pristane and n-C18/phytane which were 3.3 and 2.8 in the reference 

 mousse, were 0.07-0.58 and 0.024-0.36, respectively. Becase of the 

 relative persistence of aromatic hydrocarbons (Atlas, et al, 1981; Ward 

 et al, 1980), alkylated naphthalenes, phenanthrenes and dibenzothio- 

 phenes remained in Brittany sediments at levels sufficient to study 

 weathering patterns in a long term time/depth series. The loss of 

 these compounds relative to the more persistant C„-alkylated deriva- 

 tives of dibenzothiophene (CL-DBT) is thought to be an index of weath- 

 ering (Grahl-Nielsen, et al, 1978). There is no published evidence 

 that changes in aromatic compounds relative to C„-DBT are due to bio- 

 degradation, but these compounds are subject to microbial attack (Atlas, 

 1981). 



The ratios of aromatic compounds to CL-DBT showed different 

 changes with time depending on type of sediment and sediment depth 

 (Table 3). In the AMC-4 0-5 cm interval there was a systematic de- 

 crease in nearly all ratios from December 1978 to March 1979 to No- 

 vember 1979. In muddy sediments decreases were less rapid and exten- 

 sive. By March 1979, C - and C,- naphthalenes, C„- and C,- phenan- 

 threnes and C-DBT showed: relative decreases in the Aber Wrac'h 0-5 cm 

 interval. An Aber Wrac'h core collected in November 1979 was sub- 

 divided at one centimeter intervals at the depths of greatest change in 

 Eh. In the 1-2, 2-3, and 3-4 cm intervals naphthalenes were "almost 

 entirely depleted. Relative decreases in all except C - and C,- phen- 

 anthrenes were noted compared to earlier samples, with no great differ- 

 ences among these depth intervals. Phenanthrenes were enriched rela- 

 tive to C-DBT by May 1980 in the 0-3 cm interval. Ratios of aromatic 

 hydrocarbons to C.-DBT were generally greater in deeper layers (5-10, 

 10-15 cm) than in surface layers on any given date. Nevertheless, the 

 data suggest that decreases in naphthalenes and DBT's occurred in the 

 5-10 cm interval in the one year between December 1978 and November 

 1979, despite the relative constancy of C,-DBT over the time period. 

 Results for lie Grande were similar to those for Aber Wrac'h but the 

 relative amounts of most components were greater. Between December 

 1978 and March 1979, there was a relative enrichment of all components 

 except C, -naphthalene. In March 1979, ratios were higher at 5-10 cm 

 than at 0-5 cm. Finer resolution around the depths of greatest Eh 

 change was attempted on samples collected in May 1980. There was evi- 

 dence of decreases in naphthalenes compared to earlier samples at all 

 depths, even though the concentration of C.-DBT was very high in all 

 samples. Relative decreases in C -phenanthrenes and DBT's were noted 

 in the 0-2 mm and 2-10 mm intervals. Except for C, -phenanthrenes , ra- 

 tios were always higher in the 3-4 cm interval. 



Hydrocarbon Biodegradation 



14 

 In initial experiments, various C-labelled aliphatic or aromatic 



hydrocarbons were incubated with surface sediments under aerobic condi- 

 tions, or with subsurface sediments under conditions designed to pre- 

 vent the exposure of obligately anaerobic bacteria to oxygen. The juc- 

 cess of anaerobic methods was evidenced by the reduction of SO, to 



171 



