The effects of DDT, dieldrin and 2,4-D on amphibian spawn and tadpoles

Abstract

Spawn of the common frog ( Rana temporaria) or tadpoles of the common frog, common toad ( Bufo bufo) or smooth newt ( Triturus vulgaris) were maintained for 24 or 48 h in amphibian saline to which pesticide had been added. After treatment they were transferred to fresh saline. Tadpoles that hatched from treated spawn and tadpoles that had been treated were observed for up to three weeks. DDT did not penetrate well-developed spawn and was only detected in hatching tadpoles after freshly laid spawn had been treated. These tadpoles became hyperactive after their external gills were lost. In the experiments in which frog and toad tadpoles were exposed to DDT, tadpoles were most susceptible either just before or just after developing hind limb buds and at these and later stages they became hyperactive when tissue concentrations reached 2–3 and 3–4 ppm respectively. During tail resorption small frogs, unlike small toads, were susceptible to tissue residues of DDT that had been acquired during larval development. At every stage of development, toads were more resistant to DDT than frogs, some toad tadpoles surviving despite tissue concentrations of >300 ppm. After treatment with DDT, DDe was often detected in newt tadpoles and in frog and toad tadpoles with hind limbs. Dieldrin caused lower mortality amongst tadpoles than DDT and had less effect on behaviour, although, like DDT, it produced distinct behavioural changes and morphological abnormalities. Only frog tadpoles were treated with 2,4-D. It had no visible effect and no tissue residues could be detected even after treatment in 50 ppm for 48 h.