AbstractBenomyl and carbendazim exhibited high acute toxicity to channel catfish,Ictalurus punctatus(Rafinesque), but were much less toxic to rainbow trout,Salmo gairdneri(Richardson), and bluegills,Lepomis macrochirus(Rafinesque). Changes in water temperature, pH, and water hardness altered the acute toxicity to fish of both compounds; however, the alterations were less marked in channel catfish than in rainbow trout. Carbendazim injected intraperitoneally was not readily metabolized and was the major radioactive product excreted by the three fish species. The rapid depuration of radiocarbon into the containment water and the storage of residues in the gall bladder of each species indicated that both branchial and biliary excretion were major pathways for the elimination of carbendazim by fish. In the carbendazim residue dynamic studies, rainbow trout had the highest uptake rate constant and bioconcentration factor of the three species. Much less carbendazim was accumulated by channel catfish than by the other two species, but this residue level (0.44 μg/g) appeared to be lethal after 48 h of exposure. The elimination rate constant and biological half‐life of carbendazim were similar for rainbow trout and bluegills; however, the elimination rate constant was larger and the biological half‐life shorter in channel catfish than in the other two species. It was concluded that benomyl and carbendazim were selectively toxic to channel catfish compared with rainbow trout and bluegill, but because of the instability of benomyl and the fast elimination of carbendazim, the possibility of these compounds excessively bioconcentrating in fish was re
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