Spatial patterns of microplastics in abiotic coastal matrices of the northern Oman Sea, assessed with data visualization and geostatistics

Microplastics (MPs) are ubiquitous ecotoxic contaminants. Assessing their level of contamination and distribution is crucial for identifying pollution sources, understanding their effects on aquatic ecosystems, and planning effective remediation measures. Here, innovative visualization tools have been used for the first time to study patterns in MP contamination in water from littoral coastal zones, marine surface waters and sediment along the northern shorelines of the Oman Sea, stretching from the Pozm Estuary to Gwadar Bay at the Iran-Pakistan border. On average, 42 ± 37 MPs·kg⁻¹ and 9.4 ± 7.6 MPs·L⁻¹ were found in the sediment and seawater samples, respectively. The results evidenced that MP pollution tends to float at sea, where the minimum observable size was 50 μm. Fibers and fragments, < 250 μm, were prevalent in water and sediment. The most abundant MPs were composed of polypropylene, with dark colors in both media. Significant differences were found between the MP contamination in the sediment and water, regarding the MP concentration, shapes, and colors, highlighting the uneven distribution of MPs between the media. No significant difference was found regarding MP size distribution in both media. The most contaminated site was at a commercial port in Chabahar Bay, with 155 MPs in sediment and 33 MPs in water. Weathering evidences were recognized on the surface of the particles recovered from both media. MPs presented greater fragmentation in the water, possibly due to increased exposure to weathering agents, including UV radiation from the sun, mechanical forces from waves and tidal currents, or biodegradation. This research is important to perceive, manage, and mitigate MP contamination in the northern coastal ecosystems of the Oman Sea and understand the fate of MPs in the seawater column.