Spatial Distribution Of Heavy Metals Research Articles

Effects of anthropogenic activities on the levels of heavy metals in marine surface sediments of the Thessaloniki Bay, Northern Greece: Spatial distribution, sources and contamination assessment

Surface marine sediments act as important repository of heavy metals (HMs) and play a significant role in their transport and possible release. The anthropogenic contribution to heavy metal contamination and the associated ecological and health risks should be evaluated in studied areas. The objectives of this study were to investigate the presence and spatial distribution of heavy metals (Cr, Ni, Cu, Mn, Cd, Zn, Fe and Pb) in surface marine sediments located in the Northern Thermaikos Gulf, which is an area of increased ecological, financial and social significance, using a sensitive and reliable analytical method and to evaluate the anthropogenic contribution and ecological risks related to the presence of heavy metals. The mean HM concentrations, in the sediments of Thermaikos Gulf exhibited a decreasing order: Fe > Mn > Zn > Cr > Pb ≥ Ni > Cu > Cd. A very strong correlation was demonstrated between Cu, Ni, Pb and Zn indicating that these elements originate from common anthropogenic sources. This was also supported by Enrichment Factors (EF) and Igeo values, which revealed that almost 50% of the sediments were characterized as “heavily to extremely polluted” concerning Cd, while almost 30% and 20% of the sampled sediments were characterized as “moderately to heavily polluted” with regards to Pb and Zn, respectively. Pollution Load Index (PLI) for almost all samples exhibited values >1 indicating anthropogenic pollution. Ecological Risk (Er) values for Cd indicated high to extreme risk for 50% of the samples. Cr, Cu and Pb concentrations for 74%, 95% and 74% of the samples, respectively, indicated occasional association to toxic biological effects on aquatic organisms. For Ni, 87% of the sediments frequent association with adverse biological toxic effects. Contamination Severity Index (CSI) showed that 22% of the samples reflected a moderate to high severity of contamination. Two of the samples near the industrial and shipping zone, exhibited the highest CSI values. The highest total Toxic Units (ΣTUs) were calculated in sediment samples affected by industrial wastewater and shipping activities, with Ni presenting the higher TUs compared to the rest of the HMs and contributed the most (37%) to the overall TUs revealing its high potential toxicity for the marine ecosystems in Thermaikos Gulf. The Total Risk Index (TRI) for each HM exhibited a decreasing order of Ni (3.9) > Cu (3.0) > Cd (2.6) > Pb (2.0) > Cr (1.6) > Zn (1.4). The area exhibiting the highest impact of anthropogenic HMs, coincides with the Thessaloniki's port broad area, where the industrial and shipping activities have been taking place for several years, indicating the cumulative effect of the anthropogenic load from the activities on urban coastal regions.

Geochemical determination and pollution assessment of heavy metals in agricultural soils of south western of Iran.

Soil contamination with heavy metals due to the application of fertilizers and biocides in agricultural activities is a potential threat for human health through the food chain. The present work was designed to study the spatial distribution of heavy metals, pollution level and possible reasons for their contamination in agricultural soils of Aghili plain, Khuzestan, Iran. The median concentrations of As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, V, Zn, and Hg were 2.90, 0.29, 8.10, 39.0, 17.75, 354.0, 0.97, 58.35, 5.90, 34.0, 42.0, and 0.01mg/kg, respectively. The results revealed that average concentrations of all studied heavy metals with an exception of Co, Cu, and Ni, were lower than background values. Analysis of source identification showed that Zn, Pb, and Cu (P < 0.01, r > 0.9) and Co, Cr, Mn, Ni, and V (P < 0.01, r > 0.7) were mainly from anthropogenic. In addition, Cd probably was originated from agricultural activities (application of manure and phosphorous fertilizers). Enrichment factor values of all metals (except Ni), were in the range of non to moderate enrichment (EF < 5). According to the degree of contamination (Cd) and ecological risk factor (ERF), all stations were categorized as low to moderate contaminated sites (4.5 < Cd < 17), and biological communities in some locations may be at risk (ERF >65). Results indicate that application of fertilizers, herbicides and pesticides in agricultural soils has led to soil contamination and special management and educational plans are needed for public and farmers to prevent further adverse effects.

Spatial distribution of Fe and Mn in paper mill effluent affected agricultural soils in Morigaon, Assam

The spatial distribution of heavy metals (Fe and Mn) in the paper mill contaminated area of Jagiroad, Assam, India were investigated using statistics, geostatistics and GIS techniques. The total concentration of Fe and Mn were determined for 188 samples collected from the contaminated area. The mean concentration of Fe (7629 mg kg1) was high. The highest and the lowest standard deviation were observed in the Fe (1749) and pH (0.81), respectively. Analysis of the isotropic variogram indicated that the Fe semivariogram was well described with the Gaussian model, with the distance of spatial dependence being 1354 m, while Mn was well described with the spherical model, with the distance of spatial dependence being 833 m. The ordinary kriging estimates of Fe and Mn maps showed that high concentrations of these metals occured in the low-lying areas like bils (lakes). For both the investigated heavy metals the prediction of goodness (G) value was greater than zero. This indicates that spatial prediction is better than assuming mean of observed value as the property value for any unsampled location. Thus the geostatistical method was spatial variability of Fe and Mn.

Spatial Distribution and Health Risk Assessment of Soil Pollution by Heavy Metals in Ijebu-Ode, Nigeria.

Background.Soil pollution by heavy metals in urban areas is of major concern to city planners and policy makers because of the potential threat to human health. Hence, an investigation of soil pollution is crucial to urban environmental assessment and management.Objective.To determine the spatial distribution and health risk assessment of seven heavy metals (cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn)) around Ijebu-ode, southwest Nigeria.Methods.Surface soil samples were analyzed for Cd, Cr, Cu, Mn, Ni, Pb, and Zn levels using standard procedures. Geographic information system (GIS) data, pollution indices (enrichment factor, geo-accumulation index), and the health risk assessment model, respectively, were used to analyze the spatial distribution, pollution level, and potential health risk of heavy metals.Results.Low pH was observed in the urban soils. The average concentrations of the seven heavy metals investigated were in order of Zn > Pb > Mn > Cu > Cd > Ni > Cr. There was high spatial variation in the distribution patterns of the heavy metals. The cancer risks for Cu, Mn, Pb, and Zn for children (1.50 × 10−3 – 2.71 × 10−2) and Mn, Pb, and Zn for adults (7.89 × 10−4 – 2.97 × 10−3) were higher than the acceptable range of 1 × 10−6 - 1 × 10−4.Conclusions.Anthropogenic activities from different urban land uses contribute to the pollution levels and spatial distribution of heavy metals in soils. Increasing pollution of urban soil may contribute to the occurrence of some health risk for residents in the study area.Competing Interests.The authors declare no competing financial interests.

Pollution characteristics, sources, and risk assessment of heavy metals and perfluorinated compounds in PM2.5 in the major industrial city of northern Xinjiang, China

At present, research on PM2.5 has focused on eastern and central China; little attention has been given to Xinjiang, the most northwestern part of China. Ten kinds of heavy metals (HMs) and 12 kinds of perfluorinated compounds (PFCs) in atmospheric PM2.5 are detected by inductively coupled plasma mass spectrometry and high-performance liquid chromatography-mass spectrometry, respectively. Principal component analysis and risk assessment methods are used to study HMs and PFCs and explore their pollution levels and health risks. Results show that HMs and PFCs are prevalent in atmospheric PM2.5 of Shihezi and Urumqi. The spatial distributions of HMs and PFCs in four sampling sites are development zone (B1) = industrial park (A1) > factory (A3) > school (A2) and A1 > A3 > B1 > A2, respectively. In the four sampling sites, copper, lead, zinc, and cadmium (Cd) contents are relatively high. Perfluorooctane sulfonate (PFOS), perfluorohexanoic acid (PFHxA), and perfluorooctanoic acid (PFOA) are the most prevalent PFCs. Risk assessment results show that PFCs in the atmosphere will not harm residents, but the Cd and nickel (Ni) in HMs are harmful to humans, especially Cd, which has both carcinogenic and non-carcinogenic risks. These findings indicate that the carcinogenic risk of HMs and PFCs in children is higher than in adults. In addition, HMs and PFCs may cause joint toxicity.

Prediction of heavy metals in soils of an arid area based on multi-spectral data

With the rapid and extensive development of industry and agriculture, the soil environment inevitably becomes contaminated with heavy metals, thus creating adverse environmental conditions for flora and fauna. The traditional methods for combining field sampling with laboratory analysis of soil heavy metals are limited not only because they are time-consuming and expensive, but also because they are unable to obtain adequate information about the spatial distribution characteristics of heavy metals in soil over a large area. Three hundred and ninety-four soil samples (Gobi and farmland) were collected in an arid area in Jiuquan in Northwest China and analyzed for elements concentrations. Based on these measured concentrations, as well as rapid and environmentally friendly remote sensing (multi-spectral data), stepwise multiple linear regression (SMLR) and partial least-squares regression (PLS) were combined to predict concentrations and distributions of heavy metals in the soils of the study area. Furthermore, laboratory data were used to assess the accuracy of the prediction results. Obtained results suggest that the SMLR and PLS models were able to predict the metals contents in the study area. The concentrations of Cr, Ni, V and Zn could be predicted by two regression models, while those of Cu and Mn were predicted more accurately when they were attached to the SMLR model. The spatial distribution of heavy metals derived from the two models is consistent with measured values, indicating that it is reasonable to predict the concentrations of heavy metals in the soil of the study area using the multi-spectral data.

Heavy metal imaging in fibrotic human kidney tissue using the synchrotron X-ray fluorescence microprobe.

Abnormally high exposure to heavy metals and their accumulation in some tissues are recognized as causes of many acute and chronic human diseases. Because of the roles many metals have in normal human physiology, proving cause and effect between exposure to heavy metals and pathogenesis of disease is problematic. Therefore, many illnesses that develop through occupational and environmental exposure are not considered directly related to heavy metal toxicity. The high sensitivity and spatial resolution of elements using the synchrotron X-ray fluorescence microprobe (XFM) may give a robust means to investigate spatial distribution of heavy metals in correlation with specific pathologies. For example, proven presence of different heavy metals may correlate spatially with kidney fibrosis, suggesting a mechanistic link between heavy metal-induced fibrosis and chronic kidney disease. One specific example that may benefit from such an analysis relates to a cluster of people with chronic kidney disease of unknown cause (CKDu), in a significant proportion of the population of the North Central Province of Sri Lanka. Here, it was postulated that heavy metal exposure, in particular of cadmium, in foods and agriculture may be one cause of end-stage kidney disease and premature death of patients with CKDu. Synchrotron methods had not been applied previously to this particular problem. This manuscript provides a brief review of the literature and reports some pilot data from an investigation of localization of kidney fibrosis in CKDu with selected heavy metals including cadmium.

Sediment characterisation and spatial distribution of heavy metals in the sediment of a tropical freshwater wetland of Indo-Burmese province

The sediment characterisation of wetlands belonging to the Northeastern Region of India particularly regarding the assessment of sediment carbon stock is very scanty. The presently available literature on the wetlands cannot be employed as a common model for managing the wetlands of the Northeastern Region of India as wetlands are a sensitive ecosystem with a different origin or endogenous interventions. Thereby, this research was conducted on Deepor Beel for investigating the spatial and seasonal variation of sediment parameters, the relationship between the parameters and pollution status of the wetland. Results revealed that the study area is of an acidic nature with a sandy clay loam type texture. Organic carbon, total nitrogen and available nitrogen were higher in sediments in the monsoon period. The mean stock of the sediment carbon pool of Deepor Beel is estimated to be 2.5 ± 0.7 kg m−2. The average non-residual fraction percentage (63.2%) of Pb was higher than the residual fraction. Zn content ∼490 mg kg−1 exceeding its effect range medium (ERM) was determined to suggest frequent biological adverse effects. Highest metal enrichment factor (EF) values were shown by Zn and Pb, which ranged between 78 and 255. Risk assessment code (RAC) values of Pb between 21 and 29% indicated its high bio-accessibility risk. Pearson's coefficient matrix revealed a low degree of positive correlation between organic carbon content and metal concentration. Principal component analysis revealed that the first component comprising of EC, basic cations and metals accounted for 62.3% of variance while the second component (OM, OC, TN, AN, AP) and the third component (pH) accounted for 21.8% and 7.0% of the variance, respectively. The present study revealed the adverse impact of human inputs on the Deepor Beel quality status.

Predicting spatial distribution of heavy metals in an abandoned phosphogypsum pond combining geochemistry, electrical resistivity tomography and statistical methods.

One of the wastes generated in fertiliser production from phosphoric rock is phosphogypsum, whose mismanagement lead to environmental and health risks. Therefore, a detailed evaluation of the chemical composition of phosphogypsum is necessary to determine effective means of its management. Due to the high amount of generated waste, the cost and time consumed for this characterisation by chemical analysis is limiting. Hence, efficient tools should be developed to predict the chemical composition of this waste. Thus, this study aims to: 1) determine the physic-chemical characterisation of phosphogypsum pond using geochemical and geophysical techniques and 2) predict the heavy metals spatial distribution through statistical models. Results show that the most concentrate metal is chromium with a maximum of ≈900 mg.kg-1 and cadmium is the least concentrated (maximum ≈23 mg.kg-1). The Electrical Resistivity Tomography revealed the superposition of two layers. The top one (waste) presents low resistivity (≈17Ω.m) while the bottom layer shows higher resistivity (>124Ω.m). Metal concentrations and resistivities were combined by applying non-linear regression models. Cr showed the strongest correlation (R2 = 0.68), yielding an accurate model that was used for revealing the spatial distribution of the highest Cr concentrations in the pond, with the consequent reduction of expensive traditional methods.

Heavy metals inter-annual variability and distribution in the Yangtze River estuary sediment, China

A better understanding of the relationships between heavy metal pollution and sediment sources in different aquatic environments of estuary is needed. The purpose of this paper is to evaluate the levels and spatial distribution of heavy metals (Cu, Zn, Pb, Cd, Hg, and As) of surface sediments collected from 20 stations in the Yangtze River estuary from 2012 to 2016. The results showed that an overall decreasing trend in the concentration of these six types of heavy metals with distance from the shoreline. Typically, there was also a high concentration of heavy metals in muddy areas. Principle component analysis (PCA) and Factor analysis (FA) detected major groups of elements in which three distinct clusters of pollutants and recognized the sources of metals and validate the temporal and spatial variations that are affected by natural and anthropogenic sources linked to their seasonality.

Heavy metals contamination in urban surface soils of Medak province, India, and its risk assessment and spatial distribution.

The main purpose of the current study is to assess the contamination status, human health risk, and spatial distribution of heavy metals in the urban soils from the Medak province in India. For this purposes, a total of 40 urban surface soil samples were collected and analyzed seven heavy metals including chromium (Cr), copper (Cu), cadmium (Cd), arsenic (As), nickel (Ni), lead (Pb), and zinc (Zn). The results of the study showed that the concentration of Cr (81-751mg/kg), Cu (2-180mg/kg), Zn (25-108mg/kg), Pb (5-77mg/kg), Ni (1-50mg/kg), As (0.4-14mg/kg), and Cd (0.1-4.2mg/kg), respectively, was found above their natural background values. The geo-accumulation index analysis indicated that except Zn, all other tested heavy metals had a range of moderately to heavily polluted/contaminated in the study region. Spatial distribution pattern analysis inferred that the soil heavy metal (Cu, Cr, Zn, and Ni) pollutions in western regions of Medak were relatively larger than that in central and eastern regions. The hazard index (HI) values for Cu, Cd, Zn, As, Pb, and Ni were below 1, implying that there is no non-carcinogenic risks exposure from these heavy metals in soil for children and adults in the study region. However, HI value for Cr ranged from 3.08E-01 to 2.86E+00 for children, implying that children were relatively vulnerable population than adults in the current study region. Comparatively speaking, 67.5% and 100% total carcinogenic risks for Cr values for adults and children were larger than the acceptable threshold value of 1.0E-04, indicating chromium poses the greatest carcinogenic risk in the study region.

Establish an environmentally sustainable Giant Panda National Park in the Qinling Mountains

The giant panda (Ailuropoda melanoleuca) is one of the most endangered animals in the world and is recognized worldwide as a symbol for conservation. The Qinling subspecies of giant panda (Ailuropoda melanoleuca qinlingensis) is highly endangered; fewer than 350 individuals still inhabit the Qinling Mountains. Last year, China announced the establishment of the first Giant Panda National Park (GPNP) with a goal of restoring and connecting fragmented habitats; the proposal ignored the environmental pollution caused by economic development in panda habitats. The spatial distribution of heavy metals (Cd, Pb, Hg, Cu, Zn, Mn, Cr, Ni and As) was analyzed in giant panda feces, soil, bamboo, and water in four of GPNP's functional areas at different altitudes and latitudes. Heavy metal pollution decreased with anthropogenic influences, from outside the park through the buffer and into the core area. Cu, Mn, Ni and Zn accumulated from natural sources; As, Hg and Cr were associated with fuel combustion; and Pb and Cd were associated with traffic and agriculture sources. The presence of heavy metals at high altitudes and latitudes in the proposed GPNP is due to emissions from Xi'an and other upwind industrial cities. We conclude that reducing emissions and heavy metal input should be included in the design of the GPNP. Policy interventions should consider functional zones planning, wind direction, reducing mining, and the abandonment of existing roads and farmland within the GPNP to reduce other direct human impacts on the Qinling panda.

Assessment of the impact of heavy metals in sediments along the Spanish Mediterranean coastline: pollution indices.

A comprehensive study was carried out to evaluate the occurrence, significance of concentrations and spatial distribution of heavy metals (Cr, Cd, Ni, Cu, Pb, Hg, Zn and As) in sediments along the Valencia coastline (Spain). The sampling campaign covered 476km of the coastline in a 4-year period. The highest concentrations of metals in the sediments were mainly Cr, Ni, Zn and Cd (up to 28.93mg Crkg-1 dw, 15.80mg Ni kg-1 dw, 57.13mg Zn kg-1 dw and 0.293mg Cd kg-1 dw), obtained in the northern areas, some central areas and in an isolated area on the southern coastline. The Sediment Quality Guidelines applied reveal that for all metals studied, none of them reached, or exceed, the "effects of median range" or the "probable effect level". The pollution index reveals that 75% of the stretch coastline has a low priority risk level and the rest "medium-low priority risk level". And, lastly, Potential Ecological Risk Index shows that all but one zone have low ecological risk.

Spatial variation of heavy metals and uptake potential by Typha domingensis in a tropical reservoir in the midlands region, Zimbabwe.

Pollution of aquatic ecosystems with heavy metals is now of global concern due to their dangers to human health and persistence in the environment. An investigation on the spatial distribution of heavy metals in water and sediments and the bioaccumulation potential of heavy metals by plant parts (i.e. roots, stems and leaves) of aquatic macrophyte Typha domingensis (Pers.) Steud in a tropical reservoir was carried out. The results showed no difference in spatial distribution of heavy metals (Fe, Cu, Cd, Cr, Pb, Zn, Mn) in water and sediments from the riverine to the dam wall. The concentration of heavy metals Fe, Cu, Cr and Zn in T. domingensis was of the order root > stem > leaves, but for Pb, Cd and Mn, it followed the order root > leaf > stem. The metal transfer between roots and shoots of T. domingensis followed the order Zn > Pb > Fe > Cu > Cd > Cr. The bio-concentration factor (BCF) was low (BCF < 1) for all the selected metals while the transfer factor (TF) varied among metals suggesting that T. domingensis is not an accumulator of the studied metals. The high concentration of heavy metals found in the water (0.7-16.14mgL-1) and sediments (43.6-569.18mgkg-1) present a potential risk to both ecological health and human health for the population living in the area. The results of metal concentration in water and sediments from this study are important as a baseline for future monitoring studies. Further studies on bioavailability of metals to other macrophytes and aquatic organisms are recommended.

Correction to: Spatial distribution of heavy metals and their potential sources in the soil of Yellow River Delta: a traditional oil field in China

In the original publication of the article, the sixth author name "Zhouqing Xie" has been misspelt. The correct name is given in this correction. The original version of this article was revised.

Contamination Evaluation and Source Identification of Heavy Metals in the Sediments from the Lishui River Watershed, Southern China.

Seven heavy metals (Cr, Mn, Co, Ni, Cu, Zn, Pb) were measured in surface sediments from the Lishui River watershed, an area with increased soil erosion in China. The mean concentrations of heavy metals were 61.20 mg/kg (Cr), 757.15 mg/kg (Mn), 9.39 mg/kg (Co), 25.31 mg/kg (Ni), 22.84 mg/kg (Cu), 91.66 mg/kg (Zn), and 40.19 mg/kg (Pb), respectively. The spatial distribution of heavy metals was site-specific, exhibiting a remarkably high level in the sampling stations with intense agricultural activities (Lixian) and industrial activities (Jinshi). Contamination indexes including contamination factor, pollution load index, nemerow multi-factor index, potential ecological risk index, and human health risk were used to assess the pollution degree of the river sediments. The results indicated the pollution degree of heavy metals decreased in the order of Mn > Pb > Zn > Cr > Cu > Ni > Co. Heavy metals resulted in non-pollution to moderate pollution, with low ecological risk and an acceptable carcinogenic risk caused by Cr and Ni for children and adults. Person’s correlation analysis and principal component analysis, coupled with cluster analysis, revealed that the sediments from the Lishui River were mainly influenced by two sources. Cr, Co, Ni, and Cu were mainly derived from natural sources, while Mn, Zn, and Pb originated from agricultural and industrial activities, mining, and vehicular traffic.

Spatial distribution and source identification of heavy metals in a typical Pb/Zn smelter in an arid area of northwest China

Heavy-metal pollution has become a serious problem in the vicinity of mining sites. In this study, we investigated the pollution degree and spatial distribution of heavy metals and determined their sources in soil near a typical Pb/Zn smelter in an arid area of northwest China. The pollution degree, spatial distribution and source identification of heavy metals were evaluated and analyzed by the geo-accumulation index (Igeo), enrichment factor (EF), ArcGIS-based kriging interpolation models and multivariate statistical techniques. The results showed that the average concentrations of Pb, Zn, Cd and Cu were higher than their background contents of Shaanxi Province. The results of chemical speciation fractions show that the non-residual fraction (Acid soluble + Reducible + Oxidizable) of Pb, Zn and Cd were greater than the residual fractions of the same elements, while the results of Cr, Cu and Mn were just contrary. The Igeo values demonstrated that the issue of soils contaminated by Pb, Zn and Cd in this area is very serious, where Cd pollution was the most significant. The EF values decrease in the following order: Cd > Zn > Pb > Cu > Cr, and indicating Cd was extremely severe enrichment. The spatial distribution indicated that Pb, Zn, Cd and Cu mainly originated from smelting activities, which were heavily accumulated in topsoils and decreased with increasing soil depth in the profile distribution. The indexes of Igeo and EF showed that Pb, Zn, Cd and Cu were the most important contaminants, which had the same sources, deriving from anthropogenic metal smelting activities. These results can serve as a basis for designing effective strategies to prevent, control and reduce further heavy-metal contamination of the soils. Meanwhile, the relevant study methods, study hypotheses and methodologies may provide certain reference significance for the study of soil pollution from similar heavy metals.

Distribution of heavy metals in habitation land-use soils with high ecological risk in urban and peri-urban areas

The study investigated spatial distribution of heavy metals in soils of urban, peri-urban and rural habitation land-uses, and the ecological risks associated with them in the Indian Himalayan state of Himachal Pradesh. Soils of undisturbed forest were taken as control. A total of 72 soil samples were collected and assayed by atomic absorption spectrophotometer for cadmium, chromium, lead, manganese, nickel and zinc. Positive correlations were observed between cadmium–chromium, cadmium–manganese, cadmium–nickel, chromium–manganese, chromium–nickel and manganese–nickel. Higher concentrations (mg/kg) of cadmium (4.956 ± 0.031), chromium (17.299 ± 0.567), manganese (76.473 ± 0.031) and nickel (82.225 ± 7.342) were recorded in urban land-use soils. Lead (44.882 ± 3.202) and zinc (192.613 ± 34.180) reported maximum values in peri-urban and rural land-use soils, respectively. Peri-urban and urban land-use soils were extremely polluted with loads of lead and cadmium, respectively. However, control site was contamination-free. High values of contamination factor and geo-accumulation index in urban and peri-urban land-use indicated contamination in order of cadmium > nickel and > zinc. Degree of contamination and associated ecological risk index were also high in urban and peri-urban as compared to rural and control soils.

Spatial distribution of heavy metals and their potential sources in the soil of Yellow River Delta: a traditional oil field in China

In this study, soil samples were collected from different layers throughout the whole Yellow River Delta (YERD), in north China. The total concentration of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), lead (Pb) and zinc (Zn) was determined to demonstrate their spatial distribution and pollution status in different layers of soils throughout the whole YERD. The obtained results suggested a relatively low contamination of heavy metals as observed through the evaluation of CF and RI. The potential ecological risk of Hg is not so severe. Also, the maximum potential threat could be noted only from Cd instead of Hg based on the widespread degree of pollution, which breaks traditional concept that oil production escalates mercury in the soil. The obtained value of EF proves a higher enrichment of heavy metals in the surface soil than in the layer of deep soil induced by human activities. Human activities only slightly elevate As, Cd and Pb. As has the strongest ability downward to lower layer, followed by Cd and Pb in YERD. The source of heavy metals predominantly stems from natural deposits, and their concentrations are controlled by the nature of their association with the mineral. Overall, it shows that the petroleum industry instead of agriculture could be treated as an important source to bring anthropogenic heavy metals in the soils. The human influence only elevated the concentration of heavy metals in the soil of the areas corresponding to the intensive production of oil. In this study some of the measures have also been proposed to avoid and control soil pollution as well as the health risk caused by heavy metals.

Factors that influence the spatial distribution of heavy metals in soil of the Yutian County, Xinjiang, China

In this study, 1165 surface soil samples for heavy metal analysis were collected in the Yutian County, Xinjiang, China. The factors that influence the spatial distribution of heavy metal elements in soils in the study area were analyzed by means of multivariate statistical analysis, geostatistics, spatial autocorrelation, spatial analysis and GIS technology. Results show that among 1165 soil samples, three of which had As contents greater than the risk screening values. The theoretical models for variation function of Cd and Pb were exponential model, while the theoretical models for variation function of Hg, As, Cr, Cu, Ni and Zn were spherical model. Nugget value of Cd was less than 25%, indicated a relatively strong spatial correlation. Nugget value of other elements ranged between 25% and 50%, indicated significant spatial correlations. The spatial autocorrelation Moran's I index of soil heavy metal contents in the Yutian County was greater than 0. There was a positive spatial correlation distribution in the county scale. The spatial distribution of soil heavy metal contents in the Yutian County showed a general decreasing trend from the center of the study area to surrounding areas. Distribution of soil heavy metal contents in the Yutian County varied in different parent materials, soil types and land use patterns. Hg, As, Pb, Cr, Cu, Ni and Zn in soil derived from the same source, contents of which were affected by soil texture.