Extended Abstract
Introduction
The increasing population growth and demand for agricultural products have led to the intensive exploitation of water and soil resources, as well as the widespread use of chemical pesticides and fertilizers. To increasing production, this trend has led to numerous environmental consequences, including the pollution of water and soil resources, particularly through the entry of heavy metals into ecosystems. Heavy metals pose a serious threat to human health, wildlife, and aquatic ecosystems. The origin of these metals can be natural or anthropogenic due to an increase in industrial activities and urbanization, the contribution of human resources to heavy metal pollution has increased significantly. Lake Tashk, as an ecologically valuable habitat, is under threat of pollution. The entry of contaminated wastewater into this lake, especially in the arid and semi-arid climatic conditions of the region, can lead to the gradual accumulation of heavy metals in the water, sediments, and salt of the lake. In addition, due to the consideration that the water of Tashk–Jahanabad Lake contains a high percentage of fine suspended particles and organic matter, the resulting residual salt layer upon complete evaporation of the water consists of a mixture of salt crystals, fine soil particles, and minor amounts of organic materials. The present research was conducted to evaluate the heavy metal concentration in the salt sediments along the shores of Lake Tashk. The study aims to help establish the current environmental condition and suggest management measures to minimize ecological risks.
Materials and methods
In this study, the aim was to investigate the level of heavy metal contamination in the salt sediments of the region. To monitor environmental pollution, surface salt sediment samples were collected from five stations located along the northern edge of Lake Tashk during the dry season in summer 2021. To account for spatial differences and improve accuracy, a composite sampling method was used. Three individual surface sediment samples, taken from a depth of 0–10 cm, were collected from each station within a 5-meter radius and carefully mixed to create one composite sample. The samples were cleaned of visible impurities, dried at 50 °C, gently ground, and passed through a 2 mm sieve. The resulting homogenized fraction was used as the analytical sample. Finally, the samples were prepared for heavy metal analysis through acid digestion, following the standard procedure of USEPA Method 3050B from 1996. Afterward, the samples were prepared for analysis. The concentration of heavy elements was measured using an atomic absorption spectrometer and lamps specific to each element. To analyze the contamination, several geochemical indices were used, including the geo-accumulation index (Igeo) to determine the level of sediment contamination relative to the background value, the contamination factor (CF) to measure the intensity of contamination of each element, and the total contamination degree (Cdeg) to comprehensively analyze the pollution load in each sample. Additionally, the assessment of potential environmental risks was conducted using the Ecological Risk Index (RI) and the Ecological Risk Factor (Er).
Results and discussions
The concentration of heavy metals was determined in the samples, and various pollution indices were used to evaluate the environmental status of the region. The results showed that the average concentration of nickel (Ni), lead (Pb), iron (Fe), zinc (Zn), copper (Cu), cadmium (Cd), and manganese (Mn) was equal to 17.89, 12.86, 9.24 2.00, 1.59, 1.51 and 1.31 mg/kg, respectively. A comparison of these values with shale reference values indicated that the cadmium concentration was higher than the standard. The contamination coefficient indicators indicated that the Cd element had high contamination, while other elements had low contamination levels. In addition, the accumulation index for Cd showed contamination within the "unpolluted to moderately polluted" range, while the other elements were in the unpolluted range. The contamination degree of the average samples corresponded to moderate pollution. Also, the potential ecological risk factor values for the mean samples indicated that Cd was classified into the considerable risk class, whereas the other elements were classified as low-risk. The overall potential ecological risk index was also evaluated within the range of average pollution, indicating a significant level of ecological concern in the saline sediments surrounding the lake. Overall, it can be concluded that the Cd element is the most significant heavy metal pollutant in the area, while other elements are at lower levels.
Conclusion
The findings of this study showed that while most heavy metals in the saline sediments of Lake Tashk are present at low contamination levels, the elevated concentration of cadmium (Cd) increased the potential ecological risk to a moderate level. This underscores the need for continuous monitoring and effective management strategies to prevent further Cd accumulation and its potential adverse ecological impacts on the lake ecosystem. The results suggest that anthropogenic activities, particularly agricultural practices and runoff-associated pollutants, likely contribute to Cd enrichment within the geochemical processes governing saline sediment. Therefore, continuous monitoring, identifying pollution pathways, assessment of spatial and seasonal variations, evaluation of food-chain transfer potential, and developing nature-based remediation strategies for heavy metal attenuation, such as microbial bioremediation, is essential. Considering the climatic and geochemical similarities of Tashk, Bakhtegan, and Maharloo lakes, these findings provide a comparative basis for environmental risk management in comparable salt lake ecosystems. Overall, this study provides a valuable scientific foundation for future research and supports sustainable protection of the ecosystem and human health in the region. |
