Acute Toxicity and Cholinesterase Inhibition in Chicks Dosed Orally with Organophosphate Insecticides

Abstract

Acute toxic effects of three commonly used insecticidal preparations of the organophosphates chlorpyrifos, diazinon, and dichlorvos were examined in mixed breed broiler chicks, and cholinesterase activity in plasma and brain were measured. The acute (24 h) oral median lethal doses (LD 50 ) of chlorpyrifos, diazinon, and dichlorvos were 10.79 mg kg -1 , 6.32 mg kg -1 , and 6.30 mg kg -1 , respectively, as determined by the up-and-down method in chicks. Signs of cholinergic toxicosis in the chicks appeared within two hours after dosing, and they included salivation, lacrimation, gasping, frequent defecation, drooping of wings, tremors, convulsions, and recumbency before death. Halving the oral LD 50 of chlorpyrifos (5 mg kg ) caused immobility and wing drooping, but not the clinical signs of cholinergic toxicity. However, at full LD 50 doses of these insecticides, chicks showed clinical signs of cholinergic toxicity similar to those seen in the LD 50 experiments. Two out of six chicks died within two hours after treatment with LD 50 doses of chlorpyrifos and dichlorvos, whereas LD 50 dosing with diazinon caused death in three out of six chicks. Compared to control values, the insecticides reduced plasma and whole brain cholinesterase activities by 29 % to 84 % and 18 % to 77 %, respectively, depending on the dose. The decrease in plasma cholinesterase correlated well (r = 0.82) with that of the brain. These data suggest that organophosphate insecticides administered orally at LD 50 doses induce clinical signs of cholinergic poisoning and concurrently reduce brain and plasma cholinesterase activities in chicks.

Acute Toxicity of Veterinary and Agricultural Formulations of Organophosphates Dichlorvos and Diazinon in Chicks

“…Acute (24-hour) LD 50 of dichlorvos and diazinon in the veterinary and agricultural formulations determined in our study are generally in agreement with other reports (18,19,(23)(24)(25)30). In our study, the agricultural formulation of dichlorvos appeared to be more lethal than the veterinary one (6.51 vs. 11.1 mg kg -1 , respectively).…”

“…The doses of the OP were chosen so that they did not cause acute signs of cholinergic toxicosis or death in chicks within one hour after the dosing. One hour after each OP dosing, chicks were euthanised to obtain the plasma and whole brain for determination of ChE activity by an electrometric method described earlier (18,19,27). All samples were kept at -20 °C, pending ChE analysis within one week.…”

“…Whole brain was homogenised in a pH 8.1 barbitalphosphate buffer solution as described earlier (18,19,27). Plasma and brain ChE activity was determined using the electrometric method as described in our earlier study (18): the reaction mixture in a 10-mL vial contained 3 mL distilled water, 0.2 mL plasma or whole brain homogenate and 3 mL of pH 8.1 buffer described above.…”

“…The toxicity of OP insecticides varies between animal species. In vivo avian studies usually involve chicks (17)(18)(19). The diagnostic or biomarker endpoint of OP poisoning in the avian species is the reduction of ChE activity in the plasma, serum, or brain (16,(20)(21)(22).…”

Acute Toxicity and Neurobehavioral Effects of Diphenhydramine in Chicks

“…Thirty minutes after the diphenhydramine treatments mentioned above, the chicks were euthanized to obtain the plasma and whole brain for determining the cholinesterase activity by an electrometric method (Mohammad, 2007;AlBadrany and Mohammad, 2007;Mohammad et al, 2008). The whole brain was homogenized on an ice bath by a glass homogenizer in a pH 8.1 barbital-phosphate buffer solution (1.237 g sodium barbital, 0.163 g potassium dihydrogen phosphate and 35.07 g sodium chloride/L of distilled water) at 3 ml/100 mg wet weight (Al-Badrany and Mohammad, 2007;Mohammad, 2007).…”