RESUMO
The acute toxicity of fonofos and phosphamidon on three age classes of Artemia salina was evaluated. An increase in toxicity of these organophosphorous (OP) insecticides was found following longer development of A. salina. The effects of pretreatment with the nonselective muscarinic antagonist atropine, the two reversible acetylcholinesterease inhibitors physostigmine and pyridostigmine, and the cholinesterase-reactivating oxime 2-pyridine aldoxime methoiodide (2-PAM), as individual and combined pretreatments, on OP-induced lethality in 24 h Artemia were also investigated. The lethal action of both OP insecticides was prevented by pretreatment of 24 h Artemia with atropine and 2-PAM, while physostigmine proved ineffective against intoxication with both OP insecticides and pyridostigmine exhibited a low synergic effect. In both cases, the inhibitory effects of combinations of atropine (10(-5)M) plus 2-PAM were greater than those elicited by either drug alone, with the maximum protection afforded being 100%. Combined pretreatment of atropine (10(-5)M) plus physostigmine practically abolished the lethal effects induced by both insecticides. Pretreatment with 2-PAM (10(-6)M) plus physostigmine afforded maximal protection of 100% and 76% on the lethality induced by fonofos and phosphamidon, respectively. The data obtained suggest that the combination of atropine plus 2-PAM or physostigmine and the combined pretreatment of 2-PAM plus physostigmine are effective in the prevention of the lethal effects induced by fonofos and phosphamidon in A. salina larvae.