Studies on the effects of oiled drill cuttings on marine sediments and on the hepatic cytochrome P-450 monooxygenases of plaice
Section 1 deals with the effects of four low toxicity oiled drill cuttings samples and one diesel oiled cuttings sample on marine sediments. The sediments were contained in 18 onshore tank systems and, after equilibration for 3 months, cuttings were added at levels comparable to those found at about 500m from North Sea oil installations. Tanks containing uncontaminated sediments acted as controls. All contaminated tanks showed identical changes in redox profiles, becoming most reduced after 3 months and gradually recovering thereafter. The highest sulphide levels were recorded in tanks with the highest total oil and n-alkane levels and these reached a peak after 3 months before declining. Levels were still elevated after 15 months in all tanks. Total oil concentrations declined in all tanks over the period of the experiment, n-alkanes and naphthalenes being degraded first. A substantial decline in nematode abundance was observed in all treated tanks in the first month following cuttings application, after which the decline in diesel and the highest oil loaded low tox tanks continued more gradually. Nematode numbers in low tox tanks with lower oil loadings showed fluctuations with abundances greater than that of controls at some points. Interstitial copepods were eliminated in all tanks within the first three months and controls showed general declines over the experimental period. End/opibenthic copepods showed a more varied response with low tox treatments exhibiting enhanced populations, those with lowest oil levels showing the greatest abundances. Abundances in control and diesel treated tanks remained low and constant throughout the experiment. In the first few days after cuttings treatment the greatest evacuation rates for the burrowing bivalve Tellina were recorded from diesel treated sediments followed by the low tox treatments in order of oil loading. It is concluded that the long and short-term impact of diesel cuttings is greater than that of low tox cuttings containing equal oil concentrations. Section 2 deals with the effects of chemical inducing agents, drilling fluid base-oils, oiled drill cutting contaminated sediments and time of year on the hepatic cytochrome P-450 dependant monooxygenase system of the marine flatfish plaice (Pleuronectes platessa). Intraperitoneal injection of 3-methylcholanthrene, Aroclor 1254 and isosafrole greatly enhance several hepatic monooxygenase activities, with each inducing agent producing a slightly different profile of activity both in the presence and absence of a naphthoflavone in vitro. Intraperitoneal injection of oils from diesel and a low tox drilling fluid also induced several monooxygenase activities, and these oils also differed slightly in their induction profiles. These results suggest that more than one isozyme is responsive to chemical induction in the livers of these fish. Induction of monooxygenase was also demonstrated in fish exposed to cuttings contaminated sediments. Plaice exhibit a seasonal cycle for the basal levels of monooxygenase activity. These results are compared with similar work on rats and other fish species and the implications for environmental monitoring, carcinogenicity and reproduction are discussed.