Effect of heavy metals on the mulberry plant and silkworm

IV. The relation between different compounds of heavy metals and their toxicity, and an absorption of heavy metals by the silkworm, Bombyx mori L.

Abstract

The toxicity of compounds of heave metals (Cd, Zn and Cu), namelly chloride, oxide, sulfate or acetate, was not influenced by the type of compounds involved, but depended solely on the concentration of each heavy metal in the diet. Sulfide of heavy metals, however, had no toxicity against the silkworm, probably because CdS, CuS and ZnS was difficult to dissolve in the digestive juice. The concentration of heavy metals in the midgut epithelium was much higher than that in the blood or in the integument. Presumably, the toxicity of heavy metals was determined by the absorption in the midgut.
The absorption of a heavy metal by the silkworm was affected by the coexistence of other heavy metals. (1) The addition of Cd in a diet increased the absorption of not only Cd but also Zn, Cu and Pb. (2) The addition of Zn usually inhibited the absorptio of Cd, and moreover, the absorption of Cu was inhibited when Cd co-existed. (3) The addition of Cu accelerated the absorption of the co-existence of Zn. (4) Pb and As did not affect the absorption of another heavy metals. (5) The combination of metals which enhanced the injury of silkworm coincided with what increased the absorption of heavy metals.