DETERMINATION OF HEAVY METALS AND CR AND PB IONS IN SOIL BY MASS SPECTROMETRIC METHODS

ABSTRACT

In this study, soil samples collected from the territory of the Almalyk Mining and Metallurgical Complex (AMMC) and surrounding areas were analyzed using mass spectrometric methods (ICP-MS). The analysis determined the concentrations of ions of heavy metals in the soil samples, including cobalt (Co), nickel (Ni), zinc (Zn), arsenic (As), scandium (Sc), copper (Cu), selenium (Se), rubidium (Rb), indium (In), cerium (Ce), chromium (Cr), and lead (Pb). The monitoring results showed that the concentrations of chromium (Cr) and lead (Pb) ions in the soil samples significantly exceed the permissible limit values (PLV) established for the area. This indicates the presence of soil contamination, which may negatively affect the quality of the surrounding environment and the health of local residents. Elevated concentrations of these heavy metals may be linked to the industrial activities of AMMC, including metal mining and processing, which necessitates further research and the development of effective measures to reduce pollution levels.

АННОТАЦИЯ

В данном исследовании были проанализированы образцы почвы, отобранные на территории Алмалыкского горно-металлургического комбината и прилегающих районов, с использованием масс-спектрометрических методов анализа (ICP-MS). В ходе исследования в почвенных пробах были определены концентрации ионов таких тяжёлых металлов, как кобальт (Co), никель (Ni), цинк (Zn), мышьяк (As), скандий (Sc), медь (Cu), селен (Se), рубидий (Rb), индий (In), церий (Ce), хром (Cr) и свинец (Pb). Результаты мониторинга показали, что содержание ионов хрома (Cr) и свинца (Pb) в почвенных пробах значительно превышает допустимые предельные значения (ПДК), установленные для данной территории. Это свидетельствует о наличии загрязнения почвы, что может оказывать негативное влияние на качество окружающей среды и здоровье местных жителей. Повышенные концентрации этих тяжёлых металлов могут быть связаны с промышленной деятельностью АГМК, в том числе с процессами добычи и переработки металлов, что требует дальнейших исследований и разработки эффективных мер по снижению уровня загрязнения.

Keywords: Heavy metals, soil, mass spectrometry, inductively coupled plasma (ICP), mass spectrometry (MS).

Ключевые слова: тяжёлые металлы, почва, масс-спектрометрия, индуктивно связанная плазма (ICP), масс-спектрометрия (MS).

Introduction

Worldwide, the development of industrial technologies, manufacturing, and construction industries has led to the spread of heavy, toxic, and carcinogenic metals into the environment, causing a global ecological problem. High efficiency in identifying and monitoring major heavy metal pollutants in the environment can be achieved by developing environmentally safe detection methods.

Chromium is largely immobile in many natural conditions. In soil, it mostly exists as Cr³⁺ ions, and the presence of organic matter facilitates its accumulation in the soil system. As an element with a small electronic radius, it strongly binds even to moist soils, and this binding intensifies with increasing pH. Soil moisture significantly affects the mobility and accumulation of chromium in plants: chromium absorption in moist soil can increase up to five times. Additionally, chromium forms complexes with soil organic matter [1].

One of the main sources of environmental pollution is lead. A hazardous source for both the environment and human health is the use of hundreds of thousands of tons of leaded gasoline in motor vehicles. Industrial waste from various factories contains lead ions that contaminate soil and water sources, posing serious risks to living organisms. Heavy metals and their compounds have strong negative effects on human health and constitute a significant group of pollutants. Heavy metals form the primary group of environmental contaminants. These metals are widely used in industrial enterprises. Environmental monitoring and pollution studies focus mainly on metals with densities of 5 g/cm³ or higher. These heavy metals pose a serious threat not only to humans but also to all organisms living on Earth. The main heavy metals include Cr, Pb, Co, Zn, Cu, Sn, Mo, As, V, Hg, Cd, Bi, Ni, Sb, Mn.

Heavy metals can be classified based on atomic mass, density, toxicity, natural distribution, and participation in natural and technogenic cycles. Toxicity is a critical factor in their classification. According to their toxicological impact, chemical substances are divided into three classes based on DST (GOST) 17.4.1.0283:

• Class I (very hazardous): As, Cd, Hg, Be, Se, Pb, Zn
• Class II (moderately hazardous): B, Co, Ni, Mo, Cu, Sb, Cr
• Class III (low hazard): Ba, V, W, Mn, Sr [90; pp. 395-401].

Olmaliq city, Tashkent region, is one of the largest non-ferrous metallurgy centers in Uzbekistan. Although Olmaliq Mining and Metallurgical Industrial Complex plays an important role in developing the Uzbek economy, it seriously affects the environment and public health [2]. Industrial waste from chemical, mining, and non-ferrous metallurgy enterprises is linked to the ecological state of Olmaliq city, causing pollution of water, soil, and atmosphere, which negatively impacts plants and animals [3].

Materials and methods

For identifying important components of soil and studying certain properties, soil samples were prepared for analysis according to DST GOST standards [4]. The collected soil was spread on clean paper and dried at room temperature. After drying, large particles were crushed and ground. For laboratory analysis, an average soil sample was obtained by dividing the soil into several portions using the envelope method, and from each portion, 10 g of soil was weighed on an analytical balance. The prepared soil was ground in a special mortar and passed through 1 mm sieves. Each soil sample collected from industrial zones was prepared for analysis using the above method [5].

From the soil samples collected in the regions, 10 g was weighed. The samples were dissolved in a 1:1 ratio, i.e., 20 ml concentrated HCl and 20 ml distilled water. The solution was heated in a water bath for 1 hour until boiling. Then, the solution was cooled and heated twice more in a water bath consecutively. After 24 hours, the solution was reheated and allowed to settle. Due to the presence of various metal ions, the solution’s color changed. The solution volume was filtered into a 250 ml volumetric flask, and the precipitate was separated [6].

To concentrate chromium and lead ions from the soil solution, an organic reagent immobilized polymer sorbent was used. The polymer sorbent was synthesized using waste fiber from the "Urganch Teks" LLC factory (natural silk fibroin) and the reaction of PAN (polyacrylonitrile) and PEPA (polyethylene polyamine) synthesized at the "Polymer Chemistry" department of Uzbekistan State University, treated with formaldehyde and phosphite acid to form synthetic fiber PPF. Organic reagents such as sulfarsazine, eriochrome black T, thoron, arsenazo (III), and sulfosalicylic acids were used. Good results were observed with sulfarsazine and eriochrome black T reagents.

A 50 ml aliquot of the soil solution sample was placed into a beaker, then 5 µg of Cr and Pb ion solutions, 5 ml of a covering agent, 0.2 g of organic reagent immobilized on silk fibroin fiber, organic reagents immobilized on PPF fiber, and 5 ml of universal buffer solution at pH=8 were added and sorbed for 10-15 minutes.

Soil samples collected from Olmaliq MMC and adjacent areas were analyzed for heavy metals using mass spectrometric (ICP-MS) methods on the "UzOU 0677:2015 (MBI No. 499-AEM/MS)" instrument. Soil samples from six locations within Olmaliq MMC were collected and monitored: the outer zone of the MMC and areas at 1 km, 3 km, 5 km, 10 km, and 20 km distances. Analysis confirmed the presence of 61 elements in the soil samples. The concentration of certain metals (in ppm, µg/g, g/t) is presented in Table 1 below.

Table 1.

ICP-MS Analysis of Elements in Soil Samples from the Olmaliq MMC Area, µg/g 

Results and discussions

The distribution of chromium (Cr) and lead (Pb) ions in soil samples collected from the Almalyk Mining and Metallurgical Complex (AMMC) is presented in Table 2. The data indicates a noticeable variation in the concentrations of these heavy metals across different locations within the studied area. A detailed analysis of the results reveals that the concentration of chromium in the soil decreases as the distance from the AMMC increases [7,8]. This suggests a clear correlation between the proximity to the industrial facility and the accumulation of chromium ions in the surrounding soil.

Specifically, soil samples collected closer to the AMMC show significantly higher concentrations of chromium, indicating that the industrial processes associated with the complex—such as mining, metal extraction, and processing—likely contribute to the increased presence of this heavy metal in the environment. In contrast, as the samples were taken at greater distances from the complex, the chromium levels gradually declined, which is consistent with the general pattern observed in pollution dispersion around industrial zones.

This distribution pattern highlights the spatial impact of industrial activities on the surrounding environment, emphasizing the need for ongoing monitoring and possible intervention to mitigate the environmental and health risks posed by such pollution. Additionally, the decline in chromium concentration with distance suggests that local soil remediation or contamination control measures might be more urgently required closer to the facility.

Table 2.

ICP-MS Analysis of Cr and Pb Ions in Soil Samples, µg/g

Development of the Sorption-Spectroscopic Method for Determining Chromium and Lead Ions in Environmental Objects. A sorption-spectroscopic method was developed to detect chromium and lead ions in environmental samples. This method is based on concentrating metals from the sample using polymer sorbents immobilized with organic reagents.

In the study, the immobilization of organic reagent solutions on sorbents was carried out using the following procedure: fiber samples with a diameter of 2 cm and mass of 0.2 g were placed in a beaker containing 50 cm³ of 0.1 M HCl solution. In this process, the initial sorbent converts to the Cl⁻ form. The carrier fibrous sorbent was then washed several times with distilled water, and 10 ml of the selected organic reagent was measured and placed into a 50 ml volumetric glass beaker. The HCl-activated fiber was then added to the beaker, and the immobilization process was conducted for a duration ranging from 5 minutes up to 24 hours. After that, the fiber was washed with distilled water, held with a glass rod, and washed twice with 50 cm³ of distilled water each time. The wet fiber was placed into a Petri dish. The amount of organic reagent remaining in the beaker was determined using absorption spectrometry, and the amount immobilized on the fiber was measured by reflectance spectrophotometry.

The complex formation between the organic reagents immobilized on the polymer fiber and metals is mainly used for sorption concentration. At room temperature, metal solutions ranging from 10 ml up to 200 ml are passed through a microcolumn containing 0.2 g of sorbent at a flow rate of 1–10 ml/min. The sorbent initially concentrates the metal ions by passing the solution through at pH values optimal for metal ion sorption. This sorption concentration and spectroscopic detection of metals help address environmental problems.

Conclusion

From the tables and Figure 1, it can be seen that the metals are arranged in descending order of concentration. The most abundant metals are Zn (447–69.5 µg/g), Cu (241–35.7 µg/g), Rb (220–62.1 µg/g), Pb (104.3–57.3 µg/g), Cr (85.7–64.7 µg/g), Ce (79.9–40.8 µg/g), Ni (47.1–22.7 µg/g), Co (14.8–10.3 µg/g), Sc (14.1–6.41 µg/g), Se (7.59–0.50 µg/g), As (6.10–3.75 µg/g), and In (0.301–0.019 µg/g). The order of abundance is Zn > Cu > Rb > Pb > Cr > Ce > Ni > Co > Sc > Se > As > In.

The predominance of zinc and copper corresponds to the fact that Olmaliq MMC primarily produces zinc and copper ores.

By creating new, cost-effective, selective, rapid, and highly sensitive modern methods for detecting Cr and Pb ions in environmental samples—specifically soil—using polymer sorbents immobilized with organic reagents, high efficiency can be achieved. The method developed using immobilized reagents is recommended for detecting heavy and toxic metal ions in soils of industrial zones in the region.

References:

1. S. A. Sokolova. Environmental Chemistry. Textbook. Voronezh, 2008, pp. 54-55.
2. I. V. Kuraeva. Geochemical indicators of the ecological state of polluted soils. Dnipropetrovsk University Bulletin, 2016, 24(2), pp. 61-69.
3. Sh. T. Kholiqulov, Kh. M. Ne’matov. “Soil contamination with heavy metals.” Theoretical and Practical Principles of Innovative Volume 3, SB TSAU Conference, 2022.
4. Yu. N. Vodyanitsky. Standards for the content of heavy metals and metalloids in soils. Soil Science, 2012, pp. 368–375.
5. GOST 17.4.4.02 – 2017. Nature Protection. Soils. Methods of sampling and preparation of samples for chemical, bacteriological, and helminthological analysis. Moscow, 2018.
6. Mamedova M., Akhmadjonov O., Smanova Z. “Monitoring and determination of heavy metals in industrial zone objects of Akhangaran district, Tashkent region.” Ekologiya xabarnomasi Journal, 2023, No. 3, pp. 76-78.
7. Khashieva Kh. Sh., Smanova Z. A., Khashieva Z. Z., Tojiboev B. Kh. New immobilized reagent for lead determination. Universum: Chemistry and Biology, 2015, pp. 76-78.
8. Smanova Z. A., Inatova M. S., Alimova D. Immobilized reagents for metal ion determination. Austrian Journal of Technical and Natural Sciences, 2016, No. 1-2, P(02.00.00, No. 2).
9. Mukhamedova S.N., Abdullaeva M.M., Levitskaya Y.V. Seasonal dynamics of the main markers of stress in Platanus orientalis leaves in the conditions of the urban environment semiaride zone// The American Journal of Horticulture and Floriculture Research. -2022, 4 (03), 1-6