Effect of diet quality on chronic toxicity of aqueous lead to the amphipod Hyalella azteca

The authors investigated chronic toxicity of aqueous Pb to the amphipod, Hyalella azteca, (Hyalella) in 42-d tests with 2 different diets: (1) the YCT diet (yeast + cereal leaf + trout pellet), fed at the uniform low ration used in standard methods for sediment toxicity tests; and (2) a new diet of diatoms + Tetramin flakes (DT), fed at increasing rations over time, that has been optimized for use in Hyalella water-only tests. Test endpoints included survival, weight, biomass, fecundity, and total young. Lethal effects of Pb were similar for DT and YCT tests (LC20 = 13 and 15 µg/L as filterable Pb). In contrast, weight and fecundity endpoints were not significantly affected in the DT test at Pb concentrations up to 63 µg/L, but these endpoints were significantly reduced by Pb in the YCT test – and in a 2005 test in our laboratory with a diet of conditioned rabbit chow (RC-2005). The fecundity and total young endpoints from the YCT and RC-2005 tests were considered unreliable because fecundity in controls did not meet test acceptability criteria, but both of these tests still produced lower Pb effect concentrations (for weight or biomass) than the test with the DT diet. The lowest BLM-normalized effect concentrations for the three tests ranged from 3.7 µg/L (weight EC20 for the RC-2005 test) to 8.2 µg/L (total young EC20 for the DT test), values that would rank Hyalella as the second or third most sensitive of 13 genera in a species sensitivity distribution for chronic Pb toxicity. These results demonstrate that toxicity tests with Hyalella fed optimal diets can meet more stringent test acceptability criteria for control performance, but suggest that results of these tests may underestimate sublethal toxic effects of lead to Hyalella under suboptimal feeding regimes. This article is protected by copyright. All rights reserved