Toxicity of silver to steelhead and rainbow trout, fathead minnows and <i>Daphnia Magna</i>

Abstract

Abstract Rainbow (Salmo gairdneri) and steelhead (Salmogairdneri) trout and fathead minnows (Pimephales promelas) were exposed to silver for 96 h in replicated flow-through tests. Rainbow trout, fathead minnows and Daphnia magna were exposed to silver in replicated static acute tests. Steelhead trout embryo-larval stages were tested in a flow-through system for 60 d, and D. magna were exposed through complete life cycles in replicated static-renewal tests. All silver concentrations were measured values. No differences were seen between flow-through and static LC50 values. Rainbow trout 96-h flow-through LC50 values were 8.6 and 9.7 μg/L silver; static values were 10.9 and 8.5 μg/L. The 96-h LC50 for steelhead trout in the flow-through test was 9.2 μg/L. Fathead minnow 96-h flow-through LC50 values were 5.6 and 7.4 μg/L silver; static values were 9.4 and 9.7 μg/L. The absence of food in static tests with D. magna caused silver to be about 10 times more toxic; the 48-h static mean EC50 value for D. magna without food was 0.9 μg/L, compared to 12.5 μg/L in the test with food. The early-life-stage test with steelhead trout, from newly fertilized eggs to post-swimup juveniles, showed complete mortality at 1.3 μg/L and significant reduction in fish survival at 0.5 μg/L silver. Mean weight and length at end of test were greatly reduced at 1.1 μg/L, and were significantly different from controls at 0.1 μg/L. The mean 21-d EC50 value for the D. magna test with food was 3.5 μg/L. The 21-d lowest significant (α = 0.05) effect on survival occurred at 4.1 μg/L. The mean silver concentration at which there was a significant decrease in total Daphnia young/female/day after 21 d, compared to the control was 10.5 μg/L silver.