ABSTRACT
The acute toxicity of diesel oil associated with discharged cuttings became a major concern in the North Sea in the late 1970s. A different base oil, with a lower aromatic hydrocarbon content and lower acute lethality, began to be used to replace diesel oil in drilling muds in the early 1980s. Hinds et al. (1983) demonstrated that when fish and marine invertebrates were exposed to water-soluble fractions (WSF) of low toxicity oils the 96h LC50s were typically greater than 10 000 ppm as compared to LC50s of less than 2000 ppm for diesel oil. Studies conducted by Barchard & Doe (1984), Doe et al. (1984) and Hutcheson et al. (1984) on cuttings, base oils and drilling muds, respectively, collected from the Alma F-67 well drilled near Sable Island, indicated that discharged cuttings with their retained oil were toxic to selected marine invertebrates.
