A comprehensive review of oil residues in the world oceans: types, characteristics, sources and distribution.

The increasing industrialization and extensive utilization of petroleum products, resulting in the emergence of its residues, contribute to the formation of tar. Their accumulation is strongly influenced by environmental factors, including winds, currents, and coastal geomorphology. This review explores the physical characteristics and primary sources of tar residues, with particular focus on tanker operations and oil spill incidents. It further synthesizes the existing literature, focusing on regional tar surveys in the North Atlantic, Pacific and Indian Oceans, the Mediterranean Sea and the Arabian Gulf, aiming to consolidate current knowledge and compare regional tar concentrations. Global assessments of tar concentrations reveal notable spatial variability, with the Mediterranean Sea exhibiting the highest concentration, followed by the Arabian Gulf and the Caribbean Sea. Lower concentrations were recorded in the Pacific's Bering Sea and Gulf of Alaska areas characterized by limited shipping activity. However, non-standardized sampling strategies, inconsistencies in tow techniques, and irregular tar surveys introduce considerable uncertainty in assessing the distribution of tar residues. Significant gaps are identified in quantitative and qualitative assessments and source identification, resulting in systematic documentation of coastal tar concentrations. Despite regulatory advancements including the implementation of MARPOL Annex I, and technological improvements like segregated ballast systems, tar pollution remains a global concern. The review also highlights the urgent need for long-term monitoring, standardized methodologies, and improved risk assessment to inform effective management, particularly in tourism-dependent coastal regions.