Preliminary assessment of the acute toxicity of malathion in animals

Laboratory studies were conducted to acquire information concerning the acute toxicity of malathion in animals under various conditions of exposure. The responses in rabbits and quail exposed to aerosols generated from technical grade malathion (95%) and approximating an ultra-low volume ground spray were compared with those from a 6% malathion/No. 2 fuel oil mixture simulating a high volume spray. Results indicate that technical grade malathion (95%) as an ultra-low volume spray and at effective insecticidal concentrations in particle sizes having a mass median diameter of about 12 µ is relatively nonhazardous compared to the possible toxic fuel oil effects of a 6% malathion/No. 2 fuel oil mixture with a mass median diameter of 25 µ. Based on blood plasma cholinesterase activity analyses, quail were more sensitive to equivalent malathion exposure concentrations than were rabbits. Oral administration of technical grade malathion to rabbits resulted in reduction of plasma and erythrocyte cholinesterase activity at dosages of 120, 300, and 600 mg/kg with death resulting from 1200 mg/kg.The opinions contained herein are those of the authors and should not be construed as official or reflecting the views of the Department of the Army or the Department of Defense. Mention of proprietary products is for the purpose of identification only and does not imply endorsement by the Department of the Army.The experiments reported herein were conducted according to the Guide for the Care and Use of Laboratory Animals (1972) as prepared by the Committee on Revision of the Guide for Laboratory Animal Facilities and Care, of the Institute of Laboratory Animal Resources, National Research Council.