Origin of biomarkers (PAH, n-alkane, hopane, estrane) in different colors of plastic resin pellets and surface sediments from coastal area of the Makuran-Oman Sea

Abstract

The unique attributes of the study area, situated near the Strait of Hormuz—an extensively utilized oil shipping corridor for Iran and neighboring Arabian nations—encompass oil extraction and exploitation, the establishment of an oil export hub, the advancement of petrochemical industries, as well as tourism and transportation activities. This research represents the first examination of the sources of plastic resin pellet release, addressing both local and non-local contributions. To conduct this study, samples of plastic resin pellet and coastal and intertidal surface sediments were collected from seven stations on the shores of the Oman Sea in Hormozgan province (Sirik, Garook, Ziarat, Karpan, Koohestak, Gohardo, and Kargan) with four replications to determine the origin and spatial distribution pattern of hydrocarbons and the diffusion source of plastic resin pellets (offshore or regional). Plastic resin pellets were separated based on color (white, yellow, brown, and black). Soxhlet was used to extract hydrocarbons, two stages of column chromatography were used to separate compounds, and gas chromatography–mass spectrometry (GC–MS) was used to identify and determine their concentration. The total n-alkanes concentration ranged from 2940 to 18,711 (μg/g) in coastal surface sediments, from 19,721–1678 (μg/g) in intertidal surface sediments, and from 11,481.50 to 55,601.41 (μg/g) in plastic resin pellets. A similar trend was found for the total PAH concentration which ranged from 135.57 to 3890.62 (ng/g) in coastal sediments, from 1820.28 to 6579.55 (ng/g) in intertidal sediments, and from 3714.19 to 66/1920451 (ng/g) in plastic resin pellets. According to the sediment pollution criteria, a high pollution level was assessed in most of the stations. In most of the surface sediments and plastic resin pellets, the presence of unresolved complex mixture (UCM), the carbon preference index (CPI) lower than 1, and the diagnostic ratios of PAH, hopane, and sterane compounds indicated petrogenic origin for hydrocarbons. The results of principal component analysis based on 16 diagnostic ratios of PAH, n-alkane, hopane, and sterane compounds showed that brown and black plastic resin pellets were placed in a different group than the coastal and intertidal sediments and white and yellow plastic resin pellets. Most likely, the diffusion source of brown and black plastic resin pellets is different and through open water.