'Catastrophic' oil spill still polluting idyllic Mauritius wetlands three years on

A new analysis by Australian researchers confirms that the previously pristine mangroves around Mauritius remain contaminated by ship fuel three years after the "catastrophic" Wakashio oil spill. In July 2020, the Japanese bulk carrier Wakashio ran aground on a coral reef about 1.6 kilometers off the coast of Mauritius, at which time environmentalists warned that the severe consequences could last for decades.

Due to the long-term impact of waves, the ship broke apart, and an estimated 1,000 tons of new ship fuel leaked into the Indian Ocean near the internationally recognized Blue Bay Marine Park. Although the volume of this spill was smaller than some of the world's largest spills, such as the BP Deepwater Horizon spill in the Gulf of Mexico in 2010, it occurred near some of the world's most sensitive marine habitats, including coral reefs, mangroves, and seagrass.

Dr. Alan Scarlett of Curtin University stated, "Since the Wakashio oil spill, the local community in Mauritius has been aware of oil contamination in the mangrove wetlands, but there has been no official confirmation of the source of the pollution." Scarlett and his research team at Curtin University's Western Australian Organic and Isotope Geochemistry Centre collected samples from the mangrove wetlands and analyzed them using advanced chemical techniques.

Dr. Scarlett said, "We confirmed that there was no oil contamination at the reference site, while another site contained oil from the Wakashio's fuel tanks." They found that the chemical "fingerprint" of the oil in the mangrove sediments almost perfectly matched the very low sulfur fuel oil (VLSFO) that was leaked from the Wakashio in 2020. At the time, this was the first recorded spill involving this type of fuel.

Since the accident, the spilled oil has undergone significant weathering and biodegradation, reducing the levels of many toxic compounds. Dr. Scarlett said, "However, the continued presence of oil may still pose unknown risks to the sensitive mangrove ecosystem."

The Curtin University research team also used a model developed by the US National Oceanic and Atmospheric Administration to compare the behavior of the new type of oil with traditional heavy ship fuel oil. They found that compared to traditional fuel, more of the fuel evaporates, disperses naturally, or sinks, but its impact on organisms remains unclear. The full results of the study were published this week in the journal Marine Pollution Bulletin.