Aquatic Toxicology 126 (2013) 274–282 Contents lists available at SciVerse ScienceDirect Aquatic Toxicology j ourna l ho me p ag e: www.elsevier.com/l ocate/aquatox The interactive effects of selenomethionine and methylmercury on their absorption, disposition, and elimination in juvenile white sturgeon Susie Shih-Yin Huang a , Anders Bjerring Strathe b , James G. Fadel a , Michael L. Johnson c , Pinpin Lin e,d , Tsung-Yun Liu e , Silas S.O. Hung a,∗ a Department of Animal Science, University of California, Davis 95616, USA b Department of Basic Animal and Veterinary Sciences, University of Copenhagen, Copenhagen DK-1870, Denmark c John Muir Institute of Ecology, University of California, Davis 95616, USA d Division of Environmental Health and Occupational Medicine, National Health Research Institutes, Zhunan 350, Taiwan e Institute of Environmental and Occupational Health Sciences, College of Medicine, National Yang-Ming University, Taipei 112, Taiwan a r t i c l e i n f o Article history: Received 13 June 2012 Received in revised form 18 September 2012 Accepted 22 September 2012 Keywords: Selenium Mercury Acipenser transmontanus Kinetics Metabolism Bayesian modeling a b s t r a c t Selenium (Se) and mercury (Hg) are prevalent pollutants of industrialized watersheds. However, when co-administered, Se has protective effects on organisms from Hg. The mechanism is not fully understood, but it is thought that Se reduces Hg availability, either by forming biologically inert complexes and/or associating with selenoproteins. Despite concerns with aquatic contaminations, relatively little informa- tion is available on the interaction in aquatic organisms. In the present study, the interactive effects of Se and Hg on their absorption, disposition, and elimination were examined in juvenile white sturgeon, a benthic fish species at high risk to exposures of both contaminants. Selenium and Hg were provided as l-selenomethionine (SeMet) and methylmercury (MeHg), respectively. Groups of 10 sturgeon were orally intubated with a single dose of either 0 (control), SeMet (500 g Se/kg body weight; BW), MeHg (850 g Hg/kg BW), or their combination (Se/Hg; 500 g Se/kg and 850 g Hg/kg BW). The blood was repeatedly sampled and urine collected from the fish, over a 48 h post intubation period. At 48 h, the fish were sacrificed for Se and Hg tissue concentration and distribution. The co-administration of SeMet and MeHg significantly (p < 0.05) lowered blood concentrations of both Se and Hg and tissue Se concen- trations. Similarly, assimilation of Se and Hg was also reduced significantly. The interaction has a more quantitative effect on Se metabolism because the reduction in the overall tissue Se is a consequence of reduced Se absorption at the gut and not from the metabolic effects after absorption. In contrast, given the pulse increase in blood Hg concentration, tissue redistribution, and increased urinary elimination, the interactive effect on tissue Hg concentration is likely to be post-absorption. Even in the absence of exogenous SeMet, Se and Hg co-accumulated in tissue at a Se:Hg molar ratio greater than 1. Thus, similar to mammals, maintaining at least a 1:1 molar ratio of Se and Hg is of great physiological importance in the white sturgeon. Interestingly, SeMet did not divert Hg from the brain. Allocation of Se from the kidneys may have occurred in order to maintain the high Se:Hg molar ratios in the brain of white sturgeon. In the current study, the combined use of kinetic analysis and that of the conventional approach of measuring tissue concentration changes provided a comprehensive understanding of the interactive effect of SeMet and MeHg on their respective metabolic processes in juvenile white sturgeon. © 2012 Elsevier B.V. All rights reserved. 1. Introduction At low concentrations, selenium (Se) is essential for all ani- mals including fish. At levels found in some environments, Se is Abbreviations: Hg, mercury; MeHg, methylmercury; Se, selenium; SeMet, l- selenomethionine; Met, methionine; MDL, method detection limit; RWB, remaining whole body; BBB, blood–brain barrier. ∗ Corresponding author at: Department of Animal Science, University of California, Davis 95616, USA. Tel.: +1 530 752 3580; fax: +1 530 752 0175. E-mail address: sshung@ucdavis.edu (S.S.O. Hung). a potent reproductive and developmental toxicant because of the narrow range between deficient and excessive levels in animals (0.1–1.0 g/g diet or ml drinking water; NRC, 2005). However, Se is also known to interact with various metals/elements in organisms, altering the toxicity of not only the interacting metals/elements but also itself. Among many, the interaction between Se and mercury (Hg) is the most well-known. The urban estuary of San Francisco Bay Delta (SFBD) has a long history of both Hg and Se contaminations. The historical gold rush and subsequent hydraulic mining released over 400 million cubic meters of sediment laden with approximately 9 million kg of liquid Hg into the Delta (Thompson and Parchaso, 2004). Major sources 0166-445X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aquatox.2012.09.018