Aqueous ractopamine exposure below 0.22 mg/L has no effect on mortality, malformation, or growth of developing Xenopus laevis tadpoles

Ractopamine, a β-adrenergic receptor agonist, is commonly used as a repartitioning agent and growth promotor in animal agriculture. There is evidence that ractopamine can enter natural water sources from livestock wastes, at concentrations in the low ng/L range. Currently, aquatic toxicity data for ractopamine is scarce. Therefore, in two separate experiments Xenopus laevis tadpoles were exposed to ractopamine in tank water at concentrations ranging from 2 ng/L to 2.2 mg/L for up to 14 d utilizing FETAX methodology. No overt signs of toxicity were identified in measured endpoints including survival, growth, malformation, and developmental stage. Oral ractopamine exposure in mammals and fish is associated with cardiotoxicity, increased mortality, and physiological alterations; however, this study suggests that aqueous ractopamine is not a developmental toxicant or overtly toxic to amphibians at environmentally relevant concentrations.