Mixture toxicity of nitrobenzene and trinitrobenzene using the marine bacterium Vibrio harveyi as the test organism

Vibrio harveyi a bioluminescent marine bacterium, was used to evaluate combined or mixture toxicity of two organic compounds, nitrobenzene and trinitrobenzene. An estimated median effective concentration (EC(50)) and confidence interval were determined for each chemical. These chemicals at their EC(50) were evaluated in combination and an additive index method was used to determine a numerical toxicology value. Combinations at 20% intervals of the EC,, were performed using isopleths. The isopleths employed were the isobole plot and the isobologram. Bioluminescent change was also determined and graphed for evaluation of toxicity. Statistical evaluation of isopleths and the additive index method were employed by incorporating confidence intervals. Bioluminescent change and isopleths suggest that mixtures of nitrobenzene and trinitrobenzene are additive, while the additive index method is suggestive of synergism. Statistical evaluation between mixtures and single values, using the z test, was in some cases different at the 5% level. These data suggest that interaction of combinations should be evaluated and described by multiple methodologies. Evaluation of these data suggests, in part, that one mixture is statistically different for antagonism. This study supports the use of bioluminescent microbial toxicity tests with various evaluative methodologies for the determination of mixture interactions. (C) 1997 Academic Press.