ASSESSING THE BIOLOGICAL IMPACT OF OIL SPILLS: 

 A NEW ROLE FOR EPA BIOLOGISTS 



Royal J. Nadeau 



Whether an oil spill is the result of a catastrophic, highly publicized 

 event like a platform blowout or the sinking of a tanker or a more common- 

 place, but less publicized event, such as a storage tank release, it has 

 a definite effect on the aquatic environment. Storage tank releases, though 

 smaller in terms of the volume of oil spilled, occur more frequently, and, 

 in terms of overall impact, are just as critical as the more catastrophic 

 spills. The effect that an oil spill has on aquatic ecosystems is influenced 

 by a number of factors: type of oil spilled and volume, hydrography of the 

 oil spill area, climatic and seasonal changes, indigenous biota, treatment 

 methods used during the cleanup, and previous exposure of the spill area 

 to oil pollution. 



FACTORS AFFECTING BIOLOGICAL IMPACT 



TYPE OF OIL SPILLED AND VOLUME 



Chemically, oil is not a single compound, but a mixture of compounds, 

 each with its own unique set of physical/chemical characteristics. Some 

 of these compounds are more toxic than others to aquatic organisms. Some 

 are more soluble than others, thus entering the water column and increasing 

 the likelihood of contact with living organisms. 



For example, a No. 2 fuel oil, which contains toxic and soluble hydro- 

 carbon compounds, is likely to have a greater impact on living aquatic systems 

 than a No. 6 or a bunker fuel, which has fewer highly toxic or soluble compounds. 



Obviously, the amount of oil that is spilled will influence the impact 

 the spill has on aquatic life. The greater the volume of oil, the more likely 

 it is that the oil will contaminate extensive areas of biological importance. 



HYDROGRAPHY OF OIL SPILL AREA 



Salt marshes and freshwater wetlands are examples of ecologically important 

 and highly productive ecosystems, which are acutely affected by an oil spill. 

 Because of their unique hydrographic characteristics, areas such as these 

 often sustain long-term effects. Oil, for example, is easily entrapped or 

 absorbed onto marsh soil and may remain unchanged there for many years. 

 Because of this, there is the likelihood that the oil will be cycled through 

 existing aquatic life in the marsh ecosystem. 



U.S. Environmental Protection Agency 

 Region II 

 Woodbridge Avenue 

 Edison, New Jersey 08817 



55 



