The acute toxicity of piperonyl butoxide was studied in animals by oral administration of the chemical in an emulsion and in undiluted form, and also in a deodorized petroleum oil spray concentrate containing pyrethrins; by subcutaneous injection of the undiluted chemical; and by application of the undiluted chemical, of oil solution containing it alone and in conjunction with pyrethrins, and of a water emulsion containing the chemical and pyrethrins, both to the eyes as a test for primary irritation, and to the skin in tests for primary irritation, chronic irritation and toxicity, and sensitization. The results of inhalation tests made by a cooperating laboratory are also cited briefly.
Small doses of a 5 per cent emulsion of piperonyl butoxide were not toxic to rats and rabbits fed respectively 6 and 3 doses at weekly intervals. Undiluted piperonyl butoxide was fatally toxic to rats and rabbits only when fed by stomach-tube in very large doses repressenting high dosage rates. The LD50 dose fell between 7.5 and 10 ml./kg. for rats, and between 2.5 and 5.0 ml./kg. for rabbits, and was apparently above 7.5 ml./kg. for cats and dogs.
A Special Spray Concentrate containing 20 per cent of piperonyl butoxide and 2.5 per cent of pyrethrins in base oil gave an oral toxicity LD50 of above 7.5 ml./kg. for both rats and rabbits, and seemed little if any more toxic for rats than deodorized petroleum oil alone. The relatively non-toxic and non-irritating nature of piperonyl butoxide was strikingly revealed by its lack of toxicity, and non-absorption, when injected subcutaneously into rats, and by the absence of marked eye or skin irritation when the undiluted chemical and oil solutions and a water emulsion of it were applied to the eye and skin of albino rabbits as a test for primary irritation. The undiluted chemical was mildly irritating to rabbit skin upon repeated application, but not oil solutions containing four per cent of it with and without pyrethrins, nor a water emulsion containing four per cent of it plus pyrethrins. Neither the undiluted chemical nor the solutions containing it caused sensitization. Tests at a cooperating laboratory showed no convincing evidence of toxicity in groups of rats exposed for 30 minutes a day on 24 days to abnormally heavy concentrations of insecticidal sprays and aerosols containing piperonyl butoxide and pyrethrins.
It is concluded that, since piperonyl butoxide is not a markedly toxic compound alone, and since solutions containing practical concentrations of it are relatively non-toxic and non-irritating to animals, there should be no appreciable toxicity or irritation hazards involved in the practical use of this compound in insecticides, and that piperonyl butoxide is one of the safest and least toxic insecticides.