Short Communication Physiological effects and tissue residues from exposure of leopard frogs to commercial naphthenic acids Judit E.G. Smits a, ⁎, Blair D. Hersikorn b , Rozlyn F. Young c , Phillip M. Fedorak c a Faculty of Veterinary Medicine, University of Calgary, TRW 2D20, 3280 Hospital Drive NW, Calgary AB Canada T2N 4Z6 b Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, Canada S7N 5B3 c Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9 HIGHLIGHTS ► Northern leopard frogs were exposed to two concentrations of commercial (Merichem) NAs under saline conditions for 28 days. ► These laboratory exposures resulted in proportional NAs concentrations in muscle tissue of the frogs. ► Innate immune function, thyroid hormone levels, and hepatic detoxification enzyme induction where not affected by the NAs. ► Exposure to NAs caused a statistically significant increase in frog body weight. abstract article info Article history: Received 11 May 2012 Accepted 11 July 2012 Available online xxxx Keywords: Naphthenic acids Amphibians Biological effects Tissue residues Northern leopard frog 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 resi- dues 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 con- ditions 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 subse- quently 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 detoxifica- tion 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 de- posited in muscle tissue, yet they show few negative physiological or toxicological effects on the frogs. © 2012 Published by Elsevier B.V. 1. Introduction The commercially valuable petroleum product resulting from extraction of Athabasca oil sands in northern Alberta, Canada, is a vis- cous, tar-like material called bitumen. The aqueous extraction process required to remove the bitumen from sand produces tailings water which contains, among other things, polar organic carboxylic acids that MacKinnon and Boerger (1986) named “naphthenic acids”. Naphthenic acids (NAs) are chemically stable, complex mixtures of mainly acyclic and cyclic aliphatic, mono carboxylates, with molecular masses b 500. They are commonly classified by their number of carbon atoms and their structure (Headley and McMartin, 2004). This varied group of compounds has different toxicological, chemical and physical properties depending on its non-volatile and polar characteristics, plus the high solubility in water allows NAs to act as surfactants (Clemente and Fedorak, 2005). Research has been carried out to determine the toxicological risks from exposure to NAs. These organic acids are currently felt to be one of the most important aquatic contaminants associated with the oil sands industry and are frequently associated with negative effects on environmental health in the oil sands (Kean, 2009; Tenenbaum, 2009). NAs have been shown to be toxic to aquatic organisms (fish, algae, microorganisms) and mammals, with some evidence that the Science of the Total Environment 437 (2012) 36–41 Abbreviations: 9-FCA, 9-fluorenecarboxylic acid; DMSO, dimethylsulfoxide; EROD, Ethoxyresorufin-O-deethylase; GC–MS, gas chromatography–mass spectrometry; OSPW, oil sands process-affected water; T3, triiodothyronine; T4, thyroxine; NAs, naphthenic acids; SIM, selective ion monitoring. ⁎ Corresponding author. Tel.: +1 403 210 7407; fax: +1 403 210 9740. E-mail address: judit.smits@ucalgary.ca (J.E.G. Smits). 0048-9697/$ – see front matter © 2012 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.scitotenv.2012.07.043 Contents lists available at SciVerse ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv