Effects of natural organic matter source on reducing metal toxicity to rainbow trout (Oncorhynchus mykiss) and on metal binding to their gills

Juvenile rainbow trout (Oncorhynchus mykiss, 3 g) were exposed for 74 h in ion-poor (soft) water to a mixed-metal solution in the presence of 4, 6, an d 10 mg C/L natural organic matter (NOM). The metals were 0.2 muM Ph, 0.1 m uM Hg, 0.1 muM Cd, 1.3 muM Cu, 0.05 muM Ag, and 3.5 muM Co, and the natural organic matter was isolated by reverse osmosis from three sources in south ern Ontario, Canada. The six-metal solution alone was extremely toxic to th e fish. Increasing concentrations of each NOM increased trout survival, but the NOM having the most allochthonous properties (from Luther Marsh) incre ased fish survival most, while the NOM having the most autochthonous proper ties from Sanctuary Pond, Point Pelee) increased fish survival least. This pattern was reflected in the degree of reduction of Ph and Cu accumulation by the gills. Relatively simple chemical characterization of NOM, such as p rotein-to-carbohydrate ratios, or optical characterization, such as absorba nce-to-fluorescence ratios (e.g., representing aromaticity), may adequately reflect these biologically relevant differences in organic matter quality.