PHYSICAL AND CHEMICAL CHARACTERISTICS

The physical behavior and biological effects of an oil spill seem to be influenced to a large extent by the type of oil spilled. Of concern are both crude oils and their distillate products. The crudes are extremely complex mixtures of hydrocarbons (compounds made up entirely of carbon and hydrogen) with small amounts of sulfur, oxygen, and nitrogen compounds and trace amounts of inorganic and organometallic compounds.

The type of oil, with its attendant physical characteristics, largely determines the thickness and spreading of a slick, the formation of emulsions (either oil in water or water in oil), the attenuation of light and oxygen in underlying substrates, and the effectiveness of various cleanup techniques. The extent of biological damage is also apparently related to the type of oil. Obviously such things as the capacity to smother or physically remove organisms hinges largely on an oil's physical characteristics. The toxicity of oil, on the other hand, seems to be a function of its chemical composition.

There are three basic classes of hydrocarbon compounds in petroleum oils: alkanes (also referred to as paraffins or saturates), alkenes (olefins), and aromatics. Alkanes are chains of carbon atoms with attached hydrogen atoms and may be simple straight chains (normal), branched chains, or simple rings (naphthetic). As with most classes of organic compounds the higher the number of carbon atoms in a molecule, the higher its boiling point and the less volatile it is. Low boiling alkanes produce anaesthesia and narcosis at low concentrations and at high concentrations can cause cell damage and death among a wide variety of lower invertebrates (). Higher boiling alkanes are naturally produced by life processes and are found in all marine organisms. Higher boiling alkanes of petroleum origin are not normally toxic; however, they may affect chemical communication and interfere with metabolic processes.