Relationship between acute and chronic exposures in mutagenicity studies in mice.

The relationship between acute and chronic exposures in mutagenicity studies on mammals still lacks experimental data that might permit the decision whether or not the long-term exposures are of significance mutagenicity testing. Fractional application of TEPA, THIOTEPA, EMS, cyclophosphamide and sodium arsenite was made in experiments with mice, by using the dominant-lethal test and cytogenetic analysis of bone marrow. In most experiments the repeated application yielded the same or higher genetic injury than the same total dose at a single application. Negative results are discussed in relation to the threshold dose and the different sensitivity of the germ-cell stage. Possible interaction of mutagens was also studied by analysing the combined effect of a long-term exposure to sodium arsenite, which probably affected the repair mechanism, and of a single dose of TEPA. It is concluded that the present stage of knowledge requires acceptance of the opinion that the genetic risk induced by chronic exposure to a chemical is as serious as that induced by acute exposure.