Behavioral Response and Kinetics of Terrestrial Atrazine Exposure in American Toads (Bufo americanus)

Amphibians in terrestrial environments obtain water through a highly vascularized pelvic patch of skin. Chemicals can also be exchanged across this patch. Atrazine (ATZ), a widespread herbicide, continues to be a concern among amphibian ecologists based on potential exposure and toxicity. Few studies have examined its impact on the terrestrial juvenile or adult stages of toads. In the current study, we asked the following questions: (1) Will juvenile American toads (Bufo americanus) avoid soils contaminated with ATZ? (2) Can they absorb ATZ across the pelvic patch? (3) If so, how is it distributed among the organs and eventually eliminated? We conducted a behavioral choice test between control soil and soil dosed with ecologically relevant concentrations of ATZ. In addition, we examined the uptake, distribution, and elimination of water dosed with ¹⁴C-labeled ATZ. Our data demonstrate that toads do not avoid ATZ-laden soils. ATZ crossed the pelvic patch rapidly and reached an apparent equilibrium within 5 h. The majority of the radiolabeled ATZ ended up in the intestines, whereas the greatest concentrations were observed in the gall bladder. Thus, exposure of adult life stages of amphibians through direct uptake of ATZ from soils and runoff water should be considered in risk evaluations.