Accumulation and migration of heavy metals in soils of the Rostov region,south of Russia

Purpose

The main aim of the study performed during 6 years was to determine the specific features of heavy metal contamination of soil cover in the city of Rostov-on-Don and its agglomeration. It was supposed to answer the question: Does soil inherit heavy metals mainly from the parent rocks, or they enter the soil mainly as a result of anthropogenes in the city condition.

Materials and methods

Seventeen soil profiles were established in different parts of the Rostov agglomeration, within the city and in the urbanized agricultural region. The following objects were studied: (1) calcareous ordinary chernozem under steppe vegetation (fallow) and under trees (parks): soils of natural structure insignificantly affected by urbanization processes; (2) urbostratozems: soils of natural structure overlain by loose anthropogenic deposits; (3) screened urbostratozems (or ecranozems): soils of natural structure overlain by asphalt and/or another impermeable surface. The contents of heavy metals were determined by X-ray fluorescence. The degree of soil contamination with heavy metals was assessed by comparing their content with the MPC values (danger coefficient method) or using the total contamination factor Zc.

Results and discussion

The comparison of chernozems under different plant covers shows that the woody plants capable of retaining moisture in the soil and more deeply wetting the soil layer decrease the accumulation of vanadium, chromium, cobalt, nickel, and copper in the surface layer. The accumulation coefficients of these metals in urbostratozems are still lower for some reason. At the same time, an increase in the accumulation of zinc and lead is observed in the surface layer of soils under the forest canopy, as well as in the urbostratozems. In the Urbostratozems, screened by dense surfaces, a high variation is observed, which is related to the different times of soil sealing with asphalt.

Conclusions

The results showed that the concentrations of most elements in the parent rock of Rostov-on-Don exceed the background values, and those of some elements exceed the MPC levels. The main source of accumulation of these elements in the soil profile is the parent rock. Additional input from anthropogenic sources is contributed by the accumulation of such elements as chromium, nickel, zinc, and lead.

     

Fractional and group composition of the Mn, Cr, Ni, and Cd compounds in the soils of technogenic landscapes in the impact zone of the Novocherkassk Power Station

The compounds of Cr, Ni, Mn, and Cd in the soils around the Novocherkassk Power Station and the influence of the technogenic and natural factors on their composition were investigated. The data on the fractional and the group composition of these compounds proved to be informative for assessing the ecological state of the soils. The soil components specifying the accumulation and the properties of the heavy metal compounds in the polluted and unpolluted areas were identified.     

Assessment of soil contamination by the content of heavy metals in the soil profile

A new soil-ecological definition of the maximal permissible concentration (MPC) of heavy metals in soils is suggested that regulates the sampling in contaminated territories. Instead of the shallow pits usually used for collecting surface samples for soil-hygienic and other investigations, it is proposed to fulfill a detailed analysis along the entire soil profile including not only the determination of the heavy element content in certain horizons but also the soil density in these horizons. For the polyelemental contamination Zc (according to the Saet equation) based on the background (clarke) excess, the established Zc values ranging from 1 to 128, may reach absurd values of 800–900 upon taking into consideration only one surface layer. At the same time, the use of the weighted average content of the metals in the soil profile adjusts the Zc values for the existing natural conditions. Upon aerial impact, the consideration of the heavy metal contents along the soil profile instead of their contents in the surface horizon only leads to a decrease in the indices of the soil contamination degree. Upon the hydrogenic impact, the transition from the heavy metal contents in the surface horizon to their contents in the soil profile gives higher values of the soil contamination.     

Snow contamination by heavy metals and sulphur in Cracow agglomeration (Southern Poland)

The concentration of heavy metals (Cd, Pb, Zn, Fe), light metals (Ca, Mg), sulphate (SO _inf4 ^sup2? ) and pH in snow samples collected along 35 km transect from a large steel mill was determined. The concentration of heavy metals, light metals and sulphate decreased with the increasing distance from the emittors, whereas the snow acidity increased. Significant differences in the concentration of pollutants in snow between forest and open stands, between deciduous and mixed forests as well as with the date of snow collection were found.     

Group composition of heavy metal compounds in the soils contaminated by emissions from the Novocherkassk power station

The effect of natural and technogenic factors on the mobility and transformation of metal compounds was studied from an analysis of the fractional-group composition of Cu, Zn, and Pb compounds in the soils of areas adjacent to the Novocherkassk power station. Changes in the composition of Cu, Zn, and Pb compounds in the soils of technogenic landscapes were estimated. The effect of aerosol technogenic emissions on the mobility of metal compounds was revealed; a higher metal mobility was found in soils with low buffering capacity. Common and specific features of the formation of Cu, Zn, and Pb compounds in soils were determined. The role of individual soil components in the retention of metals in clean and contaminated soils was established.     

Use of regulatory documents for assessing the contamination of soils with heavy metals

The chronological review and analysis of the existing regulatory documents relevant to the assessment of soil contamination with heavy metals have been presented. Attention has been given to the incorrect use of the term “total heavy metal content” and the method of its determination in a 5 M nitric acid solution recommended by some regulatory documents. The maximum permissible concentrations (MPCs) and tentatively permissible concentrations (TPCTPCs) for the total heavy metal contents are based on the above method; therefore, the conventional methods of determining the true total contents of heavy metals overestimate the degree of contamination. To avoid confusion, it has been proposed to call the content of a heavy metal in a 5 M nitric acid solution the “pseudototal” content and to compare the experimental results with the MPC or TPCTPC values only if the methods recommended by the regulatory documents were used.     

Effect of soil components on the adsorption of heavy metals under technogenic contamination

The adsorption of copper, zinc, and lead by two urban soils with different degrees of contamination was studied. Changes in the sorption capacity of the soils and the binding strength of the metals with the soil were determined after the removal of organic matter and iron minerals with a potassium pyrophosphate solution and Tamm’s reagent. The selectivity of these solutions for the dissolution of soil components was estimated.     

Soil contamination in the impact zone of mining enterprises in the Bashkir Transural region

The results of long-term studies of the contents of bulk forms of metals (Cu, Zn, Fe, Ni, Pb, Mn, Co, and Cd) and their mobile compounds in soils of background and human-disturbed areas within the Krasnoural’sk–Sibai–Gai copper–zinc and Baimak–Buribai mixed copper mineralization zones in the Bashkir Transural region are discussed. It is shown that soils of the region are characterized by abnormally high natural total contents of heavy metals (HMs) typomorphic for ore mineralization: Cu, Zn, and Fe for the Sibai province and Cu, Zn, and Ni for the Baimak province. In the case of a shallow depth of the ores, the concentrations of HMs in the soils are close to or higher than the tentative permissible concentration values. The concentrations of mobile HM compounds in soils of background areas and their percentage in the total HM content strongly vary from year to year in dependence on weather conditions, position in the soil catenas, species composition of vegetation, and distance from the source of technogenic contamination. The high natural variability in the content of mobile HM compounds in soils complicates the reliable determination of the regional geochemical background and necessitates annual estimation of background parameters for the purposes of the ecological monitoring of soils. The bulk content of Cu and Zn content in soils near mining enterprises exceeds the regional geochemical background values by 2–12 times and the tentative permissible concentrations of these metals by 2–4 times. Anthropogenic contamination results in a sharp rise in the content of mobile HM compounds in soils. Their highest concentrations exceed the maximum permissible concentrations by 26 times for Cu, 18 times for Zn, and 2 times for Pb. Soil contamination in the impact zone of mining enterprises is extremely dangerous or dangerous. However, because of the high temporal variability in the migration and accumulation of HMs in the soils, the recent decline in the ore mining activities, and the construction of purification facilities, no definite temporal trends in the contents of HMs in the soils have been found in the studied region for the period from 1998 to 2015.     

Equations for assessing the total contamination of soils with heavy metals and metalloids

Cities and industrial regions are usually subjected to the impact of multi-element pollution, which requires the comprehensive characterization of the soil contamination with heavy metals and metalloids. The Saet index is the most popular among soil scientists and geochemists, because is supported by a system of critical values of the contamination hazard. However, with the use of this index, some questions arise that need to be clarified. It is recommended to make allowance for only the accumulated elements (with Kk(crit) > 2) and to assess only the elements with Clarke values above 1 mg/kg. We propose a new index of the total soil contamination that takes into account the different toxicity of the heavy elements and that is based on the calculation of the average geometrical values of the Kk concentration coefficients. Saet’s system of critical values of the contamination hazard may be used for this index.     

Determination of deposition rate of heavy metals in the soils of a forest-steppe zone

The element content of the snow at one of the central regions of the European part of the U.S.S.R. was studied by means of atomic absorption analysis. The distribution of various elements, including heavy metals, between liquid and solid phases is reported. The deposition rate of heavy metals on the soils of the forest-steppe zone has been calculated.     

Assessment of background concentrations of heavy metals in soils of the northeastern part of European Russia

The assessment of background concentrations of heavy metals in soils of the southern regions of the Komi Republic has been performed. Within the accumulative landscapes, soils are enriched with virtually all the studied heavy metals in comparison with the eluvial landscapes. A database of the content of heavy metals has been developed using GIS technologies, and maps showing the distribution of heavy metals in soils of the southern part of the Komi Republic have been obtained.     

Characterization of contamination levels of heavy metals in agricultural soils using geochemical baseline concentrations

Journal of Soils and Sediments - It is currently very difficult to accurately evaluate the soil contamination by heavy metals (HMs) attributed to the unavailability of local geochemical background...     

Contents and toxicity of heavy metals in soils of the zone affected by aerial emissions from the Severonikel Enterprise

In 2009, the zoning of the terrestrial ecosystems in the area exposed to aerial emissions from the Severonikel Enterprise (Murmansk oblast) was performed on the basis of the parameters characterizing the state of the soils, including the contents of the main heavy metal pollutants and exchangeable calcium and magnesium, the soils’ pH, the ratio of the organic to mineral soil components, and the state of the soils’ microbiota. Three zones differing in the degree of the soil pollution were delimited. These were the zones of heavy, moderate, and weak pollution, which extended for up to 3, 25, and 50 km from the emission source in the prevailing wind direction. The data on the amount of bacterial and fungal biomass provided evidence of the profound degradation of the soils in the heavily polluted zone. In particular, the biomass of the soil microbiota, including its prokaryotic and eukaryotic components, was two to six times lower in this zone than in the background (control) area. The soils of the heavily polluted zone can be classified as strongly toxic for plants, and most of the soils of the moderately polluted zone also fall into the same category.     

三峡库区消落区表层土壤重金属污染评价及源解析

三峡库区是我国重要的水源地, 研究库区水陆交错带消落区内土壤重金属污染程度并解析其来源,对水库的水环境和土壤环境具有重要意义。本研究采用地质累积指数, 对三峡库区消落区175 m 水位蓄水前12 个采样区表层68 个土样的土壤重金属Cu、Pb、Zn、Cd、Hg、As 和Cr 污染进行评价, 结果表明: 整个研究区不受Cr 污染, 研究区70%以上面积不受Pb、Cu 和Zn 污染; 研究区As 污染最严重, 其次为Cd 和Hg。利用因子分析法对这7 种重金属来源进行解析的结果表明, 库区消落区土壤重金属源可分为2 大类别:“自然因子”类别元素(Cr、Pb、Cu 和Zn)和“工业污染因子”类别元素(Hg、As 和Cd)。消落区表层土壤重金属污染评价及源解析可为消落区生态环境的综合治理提供参考。     

Effect of individual trees on the pH and the content of heavy metals in forest litters upon industrial contamination

The influence of individual spruce and birch trees on the distribution of heavy metals (Cu, Pb, Cd, and Zn) and hydrogen ions in the forest litter is considered in a territory subjected to long-term industrial pollution by emissions of the Ural copper smelter (town of Revda, Sverdlovsk oblast, southern taiga). In the background territory, the content of the elements regularly decreases from the tree trunks to the canopy gaps, whereas, in the contaminated territory, this relationship is either not traced at all (for the metal concentrations) or more weakly pronounced (for the metal reserves and pH values). The influence of trees on the spatial distribution of metals in the litter is specific for various elements and differs in coniferous and deciduous biotopes.     

Assessing the technogenic contamination of urban soils from the profile distribution of heavy metals and the soil bulk density

The contamination of soils with heavy metals in the city of Moscow has been assessed using the conventional procedure and a new resource approach developed at the Faculty of Soil Science of Moscow State University. The approach involved the consideration of the profile distribution of a pollutant and the variation in the bulk density of the enclosing soil. The integral parameter of contamination was the reserve of the pollutant in a conventional normative soil layer 1 m in thickness according to the Moscow Law On the Urban Soils. In the soil samples taken in the main administrative districts of Moscow, the contents of heavy metals of the first (zinc, lead, cadmium, arsenic, and mercury) and second (nickel and copper) hazard classes were determined. For each profile, distribution graphs of all of the above elements have been developed, and the element reserves have been calculated in the upper 1-m-thick layer with consideration for the changes in the soil density with depth. The obtained data have been compared with the normative reserves of heavy metals and the estimates of technogenic contamination derived using the conventional procedure. An increase in the total reserves of pollutants has been observed at the increase in their concentrations with depth; therefore, a clean soil according to the conventional procedure can be classified as contaminated. Analogously, a decrease in the total reserve of a pollutant in the upper 1-m-thik layer and, hence, a decrease in the degree of soil contamination have been observed when the concentration of the pollutant reduced with the depth. In general, the profile distributions of heavy metals and the soil bulk density strongly interfere with the estimation of the contamination of the soil as a spatially heterogeneous body and should be taken into consideration in the development of a present-day system of quality criteria and norms for urban soils.     

南洞庭湖洲垸土壤中四种重金属的分布特征及污染状况评价

对南洞庭湖10个洲垸地点的土壤进行了4种重金属Cd、Pb、Cu、Sb含量的测定与分析,并运用地积累指数法对每种重金属的污染状况进行初步评价,结果表明,重金属Cd的污染普遍较为严重;重金属Pb未达到明显的污染水平;重金属Cu的污染程度虽较轻,但需控制其发展;重金属Sb在某些地点污染较严重,其分布规律呈现较强的不均衡性。     

Assessment of soil tolerance toward contamination with black oil in the south of Russia on the basis of soil biological indices: A model experiment

The effect of soil contamination with black oil added in amounts of 0.1, 0.5, 1.0, 2.5, 5, 10, 25, and 50% of the soil mass on the biological properties of ordinary and leached vertic chernozems, brown forest soils, and gray sands in the south of Russia was studied in a model laboratory experiment. It was shown that the soil contamination causes a drop in the catalase and dehydrogenase activities, the cellulolytic capacity, the number of Azotobacter bacteria, and the characteristics of the plant germination. The ordinary and vertic chernozems were more tolerant toward the contamination than the gray sands and brown forest soils. The changes in the biological soil properties in dependence on the degree of the soil contamination differed considerably for the soils with different properties (the chernozems, brown forest soil, and gray sands) and were similar for the soils with similar properties (the ordinary and vertic chernozems). One soil (the brown forest soil) could be more tolerant toward the contamination than another soil (the gray sands) at a given concentration of black oil (<2.5%) and less tolerant at another concentration of black oil (>2.5%). The ecologically safe levels of the soil contamination with black oil do not exceed 0.7% in the ordinary chernozems, 0.3% in the compact chernozems, 0.1% in the brown forest soils, and 0.06% in the gray sands.