چكيده انگليسي :
The mass production and use of plastic products have brought convenience to people while leading to the accumulation of plastic pollutants in the environment. As a result, the contamination of water and soil resources with microplastics and their associated environmental risks have recently become a global concern. Microplastics are generally defined as plastic particles smaller than five millimeters in size, primarily originating from the degradation of larger plastic particles released into nature.Studying the presence and effects of microplastics in soils is of great importance, as soils provide a wide range of ecosystem services essential for life on Earth. The introduction of pollutants, including microplastics, into the environment from various sources has negative consequences on human, plant, animal, and ecosystem health. These plastic particles enter terrestrial ecosystems through various routes, including the application of sewage sludge, organic fertilizers, plastic mulches, and improper waste management, affecting the physical, biological, and chemical properties of soil. Despite the importance of having statistics and information about the abundance and characteristics of microplastics in soils, there is limited information on this topic worldwide, especially in Iran. To date, no study has been conducted on the amount and types of microplastic particles in the soils of Isfahan city. Therefore, this research was carried out to gather information about the abundance and characteristics of microplastics in Isfahan's soils. Soil sampling points (60 points) were determined using the map of Isfahan in five different land uses, including recreational, residential, commercial, agricultural, and industrial areas. Soil sampling was conducted by removing the surface layer and collecting composite samples from 0-10 cm depth at each point. All soil samples were placed separately in aluminum foils, transferred to the laboratory, air-dried, and passed through a 5 mm sieve. In the microplastic separation experiment, organic matter was first removed from the soil samples using 30% hydrogen peroxide. To release MPs trapped in soil aggregates, an ultrasonic device with 60 J/ml energy was used for 100 seconds. Then, the samples were centrifuged, and saturated NaCl solution with a density of 1.2 g/cm³, followed by ZnCl₂ solution with a density of 1.55 g/cm³, was added to the samples. Floating microplastics in each solution were collected on filter paper and counted under an optical microscope with 1500x magnification, grouped based on size, shape, and color. Additionally, microplastic distribution maps in Isfahan's soils were prepared using ArcGIS software. The polymer type in some microplastics was identified using Raman spectroscopy. Results showed that microplastic particles were present in all soil samples, with their abundance ranging from 178 to 8,635 particles per kilogram of soil. The highest abaundance of microplastics was found in commercial areas, followed by residential, recreational, industrial, and agricultural areas. Most of the microplastics found (70.59%) were smaller than 0.5 mm. The extracted microplastics were mainly fragmentary (62.42%) and fibrous (34.18%), with film (2.07%) and pellet (1.32%) microplastics also observed. A wide variety of colors was observed in the examined samples, but brown (45.44%) was the most frequent color among microplastics. Polyethylene, polyamide, polystyrene, polypropylene, and polyvinyl chloride polymers were identified by Raman spectroscopy in selected samples. The information acquired in this study is valuable for urban planning and policy development, aimed at understanding, mitigating, and preventing microplastic pollution in urban environments.
