Keywords

Soil is a special biogenic–abiogenic system. Its formation and geochemical characteristics are caused by biogenic influence on rocks, which are abiogenic. Several factors also affecting the results of this influence are geomorphological and climatic features of the area, the duration of interaction, etc. These factors were first discussed in detail in the works of V.V. Dokuchaev, and were widely studied by many other researchers. Technogenic processes have a great (and in some cases even critical) impact on the considered interaction of biogenic and abiogenic substances in recent decades. Their maximum influence on the forming and already formed soil occurs in human settlements. It includes both abiogenic pressure, consisting mainly in the physical and chemical changes in soil, as well as biogenic pressure. The latter is most often associated with the destruction of certain soil organisms and the cultivation of new plant and animal biota. The change of geochemical features of urban soils is a certain result of such interaction. This, in turn, has an influence on many biogenic systems, including humans in settlements.

The overwhelming majority of the Earth’s population is concentrated within the boundaries of cities, although settlements occupy less than 5 % of the land area. In this regard, the study of urban soils is of crucial scientific and also practical importance. In this Chapter, we consider the impact of population number in cities on geochemical characteristics of urban soil.

1 Introduction

Soils are among the most important natural resources, defining sustainable development and independence of states. Preservation of soil fertility should be a major concern and a priority for economic development. In recent decades, the geochemical characteristics of soils have undergone significant changes under the influence of anthropogenic activities worldwide. The most dangerous changes occur in content and distribution of metals (Motuzova et al. 2014).

Soil as a deposing medium is a summary indicator of ecological–geochemical changes occurring in the study area (Perel’man 1989; Vernadsky 1965). Investigations have shown (Alekseenko and Alekseenko 2013; Kabata-Pendias and Pendias 2001) that in large industrial centres, urban soils continue to carry the geochemical information about the pollution happened even after the liquidation of main contamination sources. Let us also remember that human settlements occupying only about 5 % of the land is home to almost the whole population of the Earth. All this allows us to consider the study of soil geochemical characteristics, especially in settlements and agricultural landscapes, as a priority task for ecology and geochemistry (Adriano 2001; Gerasimova et al. 2003; Norra and Stüben 2003; Pashkevich et al. 2015). At the same time, we note that quantitative soil geochemical data is necessary for the subsequent adoption of specific measures to improve environmental situation (Kasimov et al. 2011; Syso et al. 2010; Tsolova et al. 2014; Tume et al. 2011). This paper presents quantitative information about the ecological state of soils in different categories of settlements.

2 Materials and Methods

The ongoing studies included sampling, chemical analysis and processing the received information. The geochemical properties of urban soils from more than 300 cities in Europe, Asia, Africa, Australia, and America were evaluated. Methodology of these works with the list of studied cities, methods of analysis of soil samples, their internal and external control and statistical process has been considered in detail (Alekseenko et al. 2013; Alekseenko and Alekseenko 2014b). The number of samples in each locality is ranged from 30 to 1000. Calculation of random and systematic errors showed high analyses repeatability and correctness, and allowed to consider the analytical laboratory work as good. All ordinary analyses were carried out in the single certified and accredited Central Testing Laboratory at “Kavkazgeolsyomka” using emission spectral analysis. The external control was conducted in the laboratories of “CentrKazGeology,” “MagadanGeology,” Southern Federal University (X-ray fluorescence and gravimetric analyses), and Institute of Ore Geology, Petrography, Mineralogy, and Geochemistry of the Russian Academy of Sciences (neutron activation analyses).

For every city, the average concentrations of elements in soils were determined. To avoid the errors related to unequal number of samples, each city was then represented by only one “averaged” sample. The published data and the materials kindly provided by a number of geochemists were also incorporated into research. As a result for all the elements were written the rows in which each city was presented by an average content of chemical elements in soils. The statistical processing of these data allowed to calculate the average concentrations of chemical elements in urban soils. They can be considered as the abundances (average concentrations) of chemical elements in urban soils (Alekseenko and Alekseenko 2014a).

Several samples selections were prepared for different groups of settlements. Each city was represented only by the average content of chemical elements in soils (as well as in abundances establishing). Criteria for these groups separation are considered further in this work. Statistical processing of the analysis results allowed to establish the average content of elements in soils of all selected groups (Table 1).

Table 1 The abundances and average concentrations of chemical elements in soils of different cities groups (mg/kg)
Full size table

In what follows, we compared the average contents with abundances in the Earth’s soils (Vinogradov 1959) and with abundances in urban soils (Alekseenko and Alekseenko 2014b). A number of indicators introduced by one of the authors in 1997 were used.

Indicator of Absolute Accumulation (IAA) shows the mass of a certain chemical element (or its compound) accumulated in a particular part of the system as a result of geochemical processes occurring per unit area. Soils, all the vegetation of a specific area, plant species, surface or groundwater, etc. could be studied as the parts of landscapes. During the investigations of soils in the study area of 1 km2 the difference is determined between the background content before the start of these processes (C 1) and after their completion (C 2): IAA = C 2 − C 1. When after the end of the processes the content (C 2) has decreased (i.e., it has occurred the loss of elements), the IAA value is negative. The study of technogenic changes in the vertical soil profile showed that they usually develop in agricultural and residential landscapes to a depth of 30 cm.

The determination of the average density of soils in Southern Russia allowed to assume after accounts that the increase (decrease) in the concentration of chemical elements in soils by an amount equal to 10 mg/kg, within the upper 30 cm layer corresponds to an increase (decrease) of their weight by 6 tons on an area of 1 km2.

However, such a quantitative measure as IAA required for many decisions related to environmental issues does not provide sufficient information about the most negative impact of certain chemical elements in each case. Let us consider the following example. An increase of hundreds of tons per 1 km2 of iron content in soils is less hazardous for organisms than an increase of 10 tons of mercury and arsenic. It happens due to the different abundances of elements (average concentrations) in the Earth’s crust. High content of Fe (abundance 4.64 %) is “habitual” for organisms over a long period of development and evolution; otherwise, high concentrations of Hg (83 mg/kg) or As (17 mg/kg) are unaccustomed. The Indicator of Relative Accumulation (IRA) was proposed to overcome this geochemical feature.

IRA shows the ratio between the mass of the element accumulated (lost) as a result of the processes occurring in a certain part of the geochemical system (i.e., IAA) and the background content (or the average concentration in the Earth’s crust). Thus, we can assume that IRA = IAA/C 1.

Absolute Spread (AS) of chemical elements is a new environmental index to describe the behavior of elements in geochemical systems. It was offered by V.A. Alekseenko in 1997. AS is the ratio of the maximum background element content (abundance) in one part of geochemical system to the element content in the other system part. We have calculated the value of AS for rocks and soils of continents (Alekseenko 2006). All the chemical elements are divided into three groups according to the AS value: (1) AS > 100 (up to 4250); (2) AS from 10 to 100; (3) AS < 10. Elements belonging to each group differ in crystal-chemical parameters: ionisation energy and electronegativity (Fersman 1952–1959).

Some elements are characterised by natural high values of AS. Living organisms become “accustomed” to the large variations of these elements contents during the process of biota development and evolution. In this regard, it can be assumed that fluctuations of the third group elements content (Bi, W, Au, Br, P, Zn, Ag, I, and Be) in environment are the most dangerous for living matter. But it should make a reservation that they are dangerous, if they occur mainly in forms available for organisms.

3 Results and Discussion

The analysis of anthropogenic load on urban soil allows to conventionally divide them into six main groups. The key technogenesis indicators were taken as the basis of this division (Alekseenko 2015). Let us briefly consider them.

The volume of food, building materials, and industrial goods imported in cities depends on the number of inhabitants, i.e., the size of settlements. The same factor causes the development of urban transport (both public and private). Transport is a constant source of specific compounds income in the environment: dust from wear of car and bus tires, wheels and rails of trams; exhaust gases of automobiles, etc. The amount of waste, incoming into the landscape as a result of life activity, depends on the number of inhabitants. The population number controls in a great measure the amount of wastes removed from the landscape, their purification rate and methods of disposal (recycling). Thus, the size of settlement (number of inhabitants) largely determines the balance of technogenic elements migration in landscapes.

However, the amount and composition of imported raw materials in the settlement, its way of treatment, the amount of waste resulting, as well as the forms of occurrence of elements in raw materials and wastes, are caused by profiles of enterprises operating in this city. Specialisation of main enterprises often has a significant impact on the cleaning system and method of waste disposal from the entire city or from its separate areas. In such a way, the second most important factor, largely connected with the number of inhabitants and the defining features of technogenic migration of elements in urban landscapes, is an area of specialisation of companies operating in city.

We carry out the classification of residential landscapes considering two most important factors that determine the features of technogenic migration (Fig. 1).

Fig. 1
figure 1

The classification scheme of urban landscapes

Full size image
  1. I.

    In accordance with the scheme above, we first consider separately identifiable landscapes of millionaire cities, the industrial centres of national importance. They include cities with population over 700 thousand people. Calculations of many researchers show that only in ordinary life activity inhabitants of the city with one million population every day emit about 0.5 million m3 of carbon dioxide and 1200 m3 of water vapor and sweat gland secretions. The supply of food and various industrial products in major cities is approximately the same and depends more on the number of inhabitants than on features of natural zone in which the city is situated. Systems of municipal wastewater treatment and disposal methods for solid urban waste are more and more close to typical (standard) in big cities. Roughly the same pollutants in similar amounts are emitted in these residential landscapes by public and private transport. In such a way, the manmade migration of elements in large cities is directly related to the inhabitants life support, and has much more in common than specific differences.

    Industry of cities with more than one million inhabitants has some variety, but almost always includes food, chemical, and consumer goods enterprises and industries associated with the processing of metals, and construction companies. These data allow to tentatively assume that in such cities composition and number of polluting elements entering urban landscapes as a result of industrial activity is about the same when calculated per inhabitant. Therefore, the unification of cities with population about 1 million residents in a particular type of landscape has a certain geochemical substantiation.

  2. II.

    Landscapes of half-millionaire cities are settlements with a population of 300,000–700,000 people. Just as in the previous group, for the life support of such number of inhabitants it is necessary to deliver the same amount of food and materials. Approximately, the equal number of companies associated with necessary works for the life support of specified number of people is always located in these cities. People and goods movement through the city with a population of 300,000–700,000 is also provided by the same vehicles.

    However, in some cases, development of certain large companies in cities of this group may have a significant impact on the anthropogenic entry and redistribution of elements complexes. Ecological-geochemical impacts of such large enterprises impose specific patterns of prevalence and distribution of chemical elements in air, water, soil, and organisms. In this regard, especially with increasing of studies scale, it is possible to consider such cities separately according to the prevailing companies specialisation. For example cities, where oil refining or cement companies are most common, should be distinguished separately.

  3. III.

    Large enterprises have even greater impact on the technogenic features of migration in urban landscapes of local importance: cities with population 100,000–300,000 inhabitants. Therefore, during the detailed landscape-geochemical studies (especially those related to solution environmental problems), it is advisable to divide landscapes on the same principle as in half-millionaire cities.

  4. IV.

    In this study, the so-called “small cities” with population less than 100,000 residents are studied as a separate group. These settlements are quite common, and hence they are home to fairly large number of people in total.

  5. V.

    Landscapes of villages, hamlets, and farms occupy the smallest area among other residential areas. They are like the transition from agricultural landscapes to settlements with quite intense biological cycle of elements. They differ from resorts landscapes by significantly lower number of residents, lower role of transport in technogenic elements addition, and a unique elements’ biological cycle, close to ones in surrounding agricultural or biogenic (natural) landscapes.

  6. VI.

    Landscapes of recreational and tourist localities should be considered separately. Among these, a technogenic migration is mainly determined by the vital activity of small number of permanent and a large number of visiting inhabitants, as well as peculiarities of transport and, quite often, the composition of underground saline water used for treatment. A large role of biological cycle in migration of the main elements is often an important characteristic of these landscapes.

Landscapes of settlements in mines and enrichment plants adjacent areas are combined into a single group. Within these landscapes, migration and concentration of chemical elements are determined much more by mineral deposit characteristic than the number of inhabitants.

Natural factors influencing the migration of elements (especially those related to climatic conditions), must also be taken into account when dividing the groups of urban areas. For example, the process of various substances migration will be very different in landscapes of Cairo and Novosibirsk, especially in winter season. However, studies and mapping of geochemical landscapes for solving environmental problems are usually carried out in a single climatic zone. In addition, the influence of anthropogenic factors in settlements is incomparably stronger than natural. Given all this, it is suggested to conduct further residential landscapes segregation, if necessary, according to climatic conditions after the separation discussed above.

The data on the average chemical elements content that characterise soils of allocated settlements are shown in Table 1. Earlier studies showed that urban soils differ significantly in the content of chemical elements from the Earth’s soil cover, and the association of elements with significantly increased contents has no natural analogues. These differences, in conjunction with the above data on residential landscapes, have forced to identify separately such geochemical system as urban soils (as one of the most important from an environmental viewpoint) with specified average contents, abundances of chemical elements (Alekseenko and Alekseenko 2014b).

We pay a particular attention to such elements as Zn, Pb, Ba, Sr, Ca, Hg, B, Cu, and Co in the soils of all settlements. We believe that their high content in this geochemical system is due to mainly technogenic processes, i.e., environmental pollution. This is confirmed by the fact that these elements’ content in the Earth’s soil cover is less than in the Earth’s crust (Vinogradov 1959). Consequently, the overall processes of soil formation did not result in accumulation of these elements in soils. All of this leads us to identify Indicators of Absolute and Relative Accumulation of these metals in geochemical system representing all urban soils in relation to the Earth’s soil cover, for making informed decisions to improve the ecological state of human settlements. Somewhat arbitrarily, these figures are characteristic of technogenesis in urban soils, considered as a separate geochemical system. IAA rows of elements accumulation (t/km2) in urban soils are as follows:

$${\text{Ca}}\left( { 24{,}060} \right) > {\text{Ba}}\left( { 2 10} \right) > {\text{Sr}}\left( { 9 4. 8} \right) > {\text{Zn}}\left( { 6 4. 8} \right) > {\text{Pb}}\left( { 2 6. 5} \right) > {\text{B}}\left( { 2 1.0} \right) > {\text{Cu}}\left( { 1 1. 4} \right) > {\text{Co}}\left( { 3. 6} \right) > {\text{Hg}}\left( {0. 5 2} \right)$$

They allow to consider that technogenesis in urban conditions led to the largest (by weight) concentrations of Ca, Ba, and Sr in soils and lower accumulation of Hg, Co, and Cu. In order to establish the highest ecological–geochemical significance of this process, we consider the series of Indicator of Relative Accumulation (IRA): Hg > Ba > Pb > B > Ca > Zn > Cu > Co > Sr.

As can be seen from this row, the highest ecological–geochemical changes of urban soils can be associated with increased concentrations of Hg, Ba, and Pb, although they have accumulated in tens and tens of thousands of times smaller quantities (t/km2) than, for example, Ca.

In addition to abundances, the distribution of elements in urban soils is important ecological–geochemical indicator which is established by the values of Absolute Spread (AS). The values of AS were set in relation of the maximum average content in soils of one settlements group, allocated by the number of inhabitants, to the minimum average content established in the other group. The value of AS over 2 is marked for 18 chemical elements. They include As, Ba, Be, Bi, Ca, Cd, Cr, Cu, La, Mn, Ni, Pb, Sc, Sr, Tl, Y, Zn, and Zr. For 5 elements, the quantity of AS is greater than 4. They are As, Be, Ca, Cd, and Tl. The main thing is that for Bi and Cd, values of AS in such a geochemical system as urban soils have exceeded values in rocks and soils of continents. The quantity of Absolute Spread for Be in urban soils is close to the value in rocks and soils.

If the considered geochemical system (urban soils) was large, it could be possible to talk about the geochemical threat for a living matter. In the meantime, we note that the specified AS definitely affect the change of ecological conditions in allocated cities groups and clearly points to the significant differences in the processes of income and accumulation of substances in these groups of residential landscapes.

Changes in the average contents of 18 chemical elements in soils of different groups of settlements in more than 2 times, additionally demonstrates the need for a detailed study of such a geochemical system as urban soils, and correctness of our approach to this division.

Let us now consider some of soil geochemical characteristics in each of these settlements groups. The main of them is the change in prevalence (contents) of chemical elements. The information about the differences between the average concentrations in soils of separate settlements groups and abundances in the Earth’s soil cover is shown in Table 2. In each group of cities, only elements which average content was more than 1.5 times higher than in the Earth’ soils were considered.

Table 2 Indexes of absolute (IAA, t/km2) and relative accumulation (IRA) of chemical elements in soils of different cities groups (in relation to the abundances in the Earth’s soils)
Full size table

Soil of settlements with the population over 700,000 (millionaire cities) can be considered as a huge Earth’s soils lithochemical anomaly, spatially divided into separate parts. As, Ba, Cd, Cl, Co, Cu, Li, P, Pb, and Zn constitute an anomaly. These elements’ mass has increased and makes the following IAA series (in parentheses hereinafter t/km2):

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation }}\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{millionaire}}\;{\text{cities}}}]{{{\text{P}}\left( {342.7} \right)\; > \;{\text{Ba}}\left( {228} \right)\; > \;{\text{Cl}}\left( {124.2} \right)\; > \;{\text{Zn}}\left( {90.7} \right)\; > \;{\text{Pb}}\left( {33.7} \right)\; > \;{\text{Cu}}\left( {21.0} \right)\; > \;{\text{As}}\left( {11.8} \right)\; > \;{\text{Li}}\left( {9.2} \right)\; > \;{\text{Co}}\left( {4.7} \right)\; > \;{\text{Cd}}\left( {1.4} \right)}}$$

In the same area, as compared with the Earth’s soil cover, the following elements content has decreased:

$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{millionaire}}\;{\text{cities}}}]{{{\text{Fe}}\left( {{{{-}11.040}}} \right) > \;{\text{Cr}}\left( {{{{-} 70.4}}} \right) > \;{\text{Y}}\left( {{{{-}15.9}}} \right) > \;{\text{Be}}\left( {{{{-}1.9}}} \right)}}$$

These data (t/km2) are necessary to make informed decisions for urban soils rehabilitation. However, these figures do not fully reflect the ecological–geochemical changes that have occurred in soils of cities with population over 700,000 people. For more information, we constructed a series of changes in the value of IRA:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{millionaire}}\;{\text{cities}}}]{{{\text{Pb}} > {\text{Cd}} > {\text{As}} > {\text{Zn}} > {\text{Cl}} > {\text{Cu}} > {\text{Co}} > {\text{Ba}} > {\text{P}} > {\text{Li}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{millionaire}}\;{\text{cities}}}]{{{\text{Cr}} > {\text{Y}} > {\text{Be}} > {\text{Fe}}}}$$

Thus, the content of P, Ba, and Cl increased the most, but the greatest ecological–geochemical changes are caused by accumulation of Pb, Cd, As, and Zn in soils of these cities. The highest priority should be paid to these elements while developing various ecological measures. Also the special attention should be given to reducing the concentration of Cr, Y, and Be, but not for Fe.

The average contents of As, Ba, Be, Ca, Cd, Cl, Co, Cr, Cu, Fe, Li, Mg, Pb, Sn, Y, and Zn have changed significantly in soils of cities with population about 500,000 (300,000–700,000) inhabitants. Their IAA rows have the following forms:

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation}}\;\left( {{\text{t/km}}^{{\text{2}}} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{half-millionaire}}\;{\text{cities}}}]{{{\text{Ca}}\left( {{{38{,}036}}} \right) > {\text{Mg}}\left( {{{2282}}} \right) > {\text{Ba}}\left( {{{354}}} \right) > {\text{Cl}}\left( {{{127}}} \right) > {\text{Zn}}\left( {{{39}}} \right) > {\text{Pb}}\left( {{{21}}} \right) > {\text{Li}}\left( {{{13}}} \right) > {\text{Cu}}\left( {{{6}}{{.1}}} \right) > {\text{Co}}\left( {{{3}}{{.8}}} \right) > {\text{As}} > {\text{Cd}}\left( {{\text{0}}{{.2}}} \right)}}$$
$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\;\left( {{\text{t/km}}^{{{2}}} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{half-millionaire}}\;{\text{cities}}}]{{{\text{Fe}}\left( {{{{-}10{,}737}}} \right) > {\text{Cr}}\left( {{{{-}87}}} \right) > {\text{Y}}\left( {{{{-}16}}} \right) > {\text{Sn}}\left( {{{{-} 2}}{{.1}}} \right) > {\text{Be}}\left( {{{{-}1}}{{.9}}} \right)}}$$

Series constructed from the values of the IRA are as follows:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{half-millionaire}}\;{\text{cities}}}]{{{\text{Ca}} > {\text{Pb}} > {\text{Cl}} > {\text{Zn}} > {\text{Ba}} > {\text{As}} > {\text{Co}} > {\text{Li}} > \left( {{\text{Cd}},{\text{ Mg}}} \right) > {\text{Cu}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{half-millionaire}}\;{\text{cities}}}]{{{\text{Cr}} > {\text{Y}} > {\text{Be}} > {\text{Fe}} > {\text{Sn}}}}$$

As seen from the data, Pb, Cl, and Zn are in the last place by accumulated mass, but they provide (along with Ca) a major impact on changes in environmental conditions in soil during the formation of cities with population half a million inhabitants. Cr, Y, and Be have the greatest impact on the ecological–geochemical soil appearance in this cities group among the decreasing elements.

Significant changes in soils of cities with a population between 100,000 and 300,000 inhabitants have occurred to the average contents of As, Co, Cr, Li, Mn, Mo, P, Pb, and Zn. Their IAA rows have the following forms:

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{cities}}\;{\text{with}}\;100{-}300\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{P}}\left( {{{316}}} \right) > {\text{Zn}}\left( {{{29}}{{.7}}} \right) > {\text{Pb}}\left( {{{20}}{{.0}}} \right) > {\text{Li}}\left( {{{12}}{{.2}}} \right) > {\text{As}}\left( {{{9}}{{.5}}} \right) > {\text{Co}}\left( {{{2}}{{.8}}} \right) > {\text{Mo}}\left( {{{0}}{{.96}}} \right)}}$$
$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{cities}}\;{\text{with}}\;100{-}300\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Mn}}\left( {{{ {-} 182}}} \right) > {\text{Cr}}\left( {{{{-}94}}{{.7}}} \right)}}$$

Rows of IRA:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{cities}}\;{\text{with}}\;100{-}300\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Pb}} > {\text{As}} > {\text{Zn}} > {\text{Mo}} > {\text{Li}} > {\text{P}} > {\text{Co}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{cities}}\;{\text{with}}\;100{-}300\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Mn}} > {\text{Cr}}}}$$

Pb, As, and Zn have the greatest influence on the change of ecological–geochemical state of soils of this cities group, despite their relatively small accumulated mass.

In soils of group of small towns with population less than 100 thousand inhabitants the increased contents are marked for Ba, Ca, Cd, Cl, Co, Li, Pb, and Zn, and low contents are marked for Be, Cr, Mn, and Y. Rows of these elements accumulation (IAA) are as follows:

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{small}}\;{\text{cities}}\;{\text{with}}\; < 100\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Ca}}\left( {{{37{.}784}}} \right) > {\text{Ba}}\left( {{{288}}} \right) > {\text{Cl}}\left( {{{83}}{{.7}}} \right) > {\text{Zn}}\left( {{{25}}{{.4}}} \right) > {\text{Pb}}\left( {{17.7}} \right) > {\text{Li}}\left( {{{9}}{{.5}}} \right) > {\text{Co}}\left( {{{4}}{{.0}}} \right) > {\text{Cd}}\left( {{{0}}{{.6}}} \right)}}$$
$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{small}}\;{\text{cities}}\;{\text{with}}\; < 100\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Mn}}\left( {{{{ -} 235}}} \right) > {\text{Cr}}\left( {{{{ -} 71}}{\text{.0}}} \right) > {\text{Y}}\left( {{{ {-} 14}}{{.7}}} \right) > {\text{Be}}\left( {{{ {-} 2}}{{.5}}} \right)}}$$

Rows of IRA constructed to establish the relative influence of these elements on ecological–geochemical environmental changes are presented as follows:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{small}}\;{\text{cities}}\;{\text{with}}\; < 100\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Ca}} > {\text{Pb}} > {\text{Cd}} > {\text{Cl}} > {\text{Ba}} > {\text{Zn}} > {\text{Co}} > {\text{Li}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{small}}\;{\text{cities}}\;{\text{with}}\; < 100\;{\text{thousand}}\;{\text{inhabitants}}}]{{{\text{Be}} > {\text{Cr}} > {\text{Y}} > {\text{Mn}}}}$$

Thus, despite the much smaller increase in masses of such chemical elements as Pb, Cd, and Be, they provide (judging by the soil characteristics) the major ecological–geochemical changes of environment in cities with population less than 100,000.

In soils of villages and hamlets, the changes are associated to a greater extent with a significantly reduced (compared with the Earth’s soil cover) content of chemical elements: Ag, Cd, Cr, Sn, V, Y, and Zr. The increased contents are marked for Cu, Li, Mo, P, Pb, and Zn. The greatest ecological-geochemical changes noted in soils of this group are associated with the increasing content of Pb, Zn, Mo, and Cu and with decreasing content of Ag and Cr. Rows of these elements accumulation (IAA) are as follows:

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{villages}}\;{\text{and}}\;{\text{hamlets}}}]{{{\text{P}}\left( {{{311}}} \right) > {\text{Zn}}\left( {{{28.6}}} \right) > {\text{Li}}\left( {{{12.2}}} \right) > {\text{Cu}}\left( {{{8.8}}} \right) > {\text{Pb}}\left( {{{7.6}}} \right) > {\text{Mo}}\left( {{{1}}{{.0}}} \right)}}$$
$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{villages}}\;{\text{and}}\;{\text{hamlets}}}]{{{\text{Zr}}\left( {{{ {-} 101}}} \right) > {\text{Cr}}\left( {{{ {-} 88}}} \right) > {\text{V}}\left( {{{ {-} 21.3}}} \right) > {\text{Y}}\left( {{{ {-} 19.5}}} \right) > {\text{Sn}}\left( {{{ {-} 2.26}}} \right) > {\text{Cd}}\left( {{{ {-} 0.19}}} \right) > {\text{Ag}}\left( {{{ {-} 0.15}}} \right)}}$$

Their IRA rows are as follows:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{villages}}\;{\text{and}}\;{\text{hamlets}}}]{{{\text{Pb}} > {\text{Zn}} > {\text{Mo}} > {\text{Cu}} > {\text{Li}} > {\text{P}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{villages}}\;{\text{and}}\;{\text{hamlets}}}]{{{\text{Ag}} > {\text{Cr}} > {\text{Y}} > {\text{Cd}} > {\text{Zr}} > {\text{Sn}} > {\text{V}}}}$$

Recreational and tourist centres have a special place among the settlements. The higher average contents of As, Ba, Ca, Cl, Co, Cu, Li, Mg, Pb, Sr, and Zn and low contents of Be, Cr, Sn, Y, and Zr are marked in their soils. Their accumulation and loss rows (IAA) have the following forms:

$$\xleftarrow[{{\text{Absolute}}\;{\text{accumulation}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{recreational}}\;{\text{and}}\;{\text{tourist}}\;{\text{centres}}}]{{{\text{Ca}}\left( {{\text{34,488}}} \right) > {\text{Mg}}\left( {{\text{2256}}} \right) > {\text{Ba}}\left( {{\text{290}}} \right) > {\text{Sr}}\left( {{\text{150}}} \right) > {\text{Cl}}\left( {{\text{104}}} \right) > {\text{Zn}}\left( {{\text{90}}} \right) > {\text{Pb}}\left( {{\text{27}}} \right) > {\text{Cu}}\left( {{\text{22}}} \right) > {\text{Li}}\left( {{\text{13}}} \right) > {\text{As}}\left( {{\text{9}}{\text{.6}}} \right) > {\text{Co}}\left( {{\text{6}}{\text{.1}}} \right)}}$$
$$\xleftarrow[{{\text{Absolute}}\;{\text{loss}}\;\left( {{\text{t}}/{\text{km}}^{2} } \right)\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{recreational}}\;{\text{and}}\;{\text{tourist}}\;{\text{centres}}}]{{{\text{Zr}}\left( { {-} 67.4} \right) > {\text{Cr}}\left( { {-} 67.1} \right) > {\text{Y}}\left( { {-} 18.8} \right) > {\text{Be}}\left( { {-} 2.2} \right) > {\text{Sn}}\left( { {-} 2.1} \right)}}$$

Series constructed from the values of the IRA are as follows:

$$\xleftarrow[{{\text{Relative}}\;{\text{accumulation}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{recreational}}\;{\text{and}}\;{\text{tourist}}\;{\text{centres}}}]{{{\text{Pb}} > {\text{Ca}} > {\text{As}} > {\text{Zn}} > {\text{Cu}} > {\text{Cl}} > {\text{Co}} > {\text{Ba}} > {\text{Sr}} > {\text{Li}} > {\text{Mg}}}}$$
$$\xleftarrow[{{\text{Relative}}\;{\text{loss}}\;{\text{in}}\;{\text{soils}}\;{\text{of}}\;{\text{recreational}}\;{\text{and}}\;{\text{tourist}}\;{\text{centres}}}]{{{\text{Y}} > {\text{Be}} > {\text{Cr}} > {\text{Zr}} > {\text{Sn}}}}$$

The value of Absolute Spread (AS), based on the average elements content in urban soils, is also changed quite significantly in different groups of settlements. The distribution of chemical elements with an increased content (compared with the Earth’s soils) in the studied millionaire cities is sometimes changing in a relatively wide range. For instance, AS is 51 for Cd (from 0.15 in Samara to 7.7 mg/kg in Almaty); is 6.6 for Zn (from 79 in Minsk to 280–520 mg/kg in Hamburg, Shenzhen, and Krasnoyarsk); is 4 for Pb (from 50 in Minsk to 140–200 mg/kg in Cologne, St. Petersburg, Paris, and London).

However, in the majority of cities (excluding single settlements with the minimum and maximum content of certain elements in soils), the fluctuation around the average for the whole group is small. The existence of separate cities with anomalously low and high elements content in soils is explained in most cases by the specificity of human activities. This is also probably related to soil sorption peculiarities (Perel’man 1986); that is mostly typical for Zn distribution.

Let us consider the distribution of the same elements (Cd, Zn, Pb) average contents, but in soils of several cities with a half-million population. AS of Cd increased sharply compared with the millionaire cities and reached the value of 1370 (from 0.01 in Irkutsk to 13.7 mg/kg in Pavlodar). For Zn, the AS increased to 40 (from 22 in Brest to 888 mg/kg in Ust-Kamenogorsk). AS for Pb reached the value 32.5 (from 7.8 in Taraz to 254 mg/kg in Ust-Kamenogorsk).

The above data show that the relative uniformity of distribution of chemical elements, common in millionaire cities, violated in half-millionaire cities. This is connected with the fact that some cities of this group have developed manufacture complexes of one branch. For example, in the city of Ust-Kamenogorsk, there are several very large enterprises arising within the scope of nonferrous metallurgy. Such industrial centres are similar to “monotowns” (one-company cities) having one key facility, which is the dominant pollution source.

However, unless taking into account such cities, the distribution of elements in soils of considered settlements is very uniform. For example, the average content of Pb in soils of the vast majority of cities in the group varies from 20 to 67 mg/kg (AS is 3.3).

In soils of cities with the population of 100–300 thousand inhabitants the AS of these elements content increased and became equal to 32 for Zn (from 10.4 in Uralsk to 320 mg/kg in Bratsk), and 42 for Pb. This is explained by the same factors as the AS increase in the cities group discussed above.

In soils of villages, the value of AS for practically all the chemical elements, became the lowest compared with other groups of settlements. The main reason is low average content of elements, close to abundance in the Earth’s soils, in some localities.

The value of AS for many elements is quite large in soils of tourist-recreational centres. The large AS of the mean values, marked in a number of cases, is primarily explained by the different remote of localities from industrial sites and agricultural land, changing in the transport structure and using medicinal waters and mud with different composition. So the AS for Pb is 46 (from 6.5 on Saipan island to 300 mg/kg in Alupka, Crimea) and for Zn AS is 100 (from 5 on Saipan island to 500 mg/kg in the village on the Black Sea coast).

4 Conclusions

  1. 1.

    Quantitative ecological–geochemical data on the composition of soils confirmed the environmental and geographical information on the necessity for separate consideration of urban soils and division of settlements into separate groups according to the number of inhabitants. The greatest elements accumulation comparing with the Earth’s soils (tens of thousands of tons per 1 km2) is marked in soils of settlements groups with the half-million and less than 100,000 number of inhabitants, and in recreational and tourist centres. In all these systems, it is associated with an increase in the content of Ca and Mg.

  2. 2.

    Considering the environmental significance of chemical elements accumulation in soils, we note the primary role of Pb and Zn in all groups of cities. The accumulated mass of Pb fluctuates from 17.7 to 33.7 t/km2, decreasing to 7.6 t/km2 in soils of villages comparing with the Earth’s soils. The concentration of accumulated Zn usually ranges from 25.0 to 39.0 t/km2 and only in tourist-recreational centres and millionaire cities is up to 90.0 t/km2. Out from the rest pollutants it is necessary, first of all, to note As and then Cu and Cl, which are the main contaminants in four of six cities groups. In two groups of settlements Cd and Co are important soil pollutants. In three groups, a considerable increase in the Ca content significantly modifies ecological-geochemical state of soils.

  3. 3.

    The reduced content of Cr, and often Y and Be noted in soils of all selected settlements groups comparing with the Earth’s soils. The greatest mass loss is typical for Fe (over 10,000 t/km2) and Cr (from 67 to 95 t/km2).

  4. 4.

    Highlighted settlements groups also differ from one another in the values of chemical elements Absolute Spread. The greatest variation is typical for groups of settlements, which are characterised by complex of enterprises in one industry, such as nonferrous metallurgy.