture area (sample 4#) were higher than that of emergent plant area (sample 1#), and floating plant area (sample 2#). The average fluxes of heavy metals (except Ni and Zn in sample 3#, F value > 0 pg/cm2/d) in the four sampling sites were observed in the lower reaches (F value < 0 pg/cm2/d). The vertical distribution of heavy metals was extracted by DGT, such as As (exclude 2#), Co, Fe, Mn, and Zn (contain 4#) showed an increased content with increasing depth in the four sampling sites. In the pore and overlying water, concentrations of heavy metals from the sample 3# and 4# were higher than those of sample 1# and 2#. Heavy metal pollution in anthropogenic activity areas was higher than those in areas with ecological vegetation, and risk control in this area should be strengthened.

Vertical distribution and contamination assessment of heavy metals in sediment cores of ship breaking area of Bangladesh.

Vertical heavy metal profiling reflects the history of the deposition of metals and helps to understand the characteristics of accumulation in various layers of the sediment. Nevertheless, no previous studies in Bangladesh had focused on the vertical distribution of heavy metals in core sediments. In this study, vertical distribution, contamination level and potential ecological risks of six heavy metals (Zn, Cu, Pb, Cr, Ni, Mn) from the core sediment of ship breaking were assessed and compared with the non-ship breaking area of Bangladesh. The concentration (µg/g) of heavy metals in the 0-10cm (surface), 10-20cm (middle) and 20-30cm (bottom) of sediment cores was as follows, respectively: Zn (35.54-100.68, 37.27-258.02, 42.78-66.45); Cu (16.38-75.25, 30.64-92.02, 34.99-52.98); Pb (4.84-132.08, BDL-204.48, BDL-23.51); Cr (14.57-42.13, 25.31-42.71, 15.26-36.34); Ni (4.02-42.23, 4.94-43.70, 4.40-43.13); Mn (198.74-764.16, 257.77-980.50, 255.62-856.44). The heavy metal content of core sediment from the shipbreaking region was substantially higher than that of non-shipbreaking area. Except for Ni, heavy metal content was highest in the middle layer, followed by the upper and lower layers of the sediment core. Contamination exponents such as enrichment factor, contamination factor and geo-accumulation index (Igeo) revealed contamination by Zn, Cu and Pb while potential ecological risk factor ([Formula: see text]) and risk index suggested low ecological risk by studied heavy metals except for Pb. Correlation matrix, cluster analysis and principal component analysis indicated that all studied heavy metals could have similar anthropogenic origins.

Spatial Distribution and Ecological Risk Assessment of Heavy Metals in Sediments of a Heavily Polluted Maozhou River, Southern China.

In this study, eighteen 3.30-m-long sediment profiles were sampled in Maozhou River. In order to investigate the sediment pollution status and potential sources of heavy metals, we performed heavy metal contents, grain size, organic matter concentration, moisture concentration and total phosphorus analysis, and assessed the ecological risk of heavy metal pollution in the study area using enrichment coefficient, geo-accumulation index and potential ecological risk index. The results indicated that the heavy metal concentrations in the Maozhou River sediments were 3.73-417 times higher than the soil background in Guangdong Province and the average concentrations were 0.447-15.1 times higher than Chinese lacustrine sediments. The Cr, Ni, Cu, Zn, Cd and Pb contents were significantly correlated with each other (p < 0.01), indicating similar deposition process. In addition, spatial and vertical distribution of heavy metals showed similar variation patterns and extreme high contents are distributed in the interchange area. The ecological risk of Maozhou River was much higher than other river sediments in Guangdong Province, especially for Cu, Cd and Ni. The variation pattern of potential ecological risk index is similar with that of heavy metals and the assessment results indicated high ecological risk in the Maozhou River sediments, which is in good agreement with the EF and Igeo results. This study would provide some references for the treatment of heavy metals' pollution in Maozhou River.

Analysis of the spatial distribution of heavy metals in an area of farmland in Sichuan province, China

To accurately visualize the spatial distribution of heavy metal pollution and provide information that assists in remediating farmland soil, this study employed GIS technology and collected 0–20 cm-depth surface soil and shallow groundwater samples from farmland in Jianxin Village, Xiba Town, Wutongqiao City, Sichuan Province, China. The soil samples were decomposed using a high-temperature closed digestion method, and the contents of Cr, Cd, Pb, As, Cu and Zn were determined using ICP-MS. A geographic semi-variogram analysis was then conducted to delineate spatial variations in the heavy metal concentrations within the soil, and a spatial distribution map of heavy metals in the soil was drawn using ArcGIS10.2 software based on a GIS Kriging interpolation spatial structure analysis. The results showed that all heavy metal element concentrations exceeded the soil background values of Sichuan Province; the exceeded rates of Cr, Cd, and Zn were 100%. All Cd samples exceeded the soil baseline value, and the pollution accumulation of Cr, Cd, and Zn was determined as being serious. Through a comparison of cross-validation methods, a theoretical optimal semi-variogram model of six heavy metal elements was obtained. Indexes C0/(C0 + C) of Cd, Pb, As, Cu, and Zn were in the range of 48–75%, which showed that their contents related to structural factors, such as the soil parent material and topography, and also to non-structural factors such as human activities. The index C0/(C0 + C) of Cr was more than 75%, which indicates that its content is mainly related to non-structural factors and human activities. The spatial correlation followed the order of Cu > Cd > Pb > Zn > As > Cr. The vertical distribution of heavy metals was greatly affected by the soil physical properties: the Cu and Pb contents of sandy soil decreased at first and then increased with depth; the Cr, Zn, and As contents first increased and then decreased with depth; and the Cd contents decreased with depth. In clay soil, there was little change in the Cu content with depth; the Cd, Zn, Pb, and As contents first decreased and then increased with depth, and the Cr content increased first and then decreased with depth. These results show that visualizing the spatial distribution of heavy metal contamination using GIS technology is significant for providing information that can be used to remediate farmland soil.

Heavy metal pollution in urban river sediment of different urban functional areas and its influence on microbial community structure.

In this study, the Songgang River (SR) was selected as a typical contaminated urban river in a highly urbanized city (Shenzhen) that is extensively polluted by heavy metals (HMs). Five representative sampling sites were selected from different urban functional areas along the SR, and the spatial and vertical distributions of HMs and the related environmental risk were investigated. In addition, the distribution variability, composition, and abundance of microbial communities, as well as the correlation between the abundance of the operational taxonomic units (OTUs) and the HM contents were analyzed. The spatial distribution of HMs in the sediment revealed wide variation among the different urban functional areas. Industrial and residential areas had higher HM contents, following the order of Cu>Zn>Ni>Cr>Pb. In addition, the vertical characterization (5-300cm) of HM content showed a decreasing trend with depth, with a distinct layer around 120-180cm that might have been caused by anthropogenic activity. An ecological risk assessment indicated that Cu, Ni, and Cr pose high potential risks in these industrial and residential areas (at the depth of 5-180cm). Furthermore, microbial community analysis indicated that some HM-tolerant bacteria (e.g., Gallionella, Acidovorax, Arenimonas, Curvibacter, and Sideroxydans) were dominant in the 5-120cm layer, corresponding to high HM contents. A canonical correspondence analysis and co-occurrence network further confirmed that there was a strong correlation among the urban functional areas, HM contents, and the abundance of microorganisms in the urban river sediment. The results of this study have the potential to provide a bio-augmentation strategy for the in-situ bioremediation of sediment contaminated by HMs.