ACUTE TOXICITY OF SEVERAL ORGANOPHOSPHOROUS INSECTICIDES AND PROTECTION BY CHOLINERGIC ANTAGONISTS AND 2-PAM ON ARTEMIA-SALINA LARVAE

The acute toxicity of chlorpyrifos, methylchlorpyrifos, parathion and methylparathion to three age classes of Artemia salina was determined. In general, A. salina 24-h old was less sensitive to these organophos phorous insecticides (OPI) than A. salina 48-h old and A. salina 48-h old was significantly more tolerant than A. sabina 72-h old, in contra st, chlorpyrifos was equally toxic to A. salina 48- and 72-h old. Ther e were some differences among the three age classes of A. salina in th e relative order of toxicity of OPI tested. The rank order of toxicity to A. salina 48-h old was methylparathion <parathion <methyl-chlorpyr ifos <chlorpyrifos, while to A. salina 24- and 72-h old it was methylp arathion=parathion <methyl-chlorpyrifos <chlorpyrifos. The protective effect of the cholinergic antagonists atropine, hexamethonium, pirenze pine and 11-(2-((diethyl-amino) iperidinylacetyl)-5,11-dihydro-6H-pyri do(2,3-b)-(1 ,4)-benzodiazepine-6-one (AF-DX 116) and a cholinesterase reactivating oxime 2-pyridine aldoxime methochloride (2-PAM) on the m ortality due to four selected OPI in Artemia salina 24-h old was inves tigated. The lethal action of OPI tested was completely prevented by p retreatment of Artemia salina 24-h old with 2-PAM (10(-5) M) and atrop ine (10(-4)M). However no concentration of hexamethonium, pirenzepine or AF-DX 116 protected 100% of the animals poisoned by LC(84) of the O PI selected, maximum protection obtained was 71 to 88%. In contrast, t he maximum inhibition of mortality obtained with AF-DX 116 pretreatmen t was about 55% because this compound was used at concentrations which were non toxic to control Artemia salina. Atropine, hexamethonium, pi renzepine, AF-DX 116 and 2-PAM afforded 50% protection (IC50) of Artem ia salina against mortality by LC(84) of the OPI selected at concentra tions in the range of 6.62x10(-7)-1.6x10(-6) M, 2.38x10(-4)-2.05x10(-3 ) M, 8.91x10(-7)-1.24x10(-6) M, 9.66x10(-8)-1.34x10(-7) M, and 1.95x10 (-8)-2.73x10(-8) M, respectively. Pretreatment of atropine plus 2-PAM to determine whether this combination afforded greater inhibition of t he lethality induced by four OPI tested than pretreatment with either atropine or 2-PAM alone was investigated. Atropine (10(-5) M) in combi nation with 2-PAM (10(-7) M) inhibited completely the acute toxicity o f all OPI tested, while the pretreatment with atropine (10(-6) M) plus 2-PAM at the same concentration gave a inhibition of mortality (about 62%) significantly greater than each antagonist alone (about 14 and 4 6%, respectively).