Chemical fingerprinting and weathering assessment of Sanchi oil tanker spill residues that impacted the southern Japanese islands

On January 6, 2018, the Sanchi tanker, carrying 111,300 metric tons of natural gas condensate as cargo and 1900 metric tons of heavy fuel oil (HFO) for propulsion, collided with the bulk carrier Changfeng Crystal in the East China Sea. The collision caused a catastrophic explosion, and after burning and drifting for eight days, the Sanchi sank on January 14, 2018. While the incident had the potential to become the world's largest ship-source condensate spill and ninth-largest tanker spill, extensive burning likely reduced the condensate mass significantly. When the wreck sank, any remaining condensate and HFO were released into the ocean. Due to its physiochemical properties, the condensate would have rapidly evaporated or dispersed. By late January 2018, oil spill residues began washing ashore on 26 southern Japanese islands, including Amami-Oshima and Okinawa Main Island. Chemical analysis confirmed that all residues originated from a single source - the oil released from Sanchi. Diagnostic ratios and chromatographic features showed that the residues contained only HFO, with no detectable condensate, and exhibited signs of soot incorporation. This indicates that any condensate accompanying the HFO had completely weathered before reaching the shores, leaving behind only the HFO, which persisted in the environment. Additional analysis suggests that the oil spill residues underwent weathering processes, including evaporation, dissolution, and microbial degradation during ocean transit. These findings provide insight into the fate of spilled condensate and HFO from the Sanchi tanker in the marine environment.