Assessing microplastic pollution in coastal sediments of the Oman Sea: ecological risk and land-use linkages

Coastal areas are among the sensitive habitats where, today, the pollution of microplastics (MPs) is a serious threat. This study aimed to assess MPs pollution in sediments of the Oman Sea coast in Chabahar with emphasis on urban-commercial and natural land uses. Sampling of sediments was carried out in June 2024 at 9 stations along the shoreline, taking into account the land use, and in a systematic random manner. The stages of digestion and extraction of MPs were carried out using NaCl and NaI. A binocular optical microscope was used to count MPs. The type of polymers was identified by the Fourier transform infrared (FT-IR) spectrometer. The pH, EC, and soil texture were also determined for the samples. The highest frequency of MPs was related to the commercial centers of Chabahar (161 numbers/100 g of sediment), and the lowest was in the mangrove forests of Guatr (6 numbers/100 g of sediment). The frequency of MPs showed a significant difference (p = 0.001) among the studied stations. The mean abundances of MPs were obtained as 71.6 ± 28.9 and 43.25 ± 25.1 in urban-commercial and natural land uses, respectively. The MP's abundance in stations with urban-commercial, and natural uses showed no significant difference (p = 0.15). The largest particle size was identified in the range of 20-500 µm at most of the study stations. The most common forms of MPs were fiber (66%) and fragment (62%) in urban-commercial and natural land use, respectively. Detected polymers and their frequency percentage in the study station were polyethylene (39-77%), polyamide (16-40%), and polyethylene terephthalate (0-43%). The abundance of MPs showed a significant negative correlation only with soil pH (p = 0.03; r = -0.40), and it was not significantly correlated with EC (p = 0.36) and soil texture (0.07). The potential ecological risk index (PERI) was obtained in the range of 5-228. The current risk of MP pollution along the coast of the Oman Sea in the Chabahar region at 33% of stations is at a moderate level. Thus, it is essential to manage plastic waste and reduce its consumption in this region to prevent its spread in the environment.