Sorption of tetrachlorvinphos insecticide (Gardona) to the hemolymph of Periplaneta americana

Tetrachlorvinphos insecticide (Gardona, SI) 8447) sorbs to the hemolymph of the American cockroach via noncovalent bonding. The amount sorbed is dependent upon both the concentration of hemolymph and tetrachlorvinphos used. Acrylamide disc gel electrophoresis and Sephadex column chromatography of the complex revealed that tetrachlorvinphos binds to a variety of proteins in the hemolymph. No one protein serves as a specific carrier.These studies show that 80% of the LD₅₀ dose of tetrachlorvinphos can bind to the hemolymph contained in a single roach. The observed LD₅₀ value could then be considered as an inflated value, since the hemolymph can sorb large quantities of tetrachlorvinphos and thereby reduce the concentration of free compound available for inducing a toxic event. An alternative possibility, however, should not be overlooked. The binding of tetrachlorvinphos to hemolymph can be looked upon as a transport mechanism, whereby the compound is transported throughout the roach, to dissociate from the “carrier” proteins, and to penetrate into or through the cell membrane at the appropriate time. This would have the effect of actually enhancing the toxicity of the compound.