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EARLY LIFE STAGE TOXICITY OF COPPER TO ENDANGERED AND SURROGATE FISH SPECIES
Besser, J. M., F. J. Dwyer, Ingersoll, AND N. Wang. EARLY LIFE STAGE TOXICITY OF COPPER TO ENDANGERED AND SURROGATE FISH SPECIES. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-12/035, 2001.
We conducted a series of chronic, early life-stage toxicity tests with two listed species, fountain darter (Etheostoma fonticola) and spotfin chub (Cyprinella monacha), and two surrogate species, fathead minnow (Pimephales promelas) and rainbow trout (Oncorhynchus mykiss), exposed to copper (Cu). Data from the tests with the four species, which included repeated tests with three species, were used to evaluate the suitability of test endpoints and toxicity metrics.
Water quality criteria (WQC) for the protection of aquatic life have not explicitly considered the degree of protection afforded to aquatic species listed as endangered or threatened under the U.S. Endangered Species Act (listed species) . Most WQCs are based primarily on responses of a limited number of surrogate species, which are easily cultured and tested in the laboratory. Little information is available about the relative sensitivity of listed species to toxic chemicals, especially with respect to chronic toxicity. We conducted a series of chronic, early life-stage toxicity tests with two listed species, fountain darter (Etheostoma fonticola) and spotfin chub (Cyprinella monacha), and two surrogate species, fathead minnow (Pimephales promelas) and rainbow trout (Oncorhynchus mykiss), exposed to copper (Cu).
Data from the tests with the four species, which included repeated tests with three species, were used to evaluate the suitability of test endpoints and toxicity metrics. Endpoints measured included survival, growth (total length and average dry weight of surviving fish), and biomass (total dry weight of survivors). Toxicity metrics were established by hypothesis testing to determine no-observed-effect concentrations (NOEC) and lowest-observed-effect concentrations (LOEC), and by a linear interpolation technique, to estimate inhibition concentrations associated with 10% and 25% reductions of test endpoints (IC10 and IC25). The hypothesis testing and linear interpolation methods generally gave similar results, as all calculable IC10 values fell within the NOEC-LOEC range. The ?chronic value? calculated from these studies (ChV = geometric mean of NOEC and LOEC) corresponded closely to the IC10 for most species and endpoints.
For three of the four species tested, growth and/or biomass endpoints were more sensitive than survival. For fountain darters, no significant effects on growth occurred at concentrations less than LOECs for survival and biomass, and IC10 values indicated that reductions in growth (both dry weight and total length) only occurred at concentrations greater than those affecting survival. For the other three species, reductions in growth, expressed as individual dry weight, occurred at concentrations at least as low as those affecting other endpoints. However, growth in dry weight showed wide variation among three tests with fathead minnows, with ChVs ranging from 2.8 to 15.9 Fg/L. Results from tests with fathead minnows and other species suggested that growth in dry weight was affected by differences in fish density caused by differential survival among replicates and between treatments. Growth in total length was less variable than dry weight and LOECs for total length were close to those for dry weight, but IC10 values for total length were consistently greater than those for dry weight. Biomass, which reflects combined toxic effects of Cu on both survival and individual growth, was nearly as sensitive as growth in dry weight and was less variable among tests.
Sensitivity to Cu toxicity did not differ substantially between listed and surrogate species. Lowest average ChVs for the four species tested ranged from 7.7 Fg/L for the fountain darter (for reduced survival and biomass) to 15.9 Fg/L for the spotfin chub (for reduced growth and biomass). The average ChV for growth of fathead minnows from three tests (7.8 Fg/L) was nearly equal to that for fountain darters, although this value was strongly influenced by the low ChV of 2.8 Fg/L determined from one of the three tests. Evaluation of relative species sensitivities with IC10 produced similar results, with values ranging from <8.0 Fg/L for fountain darters to 23 Fg/L for spotfin chubs.
Toxicity thresholds (either ChVs or IC10s) estimated from our chronic, early life-stage toxicity tests indicated that the current chronic Cu WQC would protect the endangered spotfin chub, but may not adequately protect the endangered fountain darter or the two surrogate species tested. This finding contrasts with results of previous acute toxicity tests in our laboratory, which concluded that current acute WQC for Cu would adequately protect fountain darters. These results suggest that protection of fountain darters from chronic toxicity of Cu would require application of a safety factor of about 0.5 to the current chronic Cu WQC. This safety factor would be consistent with that estimated from previous acute toxicity studies conducted at our laboratory with surrogate and listed species.