Validation of Zinc and Nickel Biotic Ligand Models Based on Toxicity Testing in Natural Waters with Ceriodaphina dubia
Most states use outdated hardness-based criteria to regulate metals in surface waters. The slow adoption of new criteria based on biotic ligand models (BLMs) reflects uncertainty about whether these models can reliably predict toxic effects of metals on aquatic biota across the wide range of water quality conditions affecting bioavailability.
The Issue:
Biotic ligand models (BLMs) reflect the influence of multiple water quality variables that influence bioavailability, including pH, hardness [calcium and magnesium], and dissolved organic carbon (DOC). BLMs were developed and validated based on tests with wide ranges of water quality conditions, but there is still a need for validation of these models with natural waters containing extreme values of one or more water quality parameters. A series of toxicity studies using the cladoceran, Ceriodaphnia dubia, and the mayfly, Neocloeon triangulifer, were done using natural waters with varying organic carbon content and hardness. Results of these studies will be used to decrease the uncertainty about the Biotic Ligand model (BLM) and more reliably predict toxic effects of nickel and zinc on diverse assemblages of aquatic biota.
Addressing the Issue:
States in the USEPA Region 5 (Great Lakes/Upper Midwest) currently rely on inadequate hardness-based criteria for regulation of zinc and nickel in surface waters. This is based in part on uncertainty about whether these models can reliably predict toxic effects of zinc on diverse assemblages of aquatic biota across the wide range of water quality conditions occurring in the region. BLMs reflect the influence of multiple water quality variables that influence zinc and nickel bioavailability, including calcium, magnesium, pH, and dissolved organic carbon (De Schamphelaere et al. 2003). Toxicity data used to calibrate BLMs are based on tests with wide ranges of water quality, but waters with extreme values of one or more parameters may be under-represented.
CERC scientists have:
- Compared observed and BLM-predicted toxicity thresholds for C. dubia among four natural waters and CERC well water with extreme high and low values of parameters known to affect zinc and nickel toxicity (pH, hardness, DOC);
- Estimated the intrinsic sensitivity for the mayfly, Neocloeon triangulifer, based on chronic tests with four natural waters; and
- Evaluated whether BLM models reduce variation in zinc effect concentrations across a range of water chemistry as effectively for mayflies as for C. dubia.
CERC scientists generated toxicity data for natural waters representing extremes of water quality in the Midwestern US. CERC scientists sampled in two study areas: (1) central Illinois, where streams had high hardness (>300 mg/L) and moderately low levels of DOC (2-4 mg/L); and (2) northern Minnesota, where streams had high DOC (>30 g/L) and low hardness (17-27 mg/L) . CERC scientists conducted chronic toxicity tests with waters from the two study areas, plus two low-DOC (<1 mg/L) laboratory waters with hardness adjusted to match natural waters from each study area. Toxicity tests were conducted with the cladoceran, Ceriodaphnia dubia, a standard test organism that has been widely used in development and validation of BLM models.
Next Steps/Future Steps/Results:
CERC scientists will compare the observed differences in toxicity of zinc and nickel to the toxicity predicted by the BLM models. Based on the results of this study, CERC scientist can address uncertainties about the BLM and develop standards to reliably predict toxic effects of nickel and zinc on diverse assemblages of aquatic biota.
Return to Fish and Invertebrate Toxicology
Most states use outdated hardness-based criteria to regulate metals in surface waters. The slow adoption of new criteria based on biotic ligand models (BLMs) reflects uncertainty about whether these models can reliably predict toxic effects of metals on aquatic biota across the wide range of water quality conditions affecting bioavailability.
The Issue:
Biotic ligand models (BLMs) reflect the influence of multiple water quality variables that influence bioavailability, including pH, hardness [calcium and magnesium], and dissolved organic carbon (DOC). BLMs were developed and validated based on tests with wide ranges of water quality conditions, but there is still a need for validation of these models with natural waters containing extreme values of one or more water quality parameters. A series of toxicity studies using the cladoceran, Ceriodaphnia dubia, and the mayfly, Neocloeon triangulifer, were done using natural waters with varying organic carbon content and hardness. Results of these studies will be used to decrease the uncertainty about the Biotic Ligand model (BLM) and more reliably predict toxic effects of nickel and zinc on diverse assemblages of aquatic biota.
Addressing the Issue:
States in the USEPA Region 5 (Great Lakes/Upper Midwest) currently rely on inadequate hardness-based criteria for regulation of zinc and nickel in surface waters. This is based in part on uncertainty about whether these models can reliably predict toxic effects of zinc on diverse assemblages of aquatic biota across the wide range of water quality conditions occurring in the region. BLMs reflect the influence of multiple water quality variables that influence zinc and nickel bioavailability, including calcium, magnesium, pH, and dissolved organic carbon (De Schamphelaere et al. 2003). Toxicity data used to calibrate BLMs are based on tests with wide ranges of water quality, but waters with extreme values of one or more parameters may be under-represented.
CERC scientists have:
- Compared observed and BLM-predicted toxicity thresholds for C. dubia among four natural waters and CERC well water with extreme high and low values of parameters known to affect zinc and nickel toxicity (pH, hardness, DOC);
- Estimated the intrinsic sensitivity for the mayfly, Neocloeon triangulifer, based on chronic tests with four natural waters; and
- Evaluated whether BLM models reduce variation in zinc effect concentrations across a range of water chemistry as effectively for mayflies as for C. dubia.
CERC scientists generated toxicity data for natural waters representing extremes of water quality in the Midwestern US. CERC scientists sampled in two study areas: (1) central Illinois, where streams had high hardness (>300 mg/L) and moderately low levels of DOC (2-4 mg/L); and (2) northern Minnesota, where streams had high DOC (>30 g/L) and low hardness (17-27 mg/L) . CERC scientists conducted chronic toxicity tests with waters from the two study areas, plus two low-DOC (<1 mg/L) laboratory waters with hardness adjusted to match natural waters from each study area. Toxicity tests were conducted with the cladoceran, Ceriodaphnia dubia, a standard test organism that has been widely used in development and validation of BLM models.
Next Steps/Future Steps/Results:
CERC scientists will compare the observed differences in toxicity of zinc and nickel to the toxicity predicted by the BLM models. Based on the results of this study, CERC scientist can address uncertainties about the BLM and develop standards to reliably predict toxic effects of nickel and zinc on diverse assemblages of aquatic biota.
Return to Fish and Invertebrate Toxicology