About Vegetable Oil Spills

The fate, behaviour and environmental impact of spills of vegetable oils in the marine environment are not as widely appreciated as those of mineral oils. Despite this, a spill of vegetable oil can prove to be equally problematic.

What are Vegetable Oils?

Behaviour and Fate of Vegetable Oils

Impact of Vegetable Oil Spills

Response Techniques

 

What are Vegetable Oils ?

Vegetable oils are oil extractions from plants and fruit such as palm nut, sunflower, soybean, coconut, rapeseed, canola, olive, castor and corn. There are a variety of derivatives and degrees of processing. For example, in general terms, crude describes oil that has been generated by extraction with no further processing. “De-gummed” oil describes a more refined product with the resin-like compounds removed whereas the term refined oil applies to those products that have been clarified and any undesirable colour and sediment removed.

Behaviour and Fate of Vegetable Oils

As with mineral oils, vegetable oils can vary significantly and on release to the marine environment will behave differently according to their individual characteristics. These characteristics will depend on factors at the time of cultivation of the feed stock eg climate; the degree of processing; the type and specific nature of the oil, the sea state and weather conditions at the time of  the spill. In many circumstances, the influence of vegetable oil characteristics on the behaviour of the oil in the environment is not well studied or understood. Consequently, the behaviour and fate of specific vegetable oils is somewhat harder to predict than that of mineral oils.

In general, vegetable oils will behave similarly to mineral oils in the initial stage of a spill. To this extent, they will tend to float and spread on the surface of the water. However, vegetable oils tend to be even less soluble in water than mineral oils; they do not undergo dispersion in the water column nor will they evaporate to any extent.

Depending on their pour point (the temperature at which solidification commences) and the sea surface temperature, vegetable oils may form solid lumps when spilled that will float on the water surface. These discrete lumps have little tendency to coalesce as a surface slick. Over time and dependent on the prevailing conditions the product may accumulate sediment and may sink to the sea floor.

Vegetable oils are comprised primarily of triacylglycerols, or fatty acids, which, in their fresh state, may be broken down by marine bacteria. This decomposition contributes to the rancid odours typical of vegetable oil spills.

Vegetable oils will not readily form water-in-oil emulsions but may undergo a process of polymerisation to form rubbery strings and clumps. These deposits are highly impermeable curtailing oxygen diffusion and replenishment, dramatically slowing the degradation process and forming an anoxic layer. By this process, vegetable oils, particularly with the incorporation of sediment, may give rise to the formation of very tough and highly persistent deposits.

Generalised Summary Of Vegetable Oil Behaviour

Low aquatic toxicity

Limited solubility in water

Do not evaporate to any significant degree

Generally do not form water-in–oil emulsions (though water may become entrapped in polymerised lumps)

Do not undergo dispersion in water

Tendency to polymerise

Not amenable to dispersion by oil dispersants

Return to top

Impact of Vegetable Oil Spills

Historically, vegetable oils have been considered relatively benign, non-toxic and therefore of limited concern to the environment. However, this generalisation has been demonstrated to be incorrect. Previous experience has shown that both chronic and acute pollution incidents can lead to deleterious effects. This awareness has led to the reclassification of many vegetable oils as category Y (hazardous) products under Annex II of the MARPOL Convention with associated limitations on their carriage.

palm oil spill
Rock coated with palm oil
Spilled palm oil
Rock coated with palm oil
palm oil spill palm oil spill

A spill from a palm oil production plant in Colombia © Elastec

In this incident, skimmers were put to work recovering the oil © Elastec
 
(Note, the appearance and characteristics of the oil are dependent on a number of factors, such as the degree of processing, see above)

The primary environmental consequences of spills of vegetable oils are seen in relation to surface dwelling organisms where oil can lead to smothering and suffocation. Examples include oiling of bird plumage and animal fur. However, vegetable oils will also readily form solids which tend to have less smothering impact on surface organisms. A polymerised vegetable oil may form an impermeable barrier on the shoreline with potentially serious environmental and economic consequences.

Unlike mineral oils, the environmental impact associated with ingestion of vegetable oils is low. Whilst experimentation has shown some effects such as reduced growth rates, poor food conversion and liver impairment in fish and bivalves resulting from prolonged ingestion, these effects have been minimal even in cases of heavy contamination. However, vegetable oil spills can have significant effects through oxygen depletion and asphyxiation.

One of the primary concerns with vegetable oils is the uncertainty and lack of knowledge of their degradation and weathering products. Ongoing research suggests for example that the toxicity of products such as canola oil and soybean oil actually increase significantly during aerobic biodegradation. The effects of such a process in a confined, shallow environment could be significant.

Summary of Potential Environmental Impacts

Physical

Smothering

Coating fur and feathers

Suffocation through oxygen depletion and smothering

Formation of intractable lumps in sediments

Polymerised oils produce impermeable layers on shore

Chemical/ Biological

Suffocation through oxygen depletion

Anoxia in sediments and water

Amenity

Rancid odours, particularly during degradation

Fouled shorelines

Blocked water intakes

Response Techniques

With the tendency of some vegetable oils to polymerise and form solid lumps, the most appropriate response technique is that of containment and recovery. Ideally, these floating lumps should be removed from the water surface before they have a chance to accumulate sediment and sink and before they are able to reach the shoreline.

Response techniques applied during previous incidents involving a spill of vegetable oil include the use of conventional boom for containment, combined with a variety of recovery techniques. Skimmers may be used to recover vegetable oils of suitable viscosity. Manual recovery techniques employing scoops, trawls and grabs have proved to be effective in the recovery of solidified vegetable oils. The high viscosity of solidified vegetable oils may preclude certain recovery techniques, for example using pumps. Furthermore, dispersants formulated for use on mineral oils have been shown to have little or no effect on vegetable oils.

Return to top