Naphthenic acids (NAs) have been cited as one of the main causes of the toxicity related to oil sands
process-affected materials and have recently been measured in biological tissues (fish). However, adverse
effects have not been a consistent finding in toxicology studies on vertebrates. This study set out to determine
two factors: 1) whether exposure to commercial NAs (Refined Merichem) resulted in detectable tissue residues
in native amphibians (northern leopard frogs, Lithobates pipiens), and 2) whether such exposure would
produce clinical or subclinical toxicity. Frogs were kept in NA solutions (0, 20, or 40 mg/L) under saline conditions
comparable to that on reclaimed wetlands in the Athabasca oil sands for 28 days. These exposures
resulted in proportional NA concentrations in muscle tissue of the frogs, estimated by gas chromatography–
mass spectrometry analyses. Detailed studies determined if the increasing concentrations of NAs, and subsequently
increased tissue NA levels, caused a proportional compromise in the health of the experimental animals.
Physiological investigations included innate immune function, thyroid hormone levels, and hepatic detoxification
enzyme induction, none of which differed in response to increased exposures or tissue concentrations of
NAs. Body mass did increase in both the salt- and NA-exposed animals, likely related to osmotic pressure
and uptake of water through the skin. Our results demonstrate that commercial NAs are absorbed and deposited
in muscle tissue, yet they show few negative physiological or toxicological effects on the frogs