INFLUENCE OF DAYLIGHT ON POTENTIAL BIODEGRADATION OF DIESEL AND CRUDE-OIL IN ANTARCTIC SEAWATER

The effects of daylight exposure on Antarctic coastal bacterial commun ities contaminated by diesel fuel and 'Arabian light' crude oil additi on were studied in artificial mesocosms during the austral summers of 1991-1992, 1992-1993 and 1993-1994 in the Terre Adelie land area. In o rder to study the possible influence of photo-oxidation, two sets of e xperiments were conducted in covered and non-covered batches. Daily sa mpling allowed regular surveys of the changes of total bacterial abund ance, mean cell volumes, saprophytic and hydrocarbon-utilizing bacteri al communities. The results clearly revealed a significant response of the Antarctic bacterial community to crude oil addition. Two orders o f magnitude increases were observed after contamination. Concomitant e nrichments of saprophytic and hydrocarbon-utilizing bacteria occurred during these periods. Hydrocarbon-utilizing bacteria ranged from 0.001 % of the total community before contamination to more than 80% after 2 weeks of contamination with crude oil. Chemical analysis of the resid ual hydrocarbon fraction after 5 weeks of contamination confirmed this potential biodegradation. Solar radiation had no measurable effect up on crude oil-contaminated seawater. In contrast, there was a clear tox ic effect upon bacterial communities contaminated with diesel. Data su ggest that the initial state of the bacterial communities can play a m ajor role in the potential biodegradation. Some surface bacterial asse mblages seem to demonstrate a better resistance to solar radiation tha n deeper ones. (C) 1998 Elsevier Science Ltd. All rights reserved.