ITOPF has published a report explaining the possible damage and liabilities of biofuel spills, specifically focusing on biodiesels.
As explained in “Fate, Behaviour, Potential Damage & Liabilities Arising from a Spill of Biofuels in the Marine Environment” report, biofuels are seen as viable ‘transition fuels’ as, although not being zero-carbon, their upstream life cycle emission levels (also know as ‘well to tank’ emissions for fossil-derived fuels) are significantly lower than conventional hydrocarbon fuels because they are typically produced from renewable feedstocks.
In particular, biodiesels have primarily been tested as blends with traditional fuel oils, ranging from B5 (5% biofuel: 95% conventional fuel) up to B100 (100% biofuel). It should be noted that in biofuel blends, the lower the proportion of biofuels added (e.g. B5, B10), the more likely the fuel will behave like a traditional fuel oil.
This variability in composition has allowed an increasing knowledge among engine manufacturers and operators about their impact on engine operations and tank- and fuel-supply systems. The most prevalent biodiesels on the market are currently considered to be FAME and HVO, with their share of the biofuel market rapidly increasing.
FAME is a colourless liquid produced from transesterification of bio-oil (such as rapeseed and palm oil) and methanol or ethanol, which results in a mixture of fatty acid methyl esters.
HVO is a colourless liquid produced from hydrotreatment and refinement of bio-feedstocks such as vegetable or cooking oils and animal fats.
When spilled into the marine environment, biodiesels will typically behave similarly to conventional diesel in the initial stages of a spill. They will float and spread on the water, forming a slick on the surface.
Moreover, biodiesels will not mix with water due to their insolubility, but unlike conventional diesels, pure biodiesel will not evaporate due to its low vapor pressure and will therefore remain on the sea surface for a longer period in comparison to conventional diesels. If biodiesel is blended, the propensity to evaporate may increase with an increasing percentage of conventional diesels.
The temperature of the receiving water body and the biofuel’s pour point (the temperature at which a liquid loses its fluid properties) will determine its fate and behavior when spilled.
Hazards of biofuels in the marine environment
Generally, the hazards of biofuels are similar to those related to conventional oils due to the similarities in their fate and behavior. The primary environmental impacts of biodiesels on the environment are caused by smothering of wildlife and possible reduction in oxygen availability following biodegradation.
Physical Smothering
The primary impacts are likely to be on surface-dwelling organisms (e.g., seabirds, marine mammals) that have been in physical contact with the slick. The oil is likely to smother and coat the surface of the animals, particularly if the oil is of low viscosity (i.e., in warm/temperate waters). This can result in impacts on movement, feeding, respiration, thermal control, and reproduction. In the event that water temperatures are below the oil’s pour point and the oil therefore forms a solid, the potential impact on surface-dwelling organisms will be significantly reduced.
Oxygen Availability
As biodiesel is readily biodegradable, when spilled in the marine environment, it will serve as a feedstock for microbial organisms present in the water column. If the biodiesel is abundant following a spill, microbial populations will increase exponentially and subsequently so will oxygen consumption due to microbial respiration. As dissolved oxygen concentrations decline in the water column, other organisms such as fish, crustaceans, and aquatic plants will not be able to function due to hypoxic or anoxic conditions, which can lead to local mortalities.
Some microbial organisms are able to function under hypoxic or anoxic conditions and will continue, undertaking anaerobic biodegradation of the oil. In open water, anoxic conditions are unlikely to occur due to constant aquatic mixing and the buffering capacity of the ocean. However, anoxic conditions could occur in a sheltered bay or inland waterway with little turbulence and mixing.
Ecotoxicity
The GESAMP hazard profile for FAME states that the substance has a moderately low aquatic toxicity and has no bioaccumulation potential. Bioaccumulation occurs when a substance is absorbed by tissues of an organism at a greater rate than it can be metabolized, excreted, or degraded.
Studies have been undertaken to compare the toxicity of biodiesel with petroleum diesel and due to the lack of polycyclic aromatic hydrocarbons (PAHs) in both FAME and HVO, pure biodiesels are considered to be at least five times less acutely toxic than conventional diesels. However, toxicity varies widely depending on feedstock and additives.
Flammability
Flammability risk from biodiesel is considered to be low due to its high flash point (>70 °C for HVO and >101 °C for FAME) and its low vapor pressure, when compared to petroleum diesel.
Toxicity
Similarly to conventional hydrocarbon diesel, biodiesel can cause skin and eye irritation if exposed. Vapors can be harmful; however, due to its low flash point, biodiesel would require significant heating to produce vapors.
Key points for consideration
#1 Clean-up and preventive measures
In comparison to the costs associated with clean-up and preventive measures from a traditional spill of hydrocarbon bunker fuel oil, the costs for a biodiesel spill would generally be similar. As biodiesel is an insoluble liquid that floats and, in the event of a large spill, is expected to persist on the sea surface, established oil pollution clean-up measures are likely to be appropriate (e.g., collection and recovery using booms and skimmers).
#2 Environmental damage
The environmental impacts of biodiesel in the marine environment are not as widely researched as those associated with spills of conventional hydrocarbon oils.
#3 Property damage from biodiesel
Costs arising from this claims heading may be similar to conventional fuels. However, due to biodiesel’s colorless appearance in comparison to the visible black appearance of conventional oils, damage may not be as noticeable. Although considered relatively persistent, natural attenuation via biodegradation will be more rapid than traditional oils, and damage may not be as long-lasting.
#4 Economic loss
The GESAMP hazard profile states that biodiesel can have a moderate impact on amenity value and could lead to closure of impacted sites, including beaches. Following shoreline stranding, it has been noted that vegetable oils can emit pungent odors due to biodegradation, which may impact beachgoers and users of tourist destinations. This could impact local businesses, including hotels and restaurants.
In conclusion, biodiesel’s relatively similar fate and behaviour in comparison to conventional fuels means that claims arising from a spill would be similar to those associated with conventional hydrocarbon oil spills.
