Cleaning the bilge tanks: Is Brazil on the route of international oceanic dumping?

In 2019–2020, a “Mysterious” oil spill reached almost 3,000 km of the Brazilian shore. Despite the large affected area, the STFM (Spill, Transport and Fate Model) [1] time-reverse modeling indicated a relatively small Venezuelan oil volume (5000–12,500 m3) [2] and quite far from the coast [3]. These volume and position are consistent with a cleaning bilge tank procedure.

In the following years, at least three similar events were recorded, one on the equatorial coast of Brazil and two in the Fernando de Noronha archipelago (about 375 km from the coast). These events indicated that Brazil was being periodically reached by tar balls and oil slicks from unknown origin. The most likely routes were mapped and computationally tested [3] [4].

The hypothesis is that the oil/waste dumped in international waters by ships on-route to Cape of Good Hope is reaching the Brazilian coast. On that account, 9,000 probabilistic simulations (distributed in 30-year of data), each one with 20,000 Lagrangian elements, were used to estimate the probability of dumped oil residue reaching the Brazilian coast. 

About 20,000 – 35,000 ships navigate this route and the modeling results have shown that up to 28.5 % of large ships could dump oil on-route towards Cape of Good Hope. Inside the Brazilian Exclusive Economic Zone, the probability of dumped oil/waste reaching the coastline is about 62 % and quickly decreases for more distant dumping zones (Zones 2 and 3). Equatorial and Northeast shores of Brazil are the most vulnerable to oceanic dumping when compared to other regions.

Brazilian Federal Police declared that a Greek-flagged tanker (i.e., Bouboulina) is the main suspect of the 2019’s oil spill [5]. However, the simulation results suggest an alternative hypothesis: The City of Tokyo (VL Nichioh) tanker that crossed Zone 2 area between June 18th and 20th, 2019, towards Venezuela to be loaded. The drift time (72 days) is compatible with the position, also, the loading that would take place in a few days could motivate the tanker to execute a cleaning procedure, accumulating a large volume of residual oil in the bilge tank [4].

 

[1] Zacharias, D.C., et al., 2018. Offshore petroleum pollution compared numerically via algorithm tests and computation solutions. Ocean Eng., https://doi.org/10.1016/j.oceaneng.2018.01.007. 

[2] Zacharias, D.C., et al., 2021a. Mysterious oil spill on Brazilian coast: analysis and estimates. Mar. Pollut. Bull., https://doi.org/10.1016/j.marpolbul.2021.112125. 

[3] Zacharias, D.C., et al., 2021b. Mysterious oil spill on the Brazilian coast – part 2: a probabilistic approach to fill gaps of uncertainties. Mar. Pollut. Bull., https://doi.org/10.1016/j.marpolbul.2021.113085.

[4] Zacharias, D.C., et al., 2023. Oil reaching the coast: Is Brazil on the route of international oceanic dumping?  Mar. Pollut. Bull., https://doi.org/10.1016/j.marpolbul.2023.115624. 

[5] Escobar, H., (2019), Mysterious oil spill threatens marine biodiversity haven in Brazil, Science, https://www.science.org/doi/full/10.1126/science.366.6466.672.  

Keywords:  STFM; Oil spill; Oil dumping