There are many types of organophosphorus pesticides, which are divided into three categories according to their toxicity: highly toxic, moderately toxic, and lowly toxic. The oral median lethal dose (mg/kg) of organophosphorus pesticides commonly used in my country for rats is as follows: parathion (1605) is 3.5-15 mg; demeton (1059) is 4-10 mg; phorate (3911) is 2.1-3.7 mg; ethsulfate is 4 mg; sulfotep is 5 mg; phosphamidon is 7.5 mg (the above are highly toxic). Dichlorvos is 50-110 mg; methyl parathion (methyl 1065) is 14-42 mg; methyl demeton (methyl 1059, 4044) is 80-130 mg (the above are moderately toxic). Trichlorfon is 450-500mg; dimethoate is 230-450mg; malathion (4049, Marathion) is 1800mg; dibromophos is 430mg; fenitrothion (fenthion) is 250mg (the above are low-toxic). A small amount of highly toxic organophosphorus pesticides can cause poisoning, and a large amount of low-toxicity pesticides entering the body can also cause harm. The toxic and lethal doses of organophosphorus pesticides in the human body vary greatly. The symptoms of poisoning are severe and the onset is rapid if the organophosphorus pesticides are inhaled through the digestive tract at a concentration higher than normal, or absorbed through the skin; but if a large amount or too high a concentration of organophosphorus pesticides is inhaled, the disease may occur within 5 minutes and the death may occur quickly.