Uptake and Effects on Detoxication Enzymes of Cypermethrin in Embryos and Tadpoles of Amphibians

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Abstract

A number of factors have been suggested for recently observed amphibian decreases, and one potential factor is pesticide exposure. We studied the uptake and effects of environmentally relevant concentrations of the pyrethroid insecticide cypermethrin on two different amphibian species, Bombina variegata and Rana arvalis. The uptake from water of 14C-labeled cypermethrin (0.4 μg/L) by eggs and tadpoles of B. variegata was investigated. After 24 hours of exposure, 153.9 ng cypermethrin/g fresh weight were found in embryos, thus indicating that the jelly mass of the eggs does not act as a sufficient physical barrier to protect embryos from exposure to this compound. Uptake of cypermethrin into tadpoles of both species and in all exposed individuals caused dose-dependent deformities; behavioral abnormalities such as twisting, writhing, and coordinated swimming; and mortality. In tadpoles of B. variegata and R. arvalis, the activity of microsomal and cytosolic glutathione S-transferase (mGST and sGST, respectively) were measured after treatment with cypermethrin. Activities of both GST systems increased significantly with increasing duration and concentration of cypermethrin exposure, with the reaction seeming stronger in B. variegata than in R. arvalis tadpoles. Alpha-cypermethrin—a racemic mixture of two cis isomers of cypermethrin—induced a stronger enzymatic response in the cytosolic fraction of R. arvalis tadpoles than cypermethrin at the same concentration. The observed physical and behavioral abnormities caused by environmentally relevant concentrations of cypermethrin indicate that despite detoxication of the chemical via GST-system contamination of ponds by cypermethrin could result in adverse effects on the development of amphibian embryos and tadpoles.