ECOLOGICAL AND CHEMICAL STUDY OF LAKES ZABRAT AND DUZLUGOL

ABSTRACT

In order to study the degree of water pollution in the Zabrat lakes due to heavy metals, we conducted monitoring studies to determine the concentration of specific heavy metals in the water. During the monitoring, we collected water samples from various locations of the Zabrat lakes, as well as from the soil near the lakes, and analyzed them for heavy metal content using the AAS method. The results showed that the concentration of toxic substances in the water of Zabrat Lake is very high. However, the radiation background of the lake does not exceed the permissible limit. Nevertheless, a slight increase in radiation (24–35 µR/h) was observed in the bottom sediments. The content of petroleum products in the water of certain sections of Zabrat Lake exceeds the permissible limit by 20 times. Additionally, for the ecochemical study of Duzlugol Lake, water samples were taken and analyzed based on various parameters. The samples were collected from different depths using a bathometer at various stations.

АННОТАЦИЯ

С целью изучения степени загрязнения воды озер Забрат тяжелыми металлами нами были проведены мониторинговые исследования по определению концентрации некоторых тяжелых металлов в воде. В ходе мониторинга были отобраны пробы воды из различных точек озер Забрат, а также из почвы вблизи озер и проанализированы на содержание тяжелых металлов методом ААС. Результаты показали, что концентрация токсичных веществ в воде озера Забрат очень высокая. Однако радиационный фон озера не превышает допустимую норму. Тем не менее, в донных отложениях отмечено незначительное повышение радиации (24–35 мкР/ч). Содержание нефтепродуктов в воде отдельных участков озера Забрат превышает допустимую норму в 20 раз. Дополнительно для эколого-химического исследования озера Дузлугель были отобраны и проанализированы пробы воды по различным показателям. Пробы отбирались с разных глубин с помощью батометра на разных станциях.

Keywords: water mineralization, oxygen regime, wastewater, petroleum products, ecological rehabilitation, heavy metals.

Ключевые слова: минерализация воды, кислородный режим, сточные воды, нефтепродукты, экологическая реабилитация, тяжелые металлы.

In our problematic world, lakes are also facing environmental stress. The lakes of the Absheron Peninsula play an important role in regulating climate moisture and in purifying the air basin of the capital. There are more than 250 lakes in Absheron. Furthermore, the mud deposits and iodine-bromine salts of these lakes have been used for medicinal purposes and as food products since ancient times. However, today, the silt from salty lakes such as Zykh [8-9], Duzlugol Lake, and others is being used inappropriately, leading to pollution and unsanitary conditions along their shores.

The level of the Caspian Sea also influences the ecological conditions of these lakes and their hydrological regimes. As the sea level rises, the groundwater level also increases, leading to a higher water volume in the Absheron lakes. When the sea level decreases, the opposite process occurs. One of the reasons for this problem is the rapid growth of industry and the construction of new settlements in Absheron. In these newly built settlements, due to the absence of a unified sewage system, domestic wastewater is discharged directly into nearby lakes and surrounding areas, resulting in pollution and anthropogenic impacts on the water reservoirs.

Ecologists believe that the main cause of pollution in Absheron lakes is the lack of a unified sewage system on the peninsula, as well as the discharge of wastewater from newly built settlements and industrial enterprises into nearby lakes. Many residential areas, such as Khodjassan, Kyurdakhani, Bulbule, Amirajany, Zabrat, Zykh, Boyukshor, and others, are located along the shores of most Absheron lakes [3-4, p. 56]. We conducted environmental monitoring of Duzlugol Lake and Zabrat lakes and identified the sources of pollution. The study found that the main pollutants are the oil industry and wastewater. Lake Zabrat is a small lake in Absheron and is in a precarious ecological state. It is located in the center of the Absheron Peninsula, in the Sabunchu district of Baku.

For instance, on the shore of Zabrat Lake, there are wells, many of which are in a state of disrepair, resulting in oil discharges directly entering the water bodies. Potential polluters of Zabrat Lake also include oil refineries and pipelines located along its shore. Wastewater from households and other facilities is discharged into the lake, as many newly built houses around the lake in the Sabunchu district of the city lack sewage systems. Currently, 10,000 m³ of domestic wastewater enters the lake daily from 29 sources. One of the main sources of pollution for the Absheron lakes is the household waste dumps in the Duzlugol settlement of Surakhani district and the Zabrat settlement of Sabunchu district, located in the eastern part of the lakes.

For Zabrat and Duzlugol Lake, the main source of pollution has been oil spills occurring since the 1930s during oil extraction. According to statistics, about 60% of the wastewater was discharged directly through drilled wells, while the rest came from mines and was taken directly from the sea via waterlines. Since the 1970s, fecal, domestic, and industrial wastewater has been discharged into the lakes through open channels without treatment, significantly deteriorating the sanitary conditions of Zabrat Lake. The lake’s bottom and shoreline have remained covered with a bituminous layer of petroleum products, which, when evaporated in hot weather, release light fractions of oil into the atmosphere, creating a strong odor [4, p. 66; 5, p. 89]. Wastewater is discharged from households, other facilities, and private houses built around the lake that are not equipped with sewage systems in the Sabunchu district of the city. Currently, 8,000 m³ of industrial and household wastewater flows into the lake daily from various sources. One of the main sources of pollution in the lake is a landfill of household waste in the village of Zabrat, located in the Sabunchu district in the eastern part of the lake. The primary source of pollution in Lake Zabrat has been the discharge of oil spills formed during oil production since the 1930s.

 According to statistics, about 60% of wastewater was discharged directly through drilled wells, while the rest came from shafts and was taken from the sea via waterlines. Since the 1970s, fecal, domestic, and industrial wastewater has been discharged through open channels without treatment into the lake, significantly deteriorating its sanitary condition. The bottom of the lake and the shoreline are polluted with oil products and domestic waste. Due to the evaporation of oil products in hot weather, light fractions of oil are released into the atmosphere, creating a strong odor [6].

The mineralization of water in Zabrat and Duzlugol lakes classifies them as saline water lakes, with significantly higher mineralization compared to other lakes. The oxygen regime in these lakes is completely disrupted. One of the main reasons for the low dissolved oxygen in the water of Duzlugol and Zabrat lakes is the acceleration of biological processes due to the oxidation of pollutants. This leads to a much higher biochemical oxygen demand (BOD) in these lakes [6-7, 11]. As a result of natural factors and wastewater discharge, the concentrations of cations and anions in the water have also significantly increased, leading to increased mineralization. The concentrations of calcium, magnesium, and chlorides exceed sanitary norms, while sulfates are several times higher than the standard. Concentrations of petroleum products and phenols, which are the main pollutants of these lakes, are many times higher than the permissible limits. Heavy metals such as copper, cadmium, iron, zinc, manganese, and others are also present in concentrations far above permissible limits. Synthetic detergents in the Absheron lakes exceed the permissible concentration several times.

Experimental Part

To study the extent of pollution in water and soil due to heavy metals, we conducted monitoring studies to determine the concentration of specific heavy metals in water and soil samples from various locations of the Zabrat lakes. The samples were analyzed using the AAS method [1,3]. Samples were collected from different sections and depths, with the highest pollution observed in the surface layers (up to 0.5 m depth). Since both lakes are shallow, the samples were taken from a depth of 1 meter from the northern, southern, and eastern parts of the lakes. The volume of the water samples taken is 1 liter, and the volume of the samples taken from the bottom sediments is 0.5 kg. The studies were conducted using the ZEEnit 700P AAS.

Results

The physicochemical parameters of wastewater samples taken from Lake Zabrat were determined [2,10]. As shown in Table 1, the concentrations of nitrate, nitrite, and phosphate ions (with a permissible concentration limit of 0.2 mg/l) in the lake water samples exceed the permissible limit by several times. The levels of dissolved oxygen and ammonium (with a permissible concentration limit of 0.4 mg/l for ammonium) are significantly lower than the standard. The concentrations of heavy metals in all samples were determined using the AAS method with the ZEEnit 700P device.

Table 1.

Results of analyses for sample from waste water Zabrat lake

As shown in the table, the concentrations of all heavy metals in the wastewater discharged into Lake Zabrat exceed the permissible concentration limits. The second table presents the analysis results of the water from Lake Zabrat. As shown in the table, the concentrations of nitrite, ammonium, and phosphate ions in the lake water samples exceed the permissible concentration limits. The concentrations of dissolved oxygen and nitrate ions do not exceed the permissible limits. The hydrogen ion concentration is slightly higher, at 9.05.

Table 2.

Results of analyses for sample from Lake water Zabrat

As can be seen from the table, the amount of heavy metals found in water samples taken from the lake exceeds the permissible concentration limits many times over. In particular, the amount of Hg, Cd, Pb, and Ni is many times higher than the permissible concentration limits and this water is very polluted and dangerous. There is no natural soil cover in the sampled soil areas. Soil samples were taken from different depths by drilling. Soil layers cannot be determined. Pollution is observed mostly in the upper layers. Bottom sediments were taken from different depths (1m, 2m, 3m) by immersion using a special device. The most pollution was observed at the first 1m depth. Oil pollution in bottom sediments is clearly visible visually. The amount of heavy metals in the samples was determined by AAS [1,3] using ZEEnit 700 P, and the determination of organic compounds was carried out using a mass spectrum gas chromatography device (GC-MS (Agilent, USA) HP6890.

Table 3.

Results of analyses for Soil sample from Zabrat Lake

The liquid extraction method was used to prepare water samples taken from Lake Zabrat. 0.5 liter water samples were extracted 3 times with 30 ml of dichloromethane, dried with anhydrous sodium sulfate and concentrated in a rotary evaporator until the volume remained at 1 ml. Deuterated naphthalene and phenanthrene were used as internal standards. Determination of organic compounds in the samples was carried out on a gas chromatography-mass spectrometer (GC-MS (Agilent, USA) HP6890 in one-dimensional and two-dimensional modes. Ionization energy was 70 eV. Capillary silicon column RTX-5MS (30 m), temperature regime: 400C (2 min.) - 200C/min. - 3000C (10 min.).

Similarly, bottom sediment samples (1.4 and 1.6 g) were taken from the lake, extracted three times with 30 ml of dichloromethane, dried with anhydrous sodium sulfate, and concentrated in a rotary evaporator until the volume was reduced to 1 ml. Deuterated naphthalene and phenanthrene were used as internal standards. The determination of organic compounds in the samples was carried out using the same gas chromatography-mass spectrometer (GC-MS, Agilent, USA, HP6890) in both one-dimensional and two-dimensional modes. The ionization energy was 70 eV. The capillary silicon column RTX-5MS (30 m) was used with the following temperature regime: 40°C (2 min), ramped at 20°C/min to 300°C, and held at 300°C for 10 minutes [13-21].

Table 4 shows the amount of organic matter in the bottom sediments of Lake Zabrat.

Table 4.

The amount of organic substances in the bottom sediments of Lake Zabrat

The table shows that the amount of organic matter in the bottom sediments of Lake Zabrat exceeds the permissible concentration limit many times over. Organic pollution in the bottom sediments exceeds the norm. Table 5 shows the amount of organic matter in the water of Lake Zabrat.

Table 5.

The amount of organic substances in the water of Lake Zabrat

The table shows that the amount of organic matter in the water of Lake Zabrat exceeds the permissible concentration limit many times over and organic pollution in the lake water exceeds the norm.

Table 6 shows the amount of organic matter (PAHs) in the soil of the area around the Lake Zabrat.

Table 6.

The amount of PAHs in the soil of the area around the Zabrat lake

As can be seen from Table 6, the amounts of phenanthrene and naphthalene2-bromo- in the lakeside soil samples exceed the permissible concentration limit.Table 7 shows the amount of organic matter (PAHs) in the bottom sediments the Lake Zabrat.

Table 7.

The amount of PAHs in the bottom sediments the Zabrat lake

As can be seen from Table 7, the amounts of naphthalene, anthracene,  and naphthalene2-bromo in the bottom sediments samples the Lake Zabrat exceed the permissible concentration limit. In order to analyze the ecological and chemical nature of the water of Lake Duzlugel [13], samples of lake water were taken and analyzed for various parameters. Water samples were taken from different depths using a bathometer at different stations. The salinity of the water increases from west to east. The results of the analysis are given in Table 8.

Table 8.

Results of the analysis of the water sample of Lake Duzlugol

As can be seen from Table 8, the water of Lake Duzlugel is turbid, alkalinity and electrical conductivity exceed the MРC many times. Also, calcium, magnesium, sodium, potassium ions, chlorides, sulfates exceed the MРC, the water is very salty. But there are no ammonium ions, and nitrates, phosphates, nitrites, hydrocarbonates and carbonates do not exceed the MРC. The amount of surfactants slightly exceeds the MРC, and the pH and amount of soluble oxygen are normal [13].

Conclusion

The results of the study show that the water and soil of the lakes in the Absheron Peninsula are heavily polluted with heavy metals, particularly with metals such as mercury, cadmium, lead, and nickel, all of which significantly exceed permissible limits. The environmental situation in the area is critical, and immediate actions are required to address these issues. Moreover, the implementation of ecological rehabilitation projects for the Absheron lakes is essential to restore the environmental balance and improve the ecological conditions of the region.

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