CHEMICAL AND ECOLOGICAL CHARACTERIZATION OF MUD VOLCANOES IN THE SOUTHERN PART OF GOBUSTAN

ABSTRACT

This study presents a geoecological assessment of mud volcano deposits collected from the southern part of Gobustan, Azerbaijan, in January 2025. The aim of the research was to investigate the concentrations of heavy metals, petroleum hydrocarbons (C₁₀–C₄₀), and polycyclic aromatic hydrocarbons (PAHs) in volcanic mud samples. Heavy metals were analyzed using atomic absorption spectrometry (AAS), and organic pollutants were determined through chromatographic methods. The results revealed elevated levels of chromium (29 mg/kg), arsenic (14 mg/kg), and manganese (141 mg/kg), which exceed commonly accepted environmental thresholds. The total concentration of 16 priority PAHs reached 29.0 µg/kg, with notable values for chrysene, pyrene, and benz(a)anthracene. The total petroleum hydrocarbon content was 71 mg/kg. These findings indicate that while mud volcano products may have therapeutic properties, the presence of toxic and potentially carcinogenic substances necessitates environmental monitoring and caution regarding their use.

АННОТАЦИЯ

В данном исследовании представлена геоэкологическая оценка отложений грязевых вулканов, собранных в южной части Гобустана (Азербайджан) в январе 2025 года. Целью работы было изучение концентраций тяжёлых металлов, нефтяных углеводородов (C10–C40) и полициклических ароматических углеводородов (ПАУ) в образцах вулканической грязи. Тяжёлые металлы анализировались методом атомно-абсорбционной спектрометрии (ААС), а органические загрязнители определялись с использованием хроматографических методов.Результаты показали повышенные уровни хрома (29 мг/кг), мышьяка (14 мг/кг) и марганца (141 мг/кг), превышающие общепринятые экологические нормативы. Общая концентрация 16 приоритетных ПАУ составила 29,0 мкг/кг, при этом особенно высокие значения были зафиксированы для хризена, пирена и бенз(а)антрацена. Суммарное содержание нефтяных углеводородов составило 71 мг/кг.Эти данные свидетельствуют о том, что, несмотря на возможные лечебные свойства продуктов грязевых вулканов, наличие токсичных и потенциально канцерогенных веществ требует проведения экологического мониторинга и осторожности при их использовании.

Keywords:  Mud volcanoes of Gobustan, Chemical composition, Heavy metals, Polycyclic aromatic hydrocarbons (PAHs), Ecological assessment, Environmental impact.

Ключевые слова: Грязевые вулканы Гобустана, Химический состав, Тяжёлые металлы, Полициклические ароматические углеводороды (ПАУ), Экологическая оценка, Воздействие на окружающую среду.

Introduction

Mud volcanoes are unique natural geological formations that release a mixture of mineral-rich mud, gases (primarily methane), and thermal waters from deep within the Earth. Azerbaijan, and particularly the Absheron and Gobustan regions, hosts one of the world’s highest concentrations of mud volcanoes. These geological features provide valuable insights into subsurface geochemical processes and may also possess significant ecological, medicinal, and industrial potential.

Azerbaijan is home to the largest number of mud volcanoes in the world, with over 400 identified structures accounting for nearly half of all known mud volcanoes globally. These geological formations are commonly located in areas of complex tectonic structure, particularly within the collision zone of the Eurasian and Arabian lithospheric plates, making the region a unique natural laboratory for geoscientific research.

Mud volcanoes consist of a mixture of mud, water, gases (primarily methane), and mineral substances. Their activity may vary from explosive eruptions, ejecting mud tens of meters into the air, to slow, continuous effusion. These phenomena exert both beneficial and adverse effects on the environment: they can enrich soils with minerals but also contribute to land degradation and localized pollution [6-12].

The utilization of mud volcanoes in Azerbaijan is multifaceted. Their therapeutic properties are harnessed in balneology, especially in resort areas around Baku. They are also significant tourist attractions, drawing visitors with their striking natural features. In addition, mud volcanoes play an important role in hydrocarbon exploration, as their activity often correlates with deep subsurface petroleum and gas processes. Scientific studies of these formations enhance our understanding of tectonic activity and subsurface fluid dynamics.

Overall, Azerbaijan’s mud volcanoes are not only remarkable geological features but also an essential part of the country’s natural and cultural heritage. They contribute meaningfully to scientific advancement, economic development, and the nation’s global image [13].

The study of the chemical composition of mud volcano emissions—especially heavy metals and organic contaminants—is crucial for assessing their environmental impact and determining the feasibility of their use in balneology, agriculture, or land reclamation. However, naturally occurring toxic elements and hydrocarbons may pose risks to ecosystems and human health [1-5].

This research focuses on the geoecological analysis of mud samples collected from mud volcanoes located in the southern part of the Gobustan region. The primary goal is to evaluate the content of heavy metals and organic pollutants, assess the environmental quality of the deposits, and provide recommendations for their safe use.

Materials and methods

Mud samples were collected in January 2025 from active mud volcanoes located in the southern Gobustan region of Azerbaijan. Sampling was conducted in accordance with standard field protocols to avoid contamination. The samples were stored in airtight, chemically inert containers and transported to the laboratory for analysis. Heavy metal analysis was performed using atomic absorption spectrometry (AAS) to quantify elements including copper (Cu), iron (Fe), lead (Pb), chromium (Cr), nickel (Ni), cobalt (Co), arsenic (As), and manganese (Mn). The concentrations were expressed in milligrams per kilogram (mg/kg) of dry weight [14].

Organic contaminant analysis included:

• Determination of petroleum hydrocarbons (C₁₀–C₄₀) using gas chromatography (GC).
• Quantification of 16 priority polycyclic aromatic hydrocarbons (PAHs) based on EPA methods, including naphthalene, phenanthrene, chrysene, benzo[a]pyrene, and others. The PAHs were expressed in micrograms per kilogram (µg/kg) [15].

Analytical quality control included blank samples, standards, and duplicate measurements to ensure data accuracy and precision.

Results and discussions

The analysis of mud samples from southern Gobustan revealed notable concentrations of heavy metals and organic pollutants. Table 1 summarizes the concentrations of selected heavy metals and their comparison with internationally recognized threshold values.

The concentrations of arsenic (As), chromium (Cr), and manganese (Mn) significantly exceed environmental safety thresholds. Arsenic levels were over seven times the permissible limit, indicating a geogenic source with potential ecological implications. Although other metals remained within safe boundaries, several (e.g., copper and nickel) approached critical values, which warrants continuous monitoring.

Table 1.

Heavy metal concentrations in mud volcano samples

In addition to inorganic contaminants, the total petroleum hydrocarbon (TPH) content was 71 mg/kg, while the total concentration of 16 priority PAHs was 29.0 µg/kg (Table 2). These results suggest a moderate level of organic pollution, potentially originating from deep hydrocarbon-bearing formations.

Table 2.

Concentration of selected PAHs (µg/kg)

Chrysene, pyrene, and benzo(a)anthracene showed the highest concentrations, and several PAHs identified are classified as carcinogenic. While the overall levels are not extremely high, their presence underlines the need for toxicological and ecological assessments before any potential therapeutic use of the mud [15-16].

Table 1 presents the results of the analysis of heavy metal concentrations in mud samples collected from the southern part of Gobustan. A comparison of the measured values with the permissible limits (PL) revealed the following key observations:

• Copper (Cu): The concentration of copper was 53 mg/kg, which is within the permissible limit of 55 mg/kg. This value does not raise concerns as it falls within the safe range.
• Iron (Fe): The concentration of iron was 26,600 mg/kg, significantly lower than the permissible limit of 40,000 mg/kg. This indicates the high presence of iron in volcanic deposits, which is characteristic of minerals in such geological formations.
• Lead (Pb): The concentration of lead was 8.9 mg/kg, well below the permissible limit of 32 mg/kg. However, lead is a toxic metal, and its presence in the environment could have adverse effects on the ecosystem, especially at higher levels.
• Chromium (Cr): The concentration of chromium was 29 mg/kg, which far exceeds the permissible limit of 6.0 mg/kg. This is a concerning result, as chromium at such concentrations can be toxic and has carcinogenic properties.
• Nickel (Ni): The concentration of nickel was 74 mg/kg, which is within the permissible limit of 85 mg/kg. However, even small exceedances could impact the health of the ecosystem.
• Cobalt (Co): The concentration of cobalt was 15 mg/kg, which is well below the permissible limit of 50 mg/kg, indicating a low level of contamination with this element.
• Arsenic (As): Arsenic was found in a concentration of 14 mg/kg, which significantly exceeds the permissible limit of 2.0 mg/kg. This is a highly concerning result, as arsenic is a toxic element and can have carcinogenic properties.
• Manganese (Mn): The concentration of manganese was 141 mg/kg, which far exceeds the permissible limit of 60 mg/kg. This indicates a high level of manganese in the samples and potential environmental risks.

In conclusion, the results show the presence of several contaminants in the volcanic deposits, particularly chromium, arsenic, and manganese, which require further environmental monitoring.

Table 2 presents the analysis results for 16 priority PAHs, which serve as indicators of hydrocarbon pollution. The total concentration of PAHs was 29.0 µg/kg. Among these, the following compounds were detected at significant concentrations:

• Chrysene (C₁₅H₁₀): The concentration of chrysene was 6.0 µg/kg, the highest among the PAHs found. This compound is toxic and carcinogenic.
• Pyrene (C₁₆H₁₀): Pyrene was detected at 3.9 µg/kg, which is also a significant concentration, as pyrene is known to be carcinogenic.
• Benz(a)anthracene (C₁₈H₁₂): The concentration of benz(a)anthracene was 2.1 µg/kg, indicating the presence of this highly toxic and carcinogenic hydrocarbon.
• Benzo(a)pyrene (C₂₀H₁₂): Benzo(a)pyrene was found at 0.9 µg/kg, which is also linked to potential ecological and health risks due to its carcinogenic properties.
• In general, the results indicate the presence of organic pollutants in the volcanic mud, which can be harmful to the ecosystem and human health if exposed over extended periods.

The results of the analysis demonstrate that the mud volcano samples from the southern part of Gobustan contain elevated levels of heavy metals (chromium, arsenic, and manganese) as well as organic contaminants (PAHs), many of which are toxic and carcinogenic. This underscores the need for careful consideration regarding the use of these muds for therapeutic or other purposes, as well as the necessity for environmental monitoring and mitigation strategies to prevent contamination. Further research is essential to assess the bioavailability of these elements and their long-term impact on the ecosystem.

Conclusion

The geoecological investigation of mud volcano deposits in southern Gobustan have revealed the presence of both mineral-rich and potentially hazardous components. Elevated concentrations of arsenic, chromium, and manganese highlight the natural but toxic geochemical background of the region. Additionally, the presence of PAHs, including carcinogenic compounds, suggests hydrocarbon input that may stem from deep thermogenic processes.

Despite the potential therapeutic properties of mud volcano products, including their mineral composition and historical use in traditional medicine, the identified levels of contaminants indicate the need for careful regulation. Environmental monitoring, toxicological risk assessments, and further interdisciplinary studies are essential to evaluate the safe use of these natural materials for medical or recreational purposes.

Future research should also explore the bioavailability of these elements and their long-term ecological impact, especially if mud is applied to the skin, used in agriculture, or released into nearby ecosystems.

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