Abstract
Penetration and dermal accumulation of topically applied vamidothion, carbaryl and fenvalerate were investigated in the common cutworm epidermal tissue mounted on a diffusion cell system. At low doses, carbaryl showed the highest penetration rate followed by vamidothion. The penetration rate of fenvalerate, in contrast, was extremely slow. At high doses, the penetration rate decreased especially with carbaryl and fenvalerate. The dose-dependent penetration was analysed with Michaelis-Menten type kinetics. The maximum penetration rate (V) and Michaelis constant (Km) calculated by computer simulation for vamidothion, carbaryl and fenvalerate were 0.021, 0.015 and 0.0029μg/hr, and 0.072, 0.016 and 0.29μg, respectively. Besides the Michaelis-Menten type pathway, an additional process under first order kinetics was proposed; the first order rate constant, kn was 42, 6.5, and 0.74×1C-3 hr-1 for vamidothion, carbaryl and fenvalerate, respectively. At a low dose (0.1μg/individual), the radioactivity accumulated in the dermal tissue did not show a significant variation, the ratio being within 10 to 20% of the applied dose regardless of insecticides. The ratio decreased as the applied dose increased especially with fenvalerate. Effects of combination of these insecticides on penetration and tissue accumulation were investigated. Vamidothion decreased both penetration and tissue accumulation of 14C-carbaryl, while vamidothion altered only tissue accumulation of 14C-fenvalerate. The inconsistent interaction implied that factors other than simple diffusion governed by Fick's low had affected insecticide penetration through the insect cuticle.
