Effect of crude oil on denitrification and sulfate reduction in marine sediments

The denitrifying activity was measured in different types of sediment from the Mediterranean coast of France before, and after, a massive contamination (30–100 g kg^-1 sediment) of hydrocarbons. A closed system was used in order to maintain anoxic conditions and to control substrates and gaseous products concentrations. We have demonstrated that the respiratory metabolism was inhibited in all cases following an incubation time of 20 to 50 days. At this time, the addition of lactate restore the denitrifying activity. The inhibitory effect of crude oil was not related to an alteration of bacterial cells, but to changes in environmental conditions allowing denitrification. The presence of hydrocarbons in the sediments causes a decrease in the redox potential and a concomitant stimulation of the sulfate reduction.