MA4 Biotic Ligand Model
Room 16A/B, Level 4
8:00 AM - 12:00 PM, Monday, 10 November 2003
Chair: Grosell, Martin ,
Co-chair: Brix, Kevin ,
(034) Effects of pH and dissolved organic carbon on acute toxicity of zinc to larval fathead minnows.
Bringolf, R1, Morris, B1, Collyard, S2, Boese, C1, Santore, R3, Allen, H4, Meyer, J1, 1 University of Wyoming, Laramie, WY, USA2 Wyoming Department of Environmental Quality, Sheridan, WY, USA3 HydroQual, Inc., Camillus, NY, USA4 University of Delaware, Newark, DE, USA
ABSTRACT- We conducted laboratory toxicity studies in support of the development of a biotic ligand model (BLM) for the acute toxicity of Zn to fathead minnows (Pimephales promelas). To test the effect of pH on Zn toxicity, we exposed larval fathead minnows to Zn across a wide range of pH values (6.0-8.9) at narrow intervals (0.5 pH units) in 96-h flow-through toxicity tests. Intermediate pH values (7.5-8.0) produced the lowest Zn LC50s, whereas the LC50s increased at lower and higher pH values. The shallow U-shaped response curve is consistent with predictions of the Zn BLM. To test the protective effect of dissolved organic matter (DOM), we exposed larval fathead minnows to Zn in 96-h static-renewal toxicity tests conducted in basewater (pH 7.5, alkalinity and hardness of about 1 mEq/L) with and without DOM from four different sources (added concentrations of dissolved organic carbon in parentheses): Suwanee River, Georgia (17 mg/L); Cypress Swamp, Delaware (14 mg/L); Edisto River, South Carolina (9 mg/L); and a wastewater treatment facility in Wilmington, Delaware (9 mg/L). These DOM samples were extracted by reverse osmosis preceded by cation exchange (to decrease hardness). The Zn LC50s in the presence of Suwanee River and Cypress Swamp DOM were 2.0x and 1.4x their respective LC50s in the basewater, whereas the Zn LC50s in the presence of Edisto River and Wilmington DOM were only 1.1x the LC50 in the basewater. However, the Edisto River and Wilmington waters were processed through a Na-exchange column, whereas the Suwanee River and Cypress Swamp waters were processed through a proton-exchange column. Use of the Na-exchange column resulted in elevated (20-110x) concentrations of Na+ above that of the basewater, potentially influencing the toxicity results. Overall, though, the elevated Zn LC50s in the DOM tests are consistent with BLM predictions.
Key words: fathead minnow, zinc biotic ligand model, dissolved organic carbon, pH