Studies on Alkylphosphate Poisoning Part 1. Toxicity of Alkylphates

In this comparative study on the toxicity of various alkylphoshosphates, commercial substances in general use, the author obtained the following results. 1. LD(50) of alkylphosphates subcutaneously injected in the form of emulsion into mice is as follows (in mg/kg): in the case of TEPP it is 0.39 (0.33-0.45); Pestox-3, 8.2 (5.5-12.1); Ethylparathion, 10.0 (8.3-12.1); EPN, 42.8 (24.8-73.6); Methylparathion, 48.5 (23.6-99.5); Diazinon, 57.8 (37.8-88.5); Malathon, 221 (180-272): and Dipterex 252 (165-386). The toxicity of TEPP is markedly higher than others. The duration of survival after injection is within 45 minutes in the case of TEPP; 3 hours with Ethyl- and Methyl- parathion as well as with pestox-3; 6 hours with Malathon; 12 hours with EPN; 24 hours with Dipterex; and within 48 hours with Diazinon. 2. In the oral administration to mice LD(50) of Ethylparathion is 11.5 (8.1-16.4). showing hardly any great difference from that in the case of subcutaneous injection. Furthermore, in testing LD50 of Methylparathion emulsions manufactured by different makers, LD(50) ranges from 30.5 (24.8 -27.5) to 19.4 (14.4-26.0), showing a great difference though statistically not significant. From this it is obvious that the toxicity differs according to the emulsifying materials used by different makers. In addition, the toxicity of Methyl-parathion is definitely lower than that of Ethylparathion. Therfore, as the agricultural insecticide it is advisable to use the former. 3. After subcutaneous injection of alkylphosphates mentioned above and DFP into rabbits and examining the degree of inhibiton of blood cholinesterase, the order of such inhibition coincides exactly with that of LD(50) in the case of the mice mentioned above. This suggests that intoxication is mainly brought about by the inhibition of acetylcholinesterase and it is not much affected by other factor. Moreover, the period of time necessary for the inhibition is appoximately in proportion to the duration of time elapsed before death in the case of mice. 4. In measuring the amounts of parathion and p-nitrophenol excreted in the urine of the rabbits previously administered with Ethyl- and Methylparathion, the concentration and the duration of excretion are greater when the doses given are greater, but there is no other prominent characteristic