SUBACUTE TOXICITY OF A MIXTURE OF 9 CHEMICALS IN RATS - DETECTING INTERACTIVE EFFECTS WITH A FRACTIONATED 2-LEVEL FACTORIAL DESIGN

The present study was intended (1) to find out whether simultaneous ad ministration of nine chemicals at a concentration equal to the ''no-ob served-adverse-effect level'' (NOAEL) for each of them would result in a NOAEL for the combination and (2) to test the usefulness of fractio nated factorial models to detect possible interactions between chemica ls in the mixture. A 4-week oral/inhalatory study in male Wistar rats was performed in which the toxicity (clinical chemistry, hematology, b iochemistry, and pathology) of combinations of the nine compounds was examined. The study comprised 20 groups, 4 groups in the main part (n = 8) and 16 groups in the satellite part (n = 5). In the main study, t he rats were simultaneously exposed to mixtures of all nine chemicals [dichloromethane, formaldehyde, aspirin, di(2-ethylhexyl)phthalate, ca dmium chloride, stannous chloride, butyl hydroxyanisol, loperamide, an d spermine] at concentrations equal to the ''minimum-observed-adverse- effect level'' (MOAEL), NOAEL, or 1/3NOAEL. In the satellite study the rats were simultaneously exposed to combinations of maximally five co mpounds at their MOAEL. These combinations jointly comprise a two-leve l factorial design with nine factors (=9 chemicals) in 16 experimental groups (1/32 fraction of a complete study). In the main part many eff ects on hematology and clinical chemistry were encountered at the MOAE L. In addition, rats of the MOAEL group showed hyperplasia of the tran sitional epithelium and/or squamous metaplasia of the respiratory epit helium in the nose. Only very few adverse effects were encountered in the NOAEL group. For most of the end points chosen, the factorial anal ysis revealed main effects of the individual compounds and interaction s (cases of nonadditivity) between the compounds. Despite all restrict ions and pitfalls that are associated with the use of fractionated fac torial designs, the present study shows the usefulness of this type of factorial design to study the joint adverse effects of defined chemic al mixtures at effect levels. It was concluded that simultaneous expos ure to these nine chemicals does not constitute an evidently increased hazard compared to exposure to each of the chemicals separately, prov ided the exposure level of each chemical in the mixture is at most sim ilar to or lower than its own NOAEL. (C) 1997 Society of Toxicology.