experimental vials during incubation, and against the possibility that 

 compounds contaminating radiolabelled hydrocarbons were the sources of 

 C-gases. The results of these experiments were consistent with the 

 conclusion that slow anaerobic oxidation of some petroleum hydrocarbons 

 may be occurring in anoxic sediments polluted with AMOCO CADIZ oil. 



A second major objective of this work was to study the effects of 

 AMOCO CADIZ oil on the dominant anaerobic processes within sediments. 

 As mentioned above, oiling was heaviest in the surface sediments where 

 anaerobic processes occurred at maximum rates. We were unable to moni- 

 tor any immediate effects of the AMOCO CADIZ spill because our first 

 sampling trip was in December 1978, 9 months after the spill. We were 

 also limited by the lack of any data on the microbial activities in our 

 sampling sites prior to the oil spill. However, by examining unoiled 

 sites, we were able to see if any major alterations in chemistry and 

 activities had occurred in the oiled sediments. 



Comparisons between oiled and unoiled sites revealed lower rates 

 of sulfate reduction in oiled beach and marsh sediments. It is not 

 possible, however, to attribute these differences to the presence of 

 AMOCO CADIZ oil because 1) inhibition was not observed at all sites 

 where oiling occurred, 2) the magnitude of differences observed was 

 small (largest difference was 51% of the control), and 3) other dif- 

 ferences between sites which could influence sulfate reduction rate 

 (e.g., organic loading) were unknown. It is also difficult to inter- 

 pret whether rates measured in control sites were typical of unpolluted 

 sediments, as hydrocarbon analyses revealed a previous history of oil- 

 ing in control sediments. No differences in methane production or ace- 

 tate metabolism were, noted. Although preliminary results demonstrated 

 small amounts of CH, production from [2- C]-acetate at the lie 

 Grande oiled site (Winfrey and Ward, 1981), this observation was not 

 confirmed in subsequent work. Sulfate reduction always dominated me- 

 thane production and acetate was metabolized only to CO . The lack 

 of profound differences in comparative experiments performed 9-18 

 months following the spill, suggest that no long-term effects on an- 

 aerobic processes occurred in these sediments. 



We examined the effect of an unweathered oil on anaerobic pro- 

 cesses in order to determine whether any short-term effects of oiling 

 might have occurred. A fresh light Arabian crude oil did not signi- 

 ficantly effect sulfate reduction or methane production, but inhibited 

 acetate oxidation 93-97% in oiled and control sediments from lie 

 Grande. The ability of the crude oil to inhibit acetate oxidation was 

 reduced in oil samples which had been evaporated to increasing degrees. 

 Highly volatile molecules such as toluene and benzene caused 91-92% 

 inhibition in control sediments and 65-73% inhibition in oiled sedi- 

 ments. The data suggest that volatile components of the oil may be re- 

 sponsible for inhibitions to acetate oxidation. However, mousse col- 

 lected near He Grande 44 days after the AMOCO CADIZ spill also inhi- 

 bited acetate oxidation at the He Grande control site. This mousse 

 sample had lost most of its more volatile components, but was appar- 

 ently not extensively altered by biodegradation. Inhibitions were al- 

 ways greater at the control site than at the oiled site. Thus, the 

 oiled area of the marsh appears to have become less sensitive to the 



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