Metals In Topsoil Research Articles

The Dublin SURGE Project: geochemical baseline for heavy metals in topsoils and spatial correlation with historical industry in Dublin, Ireland

The Dublin SURGE (Soil Urban Geochemistry) Project is Dublin’s first baseline survey of heavy metals and persistent organic pollutants in topsoils and is part of a Europe-wide initiative to map urban geochemical baselines in ten cities. 1,058 samples were collected as part of a stratified random sampling programme in the greater Dublin area to give an overview of baseline conditions in the city. Samples were analysed for 31 inorganic elements including heavy metals. Analysis of results indicates that the concentrations of lead, copper, zinc and mercury are strongly influenced by human activities, with elevated concentrations in the city docklands, inner city and heavy industry areas. Sources of heavy metals in these areas may include historical industry, coal burning, re-use of contaminated soil, modern traffic and leaded paint and petrol. Concentrations of other inorganic elements in topsoil show patterns which are strongly related to regional bedrock parent material. The spatial distributions of heavy metals, in particular Pb and As, are explored in detail with respect to regional geology and the influence of historical industry on soil quality. Exploratory data, geostatistical and correlation analyses suggest that the concentrations of heavy metals tend to increase as the intensity of historical industrial activity increases. In particular, drinks production, power generation, oil/gas/coal, metals and textile historical industries appear to be the contamination source for several heavy metals. The data provide a geochemical baseline relevant to the protection of human health, compliance with environmental legislation, land use planning and urban regeneration.

Environmental geochemical mapping and multivariate geostatistical analysis of heavy metals in topsoils of a closed steel smelter: Capital Iron & Steel Factory, Beijing, China

A high-density survey was conducted in this study to determine the spatial distribution and possible sources of heavy metals at the former Capital Iron & Steel Factory, Beijing, China. A total of 400 surface soil samples were collected at a density of 16 samples per km2, and the concentrations of heavy metals, such as Ni, Cr, V, As, Cu, Pb, Cd, Zn and Hg, were analyzed. The spatial distribution characteristics of these metals were demonstrated by environmental geochemical mapping. The mean concentrations of Ni, Cr, V and As are close to the background values. Enrichment factors show that the soil concentrations of Cu, Pb, Cd, Zn and Hg were higher than the background values, especially Hg. Multivariate geostatistical analysis suggests that Cu, Pb, Cd and Zn have similar properties and their presence was mainly from steel-smelting activities. However, the Hg contamination was more weakly related to the steel smelting activities, partially due to other anthropogenic activities, such as the combustion of coal for heating.

Effect of sewage sludge on metal content of grassland soil and herbage in semiarid lands

Utilization for agriculture is one of the main disposal methods for sewage sludge. Subirrigated pastures are close to settlements and under intensive usage. The objective of this study was to investigate the effects of sewage sludge on subirrigated pasture soil and plant metal concentrations, and the relationship between them. Activated sewage sludge was applied to surface grassland at 25, 50, 75, and 100 t ha^{-1} year^{-1} treatments for 2 years. The concentration of all metals in topsoil (0-20 cm) increased depending on application dosages, but only Zn concentration increased in subsoil (20-40 cm) consistently. While in the second year the concentration of topsoil diethylene triamine pentaacetic acid (DTPA) metals increased significantly, it decreased in the subsoil. The ratio of organic matter increased in topsoil, but decreased in subsoil compared to the control. Doses of sewage sludge of 25 and 50 t ha^{-1} did not increase the metal content of herbage. However, the herbage's Cu, Zn, Pb, and Cd content increased at 75 and 100 t ha^{-1} treatments in comparison with both lower doses and the control. Similar to the soil concentration, the Zn content of herbage increased proportionally with higher sewage sludge application doses. Topsoil DTPA-extractable Zn, Cu, and Pb concentrations were correlated to herbage Zn, Cu, and Pb content significantly and positively. In subsoil, only DTPA-extractable Cu concentration was correlated to herbage Cu content significantly and negatively (r = -0.53**). A 25 t ha^{-1} year^{-1} application of sewage sludge can be recommended as an organic fertilizer in semiarid subirrigated pastures, as it increases topsoil organic matter and results in a low concentration of DTPA-extractable and plant metal content.

Potential risk effect from elevated levels of soil heavy metals on human health in the Niger delta

An analysis of the soil quality in the Niger Delta Area (NDA) was carried out to determine the severity of soil contamination. The United States Environmental Protection Agency (US EPA) risk assessment model was used in determining the potential health risk due to lifetime exposure (by means of ingestion, dermal contact and inhalation) of the population to heavy metal contents in the soil. Substantial levels of contamination were found indicating elevated levels of heavy metals above background concentrations from controlled samples in the areas. Median topsoil metal concentrations (0–15cm) in the NDA measured in mg/kg were: Zn 58.3±37.0, Cd 1.3±1.0, Cr(VI) 13.2±5.5, Cu 28.3±31.5, Pb 895.1±423.9, Ni 42.7±20.3, Mn 201.8±77.5 and Fe 1303.5±2028.6. Pb, Ni, Zn, Cd, Cr(VI), Fe and Mn exceeded some guideline and standard values; while the comprehensive levels of total metals contamination exceeded the environmental action level for soils, which could potentially affect human health. The collective total risk (carcinogenic and non-carcinogenic) for minors and adults were established from the model using the slope factors and reference dose of the compounds respectively. The study has shown that soil contamination in the industrial and residential regions are similarly significant; while the risk assessment proved that based on the pollutants concentration in the soil, metals with the highest cancer risk values (Pb=2.62E-02 and Cr(VI)=1.52E-02) have the potential of affecting the health status of the residents, especially for children in the region. The chronic daily intake of the metals are of major concern as their cumulative effect could result to several health complications of children and adults in the region.

Sources identification of heavy metals in urban topsoil from inside the Xi'an Second Ringroad, NW China using multivariate statistical methods

Abstract The concentrations of Co, Cr, Cu, Mn, Ni, Pb, Zn, and V in urban topsoil samples collected from inside the Xi'an Second Ringroad, northwestern China were measured by X-ray fluorescence spectroscopy. Correlation coefficient analysis, factor analysis and cluster analysis were used to analyze the data and to identify the possible sources of these heavy metals. The results show that the mean concentrations of Co, Cr, Cu, Mn, Ni, Pb, Zn, and V in urban topsoil from Xi'an are 19.3, 81.1, 54.3, 671.5, 34.5, 59.7, 186.2, and 85.2 mg kg− 1 respectively, which are higher than the background values of Shaanxi soil. The mean concentrations of heavy metals in topsoil divided by the corresponding background values of Shaanxi soil increase in the order of Ni

Screening of the Spatial Distribution of Risk Metals in Topsoil from an Industrial Complex

Screening of the Spatial Distribution of Risk Metals in Topsoil from an Industrial Complex For the sustainable development of urban areas, it is necessary to identify if environmental pollution exists and where hot spot pollution sources lie. In this study, 280 topsoil samples were collected from an industry estate in Zlin (the Czech Republic). In these samples, the presence of toxic metal was analyzed by energy dispersed X-Ray fluorescence (ED-XRF), and statistical analysis revealed that the major anthropogenic contaminants in the topsoil were Pb, Zn and Sn. Further contaminant analysis by atomic absorption spectrometry (AAS) determined the maximum contents of 28558.47 mg/kg for Pb, 1132.35 mg/kg for Sn and 2865.22 mg/kg for Zn in selected topsoil samples. According to soil pollution index results, the main proportion of topsoil is contaminated, with the possible sources of contamination being traffic and a nearby municipal heating plant. This study proves that the combination of preliminary ED-XRF topsoil analysis, a multivariative statistical approach, AAS analysis and the geographical information system (GIS) is effective and together form a powerful tool for mapping topsoil contamination and conducting an environmental risk assessment.

Concentration, Distribution and Comparison of Total and Bioavailable Heavy Metals in Top Soils of Bonab District in Zanjan Province

Heavy metal contamination of soils is a widespread problem in Zanjan province located in North West Iran due to natural pedo geochemical background and anthropogenic sources. The province is highly polluted by some heavy metals due to the presence of mineral resources notably Lead and Zinc, their improper utilization, and also the development of a number of related industries. Bonab district was selected for detail study and the objectives of the study were set to evaluate the total as well as bioavailable fraction of heavy metals in surficial soils within the studied area. 72 soil samples were collected and analyzed for heavy metal contamination by Atomic Absorption Spectrometry (AAS). The obtained results when compared with WHO and USEPA standards show a very high concentration of some toxic metals. Soils were basically polluted by Pb, Zn, Cu, and Cd. Bioavailable fraction of studied metals were also measured with formation of metal complex with Diethylene tri amine penta acetic acid (DTPA) agent. To find the share of the anthropogenic sources in the contamination of soils, the Enrichment factor (EF) and Geological Accumulation Index were measured and the distribution maps were drawn using Arc GIS (9.3). Highest concentrations of some toxic metals were found as isolated patches around the Bonab Industrial Town as well as within and around the most populated areas of the district notably Zanjan city indicating its anthropogenic origin.

Distribution of Heavy Metals, Chemical Fractions and Ecological Risks around a Molybdenum Mine in Liaoning Province, China

The total contents of lead, arsenic, mercury, chromium, cadmium, zinc, copper, molybdenum and nickel were determined in soils collected from mining and agricultural areas around the molybdenum mine in Liaoning Province, China. The distribution, chemical fractions and ecological risks of heavy metals in soils were investigated and assessed. It was found that: the degrees of warning for all soils, both mining industry areas and agricultural areas, were serious warning. The results meant that all soils were contaminated seriously by heavy metals. The observed scheme of chemical fractions for heavy metals in soils of different sites was as follows commonly: residual>oxidable> reducible>acid soluble. The sources of heavy metals in top soils around the mine were as follows: dust fall, residue in the open air, higher background in soil-forming process, accompaniment element, automobile exhaust, wear of tires and brakes, release of heavy metals from ore tailing, the application of pesticides and irrigation with wastewater.

Monitoring and assessing heavy metals in topsoils as potential diffuse pollutants in the Pyeongchang River Basin, Korea

Topsoils, mainly from crop fields, orchards, forests, and barns around the Pyeongchang River, were collected to investigate their heavy metal concentrations. Pollution load index, ecological risk index, and enrichment factor were applied to assess levels of heavy metal contamination for topsoils. The concentrations of cadmium (Cd) (1.7 mg/kg) and chromium (Cr) (4.1 mg/kg) exceeded the troublesome level in one site, whereas zinc (Zn) (396.7 to 711.1 mg/kg) and nickel (Ni) (40.1 to 95.3 mg/kg) in several topsoils exceeded the troublesome to countermeasure levels, according to soil contamination standards for the study areas. A significant risk of contamination was observed for mercury (Hg) by all indices, although the concentration in most of the topsoils was below the guideline. As expected, a positive linear correlation was observed for the values of pollution load index and ecological risk index, demonstrating lower heavy metal contamination in upstream areas compared to those downstream. High to extremely high ecological risk was observed in several samples for Zn and Ni, while all of the soils were unpolluted to slightly polluted, according to the pollution load index. A baseline study was not performed earlier for these sites, so these assessed values of heavy metals should be used as reference values for further assessment.

Spatial distribution of metals in top soils of Islamabad City, Pakistan

Present study was conducted in rapidly growing city Islamabad, and surface soils were collected from three major land cover types viz., built-up, drain side, and green areas. A total of seven physicochemical parameters and 11 metals were determined in surface soils. Factor analysis based on principal component analysis explained total variance of 68.0%, 64.5%, and 60.2% of three land cover types and showed high loadings for major elements (Mg and K) in built-up and green area and Fe in drain side. Top soil pollution index was carried out by using geo-accumulation index and metal pollution index (MPI₆). Concentration of major elements (Ca, Mg, Na, K) in surface soils is derived by parent material, whereas concentration of Fe, Ni, Pb, and Zn were mainly related with anthropogenic sources. Geostatistical methods such as kirging identified hotspot areas of metal contamination by Pb, Ni, and Zn in built-up areas influenced mainly by vehicular emissions and waste disposal. The results stresses that land clearing should be avoided to reduce contamination and management of urban soils.

Heavy metals in 3300‐year‐old agricultural soils used to assess present soil contamination

For evaluating present concentrations of heavy metals in soils, it is important to be able to determine natural or background soil concentrations. Here, we compare the content of 7 m HNO3‐extractable and 0.2 m Na‐EDTA‐extractable fractions of cadmium (Cd), zinc (Zn), lead (Pb) and copper (Cu) in present day cultivated A horizons (Ap) under different land uses and 19 buried A horizons (Apb) that have been covered by 3300‐year‐old burial mounds. The buried A horizons represent a unique opportunity to evaluate background concentrations of heavy metals in top soil. Variations in background concentrations were mainly related to clay content. Using the grain size distribution of present‐day topsoils (cultivated and forest/natural A horizons), the background concentrations were calculated and subtracted from observed concentrations prior to an evaluation of soil‐type‐ and land‐use‐specific metal accumulation. All cultivated soils were significantly enriched with respect to Cd, Pb, Zn and Cu over the last 3300 years and all forest soils were enriched with Pb. The study highlights the importance of using appropriate reference material for assessing present‐day metal concentrations and stocks.

Concentration, Distribution and Comparison of Total and Bioavailable Metals in Top Soils and Plants Accumulation in Zanjan Zinc Industrial Town-Iran

Heavy metal contamination of metal-mined soils is a widespread problem in parts of Zanjan province. The province located in North West of Iran is highly polluted by heavy metals due to the presence, improper utilization of its mineral resources notably Lead and Zinc, and also the development of a number of related industries. Soils are basically polluted by Pb, Zn and Cd and their concentrations in top soils are very high exceeding European and USEPA standards. The main objective of this study is to evaluate heavy metals concentration and bioavailable fractions of heavy metals and accumulation of such toxic metals in native plants growing naturally on the polluted sites. The information obtained from this study is of great value to obtain bioavailability of the toxic metals and their potential harmful effects for plants, animals and humans.

<b>Heavy metals contamination of topsoil and dispersion in the vicinities of reclaimed

Growing concern about reclamation of auto-repair workshop areas for residential and agricultural purposes makes risk assessment of heavy metal contamination of the study area imperative. In addition, the study is aimed at ascertaining the dispersion of contaminated Zn, Ni, Cr, Hg, and Pb within the soil profile. A total of 75 soil samples from auto-repair workshops and 18 soil samples from control sites were collected. Significant levels of contamination were found in view of elevated levels of these metals above background concentrations in control sites. Average topsoil metal concentrations (0-10 cm) in auto-repair workshop areas were: Zn 0.90 ± 0.5, Ni 11.5 ± 3.3, Cr 5.3 ± 2.3, Hg 9.4 ± 4.6 and Pb 133 ± 66 mg/kg. Lead was the most significant contaminants, and the degree of contamination was highest for Pb followed by Hg. The detailed levels of total metal contamination for Pb and Hg exceeded international thresholds for agricultural use. Enrichment factor within the soil profile metals were Zn 3.37, Ni 3.38, Cr 6.22, Hg 14.5 and Pb 21.1. The enrichment factor reflects the ratio of average concentration at a particular sampling location to average concentration at control sites. The general trend of dispersion of metal contaminants within the soil profile studied is Pb >> Ni > Hg > Cr >>Zn. KEY WORDS: Auto-repair, Lead, Mercury, Soil, Heavy metals, Dispersion Bull. Chem. Soc. Ethiop. 2008 , 22(3), 339-348.

Using Multivariate Statistical and Geostatistical Methods to Identify Spatial Variability of Trace Elements in Agricultural Soils in Dongguan City, Guangdong, China

Dongguan City, located in the Pearl River Delta, South China, is famous for its rapid industrialization in the past 30 years. A total of 90 topsoil samples have been collected from agricultural fields, including vegetable and orchard soils in the city, and eight heavy metals (As, Cu, Cd, Cr, Hg, Ni, Pb, and Zn) and other items (pH values and organic matter) have been analyzed, to evaluate the influence of anthropic activities on the environmental quality of agricultural soils and to identify the spatial distribution of trace elements and possible sources of trace elements. The elements Hg, Pb, and Cd have accumulated remarkably here, incomparison with the soil background content of elements in Guangdong Province. Pollution is more serious in the western plain and the central region, which are heavily distributed with industries and rivers. Multivariate and geostatistical methods have been applied to differentiate the influences of natural processes and human activities on the pollution of heavy metals in topsoils in the study area. The results of cluster analysis (CA) and factor analysis (FA) show that Ni, Cr, Cu, Zn, and As are grouped in factor F1, Pb in F2, and Cd and Hg in F3, respectively. The spatial pattern of the three factors may be well demonstrated by geostatistical analysis. It is shown that the first factor could be considered as a natural source controlled by parent rocks. The second factor could be referred to as “industrial and traffic pollution sources”. The source of the third factor is mainly controlled by long-term anthropic activities, as a consequence of agricultural activities, fossil fuel consumption, and atmospheric deposition.

Multivariate geostatistical analysis of heavy metals in topsoils from Beijing, China

Background. Regional soil environmental quality is a hotspot and difficulty in the environmental sciences for the spatial variability of pollutants and the relationship between them. Beijing, the capital of China, has been undergoing a rapid economical development during the past three decades, and thus might encounter the same issues as the developed countries. However, there is little information about the soil environmental quality of Beijing, especially at the regional scale. The real soil environmental situation of heavy metals remains unknown, even less the sources of possible pollutants. Objectives. The main objectives were to identify the spatial variability and main sources of heavy metals in Beijing soils by conducting multivariate statistical analyses, including geostatistical analysis assisted with GIS tools. These results will contribute to the establishment of the soil quality baseline and the management of regional environment. Materials and Methods. Seven hundred and seventy-three samples of topsoils (0–20 cm) were collected from all over Beijing, China. The samples were digested with HNO3 and H2O2. The concentrations of Cr, Cu, Ni, Pb and Zn were analyzed with a FL-AAS and those of Cd with a GF-AAS. The concentrations of As were determined with AFS-2202. Principal component analysis (PCA) and partial correlation analysis (CA) were used and geostatistics was conducted for the data processing. Results. Concentrations of topsoil As, Cd, Cr, Cu, Ni, Pb and Zn in the Beijing area were measured and contour maps were constructed to describe the metals' spatial distribution. Except for the background effect of the soils, anthropogenic factors made the soil heavy metal concentrations increase, especially in the center of the city. Combined with the PCA results, it was found that vehicle exhaust and smelters were the main sources of soil heavy metals. Pedogenic factors were also controlling the spatial features of metals. Discussion. Combined with the results of PCA, 7 heavy metals could be divided into 4 factors. F1 was the metals, i.e., Cu, Pb, Zn, mainly controlled by the human activities. Cr and Ni was in F2, Cd in F3 and As in F4. These 3 factors might be con

Influence of parent sediments on the concentration of heavy metals in urban and suburban soils in Turku, Finland

The purpose of this study was to examine the influence of parent sediment material on soil geochemistry and to locate possible pollution sources in the area of Turku town in southwestern Finland. The study area is glaciated terrain and subsurface samples were chosen to represent five different parent sediment materials: glacial till, glaciofluvial or littoral sand, clay, peat and marine mud. Elemental concentrations of surface (100 samples) and background soil (50 samples) were analysed by ICP-AES (Al, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V) and by graphite furnace AAS (As, Cd, Mo, Se). Loss-on-ignition was determined as an indicator of organic matter. Analytical results were examined using multivariate statistical methods. The results indicate that the studied soils are not heavily contaminated; there were only few sample sites with elevated heavy metal concentrations. High Pb concentrations were observed along main traffic routes, and also in places where there has been small-scale use of antifouling paints. However, concentrations of heavy metals in topsoil were in general significantly lower than those measured in large cities elsewhere. The parent material strongly affects the geochemical character of the soils. Clays naturally have a significantly higher concentration of heavy metals than sands or till material. This is also reflected in concentrations in organic topsoil. When assessing target levels for polluted soil, the primary sediment appears to be a more important factor than the amount of organic matter.

Site-specific natural background concentrations of metals in topsoil from the Trail region, British Columbia, Canada

The natural background level of elements in the surface soil of a given area is largely dependent on the geological setting of the region and the underlying soil parent material. Due to the heterogeneity of soil in various environments, it is essential to determine the site-specific natural background levels of elements to quantify the degree of influence of the anthropogenic source(s) within a given study area. This paper discusses the process involved in establishing the natural background level of trace metals and other elements in topsoil for the area surrounding the Teck Cominco zinc–lead smelter in Trail, British Columbia, Canada. The environmental assessment of soil in the Trail region is difficult due to the natural enrichment of metals in surficial material and topsoil as a result of the influence of mineralized bedrock in the region. Detailed examination of the study area based on the deposition data and previously collected soil data led to the selection of presumably the least anthropogenically influenced background sites in the study area, which also reflect the geological diversity of the region. The range of background was defined using the median plus or minus two median absolute deviations [median±(2 × MAD)], after the outliers were excluded. The outliers were identified using the Tukey boxplot concept and the cause of high metal concentrations in the outlier samples is attributed to their proximity to the historical mining sites in the region. The upper limit of the background range was estimated to be (in mg/kg): As, 11.0; Cd, 0.81; Cu, 38.1; Hg, 0.07; Pb, 27.7; Zn, 152. The resulting values are significantly more conservative estimates than would be obtained by other widely used methods (e.g. the mean plus or minus two standard deviations) due to the robust procedure, which prevents any interference by the extreme values in the collected soil background dataset. The upper background thresholds of metals estimated by the 95th percentile resulted in significantly different estimates, especially for As, Hg, Pb and Zn, from the previously reported values. This highlights the need for revision of the risk-based screening levels by environmental regulations in the study area.

Monitoring of heavy metals in topsoils, atmospheric particles and plant leaves to identify possible contamination sources

The research reveals results of metal pollution on urban topsoil in relation to the metal content in leaves of two plant species and atmospheric particles. The content of pollutants (Ba, Cd, Cu, Fe, Mn, Ni, Pb, V and Ti) was determined by ICP-OES. Twenty-two samples of soil were collected over a six-month period from two different urban sites and one from a rural zone. Regarding the pollution level, the studied soils were found to be low. Results for enrichment (EF) and concentration (CF) factors showed that soils were enriched in Pb, Ba, Cu and Ni. However, both species of plants showed a common behavior for all elements acting as excluders. ANOVA and different multivariate statistical analyses confirmed that the main pollution source of soil was traffic and fertilizers. Cd, Fe, Mn, Ti and V elements were attributed to natural sources. Also, it was suggested that N. oleander leaf is useful as a bio-monitors of soil pollution by Cu. Similarly, a direct relationship was found between the content of Cu in soils with the Cu level in PM 10 atmospheric particles. The origin was attributed to dry and wet atmospheric deposition processes.

New Metal Emission Patterns in Road Traffic Environments

The increased awareness of traffic as a major diffuse metal emission source emphasizes the need for more detailed information on the various traffic-related sources and how and where the metals are dispersed. In this study, metal emission patterns in the road traffic environment were examined from the perspective of different surrounding factors, e.g. the importance of intersections, deceleration, vehicle speed and traffic density. A total of 148 topsoil samples from 18 south Swedish roads were analysed (using GFAAS) for traffic-emitted metals, i.e. Cd, Cr, Cu, Ni, Pb, Sb and Zn. The roadside topsoil metal concentrations were used to examine correlations between metals and surrounding factors. The studied metals were divided into three groups corresponding to different emission sources: metals from decelerating activities (Cu, Sb and Zn), metals as historical residues from the combustion of petrol (Pb and Cd), and non-source-specific metals (Cr and Ni). It was found that Cu and Sb, despite their rather short history as traffic-emitted metals, have increased more than eightfold in roadside soils compared to background levels. The major source of road traffic related Cu and Sb is brake linings. The significant increase of Cu and Sb in roadside topsoil stresses the need for metal transport studies as well as effect studies of these metals. Metals emitted due to decelerating activities were not correlated to elevated concentrations near road junctions. Emission patterns of traffic-related metals alongside roads are crucial in order to be able to evaluate the optimal localization of storm water treatment ponds.

Trace-metal pollution of soils in northern England

Data from a regional geochemical survey of topsoils (n=818) in rural and peri-urban areas over a single parent material (Coal Measures) are used to identify two types of trace-metal pollution – severe local contamination at 20 sites and widespread, diffuse pollution in more densely populated areas. Median concentrations of several trace metals in topsoils were significantly higher in areas of high, compared to low, population density (percentage increases in parenthesis): As (31), Cu (39), Fe (7), Mo (26–36), Ni (29), Pb (20), Sn (40), and Zn (11). Four potential pathways of diffuse trace-metal pollution are postulated: coal-ash dispersal, atmospheric aerosols derived from coal combustion, the historical spreading of sewage waste, and those related to road vehicles. The statistical analysis of geochemical data classified by local, human population density can be an effective means of identifying the magnitude and extent of diffuse pollution, and could help to establish natural background levels.