Influence of seasonal variability of lower Mississippi River discharge, temperature, suspended sediments, and salinity on oil-mineral aggregate formation

The Role of Bacteria in the Formation and Migration of Oil-Particle Aggregates (OPAs) after Marine Oil Spills and the Associated Mechanism

Oil spills interact with mineral particles to form oil-particle aggregates (OPAs), which promotes the oil's natural diffusion and biodegradation. We investigated the effect of bacteria on the formation and vertical migration of OPAs under different concentrations and types of particles and proposed and elucidated an oil-particle-bacteria coupling mechanism. The depth of particle penetration into oil droplets (13-17 μm) was more than twice that of the nonbacterial group. Oil that remained in the water column and deposited to the bottom decreased from 87% to 49% and increased from 14% to 15% at high/low concentration, respectively. Interestingly, the median droplet diameter showed a negative correlation (R² = 0.83) and positive correlation (R² = 0.60) at high/low concentration, respectively, with the relative penetration depth first proposed. We further demonstrated that bacteria increased the penetrating depth by a combination of reducing/increasing the interfacial tension, reducing the oil amount (C₁₇-C₃₈) in the OPAs, and increasing the particle width. These effects reduced the droplet size and ultimately changed the vertical migration of OPAs. Finally, we provided a simple assessment of the vertical distribution of OPAs in nearshore environments based on experimental data and suggested that the role of bacteria in increasing the depth of particles penetrating into the oil droplets should not be ignored. These findings will broaden the research perspective of marine oil spill migration.

Performance of dispersed oil and suspended sediment during the oil-sediment aggregation process

Oil-sediment aggregation is an important transport and transformation process of spilled oil, which has been considered as a pathway of spill remediation. This work focused on the individual performance of dispersed oil and sediment during the aggregation process. Dispersion of three oils was first tested and validated in a water tank. An approach of estimating the mass variation of the sediment that has participated in forming the oil-sediment aggregates (OSAs) has been developed by density analysis. Results indicated that the density of the formed OSAs increases during the aggregation. In the context of remediation, it takes longer for sediment to reach equilibrium than for dispersed oil, especially under high mixing energy at a large sediment concentration, which results in the formation of dense OSAs, as well as high aggregation degree and rate. Roncador oil possesses a relatively high capability of capturing sediment to form dense OSAs, especially at an initial sediment concentration of over 150 mg/L. Oil sinking efficiency and the characteristic change rate of aggregated oil mass seem to be proportional to oil dispersion efficiency, and decrease with the mean size of dispersed oil droplets. The process of aggregation can further promote the dispersion of oil into water column. This study also provides fundamental data for the formation kinetics of OSAs.

Oil dispersion and aggregation with suspended particles in a wave tank

Suspended particulate matter (SPM) in marine environments plays an important role in determining the fate of spilled oil via the generation of oil-particle aggregates (OPAs). A series of mesoscale wave tank experiments and sedimentation tests were conducted to fill the knowledge gap on how the turbulent mixing, temperature, and oil type affect the dispersion of spilled oil and properties of OPAs. Generally, the oil dispersing efficiency was significantly enhanced by high wave energy, which also led to effective oil sinking, large size of OPAs and wide distribution of trapped oil. Nonlinear fitting results indicated that the oil sinking efficiency followed an exponential growth over time. The effect of temperature on oil dispersion and formation of OPAs is primarily attributed to its influence on oil viscosity and interfacial tension. Viscous oils are more likely to interact with particles above 25 °C. However, below 20 °C, a specific oil viscosity that will bring about the maximum OPAs exists. Excessive oil viscosity will lead to a weak binding between oil and SPM and a centralized distribution of trapped oil. Furthermore, spilled oil with a high asphaltene can interact more effectively with particles. Our finding suggested that early prevention of offshore oil sinking is key in summer.

A review on the sinking mechanisms for oil and successful response technologies

A rise in the shipping of heavier hydrocarbon products increases the potential for an oil to sink after a spill. Further, sunken oil is difficult to locate and recover, and appropriate response technologies depend on the sinking mechanism. In this review, principal sinking mechanisms for oil are described and appropriate response technologies are suggested. Then, models appropriate for tracking sunken oil are compared. Oil may sink as burn residue, microscopic oil-particle aggregates (OPAs) or macroscopic oil-sediment mixtures (OSMs), marine oil snow during a MOSSFA event, or due to its high density. The most common mechanism is by sediment entrainment, and in such scenarios manual recovery has been reported as a successful response option. Among oil tracking models, trajectory models and Bayesian oil search models are compared for sunken oil capabilities. Many oil spill models require hydrodynamic inputs, whereas Bayesian models infer parameters based on available field concentration and bathymetric data.

Formation of OSA and dispersion of polycyclic aromatic hydrocarbons in a tropical estuary as a tool in the prevention of environmental impacts: influence of the biogeochemical characteristics of the estuary

The formation of an oil-suspended particulate material aggregate (OSA) is one of the weathering processes that occur after the spill of oil in marine environments, responsible for the dispersion of hydrocarbons. Oil and particle aggregates are formed from the interaction between small oil droplets and suspended particulate matter (SPM). In general, SPM are fine particles which may be inorganic minerals or organic particles in the water column. OSAs provide vertical dispersion of oil along the water column depending on the acquired density (buoyancy), and may remain near the surface, water column, or bottom of water bodies. The present study examines the formation of these aggregates through the laboratory simulation of an oil spill in the waters of the São Paulo river estuary. The main objective was to investigate the dispersion of polycyclic aromatic hydrocarbons (PAHs), verifying which estuary characteristics most influenced the formation of OSAs and in addition to determine the regions of probable ecotoxicological impact due to the negative buoyancy of the formed aggregate. The results show that there was greater dispersion to the water column, mainly of lighter PAHs, ranging from 85,804.05 ng g^-1 (P11C) to 566,989.84 ng g^-1 (P17C). The percentage of dispersed PAH concentration per experimental unit ranged from 9.90% in unit P2 to 75.27% in unit P18. The formation of OSAs was influenced mainly by salinity and chlorophyll a. As the most vulnerable regions, the impacts are one mouth (P2 and P4), one central region (P7, P8, and P10), and one source (P18).

A critical review of marine snow in the context of oil spills and oil spill dispersant treatment with focus on the Deepwater Horizon oil spill

Natural marine snow (NMS) is defined as the "shower" of particle aggregates formed by processes that occur in the world's oceans, consisting of macroscopic aggregates of detritus, living organisms and inorganic matter. Recent studies from the Deepwater Horizon oil spill suggest that marine snow is also formed in association with oil spills and was an important factor for the transport of oil to the seabed. This review summarizes the research and literature on MS, mainly from the DWH oil spill, with a focus on the relation between the use of oil spill dispersants and the formation and fate of oil-related marine snow (ORMS). Studies are still required to determine ORMS processes at oil concentrations as relevant as possible for chemically dispersed oil.

Chemical dispersion of oil with mineral fines in a low temperature environment

The increasing risks of potential oil spills in the arctic regions, which are characterized by low temperatures, are a big challenge. The traditional dispersant method has shown limited effectiveness in oil cleanup. This work studied the role of mineral fines in the formation of oil-mineral aggregates (OMAs) at low temperature (0-4 °C) environment. The loading amount of minerals and dispersant with different dispersant and oil types were investigated under a full factorial design. The shapes and sizes of OMAs were analyzed. Results showed that the behavior of OMA formation differs when dispersant and mineral fines are used individually or together. Both the experimental and microscopic results also showed the existence of optimal dispersant to oil ratios and mineral to oil ratios. In general, poor oil removal performance was observed for more viscous oil. Corexit 9500 performed better than Corexit 9527 with various oils, in terms of oil dispersion and OMA formation.