UDC:551.521.3,551.583

CONTENT OF RARE EARTH ELEMENTS IN SOILS OF THE SOUTH-EASTERN PART OF THE SUGHD REGION

¹Rahmatov M.N., ²Abdullozoda S.F., Ismoilov K.A.,

¹State Educational Institution “Khujand State University named after Academician Bobojon Gafurov”

²Physical and Technical Institute named after S.U. Umarov

Despite the fact that in recent years many review papers have been published devoted to the study of the geochemical behavior of rare earth elements (REE) in soils and plants [1, p. 75; 2, p. 57; 3, pp. 101-107], their concentrations in water and precipitation [4, p. 648; 5, pp. 125-131], it should be noted that there is an almost complete absence of general works on the geochemical cycle of REE in the lithosphere-atmosphere system.

Currently, there is a general idea that rare earth elements (REE) are increasingly being studied as indicators of technogenic pollution of soils of the studied territories and ecological and geochemical zoning. According to a number of researchers [6, p. 102; 7, p. 18; 8, p. 17], this is primarily due to the fact that REE are currently actively mined throughout the world and are widely used in microelectronics, industry, electrical engineering, energy, communications and other sectors of the national economy [1, p. 6]. As noted by environmental experts [9, pp. 57, 58; 10, p. 69], in Central Asia, Russia and other regions of the planet, soil pollution with rare earth elements from anthropogenic sources leads to pollution of the most important life-supporting natural environments [10, pp. 1-11; 12, pp. 107047; 13, pp. 1285-1303].

It is quite obvious that soils with different ecological and geochemical layers experience intense anthropogenic load, which often leads to their degradation and, accordingly, to disruption of normal functioning, which has both direct and indirect negative impact on living organisms (including humans). According to the research of Yu. N. Vodyanitsky [1, pp. 76-80; 10, pp. 70-74], since REE are used as microfertilizers in soils, when they are in excess, they become dangerous for the natural environment. According to N. N. Pigareva et al. [14, p.60,61] REE are divided into 2 subgroups: 1 - light rare earth elements (or elements of the cerium subgroup, their atomic mass <153, and ionic radius >95 nm: these include La, Ce, Pr, Nd, Sm, Eu; 2 - heavy rare earth elements. The atomic mass of heavy REE is >153, and the ionic radius is <95 nm. This subgroup includes Dy, Ho, Er, Tm.

From modern research in this direction in Northern Tajikistan, it should be noted that earlier in the works of Tajik scientists such as U. Mirsaidov, H. Murtazaev, and others, quite a lot of work began to be carried out from the end of the 90s of the last century and continues to the present day, on a variety of topics: the study of radioactive isotopes, radon exhalation, physical and chemical characteristics of uranium-containing waste, data on the general radiation background and samples of ore rocks, as well as the analysis of water samples outside the tailings pond of Northern Tajikistan, which was reflected in a number of scientific articles, monographs and dissertations [15, p. 164; 16, pp. 47-50, 17, pp. 3-5; 18, pp. 5-7].

In recent years, methods of mass spectrometric analysis have become increasingly used in the field of geoecology [19, pp. 5-11; 20, pp. 6-19;]. Most publications are devoted to identifying the content, distribution, and behavior of rare earth elements in soil [20, pp. 6-16; ].

For most regions of Central Asia, there is insufficient data on the elemental composition of soils, especially on rare earth elements. However, information on the content and distribution in the surface horizons of soils in the southeastern part of the Sughd region has not been studied, although these data are necessary to assess the influence of the nature of REE on the features of their distribution in the surface horizons of soils.

From this we can conclude that the study of the content, distribution, and behavior of REE in the soil is of great scientific importance. Thus, the relevance of the study of REE in local areas is due to both global changes in their migration and the high indicator role of their concentration and comparison in areas with natural and man-made geochemical anomalies [21, pp. 700-702; 22, pp. 73-79]. Thus, the purpose and main objective of this work is to establish patterns of accumulation and generalization of data on the content and distribution of rare earth elements in various ecological and geochemical stratifications of the territories of the southeastern part of the Sughd region.

MATERIALS AND METHODS

The work was carried out in accordance with the general methodological principles of ecological and geochemical studies [23, p. 5-8]. Field work was carried out in the period 2020–2022. Soil samples were collected from the upper horizons at a depth of 0–5 cm using the envelope method at points corresponding to different areas of the southeastern part of the Sughd region. A total of 30 samples were collected and analyzed. After collection, the samples were dried to an absolutely dry state, crushed and analyzed for REE content using inductively coupled plasma mass spectrometry (ICP-MS). Analytical work was carried out at the accredited Problem Research Institute of Mineralogy, Ural Branch of the Russian Academy of Sciences (Miass, Chelyabinsk Region) [24, p. 305; 25, pp. 93-101]. The layout of sampling points is shown in Figure 1. The mathematical processing of the obtained results was carried out in accordance with the requirements of quantitative elemental analysis methods. Statistical processing was performed using Microsoft Excel 2019. The relationships between elements were calculated using the pair correlation coefficient, their values were considered significant at a confidence level of P = 0.95. MACs for rare earth elements in soils have not been developed. In this case, when standardizing the content of REE, a concentration not exceeding twice the clarke is usually taken as the norm. The method for processing the results included the calculation of the following ecological and geochemical indicators: enrichment factors, concentration coefficient, concentration clarke and dispersion clarke separately.

The Enrichment Factor (EF) is widely used to assess anthropogenic impact on soil [25, pp. 93-101; 26, pp. 2-6]. EF is based on the normalization of measured REE by a reference element and is determined by the following formula

where: EF is the enrichment factor,  and  are the concentrations of the REE in question and the standardizing element, respectively, either in the sample or in the earth's crust.

Theoretically, as a reference element, it should not be affected by anthropogenic activities and should not be strongly affected by weathering processes. The most commonly used reference elements are Al, Ca, Fe, Li, Mn, Sc and Sr. In this work, the concentration of Sc was used as a reference element to calculate the EF of REE [25, p.93-101; 26, p.2-6]. If the EF values are greater than 1, this indicates anthropogenic sources of REE, and less than 1 - the lithogenic nature of REE. Also, EF can provide an understanding of the separation of anthropogenic source from natural. In addition, EF also helps to determine the degree of soil contamination by an element. Enrichment factors allow identifying five levels of TM accumulation: EF < 2 indicates deficiency up to nominal enrichment, (2) 2 ≤ EF < 5 indicates reasonable enrichment, (3) 5 ≤ EF < 20 indicates significant enrichment, (4) 20 ≤ EF < 40 indicates excessive enrichment, and (5) EF ≥ 40 indicates extremely high enrichment [25, pp. 93-101; 26, pp. 2-6].

The concentration coefficient (Contamination Factor - CF) of the rare earth element CF was calculated based on the ratio of the actual content of REE in soil samples (C_REE) to its background level (Cf) in a similar object:

where is the concentration of the rare earth element, and С_фон is the background value for the rare earth element under study. The average value of the geochemical background in the earth's crust for impurity metals is used as the background value of REE [18, 25]. CF was divided into four groups: (1) CF < 1 means no pollution, (2) 1 ≤ CF < 2 – slight pollution, (3) 2 ≤ CF < 3 moderate pollution, (4) 3 < CF > 5 – strong pollution, CF > 5 – very high pollution [27, pp. 52-59]. The pollution coefficient is the main one for calculating complex pollution indicators.

To characterize the accumulation of REE in the surface horizons of soils, Clarke concentrations (CC) were estimated using the formula:

where   is the REE in the soil,  is the Clarke of this element in the earth's crust [28, pp. 6-8].

According to famous scientists, if Clarke is greater than one, this indicates enrichment with the element, if less – a decrease in its content compared to Clarke as a whole [28, pp. 6–8; 29, pp. 125-127].

According to researchers [1, p. 77], the comparison with the crustal Clarke, but not with the soil Clarke, is due to the fact that the latter is less reliable than the crustal Clarkes: the content of rare metals in the lithosphere of these data is much greater than in soils.

The concentration Clarke shows how many times the content of a chemical element (in our case, REE) in soil samples exceeds its content in the earth's crust, and allows us to judge the degree of concentration of the element in the soil relative to the earth's crust [28, pp. 44-49].

The dispersion Clarke is a value inverse to the concentration Clarke, which shows how many times the Clarke of the element under study in the earth's crust (K) is greater than its content in the soil or another natural object. If it is necessary to show how many times the element's content in the rock is lower than its content in the lithosphere, the inverse of the concentration Clarke is used [28, pp. 6-8; 30, pp. 46, 47].

where С_i is the content of the i element in the studied soil samples; К_i is the Clarke of the i element in the upper part of the continental crust, mg/kg.

The coefficient of variation (CV) of rare earth element concentration can reflect variability as well as the influence of human activities on pollution; a high CV value suggests greater anthropogenic interference [10]. The CV coefficient shows how large the deviations in the values of rare earth element concentrations in soils are. The higher the CV, the greater the spread in values and the less accurate the data. It is calculated using the following formula:

where σ is the standard deviation of REE, and <C> is the average REE content in the soil. According to [31, p.135], CV ≤ 0.15 indicates low variation, 0.15 < CV < 0.35 indicates moderate variation, and CV > 0.35 corresponds to high variation.

Figure 1. Map w ith the sampling location of soil sampling in the south-eastern part of Sughd region (1. Ayni; 2. Penjikent; 3. Mountainous-Matcha district; 4. Shakhristan; 5. Istaravshan; 6. Devashtich)

RESULTS AND DISCUSSION

Despite the growing interest in the study of TM and the growth of publications on their study in natural objects, some chemical elements, including rare earth elements, remain unstudied. Assessment of the regional background level of rare earth elements in soils is a necessary step in creating a basis for monitoring and studying the degree of pollution. In the southeastern part of the Sughd region, the content and ranges of 11 rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm) were determined using inductively coupled plasma mass spectrometry (ICP-MS).

Statistical processing of the experimental data was carried out using the Microsoft Excel software package. The average, minimum and maximum values, median, standard deviations, variation coefficient, skewness, kurtosis and Pearson correlation coefficients were calculated. The statistical variation parameters of the rare earth element content in the soils of the southeastern part of the Sughd region are presented in Table 1. The concentrations of rare earth elements in the soils of the southeastern part of the Sughd region vary within narrow intervals (Table 1). The distribution of REE is uniform in the study area (2.44-9.72%). To calculate the geoecological parameters of REE accumulation in the study areas, we considered a number of coefficients: the enrichment factor, the concentration coefficient relative to the background REE content, concentration Clarkes and dispersion Clarkes relative to background soils. The values of the concentration and dispersion Clarkes of REE given in Tables 2 and 4 characterize the concentrations or dispersions of REE in the study soil relative to the earth's crust. If the element under study accumulates in the soil, the value of its concentration Clarke will be higher than one − Kk > 1 [28, pp. 6-8; 30, p.46-48]. The maximum lanthanum content was found in the soils of the Panjakent region, which is 30.07 mg/kg. The range of changes in the La content according to our studies in the soils of the southeastern part of the Sughd region was from 18.2 to 30.7 mg/kg. The average La content in the continental crust is 29 mg/kg [20, p.8]. Analysis of the average La content in the studied soils shows that La concentrations have near-Clark values.

Based on the results of the soil sample analysis, it was established that the REE content does not belong to the series of accumulating elements in the studied soils, i.e. it is not included in it.

The average content of the studied cerium in the studied soil was 46 mg/kg, which was 2-247 times higher than La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm. The maximum level of cerium content – 53.8 mg/kg – was noted in the Panjakent district. Analysis of the variation coefficients showed that the cerium content in the southeastern part of the Sughd region is uniform, the values are within 5.5% (see Fig. 2). For the REE content in all the studied soil samples, the variation coefficient was less than 10%, which indicates an insignificant dispersion of REE in the soils of the southeastern part of the Sughd region. The obtained results show that the content of rare earth elements in the studied soils of the south-eastern part of the Sughd region is characterized by a moderate spread of values for all elements and a slight positive asymmetry in the distribution of some of them.

Figure 2. Coefficient of variation (CV) of rare earth elements (La, Ce, Pr, Nd, Sm, Eu) in soil samples

Figure 3. Coefficient of variation (CV) of rare earth elements (Gd,Tb,Dy, Ho, Er, Tm) in soil samples

 

Compared with La, Ce and Nd in the soil samples, the content of Pr, Sm, Eu, Gd, Dy, Ho, Er, Tm in the studied soils is 10-100 times lower. Coefficients that would exceed these variations were not observed for the studied elements.

The content of cerium in the soils of the south-eastern part of the Sughd region varies from 41.4 to 55.53 mg / kg. With a generally low level of soil contamination with cerium, high concentrations of this element were not noted. It was found that the studied soils are characterized by a uniform distribution of Ce with an average content in the soil and are within its clarke in the earth's crust (see Fig. 4). Based on the data obtained, a series was compiled according to the average content of rare earth elements: >  > > > >  > > > > > , while the content of La, Eu and Gd was found to be very close to the clarkes of the earth's crust, and lower for Ce, Pr, Nd, Sm, Dy, Ho, Er, Tm. The highest concentrations are cerium, lanthanum and neodymium, the lowest concentration is praseodymium, gadolinium, samarium, dysprosium, erbium, europium, terbium and holmium. The distribution of all the rare earth elements under study is close in terms of asymmetry and excess, which is observed for some elements.

	La	Ce	Pr	Nd	Sm	Eu
Minimum	18,2	41,4	5	19,12	3,71	1,01
Maximum	30,07	55,53	6,66	25,14	4,97	1,43
Mean	22,96	46,9	5,56	21,24	4,21	1,18
Median	20,48	44,56	5,26	20,29	4,14	1,15
Standard Error	2,23	2,58	0,29	1,01	0,17	0,07
Coefficient of Variation	9,72	5,5	5,14	4,75	4,06	6,06
Skewness	0,82	0,6	0,91	1,13	1,25	0,39
Kurtosis	-1,88	-2,06	-0,87	0,26	2,8	-1,93
	Gd	Tb	Dy	Ho	Er	Tm
Minimum	3,91	0,48	2,62	0,48	1,32	0,17
Maximum	4,59	0,56	3,16	0,57	1,72	0,22
Mean	4,3	0,53	2,93	0,53	1,52	0,19
Median	4,31	0,55	2,96	0,54	1,52	0,2
Standard Error	0,1	0,01	0,09	0,02	0,07	0,01
Coefficient of Variation	2,44	2,6	3,01	3,26	4,82	4,95
Skewness	-0,63	-0,8	-0,42	-0,35	-0,01	-0,15
Kurtosis	0,55	-1,31	-1,67	-2,42	-2,75	-1,63

 

Table 1. Statistical indicators of individual indices of surface soil layers in the south–eastern part of Sughd region

In the soil samples collected in the south-eastern part of the Sughd region, the average lanthanum content does not reach the KK value. The most significant enrichment of La in the studied soils was not observed, only in two areas is La (Kk>1) accumulated.

Clarke analysis of the concentration (Kk) of rare earth elements in soil samples relative to the crustal clarke showed that in all samples taken in the south-eastern part of the Sughd region, the La content was near-Clarke values only in two areas – in Gorno-Matcha district – 1.02; in Panjakent district – 1.04, in the remaining districts it was recorded below one. For Eu, near-Clarke values were also observed at two sampling points: in the Gorno-Matcha district – 1.1 and in the Devashtich district – 1.01, in other districts it is noted below one. The Gd content in almost all areas is recorded within the Clarke values, with the exception of Devashtich district, where it is noted below one. Calculations of the ecological and geochemical indicators of the accumulation of rare earth elements in the studied soils showed no excess relative to the Clarke of the earth's crust, this indicates that the elements in question are not enriched relative to the Clarke values. The content of rare earth elements in the upper layers of the soil does not accumulate or dissipate. According to researchers, in such cases the concept of “Dissipation Clarke” is usually used. The values of the concentration Clarke and the dispersion Clarke allow us to identify rows or groups of accumulating and dissipating chemical elements.

Figure 4. Contents of rare earth elements relative to Clarke in the earth's crust (Mountainous Matcha district, Ayni, Panjakent, Shahristan)

Figure 5. Contents of rare earth elements relative to Clarke in the earth's crust (Istaravshan, Devashtich)

 

Figure 6. Ratio of the clarke of rare earth elements in the earth’s crust to its content in the studied soil (Mountainous Matcha district, Ayni, Panjakent, Shahristan)

Determination of the Clarke concentration relative to the Clarke in the earth's crust of these elements in the studied soils gives the following series of elements according to the accumulation tendency in soils: > >   > > > > > >  > > .Almost all the studied soil samples are characterized by weak accumulation of rare earth elements.

 

Figure 7. Ratio of the clarke of rare earth elements in the earth’s crust to its content in the studied soil (Istaravshan, Devashtich)

 

The concentration coefficient shows how much the content of rare earth elements in the soil exceeds the natural minimum level (background). Below is a series of rare earth elements, sorted by decreasing concentration coefficient. Lanthanum (La) is at the top of this list, followed by europium (Eu), erbium (Er), thulium (Tm), etc.; gadolinium has the lowest value. The series by concentration coefficient: > > > > >  > >  >  >  > . The value of the concentration coefficient indicates the absence of processes of accumulation of rare earth elements in the upper soil horizons. The content of most rare earth elements in soil samples of this region is at the level of their background concentrations, for all REE in the Gorno-Matcha district, almost twofold excess of the background is typical (Kk = 1.12 - 1.63). In the upper layers of the studied soils, a different pattern was established, the content of most of the studied rare earth elements in the soil samples is below their background concentrations.

 

 

 

 

	La	Ce	Pr	Nd	Sm	Eu
Gorno-Matcha district	1,63	1,34	1,23	1,20	1,15	1,41
Ayni	1,00	1,00	1,00	1,02	1,09	1,01
Panjakent	1,65	1,30	1,33	1,33	1,34	1,24
Shahristan	1,16	1,14	1,10	1,10	1,10	1,05
Istaravshan	1,03	1,02	1,00	1,00	1,00	1,00
Devashtich	1,09	1,01	1,00	1,02	1,13	1,30
	Gd	Tb	Dy	Ho	Er	Tm
Gorno-Matcha district	1,12	1,12	1,18	1,19	1,30	1,32
Ayni	1,08	1,04	1,07	1,02	1,00	0,98
Panjakent	1,17	1,17	1,08	1,08	1,02	1,00
Shahristan	1,14	1,17	1,19	1,19	1,28	1,20
Istaravshan	1,08	1,16	1,20	1,18	1,23	1,24
Devashtich	1,00	1,01	1,00	0,99	1,07	1,13

Table 2. Values of rare earth element concentration coefficients in the soils of the southeastern part of Sughd region

 

Fig. 8 and 9 show the enrichment factors of rare earth elements in the composition of soil samples taken in the southeastern part of the Sughd region. The average values of enrichment factors for each region are considered. The analysis of the calculation of enrichment factors in the studied samples shows that the composition of soil samples in the study areas does not include elements of technogenic origin from the studied REE. Since the calculated enrichment factors for REE are within one or have values below 1, this indicates the absence of intensive enrichment of rare earth elements in the soils of the areas under consideration.

The average EF values for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm in all samples of aerosol particles are at the level of one, i.e., the soils are not enriched with these elements; this indicates that the sources of the mentioned elements are localized. The enrichment factor level of rare earth elements in soil samples taken in the Gorno-Matchinsky district reflects the following elemental series constructed in descending order of the average EF values of elements: > >   > > > > >   > > >  Relatively high average enrichment factors of Gd, Eu and Ho in the territories of the Gorno-Matcha district may be of technogenic nature.

The analysis of the enrichment factor values ​​in Aini shows that the aerosol particles were enriched in these elements: Gd, Eu and Ho. However, the decreasing series of the average enrichment factor values of the selected rare earth elements is as follows: > > > > > > > > > > >   

The enrichment coefficient values for soil samples taken in Panjakent have the following sequence: > > > > > > > >

The series with the highest enrichment factors in samples taken in the Shahristan region are: > > > > > > >

According to the enrichment coefficient in these soils in the Istaravshan region, rare earth elements form the following series: > > > > > >

According to the enrichment coefficient, rare earth elements in the soils of Devashtich form the following series: > > > > >

 

Figure 8. Calculated enrichment factor (EF) values for rare earth elements (La, Ce, Pr, Nd, Sm and Eu,) in soil samples taken in the south-eastern part of Sughd region

 

Figure 9. Calculated enrichment factor (EF) values for rare earth elements (Gd, Tb, Dy, Ho, Er and Tm) in soil samples taken in the south-eastern part of Sughd region

 

Table 3 presents the calculated correlation coefficients between the concentrations of the studied rare earth elements in the soil samples. We have established a significant correlation between the content in the soil samples Ce и La (r = 0,98), Pr and La (r = 0,97), Pr and Ce (r = 0,95), Nd and La (r = 0,94), Nd and Ce (r = 0,91), Nd and Pr (r = 0,99), Sm and Pr (r = 0,86), Sm and Nd (r = 0,86), Sm и Nd (r = 0,91), Gd and Pr (r = 0,81), Tb and Gd (r = 0,84), Er and Dy (r = 0,84), Er and Ho (r = 0,90), Tm and Er (r = 0,94) which indicates their lithogenic origin. Based on the results of the correlation analysis of the content of the rare earth element in the studied soil samples, we can judge the nature of the pollution of the territory and its source.

	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm
La	1,00	0,98	0,97*	0,94	0,79	0,72	0,69	0,42	0,11	0,27	0,13	0,12
Ce		1,00	0,95	0,91	0,70	0,65	0,76	0,53	0,27	0,43	0,29	0,22
Pr			1,00	0,99	0,86	0,56	0,81	0,54	0,10	0,25	0,04	-0,05
Nd				1,00	0,91	0,53	0,79	0,51	0,02	0,16	-0,06	-0,15
Sm					1,00	0,53	0,55	0,20	-0,39	-0,25	-0,42	-0,46
Eu						1,00	0,01	-0,20	-0,26	-0,07	0,10	0,28
Gd							1,00	0,84	0,48	0,54	0,20	-0,05
Tb								1,00	0,75	0,79	0,48	0,26
Dy									1,00	0,97	0,84	0,69
Ho										1,00	0,90	0,75
Er											1,00	0,94
Tm												1,00

Table 3. Correlation coefficients for the content of rare earth elements in the soils of the southeastern part of Sughd region

CONCLUSIONS

• the results of the monitoring study presented in the work based on the obtained factual material for the first time served as an information base on the elemental composition of soils for a multifactorial environmental assessment of soil quality in the southeastern part of the Sughd region;
• in the upper horizons of the studied soils taken in the southeastern part of the Sughd region, rare earth elements do not accumulate, which indicates their weak participation in biogenic migration and accumulation;
• based on the calculated values of the REE concentration coefficients in soils relative to the background indicators of the territory, it was established that the surveyed soils are characterized by a category of moderate levels of accumulation and enrichment;
• excess of the clarke value by some rare earth elements, especially atypical for the studied soil samples, and in particular, the distribution of these REE, may indicate their anthropogenic origin;
• calculated ecological and geochemical indicators indicate the absence of enrichment of soils with rare earth elements compared to the background, Clarke of the earth's crust, which is confirmed by the calculations of the enrichment factor;
• among the considered areas of the south-eastern part of the Sughd region, the Gorno-Matcha and Panjakent districts stand out for their relatively high content of almost all the studied rare earth elements in soil samples, which is apparently typical for the studied soils;
• we have established that there is a significant correlation between almost all the studied elements.

REVIEWER: Islomzoda M. B.,

 Doctor of Chemical and Mathematical Sciences,

Professor

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CONTENTS OF RARE EARTH ELEMENTS IN THE SOILS OF THE SOUTH-EASTERN PART OF SOGHDIAN REGION

The article presents the results of the study, obtained original data on the content and distribution of rare earth elements in the soils of the south-eastern part of Sughd region. The concentrations of rare earth elements were determined by using a highly sensitive inductively coupled plasma mass spectrometry method. A total of 30 samples were collected and analyzed. Peculiarities of accumulation of rare earth elements depending on regional characteristics have been revealed. The average concentrations of the studied rare earth elements are within the clarke index and below. The use of variational-statistical methods for processing the obtained results made it possible at least to some extent, streamline the results of analytical studies of soils within the south-eastern part of the Sughd region. Concentrations of rare earth elements in the soils of the southeastern part of the Soghd region vary within narrow intervals. At the same time, the distribution of REE bears a regular character in the areas (2.44−9.72%) under study. Quantitative criteria degree of accumulation and enrichment of soils have been calculated: here refer factors of enrichment, concentration coefficient, concentration clarke and dispersion clarke. On the base of the obtained values of these indicators it is shown that the soils of the studied points are characterized by a moderate level of accumulation and enrichment. Based on the data obtained, a series was compiled for the average content of rare earth elements: >  > > > >  > > > > > , while the contents of La, Eu and Gd are very close to the clarkes of the earth’s crust, lower – Ce, Pr, Nd, Sm, Dy, Ho, Er, Tm. The highest concentrations are cerium, lanthanum and neodymium, the lowest concentrations are praseodymium, gadolinium, samarium, dysprosium, erbium, europium, terbium and holmium. The distribution of all studied rare earth elements is close in terms of asymmetry and kurtosis, and is observed for some elements. We have established a significant correlation between the content of Ce and La (r = 0,98), Pr and La (r = 0,97), Pr and Ce (r = 0,95), Nd and La (r = 0,94), Nd and Ce (r = 0,91), Nd and Pr (r = 0,99), Sm and Pr (r = 0,86), Sm and Nd (r = 0,86), Sm and Nd (r = 0,91), Gd and Pr (r = 0,81), Tb and Gd (r = 0,84), Er and Dy (r = 0,84), Er and Ho (r = 0,90), Tm and Er (r = 0,94),which indicates to their lithogenic origin.

Keywords: soil, rare earth elements, inductively coupled plasma mass spectrometry method, statistical analysis, factor of enrichment, concentration coefficient, concentration clarke, scattering clarke, correlation analysis.

Information about the authors: Rakhmatov Mukhamadi Nuridinovich – Khujand State University named after academician B. Gafurov, candidate of physical and mathematical sciences, Associate Professor of the department of general physics and solid body under. Address: 735700, Republic of Tajikistan, Khujand, Mavlonbekov passage, 1. Phone: (+992) 929-43-19-92. E-mail: muhamadi. rahmatov@yandex. com.

Abdullozoda Sabur Fuzail – Head of the Laboratory of Atmospheric Physics named after S.U. Umarov Physycal-technical Institute of the National Academy of Siences of Tajikistan, Doctor of Physicol-Mathematical Sciences, Professor. Address: 734063, Republic of Tajikistan, Dushanbe, Aini Street, 299/1. Phone: (+992) 934-89-60-14. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it..

Ismoilov Komronjon Alisherovich – Khujand State University named after academician B. Gafurov, claimant for candidate degree under the department of general physics and solid body under. Address: 735700, Khujand,  Tajikistan, Mavlonbekov passage, 1. Phone: (+992) 928-88-99-80. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Article received 19.03.2024

Approved after review 27.05.2024

Accepted for publication 16.09.2024