ACUTE AND SUBCHRONIC TOXICITY OF SEVERAL PHENOLIC UNCOUPLERS OF OXIDATIVE PHOSPHORYLATION IN FATHEAD MINNOWS (PIMEPHALES PROMELAS)

Abstract

Acute and early life stage_ (ELS) toxicity tests were conducted with fathead minnows (Pimephales promela$) and seven chemicals: 2,4-dinitrophenol (2,4-DNP), 4,6-dinitro-o- cresol (DNOC), 2-sec -butyl--4,6-dinitrophenol (dinoseb) 2,2' methylenebis (3,4,6-trichlorophenol) (hexac lorophene), 2 2'-­ methylenebis(4-chlorophenol) (dichlorophen), 3,5-dibromo-4- hydroxybenzonitrile (bromoxynil) and salicylanilide. Data on pentachlorophenol (PCP) were available in the literature. Two of the eight chemicals, bromoxynil and salicylanilide, were notably less toxic than the others in a plot of acute toxicity and lipophilic property (g-octanol/water partition coeffi­cient). Five of the chemicals appeared to share a common mode of toxic action, the uncoupling of oxidative phosphorylation: 2,4-DNP, DNOC, dinoseb, PCP, and hexachlorophene. Although dichlorophen toxicity in both acute and ELS tests appeared to be similarly dependent upon lipophilicity as the above five chemicals, its high dissociation constant indicated a somewhat different mechanism. A predictive model was presented for estimating sub-chronic toxicity based upon partition coefficient. The acute/chronic ratio for the five uncouplers based upon the ELS test endpoint of total biomass per chamber was 4.5 ± 1.0. Using the most sensitive endpoint for the four uncouplers for which discrete MATC estimates were obtained, the ratio was 16.2 + 7.8.