AbstractA protocol for determination of “no‐effect” concentrations on hatch and survival in the zebrafish (Brachydanio rerio) has been evaluated at five laboratories for variability using chromium (K2Cr2O7) and zinc (ZnSO4× 7H2O) as toxicants. Repeatability (r) and reproducibility (R), expressed as C.V. (coefficient of variation), for logarithmic median survival time ranged between 1 and 9 forrand between 1 and 29 forRdepending upon concentration of toxicant. Variability increased at high concentrations, especially for zinc. For logarithmic median hatching time, C.V. forrranged from 6 to 24 and forRbetween 11 and 27 for the various concentrations of chromium and zinc. Estimated logarithmic “no‐effect” concentrations on survival of zinc and chromium had a C.V. forrbelow 10 and a C.V. forRbelow 15 for zinc and below 25 for chromium. Zinc delayed the time to hatch at lower concentrations than those that reduced survival time, for the estimated logarithmic “no‐effect” concentrations of zinc on hatchrwas around 75 andRaround 100. The “no‐effect” concentrations based on all nine or ten tests from the five laboratories were 15 mg Cr/L and 0.5 mg Zn/L. Because of the cumulative toxicity of chromium in fish the chronic “safe” concentration may be considerably lower, but the “no‐effect” concentration of 0.5 mg Zn/L for effects on hatching time is consistent with the chronic “safe” concentration found in other species of fish at the same
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