The effects of various water chemistry parameters on the toxicity of copper to larval fathead minnows were investigated. Increased pH, hardness, sodium, dissolved organic matter, and suspended solids each caused toxicity to decrease on the basis of total copper concentrations. In contrast, added potassium resulted in increased toxicity. Alkalinity had no observed effect on total copper LC50s, but its effects might have been masked by those of the cations added with it. In most cases, the effects of water chemistry were found to be similar for different endpoints (growth, survival at different durations), but there were differences in the relative magnitude of some effects across these endpoints. Over all experimental treatments, 96-h total copper LC50s varied 60-fold. Every water chemistry parameter also caused toxicity to vary significantly when expressed on the basis of cupric ion selective electrode measurements, sometimes more so than on the basis of total copper. Therefore, this study does not support attributing to cupric ion a singular importance in regulating toxicity to this test organism. A variety of copper species might be contributing to toxicity and it is evident that toxicity is also affected by water chemistry in ways not related to copper speciation.

The effects of water chemistry on the toxicity of copper to fathead minnows

The toxicity of mercury (HgCl2), copper (CuCl2: 5 H2O), nickel (NiSO4: 6 H2O), lead (Pb(CH3COO)2: 3 H2O) and cobalt (CoCl2: 6 H2O) was studied under standardized conditions in embryos and larvae of the zebrafish,Brachydanio rerio. Exposures were started at the blastula stage (2–4 h after spawning) and the effects on hatching and survival were monitored daily for 16 days. Copper and nickel were more specific inhibitors of hatching than cobalt, lead, and mercury. Nominal “no effect” concentrations determined from the dose-response relationships (ZEPs, Zero Equivalent Points) for effect on hatching time were 0.05 μg Cu/L, 10 μg Hg/L, 20 μg Pb/L, 40 μg Ni/L and 3,840 μg Co/L, and those for effect on survival time were 0.25 μg Cu/L, 1.2 μg Hg/L, 30 μg Pb/L, 80 μg Ni/L, and 60 μg Co/L. The “no effect” concentrations for Ni, Hg and Pb are consistent with previously reported MATC values for sensitive species of fish. The “no effect” concentrations for copper are 1–2 orders of magnitude lower than previously reported values. The major reason for the latter discrepancy was considered to be the absence of organics that can complex copper ions in the reconstituted water that we used, which had a hardness of 100 mg/L (as CaCO3) and a pH of 7.5–7.7. Unexposed controls were started with embryos from different parental zebrafishes and the parental-caused variability in early embryo mortality, median hatching time and median survival time were estimated.

J.R. Geckler

Papers

Acute and chronic toxicity of copper to the fathead minnow in a surface water of variable quality