Crude oil was incubated with raw and sterile river water samples and assayed for mutagenic activity by the Ames test to determine the ability of naturally-occurring freshwater microorganisms to form mutagenic biodegradation products from crude oil. River water samples supplemented with inorganic salts were incubated with one percent crude oil in Erlenmeyer flasks for 1-6 weeks and 4 and 20C with shaking. Replicate flasks were extracted at various time intervals with 1,1,2-trichloro-1,2,2-trifluoroethane, the solvent evaporated and the residues taken up in dimethyl sulfoxide for mutagenicity testing. The extracts were assayed for mutagenic activity by the plate incorporation method of the Ames test with Salmonella tester strains TA 100, TA 1535, TA 1537, TA 1538 and TA 98. Mammalian liver microsomes were not used in the mutagenicity test system as the oil-degrading microorganisms constituted the enzyme activation system in this study. Preliminary studies in Colorado with lagoon water and Black Hollow, Colorado crude oil showed that frameshift mutagens were produced during microbial degradation of the oil. Studies in Alaska with Chena River water and Prudhoe Bay, Alaska crude oil showed that both frameshift and base-pair substitution mutagens were present in the oil after microbial degradation. Mutagenic activity was not detected in either of the crude oils tested prior to incubation. The presence of mutagenic products may be related to the presence of mutagenic products in microbiologically-degraded crude oil.

Caption title. "Sep. 1981." "EPA-600/3-81-053." Microfiche.