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In this study, we investigate the circulation and chemical processes associated with the deposition of the largest oil spill that reached the northeast coast of Brazil during the second half of 2019. Using the Oil Spill Contingency And Response model (OSCAR), we performed both deterministic and probabilistic simulations of oil spills from tanker ships that were present in the sea in the region at the time. The study used a dataset comprising the latitudinal distribution of oil sightings along the coast between 31 August and 2 December 2019 (box plot analysis) provided by the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA). The total amount of oil that reached the coast during this period (approximately 5000 tons) and the date and location of the first sighting (30 August, in the southern part of the state of Paraíba (PB)) were also used as parameters to assess the results of the 31 simulations conducted for ships en route near the area of interest between July and August 2019. The results indicate that a leak having occurred through a mobile source is the most plausible hypothesis for explaining the observed temporal–spatial arrival of the oil leaks along the Brazilian coastline. We suggest that prevention, monitoring, and international cooperation are essential for reducing the risks of future environmental accidents of the kind analyzed in this study and to protect the environment and communities affected. [ABSTRACT FROM AUTHOR]

In this study, we investigate the circulation and chemical processes associated with the deposition of the largest oil spill that reached the northeast coast of Brazil during the second half of 2019. Using the Oil Spill Contingency And Response model (OSCAR), we performed both deterministic and probabilistic simulations of oil spills from tanker ships that were present in the sea in the region at the time. The study used a dataset comprising the latitudinal distribution of oil sightings along the coast between 31 August and 2 December 2019 (box plot analysis) provided by the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA). The total amount of oil that reached the coast during this period (approximately 5000 tons) and the date and location of the first sighting (30 August, in the southern part of the state of Paraíba (PB)) were also used as parameters to assess the results of the 31 simulations conducted for ships en route near the area of interest between July and August 2019. The results indicate that a leak having occurred through a mobile source is the most plausible hypothesis for explaining the observed temporal–spatial arrival of the oil leaks along the Brazilian coastline. We suggest that prevention, monitoring, and international cooperation are essential for reducing the risks of future environmental accidents of the kind analyzed in this study and to protect the environment and communities affected.

The various complex forms of transport as well as many other fate processes ongoing in the marine water column require research for the understanding and prediction of impacts of deepwater releases on the marine ecosystem. Such research is useful for assessing the context and limits of future deepwater oil and gas development in the Gulf of Mexico. The Deepwater Horizon incident in the Gulf represents the first oil spill occurring at significant depth, ∼5,000 ft (1,500 m). It is also the first situation where dispersants were directly added to the hydrocarbon effluent from the wellhead in efforts to disperse the droplets over a large volume of the water column. In this regard, this perspective is an original work in that it provides an in-depth analysis of gaps and needs, which will guide future work in the field. Preliminary reports have led to a variety of images that highlight new physiochemical phenomena whose comprehensive understanding will be needed in assessing the oil and associated hydrocarbon chemical fate and environmental impact. Camera images of the oil and gas entering the water at depth and subsurface remote-operated vehicles have revealed droplet clouds and hydrocarbon plumes suspended thousands of feet below the surface moving horizontally with the water currents. Although preliminary, these and other observations are sufficient to piece together new hypothetical deepwater chemodynamic processes and phenomena that have yet to be fully understood. This position article focuses on unique and new research issues raised and relevant to this spill specifically. The ultimate fate of the oil constituents is a very broad subject. Our objective was concerned with the deepwater spill-initiating event. We focused on selected fate processes associated with the oil and dispersant chemodynamics from the blowout point, on the seabed, in the water column upward, and finally, into the marine surface mixed layer. An observation-conceived, process-based, mass balance-crafted engineering science predictive tool is proposed. It is needed for forecasting, projecting in anticipation of and managing the next spill, and answering the question 'where does it all go?' [ABSTRACT FROM AUTHOR]

Model predictions of oil transport and fate for the 2010 Deepwater Horizon oil spill (Gulf of Mexico) were compared to field observations and absolute and relative concentrations of oil compounds in samples from 900 to 1400 m depth <11 km from the well. Chemical partitioning analyses using quantitative indices support a bimodal droplet size distribution model for oil released during subsea dispersant applications in June with 74% of the mass in >1 mm droplets that surfaced near the spill site within a few hours, and 1–8% as <0.13 mm microdroplets that remained below 900 m. Analyses focused on 900–1400 m depth <11 km from the well indicate there was substantial biodegradation of dissolved components, some biodegradation in microdroplets, recirculation of weathered microdroplets into the wellhead area, and marine oil snow settling from above 900 m carrying more-weathered particulate oil into the deep plume. [Display omitted] • Validation of oil mass balance and budget for the Deepwater Horizon oil spill • Compared model predicted chemical partitioning in the water column to observations. • Inferred released oil droplet size distributions from sample compositions • Fractionation indices indicate bimodal droplet size distributions. • Subsea dispersant treatment was intermittent and partially effective in contacting the oil. [ABSTRACT FROM AUTHOR]

Based on oil fate modeling of the Deepwater Horizon spill through August 2010, during June and July 2010, ~89% of the oil surfaced, ~5% entered (by dissolving or as microdroplets) the deep plume (>900 m), and ~6% dissolved and biodegraded between 900 m and 40 m. Subsea dispersant application reduced surfacing oil by ~7% and evaporation of volatiles by ~26%. By July 2011, of the total oil, ~41% evaporated, ~15% was ashore and in nearshore (<10 m) sediments, ~3% was removed by responders, ~38.4% was in the water column (partially degraded; 29% shallower and 9.4% deeper than 40 m), and ~2.6% sedimented in waters >10 m (including 1.5% after August 2010). Volatile and soluble fractions that did not evaporate biodegraded by the end of August 2010, leaving residual oil to disperse and potentially settle. Model estimates were validated by comparison to field observations of floating oil and atmospheric emissions. [Display omitted] • Complete mass balance and oil budget for the Deepwater Horizon oil spill • Oil budget: ~41% evaporated, ~15% ashore, ~3% burned, 41% subsea and degraded • Model validated by field observations of floating oil and atmospheric emissions • Subsea dispersant injection reduced surfacing oil by 7%, volatile emissions by 26%. • Subsea dispersant effectiveness was limited by dispersant amounts applied. [ABSTRACT FROM AUTHOR]