It is becoming clear that heavy metal toxicities can affect iron or magnesium meta-hlism in various organisms. In plants, chlorwis caused by several heavy metals can be correctkd by iron salts( 1 ) . There is also evidence that in plants as well as in some microorganisms parallel phenomena occur ( 2 3 , 4 ) , though only recently it has been demonstrated that the influence of iron and magnesium is characteristically different (5,6). Such interrelationships have not been studied as extensively in other species; however, in rats, zinc toxicity is known to result in deranged iron metabolism ( 7,8), though the growth inhibition in this case is not reversed by additional iron(9). In Corcyrn cepha-Zonica St., an organism with nutritional requirements similar to rats( 10,11), the observed effects af zinc toxicity resemble corresponding manifestations in rats( 12,13). In view of this, the influence of iron and magnesium on cobalt, nickel and zinc toxicities has been studied in Cmcyra larvae.Methods. The technic employed in rearing Corcyra larvae, preparation of diets and in determining growth has been described ( 1 2 ) . In all cases normal 10-1 5-day-old larvae were transferred in lots of 30 to 10 g of appropriate diets, consisting of w h a t flour supplemented with metal salts as shown in tables below. Growth was followed for 3 weeks thereafter. Controls on basal diet of wheat flour alone were always maintained, since the find weights of larvae were dependent upon their initial weights as well as on environmental conditions of temperature and humidity. Metal salts (analytical grade, Merck & Co., Ltd.) used were ZnS04 7Hz0, CoC12 = 6H20, NiS04 7H20, MgS04 7Hr0 and ferric ammonium citrate; all included to provide the required amounts of metals per ~ * Supported financially by the Council of Scient Present address: A. M . Jain College, Meenam-tific & Industrial Research, India. bakkan, Madras.TABLE I. Influence of Increasing Levels of Co 011 Growth of Corcyra Larvae. Co level Weeks of exp. Wt gain at diet) Start 1 2 3 endof exp. (mg/lO g Wt of 10 larvae (mg) Nil (control) 6.3 32.5 130.8 263.0 256.7 1.0 5.5 26.6 96.7 209.3 203.8 1.5 6.1 25.0 ' 75.7 183.3 177.2 2.0 5.2 16.2 44.4 78.0 72.8 2.5 5.7 14.5 41.1 75.1 69.4 3.0 5.2 14.2 40.2 65.2 60.010 g of diet. All experiments were repeated a t least 4 times.
Results.In Tables I and I1 are presented data on the effects of increasing levels of Co and Ni on growth of Corcyra larvae. Levels beyond the highest shown herein proved lethal, hence the corresponding values have not been included. The concentrations needed to produce about 60% inhibition of growth by the end of the experimen'tal period are close to 2 mg for both Co and Ni. By comparison with the data of Sivarama Sastry et aZ.( 1 2 ) , it would appear that Co and N: 1 are more toxic to Curcyra than Zn, which has to be administered at 9 mg level for similar results.In all subsequent studies, the influence of Fe and Mg has been studied using these concentrations of toxic metals, viz., 2 mg Co, 2 mg Ni and 9 mg Zn. Fe and Mg ...
