Petroleum distillates suppress in vitro metabolic activation: Higher [S‐9] required in the salmonella/microsome mutagenicity assay

Abstract
To determine if standard conditions used in the Salmonella/mammalian microsome mutagenicity assay could reliably screen complex petroleum samples, two high‐boiling (700–1,070°F) distillates and their separated aromatic fractions were tested. The initial mutagenic activities were inconsistent with the samples' known polyaromatic hydrocarbon (PAH) contents and observed potencies in a dermal carcinogenesis bioassay. A significant mutagenic response was observed only at S‐9 concentrations 5 to 10 times higher than those used in the standard assay, supporting the use of elevated levels of S‐9 in the Salmonella/microsome assay to assess the carcinogenic potential of petroleum‐derived materials. All four samples masked the expected mutagenic activity of added PAHs (benzo[a]pyrene and perylene). Data suggested that petroleum distillates suppress the functional efficacy of the S‐9; possible mechanisms are discussed.

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