Metal Concentrations In Topsoil Research Articles

Anthropogenic increase of heavy metals in soil from a heavily contaminated area of China

ABSTRACT Evaluating the variation in heavy metal concentrations in soil caused by anthropogenic activities in heavily contaminated areas is of great significance. The degree of heavy metal pollution in soil is primarily assessed by different indices with different standards and reference elements. However, these methods cannot be used to evaluate the degree of heavy metal pollution caused by anthropogenic activities. In this study, Zhuzhou, China was selected as the contaminated area, and Yueyang, China was selected as the background area, where geological and climatic conditions are similar to those of Zhuzhou, China. The concentrations of As (6.6–23.6 mg/kg), Cd (0.125–0.757 mg/kg), Cu (33–75 mg/kg), Hg (0.032–0.202 mg/kg), Pb (17–108 mg/kg), and Zn (74–122 mg/kg) in the vertical soil profiles in the contaminated area were higher than those in the background area (ranging 1.7–20.7, 0.085–0.210, 21–47, 0.030–0.105, 17–38 and 32–88 mg/kg, respectively). K2O/Al2O3, SiO2/Al2O3, and the weathering leaching coefficient (ba) showed little difference, suggesting that the weathering degree of soil in these two areas was similar. The weathering degree of soil governs the geochemical behavior of heavy metals and reference elements. According to the prediction models for heavy metal concentrations and organic carbon, K2O/Al2O3, and SiO2/Al2O3 in the soil profiles from the background area, the increase in heavy metal concentrations in the topsoil in the contaminated area was depicted. The heavy metal concentrations in topsoil were obviously affected by anthropogenic activities. This study provides a case study for evaluating the impact of anthropogenic activities on heavy metals in soil.

Comparison of magnetic susceptibility probes relevantly used in soil contamination applications.

Magnetic susceptibility (MS) technology can achieve the efficient rough measurement, mapping, and pollution assessment of soil heavy metal concentrations in topsoil due to atmospheric dust contamination. However, previous studies of commonly used MS field probes (MS2D, MS2F, and MS2K) have not dealt with the range of magnetic signal detection and the attenuation characteristics of the signal with respect to distance. In this study, the vertical and horizontal measurement ranges of the MS2D, MS2F, and MS2K probes were explored through laboratory and field experiments, and the intensity of their magnetic signals was further compared and analyzed in the field. The results showed that the magnetic signal intensity of the three probes decreased exponentially with distance. The penetration depths of the MS2D, MS2F, and MS2K probes were 8.5, 2.4, and 3.0cm, respectively, and the horizontal detection boundary lengths of their magnetic signals were 32, 8, and 6.8cm, respectively. In the field surface soil MS detection, the magnetic measurement signals of the MS2F and MS2K probes showed a weak linear correlation with the MS2D probe (R2 of 0.43 and 0.50, respectively), while the MS2F and MS2K probes had a significantly better correlation (R2 = 0.68) with each other. In general, the MS2D probe and MS2K probe correlation had a slope close to unity, meaning MS2K probes had good mutual substitution. Furthermore, results of this study improve the effectiveness of the MS evaluation of heavy metal pollution in urban topsoil.

Impact of Long-term and Intensive Rice Cultivation on Heavy Metal Accumulation in Soil: An Observation from Mae La River Basin, Central Thailand

Intensive rice cultivation relies greatly on chemical fertilizers and pesticides, some of which contain heavy metals as impurities. Application of these agrochemicals can result in heavy metal accumulation in soil. This research discusses the current concentrations and migration pathways of heavy metals (Cu, Pb and Zn) in paddy soil subjected to long-term use of chemical fertilizers and pesticides. The study of soil pH and metal concentrations in 60 surface and subsurface samples from a relatively small river basin revealed that although highly varied, pH values and metal concentrations in topsoil were significantly different from values in subsurface soil. The soil pH as low as 5.4 was observed in topsoil. Although the observed levels in topsoil were in within safe limits according to the Dutch standard, they were significantly elevated above the subsurface concentrations. Evidence on the differences between their concentrations in paddy soil and river sediments suggests that considerable amount of metals in paddy fields have been transported into the river. A detailed study of input inventory, fluxes and migration pathways of these metals in the river basin can provide a better understanding of their mobility and measures that might needed to safeguard aquatic habitats, especially the well-known striped snakehead fish in Mae La River.
 HIGHLIGHTS
 
 Agrochemicals such as chemical fertilizers and pesticides contain heavy metals as impurities
 Long-term and continuous use of agrochemicals in rice production has resulted in lower pH and higher heavy metal contents in topsoil
 Low pH in topsoil can enhance metal mobility, suggesting that some of the heavy metals from agrochemical inputs are likely to be transported from paddy fields to their surrounding environments
 This study demonstrates that the effects of agrochemical use extend beyond agricultural soil. Impact assessment of their application, thus, should cover all major compartments/systems in the basin
 
 GRAPHICAL ABSTRACT

A spatial prioritization method for identifying potential eco-risk distributions of heavy metals in soil and birds

Geochemical approaches are popular for evaluations based on heavy metal concentrations in sediments or soils for eco-risk assessment. This study proposes a systematic geochemical approach (SymGeo) to explore six heavy metals in topsoils and bird tissues and organs of the target birds. We assume that the proposed approach based on field-collected heavy metals in topsoils and feathers can predict the areas with the potential risk of the heavy metals in birds. Finite mixture distribution modeling (FMDM) was used to identify background values of the heavy metal concentrations in topsoil. A spatial enrichment factor (EF), potential contamination index (PCI), contamination degree (Cod), and potential ecological risk index (PRI) based on FMDM results for topsoil, and a potential risk index (PRIbird) of heavy metals in the birds, were utilized for systematic prioritization of high eco-risk areas. Using multiple EF, PRI, and Cod results and multiple PRI-based maps of the heavy metals in feathers, we systematically prioritized risk areas where there is a high potential for heavy metal contamination in the birds. Our results indicate that heavy metal concentrations in the feather, liver, and kidney are not spatially cross-autocorrelated but are statistically significantly correlated with some heavy metals in topsoil due to external and internal depositions. Further, multiple EF, Cod, and RI distributions for topsoil, along with the PRI of the feather, showed that adequate coverages for potential risk for birds were greater than 71.05% in the top 30% and 84.69% in the top 20% potential eco-risk priority area of heavy metals in bird liver and kidney. Hence, our proposed approach suggests that assessments of heavy metals in bird feathers and topsoils without bird organs can be utilized to identify spatially high-risk areas. The proposed approach could be improved by incorporating water and sediment samples to enhance the crowdsourcing and the species-specific data.

From environmental data acquisition to assessment of gardeners' exposure: feedback in an urban context highly contaminated with metals.

Although growing vegetables in urban gardens has several benefits, some questions in relation with the safety of foods remain when the self-production is carried out on highly contaminated garden soils. To better assess the local population's exposure to Cd and Pb induced by the past activities of a lead smelter, a participatory program was initiated in 115 private kitchen gardens located in northern France to assist gardeners in understanding their soil environment. The challenge included contributing to the database of urban garden soils with the collection of a large number of samples: 1525 crops grouped into 12 types (leaf, fruiting, root, stem and bulbous vegetables, tubers, cabbages, leguminous plants, celeriac, fresh herbs, fruits, and berries), 708 topsoils, and 52 samples of self-produced compost. The main results were as follows: (i) topsoils were strongly contaminated by Cd and Pb compared to regional reference values; (ii) great variability in physicochemical parameters and metal concentrations in topsoils; (iii) the highest concentrations of Cd and Pb for celeriac and fresh herbs and the lowest for fruits and fruiting vegetables; (iv) a high percentage of vegetables that did not comply with the European foodstuff legislation; and (v) most self-produced compost samples were strongly contaminated. This study aimed to raise awareness and generate functional recommendations to reduce human exposure and to provide useful data that could be considered in other environmental contexts.

Impact of informal electronic waste recycling on metal concentrations in soils and dusts

Electronic and electrical equipment contains over 1000 different substances, including metals. During informal e-waste recycling some of these substances such as metals, are released into the environment causing environmental pollution. This study assessed the impact of different informal e-waste recycling activities (burning, dismantling, and repairing) on metal concentrations in top soils and various dust.A comparative cross-sectional study design was adopted to assess metal concentrations in top soils and in various dust samples from multiple e-waste recycling sites. Metal concentrations at e-waste recycling sites were compared to the concentrations at control sites in three study locations in Nigeria (Lagos, Ibadan, and Aba). In the three study locations, mean metal concentrations at the e-waste recycling sites exceeded the concentrations at the control sites and the Nigerian standard guideline values by 100 s to 1000 s times. Burning sites showed the highest pollution level, followed by dismantling sites, then repair sites.Our findings show serious environmental and public health concerns. The metal concentrations were also higher than levels reported in other studies at the same locations in Nigeria, indicating that the situation is worsening. This study provides scientific evidence for an urgent need to develop effective strategies to strengthen enforcement of existing e-waste regulations in Nigeria.

Investigating the Role of Wind in the Dispersion of Heavy Metals Around Mines in Arid Regions (a Case Study from Kushk Pb-Zn Mine, Bafgh, Iran).

The Kushk Pb-Zn mine is located in Central Iran and it has been in operation for the last 75years. To investigate the role of wind dispersion of heavy metal pollutants from the mine area, dust samples were collected during 1year and topsoil samples were collected around the mine. Results showed that the topsoil is polluted with Pb and Zn to about 1500m away from the mine. It was also found that there was not a significant difference between the metal concentrations in topsoil and dust samples. The Pb and Zn concentrations in the dust samples exceeded 200mgkg-1 and their lateral dispersion via wind was estimated to be about 4km away from the mine. It has been shown that a combination of mining activities and mechanical dispersion via water and wind have caused lateral movement of heavy metals in this area.

Preliminary Magnetic Susceptibility Results from the Northwestern Part of Madinah, Saudi Arabia: Environmental Degradation of Wadi Aqiq

Recent advances in environmental magnetism have led to new applications in understanding soil pollutions from anthropogenic sources. The utility of environmental magnetic techniques varies widely depending on biological, chemical and physical processes that create and transform soils and sediments. Researchers in some European and Asian countries have successfully studied heavy metals in top soils using magnetic susceptibility technique. Accelerated urbanization in the past two decades has significantly altered the environmental landscape of Madinah. A famous wadi Aqiq in the heart of Madinah, an important conduit for groundwater recharge, is one of the most affected. This study thus focuses on magnetic susceptibility application as environmental magnetic technique to map heavy metal concentrations in top soils along wadi Aqiq, northwestern part of Madinah. Higher values of magnetic susceptibility from soil cover than those from parent igneous rocks indicate anthropogenic origin metallic contamination in the study area. The trucks/tankers parking area reveal highest values of magnetic susceptibility. The areas close to heavy vehicular traffic along two major roads also indicate higher magnetic susceptibilities because of enhanced metallic contaminations. The areas covered by residential and commercial buildings reveal medium level of magnetic susceptibilities. The left over asphalted materials at various places in the area is another source of high magnetic susceptibilities. Widely distributed metallic objects in the area, such as hangers, cans, and construction materials also contribute to enhanced soil contamination as evident from high magnetic susceptibilities.

Heavy metal and metalloid concentrations in soils under pasture of southern New Zealand

Heavy metal and metalloid (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) levels in 284 topsoil (0–30cm) samples were measured from 20,000km2 of southern New Zealand in a systematic survey and the concentrations and patterns between samples sites were studied. Samples were analysed by the inductively coupled mass spectrometry method on an aqua regia digest. Except for Hg, median concentrations from land classed as high producing exotic grassland (pasture; 241 samples) were consistently elevated relative to median natural background levels under native vegetation. The major control of heavy metal enrichment in pasture is P-based fertiliser application (Cd, Cu, Zn), the soil parent material (Ni, Hg) or a combination of both (As, Cr, Pb), with Pb also affected by proximity to urban centres and major roads. There may be a trend of increasing heavy metal concentration with increasing intensity of land use. Comparison shows there is strong, regional variation in median heavy metal concentrations in topsoil around New Zealand and highlight a need for systematic and consistent study of heavy metals in soil nationally.

Concentration of Heavy Metals in the Soils near Some Mechanic Villages in Abeokuta Metropolis, Ogun State, Nigeria.

Soils and water bodies near auto mechanic village (MV) contain heavy metals, which pollute the environments and are hazardous to human and environmental health. Assessment of heavy metal concentration in three replicate soil and water samples from three MVs (Fajol, Id-Aba and Kotopo) in Abeokuta metropolis in Nigeria was conducted. Heavy metal concentrations in topsoil of the MVs showed copper ranging from 0.02 mgkg-1 in the topsoil at Idi-Aba MV to 126.89 mgkg-1 for topsoil at Kotopo MV. The level of copper detected in Kotopo MV soil is however higher than the allowable limits for Sweden, Netherlands and Germany. Mean concentration of zinc in soils of the MVs were 2.89, 0.91 and 86.23 mgkg-1 respectively for Fajol, Idi-Aba and Kotopo MV respectively. Metal enrichment factor indicated that the contamination degree ranged from unpolluted to moderately polluted areas. Copper is the most enriched metal in the soil of the MVs especially at Kotopo MV. Relative abundance of the metals in the topsoil (0-15cm) in Fajol MV follow the order Zn > Ni> Cr >Pb >Cu > Co> Cd. For the Idi-Aba MV, relative abundance is in the order Ni > Zn > Cr > Pb> Cu > Co and Cd, and that of Kotopo MV was Cu >Zn> Pb > Ni > Cr, Co and Cd. Mean heavy metal in the water samples were lower than those found in the soils of the MVs. Stream water near the Kotopo MV had the highest concentration of most metals. Zinc had the highest mean concentration of 2.02 mgL-1 while copper was 1.09 mgL-1. There is an urgent need to put measures in place to monitor the activities in these MVs in order to safeguard peoples’ health environmental integrity.

Estimating heavy metal concentrations in topsoil from vegetation reflectance spectra of Hyperion images: A case study of Yushu County, Qinghai, China.

In this study, we explored the feasibility of estimating the soil heavy metal concentrations using the hyperspectral satellite image. The concentration of As, Pb, Zn and Cd elements in 48 topsoil samples collected from the field in Yushu County of the Sanjiangyuan regions was measured in the laboratory. We then extracted 176 vegetation spectral reflectance bands of 48 soil samples as well as five vegetation indices from two Hyperion images. Following that, the partial least squares regression (PLSR) method was employed to estimate the soil heavy metal concentrations using the above two independent sets of Hyperion-derived variables, separately constructed the estimation model between the 176 vegetation spectral reflectance bands and the soil heavy metal concentrations (called the vegetation spectral reflectance-based estimation model), and between the five vegetation indices being used as the independent variable and the soil heavy metal concentrations (called synthetic vegetation index-based estimation model). Using RPD (the ratio of standard deviation from the 4 heavy metals measured values of the validation samples to RMSE) as the validation criteria, the RPDs of As and Pb concentrations from the two models were both less than 1.4, which suggested that both models were incapable of roughly estimating As and Pb concentrations; whereas the RPDs of Zn and Cd were 1.53, 1.46 and 1.46, 1.42, respectively, which implied that both models had the ability for rough estimation of Zn and Cd concentrations. Based on those results, the vegetation spectral-based estimation model was selected to obtain the spatial distribution map of Zn concentration in combination with the Hyperion image. The estimated Zn map showed that the zones with high Zn concentrations were distributed near the provincial road 308, national road 214 and towns, which could be influenced by human activities. Our study proved that the spectral reflectance of Hyperion image was useful in estimating the soil concentrations of Zn and Cd.

National pattern for heavy metal contamination of topsoil in remote farmland impacted by haze pollution in China

The influence of haze pollution on heavy metal transport into farmland topsoil has received little attention. This study reports on heavy metal concentrations in topsoil from remote farmland in China as well as the spatial similarity and correlation to such heavy metals in atmospheric particulate matter (APM). Heavy metal concentrations in topsoil from remote farmland significantly increased over time. Moreover, stations in the mid-eastern region of China accounted for greater than 55% of total stations that exhibited higher concentrations in 2010 than 2005. This spatial trend was consistent with changes observed in APM where mass concentrations of heavy metals were also found to be higher in the mid-eastern region of China. Heavy metals in APM have already likely caused contamination in remote farmland topsoil, particularly in the mid-eastern region of China. This is primarily due to long-range transport and deposition of APM owing that no pesticides or fertilizers have been used in the remote farmland stations selected and no industries were situated nearby. Regarding the large-scale, severe haze pollution occurring in China today, it is urgent to ascertain the accumulation of heavy metals in farmland topsoil resulting from APM as well as its subsequent potential mechanisms and ecological risks.

Effects of sewage sludge amendment on snail growth and trace metal transfer in the soil-plant-snail food chain.

Cu, Zn, Pb, and Cd concentrations in a soil plant (Lactuca sativa) continuum were measured after sewage sludge amendment. The effects of sewage sludge on growth and trace metal bioaccumulation in snails (Cantareus aspersus) were investigated in a laboratory experiment specifically designed to identify contamination sources (e.g., soil and leaves). Application of sewage sludge increased trace metal concentrations in topsoil. However, except Zn, metal concentrations in lettuce leaves did not reflect those in soil. Lettuce leaves were the main source of Zn, Cu, and Cd in exposed snails. Bioaccumulation of Pb suggested its immediate transfer to snails via the soil. No apparent toxic effects of trace metal accumulation were observed in snails. Moreover, snail growth was significantly stimulated at high rates of sludge application. This hormesis effect may be due to the enhanced nutritional content of lettuce leaves exposed to sewage sludge.

Spatial pattern and distribution regularity of soil environmental quality in East China

Random numbers of heavy metal (Cd, As, and Pb) concentrations were created by Monte Carlo simulation of 16 representative sites in five soil zones from published papers for subsequent research. Ordinary kriging and significant analyses were used in a dataset of the 16 areas. Concentration of heavy metals in topsoil was found to be mainly influenced by zonality, non-zonality, and anthropogenic inputs. Nevertheless, human-induced correlations among heavy metals could not be detected on a regional spatial scale. Soil zone and landform were found to be representations of zonality and non-zonality, respectively. It was found that in east China, heavy metals accumulated in the south, especially the southwest, and were not uniform in each soil zone, indicating that zonality was not the unique influencing factor of soil environment quality. Both soil zone and landform may be responsible for heavy metal concentrations. An analysis of variance, coefficients of divergence analysis, was applied to assess the effects of soil zone and landforms on the variation of heavy metal concentrations in the study region. The influence of soil zone and landform was relatively homogeneous in areas of the north; while in the south, landform played a dominating role. Therefore, soil environment quality formed mainly under the effect of landform. This was mainly due to the fact that landform in fluences other natural environment elements including climate, further impacting the division of soil zone.

Spatial Distribution of Heavy Metals in Top Soils Around the Industrial Facilities of Cromatos de México, Tultitlan Mexico

The environmental damage caused by industrial activities in Cromatos de México, (Tultitlán, México) has been evaluated in terms of heavy metal concentrations in topsoils of the surrounding area. The concentrations of lead, copper and zinc demonstrate a significant enrichment with respect to unpolluted levels. Their maximum enrichment factors are 37.7, 21.1 and 9.6 mg kg⁻¹, respectively; such increase is related to traffic emissions. Nickel concentrations show no significant difference in the analyzed samples. Total chromium concentrations show a significant decrease with distance from the industrial facilities, ranging from 15 to 1,837 mg kg⁻¹. The enrichment factors of chromium (total), with respect to the background values reach up to 40.8 mg kg⁻¹. In spite of this pronounced increase, only three analyzed samples show chromium (VI) concentrations over 0.5 mg kg⁻¹ (instrumental detection limit) and do not exceed the values recommended by the Mexican official norm. The current results show that the chromium present in the studied area does not represent serious health risks and environmental damage in the zone, nevertheless, it is necessary to consider that the oxidation of chromium (III) is determinate by changes in redox and/or pH conditions which would imply significant impacts upon its toxic risk. This study suggests that the waste material generated during the industrial activities of Cromatos de Mexico represents a relevant metal pollution source for the area even 30 years after the closure of the industrial facilities.

Elevated heavy metal concentrations in top soils of an Aegean island town (Greece): total and available forms, origin and distribution

Elevated heavy metal concentrations in urban top soils are principal indicators of environmental pollution; however, relative data on the heavy metal status in soils of Greek island towns, that are regional administrative centers and popular tourist destinations, are missing. A survey was conducted to examine heavy metal concentrations in the urban soils of Ermoupolis, the capital of Syros island and of the prefecture of Cyclades complex in the Aegean Sea. Total (aqua-regia extracted) and available (DTPA extracted) concentrations of Cu, Pb, Zn, Ni, Cr, Sn and Fe were determined in top soil samples collected from green areas and open spaces of the town and in surface samples from inland reference soils of the island. Mean values for the aqua-regia extracted fraction of Cu, Pb and Zn were 117, 155 and 440 mg kg(-1) respectively, up to four times higher than the respective mean values of the reference soils. Enrichment factors (EFs) for these metals indicated high accumulation in the urban top soils and the available to total concentration ratio of Cu, Pb, Zn and Fe was higher for the urban compared to the reference soils, suggesting differences in metal sequestration, resulting in higher metal availability in the urban soils. GIS analysis was used to visualize the spatial distribution of EFs of the studied heavy metals. Factor Analysis and Cluster Analysis, applied to aqua-regia and DTPA data sets, adequately elucidated the origin of metals grouped under each factor or cluster.

Mobilization of different metals between Tamarix parts and their crystal salts – soil system at the banks of river Nile, Aswan, Egypt

In order to study the relation of the mobility and distribution of metals between Tamarix parts and their crystal salts – soil system, different experiments were conducted with plant-rich and plant-free soils at the banks of river Nile, Aswan, Egypt. For these purposes, Tamarix top and subsoil samples near and far from the plant were collected from six different locations at the banks of river Nile. Elemental analysis of Fe, Mn, Ca, Mg, Cr, Cu, Ni, Zn, Cd and Pb in soil, and in different parts of Tamarix and their crystal salt samples was carried out by atomic absorption spectrometry, whereas Na and K were measured by atomic emission spectrophotometry. The bioavailability of metals in the soil samples was evaluated by determining their contents using sequential extraction single-step, providing higher metal concentrations in occluded Fe/Mn oxide fraction. The ratio of heavy metal concentrations in topsoil to that in subsoil enhancement (RTE) ranged from 0.67 to 4.4 and 0.22 to 4.61 for soil Tamarix and soil free from plant, respectively for all measured total element concentrations. Data indicate that the mobility expressed as transfer factor (TF) was obtained as Fe > Mg > Cr > Mn > Ca > K > Na, for Tamarix leaves. The major part of accumulated Na in Tamarix is retained in the plant leaves, while roots accumulated high concentration of Co.

Heavy metals distribution in agricultural topsoils in urban area

Intensive urbanisation of the Croatian capital of Zagreb has led to a situation where very good agricultural soils, developed mostly on Pleistocene eolian sediments and alluvial and proluvian Holocene sediments are entrapped within urban and suburban areas. Therefore the influence of urban and industrialised environments on the accumulation of metals in agricultural topsoils has been investigated. On an area of 860 km2 of the wider Zagreb region, 331 samples were taken according to a regular 1×1 km square mesh. Samples were dissolved in aqua regia and analysed for Cd, Cu, Fe, Mn, Ni, Pb and Zn with flame atomic aqua regia absorption spectroscopy. The following concentration ranges have been determined: Cd 0.25–3.85 mg kg–1 (average 0.66 mg kg–1), Cu 4.30–183 mg kg–1 (average 20.8 mg kg–1), Fe 5.8–51.8 g kg–1 (average 27 g kg–1), Mn 79.2–1282 mg kg–1 (average 613 mg kg–1), Ni 0.70–282 mg kg–1 (average 49.5 mg kg–1), Pb 1.50–139 mg kg–1 (average 25.9 mg kg–1), and Zn 15.2–277 mg kg–1 (average 77.9 mg kg–1). Visualisation of the spatial data is made by the aid of GIS, and selected maps of the heavy metal concentrations in topsoils are displayed. Statistical multivariate analysis was carried out for quantitative study and data were processed by means of R-mode factor analysis, applying the varimax-raw rotational technique. F1, which grouped Cd, Pb, Cu, Zn and partially Ni, is characterized as a factor with strongly scattered anthropogenic influence. The elements in F2, Fe, Mn and partially Ni are mainly of geogenic, i.e. pedogenic, origin. The variations in concentrations of the investigated elements are thus of both natural and anthropogenic origins. The variations in the main soil constituents, particularly Fe and Mn, are determined primarily by the composition of different regolithic substrates of the fluvial origin in recent pedogenesis. High concentrations of nickel are also related to morphogenetic characteristics of the wider region, primarily basic and ultrabasic magmatic rocks of the surrounding mountain range. It is, however, assumed that the anomalous nickel concentrations in the vicinity of the highway and the airport are of anthropogenic origin, i.e. caused by fuel combustion. Copper is characterized by strongly scattered anthropogenic influence, which is related particularly to uncontrolled solid waste disposals or discharges of liquid waste from households or agricultural enterprises. With Zn, Pb and Cd, there are two possible ways of diffuse pollution. The Sava River, which drains the area and feeds the abundant Quaternary aquifer spreading below the major part of the investigated agricultural areas, has been exposed to intensive pollution by mining, industry and cities in the recent history. The part of the area with the highest determined concentrations of Zn, Pb and Cd was repeatedly flooded as recently as the previous decade; therefore, the recent sedimentation of the river deposits exposed to pollution is a very probable cause of the accumulation of metals in this until recently inundation area. The other way is atmospheric deposition of particles from urban sources (industrial emission, traffic, waste disposals, heating plants, etc.). In addition to agricultural enterprises, several economically important, but ecologically risky, facilities are situated in the vicinity of the water-protection area. The area is intersected by a very busy ring road, while a marshalling yard, the city dump, pharmaceutical and chemical industry, the district-heating plant and the airport are all located in close proximity. The geochemical maps show a clear relationship between human activities and metal concentration gradients.

Effects of past sewage sludge additions on heavy metal availability in light textured soils: implications for crop yields and metal uptakes

The effect of heavy metal additions in past sewage sludge applications on soil metal availability and the growth and yield of crops was evaluated at two sites in the UK. At Gleadthorpe, sewage sludges enriched with salts of zinc (Zn), copper (Cu) and nickel (Ni) had been applied to a loamy sand in 1982 and additionally naturally contaminated Zn and Cu sludge cakes in 1986. At Rosemaund, sewage sludges naturally contaminated with Zn, Cu, Ni and chromium (Cr) had been applied in 1968–1971 to a sandy loam. From 1994 to 1997, the yields of both cereals and legumes at Gleadthorpe were up to 3 t/ha lower than the no-sludge control where total topsoil Zn and Cu concentrations exceeded 200 and 120 mg/kg, respectively, but only when topsoil ammonium nitrate extractable metal levels also exceeded 40 mg/kg Zn and 0.9 mg/kg Cu. At Rosemaund, yields were only decreased where total topsoil Cu concentrations exceeded 220 mg/kg or 0.7 mg/kg ammonium nitrate extractable Cu. These results demonstrate the importance of measuring extractable as well as total heavy metal concentrations in topsoils when assessing likely effects on plant yields and metal uptakes, and setting soil quality criteria.

Estimating variograms of soil properties by the method‐of‐moments and maximum likelihood

SummaryVariograms of soil properties are usually obtained by estimating the variogram for distinct lag classes by the method‐of‐moments and fitting an appropriate model to the estimates. An alternative is to fit a model by maximum likelihood to data on the assumption that they are a realization of a multivariate Gaussian process. This paper compares the two using both simulation and real data.The method‐of‐moments and maximum likelihood were used to estimate the variograms of data simulated from stationary Gaussian processes. In one example, where the simulated field was sampled at different intensities, maximum likelihood estimation was consistently more efficient than the method‐of‐moments, but this result was not general and the relative performance of the methods depends on the form of the variogram. Where the nugget variance was relatively small and the correlation range of the data was large the method‐of‐moments was at an advantage and likewise in the presence of data from a contaminating distribution. When fields were simulated with positive skew this affected the results of both the method‐of‐moments and maximum likelihood.The two methods were used to estimate variograms from actual metal concentrations in topsoil in the Swiss Jura, and the variograms were used for kriging. Both estimators were susceptible to sampling problems which resulted in over‐ or underestimation of the variance of three of the metals by kriging. For four other metals the results for kriging using the variogram obtained by maximum likelihood were consistently closer to the theoretical expectation than the results for kriging with the variogram obtained by the method‐of‐moments, although the differences between the results using the two approaches were not significantly different from each other or from expectation. Soil scientists should use both procedures in their analysis and compare the results.