TOXICITY OF HYDROLYSIS AND BREAKDOWN PRODUCTS OF MALATHION TO FATHEAD MINNOW (PIMEPHALES PROMELAS, RAFINESQUE)

Malathion undergoes hydrolysis in aqueous solutions; the products derived from the reaction are dependent upon the pH of the medium. It was the purpose of this investigation to evaluate the toxicity of the products of malathion hydrolysis in the fathead minnow, Pimephales promelas. The studies were conducted by toxicity bioassays of 96 hr duration and continuous exposure tests of 14 day duration. The results of the experiments demonstrated the following: 1. (1) the basic hydrolysis product, diethyl fumarate, was more toxic than malathion to the test species; 2. (2) a pronounced synergistic effect was demonstrated between malathion and its two basic hydrolysis products; and 3. (3) continuous exposure decreased the TLm concentration of malathion and its basic hydrolysis products. © 1969.