itv and 25 °C.) It was observed that for each additional aromatic ring, 

 the concentration of an aromatic hydrocarbon necessary to produce a 

 toxic effect decreased by approximately one order of magnitude. For 

 a given aromatic ring system, the addition of alkyl side chains also 

 decreased the concentration required to produce toxicity. This effect 

 was less predictable in that not only the number of side chains and 

 the number of carbons they contain but also their positions on the 

 ring control the toxicity of the molecule. Similar experiments with 

 the microalga Cyclotella menighiana indicated that this organism was 

 more susceptible to aromatic hydrocarbons than the bacteria. For ex- 

 ample, 8 ppm naphthalene only reduced the growth rate of the bac- 

 teria but completely killed C. menighiana. Other experiments have 

 shown that the aromatic hydrocarbons which were tested can interfere 

 with the ability of marine bacteria to take up substrates such as glu- 

 tamic acid and cause the leakage of metabolites such as the amino 

 acids from the cells. 



In a later series of experiments, the toxicity to marine bacteria of 

 the water soluble fractions of whole crude and refined oils was ex- 

 amined by the FSU group. Five oils, Southern Louisiana, Kuwait, and 

 Florida Jay crude oils, bunker C and No. 2 fuel oil, were used in this 

 study. Both growth rate and final cell density were determined turbi- 

 dimetrically for controls and bacteria exposed to the water soluble 

 fractions of the above oils. For each oil, the reduction in growth rate 

 and cell density were normalized to Ippm of total water soluble ma- 

 terial or 1 ppb of total aromatic hydrocarbon (equivalent to benzene 

 eluant from silica gel) . When all measures of toxicity were taken into 

 account, the relative toxicity of each of the oils was calculated to be as 

 follows: 



Concentration of Aromatic 

 Relative Toxicity Hydrocarbons in Oil 



Oil of WSF Equilberaied Sea Water (ppb) 



Florida Jay 100 192 



So. La. Crude 67 816 



Kuwait Crude 32 397 



No. 2 Fuel Oil 31 868 



Bunker C 26 2380 



Even though the aromatic hydrocarbons are known toxicants, the 

 relative toxicity of the water soluble fraction of these oils is unrelated 

 to the concentration of aromatic hydrocarbons in seawater equili- 

 brated with the oil. Most of the components of the water soluble frac- 



19 



