In August 2020, the Mauritian government called a national emergency after the Japanese bulk carrier, MV Wakashio ran aground, spilling an estimated 1,000 tonnes of oil into the ocean and leading to what scientists called ‘the worst environmental disaster Mauritius had ever faced.’

Three years on, and researchers have concluded that the impact of the incident is still being felt today with oil still present – even now – in an environmentally sensitive mangrove forest close to important Ramsar conservation sites.

It had been long-suspected that the oil left in this area had come from the fateful events of July 2020, but until now little evidence existed that directly linked the residual pollution to the bulk carrier, Wakashio. But, with help from researchers over at Curtin University – an international university with locations in Western Australia, Malaysia, and Mauritius – the picture has been made a whole lot clearer.

Lead researcher, Dr Alan Scarlett, from Curtin’s WA Organic and Isotope Geochemistry Centre in the School of Earth and Planetary Sciences, said the chemical ‘fingerprint’ of the oil found in the mangrove sediments was a “near-perfect match” for the Very Low Sulphur Fuel Oil (VLSFO) spilled by the Wakashio in 2020 – the first recorded spill involving this type of fuel.

“Local communities in Mauritius have been aware of oil contamination in the mangrove wetlands since the Wakashio spill, but no official confirmation had been made regarding the source,” said Dr Scarlett. “Identifying and acknowledging this contamination is crucial, both for the people of Mauritius and for global understanding, as little is known about how this new marine fuel behaves once spilled.”

To reach the conclusion, a study using “advanced chemical techniques” was undertaken to analyse samples from the mangrove wetland, including from a reference site thought to be unaffected by the spill.

It was discovered that the spilled oil had actually undergone substantial weathering and biodegradation in the three years since the accident and that this had removed or reduced the levels of many of its toxic compounds.

“However, the ongoing presence of the oil still poses an unknown risk to the sensitive mangrove ecosystem,” said Dr Scarlett.

In a previous collaboration with the Woods Hole Oceanographic Institution, conducted closer to the time of the original spill, the Curtin research team obtained a unique chemical ‘fingerprint’ of the oil. It was this that enabled them to ascertain that the oil found in the mangrove sediments was indeed the same oil from the same spill.

At the time of this study, Curtin University wanted to form a true understanding of the environmental impact local communities of Mauritius could anticipate from the spill. 

“Since the grounding of the Wakashio on a coral reef, there has been much speculation in the media about what oil was spilled, including headlines about so-called ‘Frankenstein fuels’, so we wanted to obtain a sample for research and analysis,” said Dr Scarlett at the time. 

“We obtained a sample of oily residue from the Mauritius coastline about eight kilometres from the grounded vessel, along with a sample of the Wakashio’s fuel oil, and using a suite of sophisticated chemical and isotopic analyses, we were able to confirm the spilled oil originated from the fuel tanks of the Wakashio.”

Further analysis revealed that the quantities of components known to be toxic to marine organisms in the spilled ship’s oil were less than in typical heavy fuel oils. At the time, Dr Scarlett posited that the impacts on marine organisms from exposure to toxic compounds in the oil “may be less severe than with previous spills that involved older types of marine fuel oil.”

To carry out this analysis, researchers employed models developed from the National Oceanic and Atmospheric Administration’s oil spill scenario tool, WebGNOME-ADIOS.

“Our modelling suggested more of the Wakashio’s fuel would evaporate, naturally disperse, or sink compared to traditional fuels, but assessing the impact on organisms remains challenging,” said Dr Scarlett.

Despite the high-profile international media coverage and potential health, social, environmental, and economic impacts on Mauritius following the 2020 MV Wakashio oil spill, there is still very limited scientific research and data accessible on the chemical composition and fate of the spilled oil beyond analysis of the source oil.

Understanding how far the oil may have travelled following the spill and which ecosystems and communities may have been impacted is crucial for clean-up strategies, future monitoring, restoration, and economic compensation for people affected by the spill. 

In addition, as so little is known about the behaviour of the VLSFO, what is discovered will have consequences globally on how to plan and respond to future spills of VLSFO. It could also prove useful for planning how to respond to any future VLSFO spills in tropical waters.

“Unfortunately, oil spills from ships continue to be a frequent occurrence, so it is likely we will see further spills involving VLSFOs,” said Dr Scarlett. “In turn, many countries, including Australia, will be re-evaluating their oil spill response strategies. Our results will help these countries and their maritime safety agencies develop new strategies.”

The paper, MV Wakashio grounding incident in Mauritius 2020: the world’s first major spillage of Very Low Sulfur Fuel Oil was published in Marine Pollution Bulletin.  

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