MP1 New Approaches to Determining Soil and Sediment Exposures
256 Portland Ballroom
1:20 PM - 4:40 PM, Monday
() Predicting Sediment Metal Toxicity Using a Sediment Biotic Ligand Model.
Di Toro, D1, McGrath, J2, Hansen, D2, Berry, W3, Paquin, P2, Mathew, R2, Wu, K2, Santore, R2, 1 University of Delaware2 HydroQual, Inc.3 U.S. EPA
ABSTRACT- An extension of the SEM/AVS procedure is presented that predicts the concentrations at which acute and chronic effects of metals in sediments occur by accounting for partitioning to sediment particulate organic carbon. It is shown that the organic carbon normalized excess SEM: SEMx,OC = (SEM - AVS)/fOC can be used to predict the sediment concentration at which metal toxicity is observed. The biotic ligand model (BLM) is used to compute the LC50 concentration of metal on sediment particulate organic carbon, that is in equilibrium with the LC50 in pore water -- following the precepts of the Equilibrium Partitioning (EqP) model -- and in equilibrium with the critical concentration at the site of action (the biotic ligand). The result is the metal concentration on the sediment particulate organic carbon that is in equilibrium with the biotic ligand. This procedure bypasses the need to compute the details of the pore water chemistry. Remarkably, the sediment organic carbon LC50 (SEM*x,OC) is essentially unchanged over a wide range of pore water hardness, salinity, DOC and any other complexing or competing ligands. Only the pore water pH is important. Both acute and chronic exposures of crustaceans in fresh and salt water sediments are compared to predictions for Cd, Cu, Ni, Pb and Zn based on Daphnia magna BLMs. Also, the sediment LC50s are similar for all the metals except cadmium . For pH = 8, the approximate values (mmol /gOC) are Cd-SEM*x,OC = 100, and for the rest: Cu-SEM*x,OC = 900, Ni-SEM*x,OC = 1100, Zn-SEM*x,OC = 1400 and Pb-SEM*x,OC = 2700. This is the explanation for an empirically observed dose-response relationship between SEM*x,OC and acute and chronic effects concentrations that had been observed previously.
Key words: sediments, biotic ligand model, metal, toxicity