M7 PM Metals in the Environment: Aquatic Biological Perspectives
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 327-329
(BIE-1117-815169) Differences in gill chloride uptake by freshwater fishes- Implications for silver toxicity.
Bielmyer, G.1, Brix, K.1, 2, Grosell, M.1, 1 University of Miami, Miami, Fl, USA2 EcoTox, Miami, Fl., USA
ABSTRACT- In freshwater teleosts, the primary mechanism of acute silver toxicity is branchial Na+/K+ ATPase and carbonic anhydrase inhibition, leading to net Na+ and Cl- loss. External Cl- protects Oncorhychus mykiss, against silver toxicity presumably by complexation to form AgCl. However, there are important exceptions because the same AgCl complex does not appear to influence silver sensitivity for Anguilla anguilla and Pimephales promelas. We hypothesize that differences in protective effects of Cl- is due to differing requirements or mechanisms for Cl- uptake among fish species. Fish, which are not dependent on branchial Cl- uptake, perhaps obtaining chloride through the diet, may not be sensitive to silver-induced inhibition of active chloride uptake at the gill. To test this hypothesis, we exposed Danio rerio, which rely on Cl- uptake across the gills, Fundulus heteroclitis, which does not take up Cl-, and P. promelas, in which Cl- uptake has yet to be measured, to ionic silver in waters of varying [Cl-]. The 96-h LC50 values of F. heteroclitis exposed to AgNO3 in soft water with and without 1 mM KCl were 1.20 and 3.88 
g/L, respectively. The 96-h LC50 values of P. promelas exposed under the same conditions were 2.32 and 2.67 g/L, respectively. Based on these results, increasing external Cl- concentration did not offer protection against ionic Ag toxicity to F. heteroclitis or P. promelas. Results from D. rerio are still being analyzed but we anticipate protective effects of Cl- in this fish, which rely on Cl- uptake across the gills. While the lack of Cl- protection in F. heteroclitus is consistent with lack of Cl- uptake, it is unknown at present whether P. promelas exhibits branchial Cl- uptake or perhaps posses a Cl- uptake pathway, less sensitive to silver. Ongoing studies are addressing the issue of Cl- transport in P. promelas.
Key words: chloride, trasport, silver, toxicity