Statistically designed experiments to screen chemical mixtures for possible interactions

For the accurate analysis of possible interactive effects of chemicals in a defined mixture, statistical designs are necessary to develop clear and ma nageable experiments. For instance, factorial designs have been successfull y used to detect two-factor interactions. Particularly useful for this purp ose are fractionated factorial designs, requiring only a fraction of all po ssible combinations of a full factorial design. Once the potential interact ion has been detected with a fractionated design, a more accurate analysis can be performed for the particular binary mixtures to ensure and character ize these interactions. In this paper this approach is illustrated using an in vitro cytotoxicity assay to detect the presence of mixtures of Fusarium mycotoxins in contaminated food samples. We have investigated interactions between five mycotoxin species (Trichothecenes, Fumonisins, and Zearalenon e) using the DNA synthesis inhibition assay in L929 fibroblasts. First, a c entral composite design was applied to identify possible interactive effect s between mycotoxins in the mixtures (27 combinations from 5(5) possible co mbinations). Then two-factor interactions of particular interest were furth er analyzed by the use oi a full factorial design (5x5 design) to character ize the nature of those interactions more precisely. Results show that comb ined exposure to several classes of mycotoxins generally results in effect addition with a few minor exceptions indicating synergistic interactions. I n general, the nature of the interactions characterized in the full factori al design was similar to the nature of those observed in the central compos ite design. However, the magnitude of interaction was relatively small in t he full factorial design.