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Bioavailability of silver and its relationship to ionoregulation and silver speciation across a range of salinities in the gulf toadfish (Opsanus beta)
Wood, C.M.; McDonald, M.D.; Walker, P.; Grosell, M.; Barimo, J.F.; Playle, R.C.; Walsh, P.J. (2004). Bioavailability of silver and its relationship to ionoregulation and silver speciation across a range of salinities in the gulf toadfish (Opsanus beta). Aquat. Toxicol. 70(2): 137-157. dx.doi.org/10.1016/j.aquatox.2004.08.002
In: Aquatic Toxicology. Elsevier Science: Tokyo; New York; London; Amsterdam. ISSN 0166-445X, more
Peer reviewed article  

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Keywords
    Bile; Drinking; Drinking; Fluids; Gills; Liver; Salinity; Silver; Stomach content; Toxicity; Urine; Opsanus beta (Goode & Bean, 1880) [WoRMS]; ASW, USA, Florida, Biscayne Bay [Marine Regions]; Marine

Authors  Top 
  • Wood, C.M.
  • McDonald, M.D.
  • Walker, P.
  • Grosell, M.
  • Barimo, J.F.
  • Playle, R.C.
  • Walsh, P.J.

Abstract
    Silver is taken up as a Na+ analog (Ag+) by freshwater organisms, but little is known about its bioavailability in relation to salinity. Adult Opsanus beta were acclimated to 2.5, 5, 10, 20, 40, 60, 80, and 100% seawater (Cl- = 545 mM) and exposed for 24 h to 2.18 μg L-1 silver as 110m Ag-labelled AgNO3, a concentration close to the U.S. EPA marine criterion and less than 0.1% of the acute 96-h LC50 in seawater. Plasma osmolality, Na+, and Cl- remained approximately constant from 100% down to 20-40% seawater, thereafter declining to 89% (osmolality) and 82% (Na+, Cl-) of seawater values at the lowest salinity (2.5% seawater), while plasma Mg2+ was invariant. Ionic measurements in intestinal fluids and urine supported the view that above the isosmotic point (about 32% seawater), toadfish drink the medium, absorb Na+, Cl-, and water across the gastrointestinal tract, actively excrete Na+ and Cl- across the gills, and secrete Mg2+ into the urine. Below this point, toadfish appear to stop drinking, actively take up Na+ and Cl- at the gills, and retain ions at the kidney. Silver accumulation varied greatly with salinity, by nine-fold (whole body), 26-fold (gill tissue), and 18-fold (liver), with the maxima occurring in 2.5% seawater, the minima in 40% seawater (close to the isosmotic point), and slightly greater values at higher salinities. Highest silver concentrations occurred in liver, second highest in gills, intermediate concentrations in kidney, spleen, and gastrointestinal tissues, and lowest in swim bladder and white muscle, though patterns changed with salinity. There were substantial biliary but minimal urinary levels of silver. The salinity-dependent pattern of silver accumulation best correlated with the abundance of the neutral complex AgCl0, though the presence of small amounts of Ag+ at the lowest salinities may also have been important. In contrast, silver accumulation in the esophagus-stomach was greatest in 100% seawater and least at the isosmotic salinity (five-fold variation), a pattern probably explained by drinking and silver uptake into the blood through the gills. Models of silver bioavailability across salinity must consider the presence of silver-binding ligands on both gills and gastrointestinal tract, changing silver speciation, and the changing ionoregulatory physiology of the organism.

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