Quantitative studies on marine biodegradation of oil, III. Comparison of different crude oil residues and effects of sea water source

Abstract

A respirometric method, which had been used previously for studying the degradation of Kuwait crude oil residue in local sea water, was used again with two different crude oil residues as substrates. However, the differences found appeared to be due mainly to the sample of sea water rather than to the type of oil. This may be due to microbial adaptation to the nutrient regimes of winter sea water contrasted with summer sea water. The supply of available nitrogen appeared to be the limiting factor at any given temperature, as was the case in the earlier work, but nitrate was not reduced to such very low concentrations. Also in comparison with this earlier work, there was rather less oxygen uptake in proportion to nutrient uptake, particularly at the higher temperatures, temperature having less effect on this relationship. About half of each crude oil residue appeared almost undegradable. Similar changes in oil properties occurred, but in the case of Forties (North Sea) oil residue, the relative density did not come to exceed that of sea water. Further work is required to find whether degradation and other weathering processes will eventually cause it and other North Sea oils to sink.