TA3 Metals in the Environment: Aquatic Biological Perspectives
254 Portland Ballroom
8:00 AM - 12:00 PM, Tuesday
() Toxicity of silver to two freshwater cladocerans and potential mitigating factors.
Naddy, R1, Stern, G1, Rehner, A1, Bell, R2, Kramer, J2, Wu, K3, Paquin, P3, Gorsuch, J4, 1 ENSR International, Fort Collins, Colorado, USA2 McMaster University, Hamilton, Ontario, Canada3 HydroQual Inc., Mahwah, New Jersey, USA4 Eastman Kodak Company, Rochester, New York, USA
ABSTRACT- The acute and chronic toxicities of silver to Ceriodaphnia dubia and Daphnia magna were determined in static and static–renewal exposures, respectively. Previous studies have shown that silver toxicity can be greatly influenced by equilibration time once food is added, therefore test solutions were aged for 3 hours prior to organism introduction. Species were similarly sensitive to silver in acute studies, however, the presence of food not only increased EC50 values dramatically, but also caused them to differ between species. Additional chronic studies indicated that D. magna were approximately 2× more sensitive to silver than C. dubia (IC25 = 3.76 and 10.53 
g dissolved Ag/L, respectively). The reason for this difference was determined to be due to the diet and amount fed to each test species. The acute–to–chronic ratios were similar for both organisms at 1.2. The toxicity of silver to D. magna did not appreciably change among the 48–h, 4–d, and 21–d studies when food was present. The addition of 
2 mg/L DOC as Aldrich® humic acid did not alter the chronic toxicity of silver to C. dubia. Additional chemical analyses were conducted during these studies to determine silver speciation and equilibration over the course of the experiment. Studies are currently underway to examine the mitigating potential of natural organic matter combined with sulfide. A companion platform presented by Bell et al. will focus on strong binding ligands in food used in the toxicity tests with these organisms.
Key words: chronic silver toxicity, acute silver toxicity, NOM, diet