Research Product

Chemical characterization and toxicity of oil drilling fluids were investigated by the Edgerton Research Laboratory from Oct. 1, 1979 to Aug., 1983 as part of a comprehensive research program sponsored by the U.S. Environmental Protection Agency to determine fate and effects of such fluids in the marine environment. Drilling muds used were supplied by EPA, the Petroleum Equipment Suppliers Association, and the American Petroleum Institute. The drilling muds were designated 'May 15,' 'May 29,' 'Sept. 4,' 'Exxon,' 'Gilson,' 'Mobile Bay,' 'Jay Field,' and 'PESA.' Investigations during the first year centered on the chemical composition and acute toxicity of drilling muds, and the effects of drilling muds on recruitment of benthic organisms. In the second year, studies focused on toxicity testing with planktonic copepods, chemical characterization of toxicity test phases, bioaccumulation studies, and effects of muds on larval and adult benthic organisms. Investigations during the third and fourth year examined sublethal effects of drilling fluids on clam larvae, trace metal and organic constituents in both drilling fluids and toxicity test-phases, and preliminary development of a drilling fluid solid phase toxicity test. Toxic components of used drilling muds tested were present as dissolved components or associated with very slowly settling particles. Some used drilling muds contained lipophilic fractions that were similar to hydrocarbons found in #2 fuel oil in the liquid fraction and suspended particulates fraction and contained #2 fuel oil in whole muds. Muds that contained those components were more toxic than those that did not. Juvenile copepods (Acartia tonsa) were not more sensitive to toxic drilling mud solutions than adults of this species. In general, Cancer irroratus larvae appeared to exhibit toxicity responses to drilling muds that were similar to copepods tested. Arrested shell development induced by exposure to drilling muds appeared to be a sensitive indicator of stress in bivalve larvae. Total chromium concentration showed no correlation to toxicity in drilling muds that were tested; however, the highest concentrations of Cr(VI), the most biologically toxic form of chromium, occurred in test phases that exhibited the greatest toxicity to Mercenaria mercenaria larvae. The muds designated 'May 15' and 'Sept. 4' appeared to be relatively non-toxic to Pseudopleuronectes americanus and to Menidia menidia, although the 'May 15' mud was toxic to Neomysis americana and to Acartia tonsa. A study of effects of drilling mud on invertebrate recolonization of defaunated sediment showed that recolonization decreased in drilling mud layered on top of sediment when muds were mixed with sediments. Capitella capitata was much more numerous in recolonization sediments that contained drilling mud. Test results showed that methods used to prepare drilling mud test media affect the apparent toxicity of the muds.