Formation, Fate, and Impacts of Microscopic and Macroscopic Oil‐Sediment Residues in Nearshore Marine Environments: A Critical Review

Abstract

Crude oil that is spilled in marine environments often interacts with suspended sediments to form residues that can impact the recovery of the affected nearshore ecosystems. When spilled oil and sediment interact, they can form either small microscopic aggregates, commonly referred to as oil‐particle aggregates, or large macroscopic agglomerates, referred to as sediment‐oil agglomerates or sediment‐oil mats. Although these different sized oil‐sediment residues have similar compositions, they are formed under different conditions and have different fates in nearshore environments; the goal of this review is to synthesize our current understanding of these two types of residues. We believe that researchers who focus solely on studying either microscopic aggregates or macroscopic agglomerates could benefit from understanding the research findings available in the other field. In this study, we compare and contrast various processes that control the formation, fate, and impacts of these two types of residues in nearshore environments and point out some of the knowledge gaps in this field. Additionally, these residues have been referred to by many names in the past, leading to confusion and misconceptions at times. In this effort, we recommend a uniform nomenclature to distinguish them based on their physical size. Our overall aim is to bridge the gap between microscopic and macroscopic oil‐sediment residue literature to foster a robust exchange of ideas, which we believe can lead to the development of efficient strategies for managing oil spills that affect nearshore environments.

A practical adsorption model for the formation of submerged oils under the effect of suspended sediments

“…Worse, it is a detrimental process because these aggregates hinder the degradation of oil and can lead to the periodic reoiling of the shoreline for years following a spill. 5…”

“…The assumptions are that oil sediment reactions will reach equilibrium owing to the limited surface sites for adsorption. 30 Rearranging eqn (1), (5) and (6), the proportion of submerged oils formation can be calculated at varying sediment concentrations,…”

“…4 Most of submerged oils are formed in nearshore environments where breaking waves and other turbulent shoreline forces facilitate the interaction of suspended sediments with the dispersed oils. 5 Research activities and advancements for understanding the formation of submerged oils in aqueous systems have intensied in the recent years. The adsorption processes of dispersed oil droplets by suspended sediments could lead the spilled oil settle onto the bottom, and this oil sediment interactions have been posited to play an important role in dispersing oils in marine environments.…”

Development of a field testing protocol for identifying Deepwater Horizon oil spill residues trapped near Gulf of Mexico beaches

“…When the floating weathered mousse approached the shoreline, it interacted with suspended sediments and sank in the nearshore environment. Gustitus and Clement recently presented a detailed conceptual model for describing the coastal transport mechanisms that facilitated the formation of sunken DWH oil spill residues [ 15 ]. After sinking, the submerged oil accumulated more sediments to form large deposits of oily mats, known as submerged oil mats or sediment-oil mats (SOMs).…”

“…After sinking, the submerged oil accumulated more sediments to form large deposits of oily mats, known as submerged oil mats or sediment-oil mats (SOMs). Waves and other shoreline transport processes eventually broke SOMs into smaller fragments, known as surface residual oil balls (SRBs) or sediment-oil agglomerates (SOAs) [ 15 ]. Typical size of SRB/SOAs found along the Alabama shoreline can range from about 0.5 cm to 8 cm [ 3 , 4 ].…”