Comparative susceptibility to atrazine of three developmental stages of Bufo arenarum (amphibia: anura) and influence on metamorphosis: non-monotonous acceleration of the time to climax and delayed tail resorption

BRODEUR, J.C; SVART1,G; PEREZ-COLL,C.S; MARINO, D.J.G; HERKOVITS, J.

Aquatic Toxicology

Elsevier

Año: 2009 p. 161 - 170

0166-445x

Acute and subchronic toxicity of atrazine was evaluated in embryos (stage 4) and in premetamorphosis(stage 25) and prometamorphosis (stage 38–39) larvae of the common South American toad Rhinellaarenarum (Anura: bufonidae). The influence of atrazine on the last stages of metamorphosis was alsoexamined by exposing prometamorphosis larvae until completion of metamorphosis. Results obtainedrevealed that larvae in premetamorphosis are more sensitive than larvae in prometamorphosis and thatthese are, in turn, more sensitive than embryonic stages. Indeed, concentrations of atrazine as high as30 mg/L had little effects on embryonic stages, the embryos surviving and developing in a similar manneras controls. LC50s of premetamorphosis larvae equaled 27.16, 7.03 and 2.32 mg/L of atrazine after 4, 14and 21 days of exposure, respectively, compared to LC50s values of 18.27 and 14.43 mg/L after 14 and21 days of exposure for larvae in prometamorphosis. In experiments with premetamorphosis larvae, therange of tested concentrations was extended to very low concentrations (down to 0.0001 mg/L) to examinewhether recent findings of greater mortality at lower doses than at higher doses were also observedin R. arenarum but no such pattern was found. Exposure of prometamorphosis larvae to concentrationsof atrazine of 10 mg/L and above widely prevented completion of metamorphosis and caused importantmortality. Alternatively, whereas all animals eventually completedmetamorphosis when exposed to concentrationsof atrazine between 0.1 and 5 mg/L, the timings of metamorphosis were altered starting from0.1 mg/L, the lowest concentration tested. Indeed, a significant decrease in the time needed for 50% ofthe larvae to reach the metamorphic climax (stage 42) was observed within this range of atrazine concentrations,the response presenting a U-shaped non-monotonic dose–response curve. Larvae exposedto these concentrations of atrazine also needed significantly more time for completing tail resorption,this effect being equivalent at all concentrations. Overall, the combination of these two different facets ofatrazine influence on metamorphosis resulted in a significant acceleration of metamorphosis at 1 mg/Land a significant increase in the duration of metamorphosis at 5 mg/L, whereas no significant differencewas observed with 0.1 mg/L.