|
1E - Speciation of chemicals (TUP/34) Waterborne sulfides offer protection from silver toxicity in rainbow trout (Oncorhynchus mykiss). Mann, Reinier1, 2, Ernste, Mike2, Bell, Russell2, Kramer, James2, Smith, Scott2, Wood, Chris2, 1 Universidade de Aveiro, Aveiro, Portugal, Portugal2 McMaster University, Hamilton, Canada, Canada ABSTRACT- Metastable sulfide complexes are known to occur in oxic surface waters at low to high nanomolar concentrations. Sulfide has a very high binding affinity for metal cations (log K for Ag[I] = 13.6), and the formation of stable Ag-sulfide complexes within waters containing elevated silver is likely to protect aquatic organisms from ionic silver (Ag+) toxicity. To test this assumption, juvenile rainbow trout (<1g) were exposed to AgNO3 in 96 h static-renewal acute-toxicity tests, either in the absence or presence of 100nM sulfide (as zinc-sulfide clusters) in moderately hard Hamilton tap water. In the absence of 100nM sulfide, the 96 h LC50 value (95% confidence limit) was 134.8 (117.9-154.1) nM. In the presence of 100nM sulfide, the 96 h LC50 was 397 (343-460) nM. The difference of 260 nM does not confirm a 1:1 Ag:S binding ratio as expected, although a comparison of [Ag] in unfiltered water samples with the [Ag] in water samples filtered through 0.458 Key words: silver, zinc sulfide, metal speciation, rainbow trout |
m polyethersulfone filters (known to exclude Ag-sulfide clusters, Bowles et al. (2002) Environ. Toxicol. Chem. 21:1286-1293) at the start of the test, suggests that a 1:1 binding ratio existed at that time. Therefore, either a change in Ag-sulfide stoichiometry or another confounding effect occurred over the course of the test. The results indicated that 100nM sulfide was protective of acute Ag+ toxicity in a static-renewal test system. Toxicity prediction models such as the Biotic Ligand Model (BLM), will benefit from the inclusion of sulfide as a competitive ligand. (Supported by Kodak Canada Inc. and the NSERC CRD program).