bacteria of the genus Moraxella, indicating that these strains are per- 

 fectly adapted to the hydrocarbons present at that particular time in 

 the culture and, being dominant, they therefore naturally and preferen- 

 tially consumed the hydrocarbons of the "saturates" fraction, as these 

 types of constituents were biodegraded during this period. At the end of 

 the culture, however, when the "aromatics" fraction was attacked by the 

 microorganisms, only the Pseudomonas strains were dominant. 



This investigation again confirms that, to observe a significant 

 degradation of hydrocarbons in a crude oil containing a wide variety 

 of compounds, a mixed culture of bacteria is certainly more effective 

 than a pure bacteria, of which the metabolism is only adapted to a 

 given type of constituent. 



1.4. Toxicity analysis of oxidation products. 



During the different ALC 240 + crude oil biodegradation experiments, we 

 always observed a substantial rise in total organic carbon (TOC) 

 concentration in the aqueous phase with the passage of time, with a 

 regular final concentration around 200 mg.l . 



We decided to evaluate the potential toxicity of these solubilized 

 products in the aqueous phase, enriched mainly in aromatics and oxi- 

 dation products of certain hydrocarbons present in the crude oil. 



In particular, the mutagenicity of two samples was determined by the 

 Ames test, the procedure of which is described in detail in Mutation 

 Research 1975, 31, pp. 347-364. The first sample was taken at the 

 start of the culture (with a TOC of 30 mg.l - - 1 -), and the second at the 

 end of the batch culture (sample with a TOC of 210 mg.l -1 ). 



The correlation between carcinogenic properties and mutagenic properties 

 of 300 compounds was pointed out in Proc . Natl. Acad. Sci., (USA), 

 1975, 72, pp. 5135-5139. 



The principle of the Ames test is to measure the mutagenic properties 

 of compounds that may be carcinogenic in Salmonella bacteria. 



The two samples were tested in a range from 0.1 to 500 jul on three of 

 the five strains used in the Ames test (TA.1538, TA.98 and TA.100) in 

 order to detect the mutagenicity of products such as HAP, for example. 



No mutagenic activity was detected in these two samples. 



It was shown finally that neither of these two samples had any toxic 

 effect on the three strains tested (TA.1538, TA.98 and TA.100). 



1.5. Study of the biodegradation of a mixture of pure hydrocarbons. 



The mixture of pure hydrocarbons consisted of two n-alkanes, hexadecane 

 and octacosane, one isoprenoid, pristane, a two-ring naphtene, decaline, 

 two mono-aromatics , p-cymene and dodecylbenzene, one di-aromatic, 

 dimethyl-naphtalene , one tri-aromatic , phenanthrene, and two sulfur- 

 containing aromatics, benzothiophene and dibenzothiophene. 



32 



