MIXTURE TOXICITY OF NITROBENZENE AND TRINITROBENZENE USING THE MARINEBACTERIUM 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 a nd trinitrobenzene. An estimated median effective concentration (EC(50 )) and confidence interval were determined for each chemical. These ch emicals at their EC(50) were evaluated in combination and an additive index method was used to determine a numerical toxicology value. Combi nations at 20% intervals of the EC,, were performed using isopleths. T he isopleths employed were the isobole plot and the isobologram. Biolu minescent change was also determined and graphed for evaluation of tox icity. Statistical evaluation of isopleths and the additive index meth od were employed by incorporating confidence intervals. Bioluminescent change and isopleths suggest that mixtures of nitrobenzene and trinit robenzene are additive, while the additive index method is suggestive of synergism. Statistical evaluation between mixtures and single value s, using the z test, was in some cases different at the 5% level. Thes e data suggest that interaction of combinations should be evaluated an d described by multiple methodologies. Evaluation of these data sugges ts, in part, that one mixture is statistically different for antagonis m. This study supports the use of bioluminescent microbial toxicity te sts with various evaluative methodologies for the determination of mix ture interactions. (C) 1997 Academic Press.