Baseline bio-accumulation concentrations and resulting oxidative stress in Synodontis zambezensis after an acute laboratory exposure to 4,4′-DDT

Abstract

The use of 1,1′-(2,2,2-Trichloro-1,1-ethanediyl)bis(4-chlorobenzene) (DDT) as a pesticide for the control of insects vectors responsible for the spread of many life threatening diseases was officially banned in 1972 by the United States Environmental Protection Agency (USEPA). It was banned throughout the world, in most developed countries, because of the toxic effects it causes in wildlife, including birds and fish. However, DDT is still used in approximately 43 African countries, including South Africa, to control the spread of malaria. The lipophilic nature of DDT and therefore its persistence in the environment makes it extremely important for laboratory based studies to be conducted in an effort to evaluate the accumulation potential and possible physiological effects of DDT in aquatic organisms under controlled conditions. The aim of this study was to establish baseline bioaccumulation concentrations within Synodontis zambezensis following an acute exposure to 4,4′-DDT. The three metabolites analysed were 4,4′-DDE, 4,4′-DDD and 4,4′-DDT. None of the 2,4′-isomers were analysed in this study since the acute exposure used a solution of 98.7% pure 4,4′-DDT (Sigma-Aldrich PESTANAL®, Analytical Standard, CAS-No 50-29-3, Batch number SZBE057XV) and not a mixture of 4,4′-DDT and 2,4′-DDT as found in technical grade DDT. Soxhlet extraction of tissue samples and liquid/liquid extraction of water samples followed by analysis through Gas-chromatography mass-spectrophotometry was completed. Mean 4,4′-DDE, 4,4′-DDD and 4,4′-DDT concentrations ranged from 15.34 ng/g to 45.34 ng/g, 28.16 ng/g to 63.25 ng/g and 28.64 ng/g to 96.21 ng/g respectively. All of the accumulated concentrations fell within environmentally relevant concentrations with no input through the food web. The accumulated concentrations of 4,4′-DDT and its three metabolites resulted in oxidative stress responses within the gills and the liver tissue of S. zambezensis. Significant differences (p ≤ .05) were observed between malondialdehyde (MDA) and reduced glutathione (GSH) within the liver and in superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) in the gills