The fate of fenitrothion microcapsule and chlordane in carp was studied using the corresponding ¹⁴C preparation. Upon single oral administration, chlordane translocated and mainly distributed in carcass of fish, no significant excretion from fish body being observed. Whereas, microcapsulated fenitrothion was rapidly excreted from fish body, 96.9% of the applied dose being recovered as unchanged parent compound in surrounding water after 24hr. Most of the ¹⁴C excreted remained inside the capsule. Thus, it was indicated that the microcapsulated fenitrothion was excreted from fish body without uptake or metabolism in fish.

View full abstract

Kayatack MC, developed by Nippon Kayaku Co., Ltd., is an aqueous suspension of microcapsulated formulation containing 25% of chlorpyrifos as an active ingredient. Acute toxicity and inhibition effect on cholinesterase activity of Kayatack MC(MC) in rats and mice were evaluated and compared with those of the conventional emulsifiable concentrate formulation (EC). Acute per oral and per cutaneous studies revealed a significantly reduced toxicity for MC. The per oral LD₅₀ of EC was 133mg/kg on a basis of active ingredient (a.i.)for male rats. Neither mortality nor toxic symptoms were observed in rats and/or mice treated with MC at the maximum applicable dose, i.e., 5, 000mg(a.i.)/kg in per oral and 500mg(a.i.)/kg in per cutaneous administrations. The inhibition effect of MC on cholinesterase activity was demonstrated weaker than that of EC. Blood cholinesterase activities in rats after a single per oral administration of MC or EC revealed that MC was 100 times less toxic than EC, Blood cholinesterase activities in rats treated with repeated per oral administrations of MC for 14 days were gradually reduced during several days in parallel with the treatments and maintained thereafter a constant level for each administered dosage level. The maximum safety dose or no observable effect level on the inhibition of cholinesterase activity for rats at the repeated administrations of MC was estimated to be 62.5mg(a.i.)/kg/day. The repeated administrations of Kayatack MC at the maximum safety dose exerted no adverse effects on the recovery of inhibited cholinesterase activity in rats.

View full abstract