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.
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.
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.
the international tanker owners pollution federation limited.2013
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