Quantitative aspects of metal ion content and toxicity in Drosophila

As a basis for both a genetic and a biochemical approach to a study of metal ion effects, a method for quantitating the toxic response of Drosophila to metal ions was developed. The response to 13 metal ions has been examined, including several chemical groups from the periodic table: the IIb ions Zn2+, Cd2+, and Hg2+; the IIa ions, Be2+, Mg2+, Sr2+, and Ba2+; the transition elements, Ni2+, Cu2+, Co2+, and Mn2+: and trivalent ions, Y3+ and Cr3+. The standard test procedure provides estimates of the median lethal concentration (LC50) and the range of the tolerance distribution both of which are obtained by the method of probit transformation. Range is defined as the change in concentration between the LC2.5 and the LC97.5. Estimation of range as the measure of the limits of the tolerance distribution was utilized to measure variation in the response to metals with time. Genetic characterization of strains will require strains of flies without overlapping tolerance ranges. Although there was a general trend of increasing values of range with increasing LC50 values, the exceptions (e.g., Cr3+ and Be2+) indicated that several factors may be involved in determining the range of lethal responses. Elemental analyses have been performed on flies before and after metal ion treatments to establish the amount of metal ion taken up and baselines for comparison. This study provides additional evidence that Drosophila is an appropriate organism for the study of specific biochemical alterations induced by metals, e.g., the cadmium-induced increase in Q(+)tRNAs.