Toxic In The Tropics: The Invisible Killer Now In Mauritian Waters

Last week, bulk carrier Wakashio broke up on the pristine coral reefs off the Indian Ocean Island of Mauritius, leading to a major oil spill and national emergency in the country.

Whilst the imagery does not show the extensive graphic spills associated with incidents like the Exxon Valdez oil tanker in Alaska in 1989 or the Deepwater Horizon oil well blow-out in the United States in 2010, four factors make the Wakashio spill in Mauritius a particularly lethal cocktail: 

  • the nature of the oil 
  • the size of the spill
  • the location of the incident
  • the effect of what happens to Heavy Fuel Oil when exposed to high ultra-violet sunlight in the Tropics – where Mauritius is located – especially with the cooler waters of the Winter months

This deadly cocktail now means that while the first phase of the cleanup nears its end, understanding the full magnitude of the much bigger second wave of this invisible killer is only just beginning.

In order to understand each of the four factors, it is first important to distinguish between the two main types of oil spills.

Two types of oil spills: Crude Oil Spills and Heavy Bunker Fuel Oil Spills

There are two main types of oil spills:

1. Crude Oil Spills

These could come from the rupture during the  transportation of oil in an oil tanker, such as the Exxon Valdez oil tanker in Alaska in 1989 or the Prestige oil tanker in Spain in 2002).  They could also come from oil well blowouts, such as the Deepwater Horizon blow out in the US Gulf of Mexico for 2010.  

Such incidents tend to be very visible with floating patches of oil and contain a high volume of oil that covers an extensive area – the worst oil spill in history at the time was the Exxon Valdez tanker that spilled 37,000 metric tons, ten times the amount in Mauritius, and was initially asked to pay over $5 billion in damages for the 1989 spill (equivalent to $10.5 billion today). Images of Crude Oil Spills are often full of many seabirds and wildlife visibly distressed and drenched in oil.  After the Exxon Valdez disaster in 1989, the laws governing international shipping changed to ban single-hull carriers from transporting oil and ensure all hulls were double-hulled, thereby creating an additional layer of protection in cases of accidents.

As the product is crude oil, this contains many of the lighter compounds that are high value and extracted during the oil refining process like aviation fuel, car fuel, petroleum ethanol, paraffin, and other petrochemicals.

2. Heavy Bunker Fuel Oil Spills (HFO Spills)

Bunker oil is the term used to refer to the oil used to power a ship’s engine, whether that vessel is a cargo, a bulk carrier or a cruise ship.  This fuel is typically low grade, unrefined and the leftover sludge from taking out all the high quality products during petroleum refining process.  It is heavily concentrated and thick.  This heavy bunker fuel is then mixed with diesel to allow it to float to the surface on water.  Bunker fuel is graded A, B or C, with C being the thickest and most viscous, often requiring heating or blending in order to make it flow.  Mixed with up to 10 percent of a lighter fuel, such as diesel, it becomes a cheap fuel for use in shipping (30% cheaper than alternatives).  It is often referred to by many names (such as Bunker Fuel, Heavy Bunker Fuel, Heavy Fuel Oil or HFO, No6 Grade C Oil).  

In the case of the Wakashio in Mauritius, the vessel appears to have been carrying the heaviest type of bunker fuel, No 6 (Grade C) fuel, that requires special handling for cleanup operations, as NOAA’s guidelines for No 6 (Grade C) bunker fuel oil spills indicate.

Although Heavy Fuel Oil is the most common form of oil used in shipping, there is significant controversy about its use and there have been strong efforts to have it banned both in order to meet Climate Change commitments, as well as the risk to the environment.  Spills from Heavy Fuel Oil are more common than Crude Oil spills due to vessel accidents, poor maintenance or vessels cleaning their engines illegally at sea, so do not receive as much media coverage.  Although visually, Heavy Fuel Oil Spills are much lower volumes than Crude Oil spills (as vessels are not transporting oil), so spills are a lot less visible on the ocean surface, they can be extremely toxic.  

The risk of HFO spills are so toxic that the international shipping regulator, the International Maritime Organization based in London, is finalizing plans to have it banned from the Arctic in the next few years due to the fragile nature of the Arctic ecosystem, and high exposure to ultraviolet light from the sun, that makes it even more lethal.  There have also been strong campaigns in the Arctic to ensure that vessels using Heavy Fuel Oil are double-hulled rather than single-hulled.  The vessel, Wakashio, that crashed in Mauritius was single hulled.

The lethal cocktail of the Wakashio oil spill

There are four factors that make the nature of the Wakashio oil spill in Mauritius particularly lethal, compared with most other Heavy Fuel Oil spills.  Let’s go through each in turn.

1. Type of oil involved: Heavy Bunker Fuel Oil (HFO)

As the incident in Mauritius involves the Heavy Bunker Fuel type of oil spill – rather than the Crude Oil type – any Natural Resource Damage Assessment should be informed by past work on large Bunker Fuel Oil Spills, such as the Cosco Busan vessel in San Francisco in 2007 or the Selendang Ayu vessel incident in Alaska in 2004 that also ran aground and split in two.  Comparisons with Crude Oil spills are not appropriate, so it is important to have a list of all Heavy Bunker Fuel Oil spills as a comparison on where the Mauritius Wakashio spill ranks. 

The legacy of the Selendang Ayu is still being felt ten years on in Alaska. In that spill it was estimated that 1250 metric tons (350,000 gallons) were spilled and not recovered. There was a discrepancy between what the investigation found and what environmentalists claimed was spilled.  Part of this discrepancy was the isolated location of the crash site in Alaska and difficulty of swiftly completing extensive sampling in time for this evidence to be admissible during the crash investigation.  Even despite the lower estimate of how much Heavy Bunker Fuel Oil was lost, the clean up settlement was over $112 million.

The highest profile example of bunker fuel pollution in the US was in 2007 when the Cosco Busan container ship collided with the Bay Bridge in fog in the heart of San Francisco Bay.

In that incident, 191 tons of heavy bunker fuel leaked in the busy San Francisco Bay (54,000 gallons of bunker oil).  This is in comparison to the 700 metric tons that has been reported to have been leaked into the pristine waters of Mauritius as of 11 August 2020 – three and a half times that of the Cosco Busan – of the 3800 metric tons that was on board at the time of the crash.

During the investigation of the impact of bunker fuel on wildlife habitats following the Cosco Busan spill, many previously unidentified harmful chemical properties of bunker fuel (chemicals called Polycyclic Aromatic Hydrocarbons, or PAH for short) were discovered causing extreme damage to local wildlife.  The impact report from the Cosco Busan highlights some of this harm on the wildlife’s reproductive health.  The compensation paid was $44 million, four years after the incident.  This payout could have been significantly higher had the accident taken place in more pristine waters, such as California’s national marine parks, just outside San Francisco.

2. Volume of bunker oil

In the case of the Wakashio, satellite analysis reveals that the vessel had just completed a refuelling stop for 18 hours in Singapore on 13 July 2020 and was only in the first 12 days of its long journey to Brazil to transport a heavy cargo of iron ore. 

As of 11 August, over 700 metric tons had been leaked and not retrieved from Mauritius’ pristine waters, three and a half times that of one of the worst Heavy Fuel Oil spill of 191 metric tons by the Cosco Busan.  It was reported that further leaks have happened overnight, and these volumes have not yet been confirmed.

3. Location of the oil spill: at the center of a network global biodiversity hotspots

Multiple global biodiversity hotspots: Whereas the Cosco Busan accident occurred in the heavily industrialized San Francisco Harbor, the Wakashio crashed into the center of a network of three internationally renown and protected nature refuges containing some of the most endangered species on the planet.  These were the two UNESCO Ramsar Protected sites of Blue Bay Marine Park, Pointe D’Esny Mangrove Forests, as well as the nature preserve of Ile aux Aigrettes that contained some of the rarest species in the country, such as Mauritius’ last remaining low lying ebony forests, not found

on any other location on the island.  The oil spill has also spread to other outlying islands – the network of Islets National Parks, that were protected nature reserves for Mauritius’ endemic species, such as Ile de la Passe, llot Vacoas, Ilot Phare, Ile aux Fouquets, Ile Marianne, Ile aux Fous, which could be seen by satellite to have been engulfed by the toxic oil slick.  By the fifth day of the spill, the slick could be seen as far as 14 miles North at the protected Ile aux Cerfs.  These have habitats and populations that have been carefully monitored for years and in the case of many endangered species under the care of the Mauritius Wildlife Foundation, had been on the path to recovery – one of global conservation’s greatest success stories.

Morphology of the HFO spill site: In addition to the species impacted, the conditions around the location of the spill site adds increasing complexity.  As a comparison, 30 years after the Exxon Valdez incident in 1989, over 20,000 gallons of oil continue to remain trapped and still ooze from the rocks, less than half (13 of 32) wildlife populations monitored had recovered, and a pod of killer whales had lost 15 of its 22 members after the spill and was expected to die off completely in the coming years.  The shores around Prince William Sound in Alaska where the Exxon Valdez ran aground was next to Alaska’s wildlife preserves and had rocky, shale-like bedrock which still trapped the residue oil.

The conditions around the Pointe d’Esny crash site of the Wakashio will make oil recovery much more challenging than the case of the Prince William Sound, which had rocky bedrock.  Looking at the direction of travel of the spill, these are some of the largest and most protected soft, sandy beaches in Mauritius interspersed with the root systems of protected mangrove forests, and contained with the largest coral reef lagoon in Mauritius. 

The strong wind and current conditions had already started dispersing the spill

around other beaches and outlying coral atolls.  These conditions are already trapping heavy oil particles amid the sand and root systems of the mangroves.  This will make the task significantly more complicated as the oil is absorbed by the roots and sandy beaches, effectively acting as giant sponges to the toxic oil.  So whilst a lot of the oil may not be visible to the naked eye or by satellite, it’s presence will be felt for many years to come.  This means that such toxins are likely to be around for many years, even if not visible to the naked eye.

4. Bunker fuel in the tropics: enhanced ultra-violet (UV) toxicity

Heavy Fuel Oil is particularly lethal in areas of high sunshine, such as the tropical climate of Mauritius. It is important to understand the science about why this is the case, as the type of oil carried by the Wakashio potentially carries increased toxicity in a tropical climate.

Small organisms readily absorb an array of chemicals from spilled Heavy Fuel Oil. Once inside an organism’s tissues, when some of these chemicals interact with ultra-violet (UV) rays of sunlight, energy is released from the chemicals that cause damaging chemical reactions. These reactions lead to tissue death, with very small organisms literally falling apart. 

When Heavy Fuel Oil interacts with ultra-violet (UV) rays of sunlight, it transforms the chemical properties of the oil, increasing its reactivity and toxicity. It is particularly lethal to translucent organisms close to the surface, such as corals as their naked skin lets in the light that can then be photo-reactive with the oil compounds. These oil chemical compounds when exposed through the translucent skin are then photo-modified and are ingested by the corals. This leads to toxicity and can cause organisms to die or dissolve in minutes, as prior research shows such as the results from from the 2007 Cosco Busan disaster, entitled ‘Sunlight and bunker oil a fatal combination for Pacific herring’ and ‘Potent Phototoxicity of Marine Bunker Oil to Translucent Herring Embryos.’

The enhanced UV toxicity of bunker fuel impacts the young of many species, such as larval fish both directly as well as through their reproductive cycles. Many coral reef fishes breed in the protected nursery grounds of the mangroves that are currently drenched in heavy oil. This nursing habitat is likely to be severely disrupted over the upcoming weeks, months and years, even if there is no immediate physical appearance of dark oil to the naked eye. The leaching of the oil over time from these habitats will continue to create a pollution hazard.

 Importantly the researchers who have studied prior oil spills have developed molecular technology that enables sampling of genes that are like a light switch- they turn on and off when exposure to toxic substances occurs. Using genomic (DNA) sensing, their advanced techniques using standard PCR technologies can indicate if fish and invertebrates are being exposed to the future. Careful collections of samples can aid in making these determinations.

 Compounding these factors, Heavy Bunker Fuel evaporates during warmer weather. Given that it is currently Winter in the Southern Hemisphere, and cool temperature prevail, remnants of the fuel will remain in the water for much longer. This creates a particularly toxic combination – the leftover oil, and the UV from sunlight weathering what oil remains.

Next steps to save nature: sample, sample, sample

In order to save nature and restore habitats to their prior conditions, it is important to understand the five phases that an oil spill response will go through.  These are listed here.

In the case of a Heavy Fuel Oil Spill, there are several clear lessons on the oil spill response from the Cosco Busan bunker fuel spill in San Francisco, which remains one of the best studied examples.

Ultimately, a Spill Impact Assessment Report will need to be written.  For the Cosco Busan bunker fuel spill, this can still be read online here.  This is critical reading for any country that experiences a Heavy Fuel Oil Spill.  Whilst there are a lot of deep scientific details, what is clear, was that the entire report revolved around the quality of the sampling.

Hence it is critical to start immediately collecting and documenting specimens of coral, fish and other wildlife at regular (daily) intervals and ensure these are time stamped and geo-tagged.  Samples will need to be frozen (ideally at temperatures of -80C) and kept in a locked repository with good security to prove the samples were not tampered with.  In many countries, the boxes that samples are stored in are locked, chained and have security cameras on to ensure no tampering, given how critical this evidence is.  Without the correct documentation, samples will not be admitted.

Given Mauritius has a large tuna fishing industry and a large offshore aquaculture sector nearby which require large freezing capabilities to permit seafood exports, such facilities should easily allow such samples to be properly collected, labelled, and stored in tamper-proof containers.  Also, given that this is currently the low point in the tourist season, there are a significant number of dive center instructors, tour boat operators and local fishermen who could be trained and mobilized in such an effort.  

Just as the mantra for Covid-19 had been ‘test, test, test,’ as Mauritius successfully protected itself from the worst effects, the mantra to address this silent and invisible killer second wave from the oil spill should be ‘sample, sample, sample.’

The cataloguing and chain of custody of the samples are equally important during this process.  The US Guide to Sample Preparation and Documentation is one of the best in the world, and contains many templates that are still in use to document samples, such as on Page 23 on NOAA’s Guide to Sample Documentation here.   These samples will ultimately be the critical tool for a Natural Resource Damage Assessment (NRDA), which is conducted at a Federal level in the US and explained here.

Preparing for the worst: hoping for the best

Whilst the entire world hopes for the best recovery of this critical habitat, it is important to start preparing for the worst.  This is at least the lesson taught to the entire world from Covid-19, and from Heavy Fuel Oil spills around the world that continue to leak their deadly poison decades later.

As lessons from all major oil spills have shown, the critical actions taken in the early days following a disaster can make all the difference between an ecosystem that does or does not recover.  It’s as simple as that.

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