The use of in situ benthic chambers to study the fate of oil in sublittoral sediments

Twelve in situ benthic chambers (2·2 m in diameter) were used to study the weathering of topped crude oil coated onto a submerged marine sediment over a period of about 440 days.The bulk (?80%) of the oil coated onto the sediment was lost during the first 40 days from both open and closed chambers. It is suggested that this oil was lost from the sediment partly into solution (perhaps after partial oxidation) or more likely, by droplet formation associated with the workover of particles by physical and biological processes. The weathering pattern of the oil remaining on the sediment was studied for a further 400 days and showed that the alkane fraction was biodegraded more rapidly than the naphthalenes, in agreement with the results from the Amoco Cadiz oil spill (Boehm et al., 1981) and that the alkyl substituted PAH homologues were biodegraded in preference to the unsubstituted parent compound. The hopane and sterane fingerprints did not change significantly over the 440 days of exposure, thus reinforcing their usefulness as long term markers of soil spills. In general the rates of biodegradation of the various classes of compounds were similar to those observed in other locations and suggested that the polycyclic aliphatics and the PAHs are very slow to degrade and will remain in the sediment for a considerable period of time.