Influence of sample manipulation on contaminant flux and toxicity at the sediment-water interface

Toxicities of sediments from San Diego and San Francisco Bays were compared in laboratory experiments using sea urchin (Strongylocentrotus purpuratus) embryos exposed to pore water and at the sediment-water interface (SWI). T oxicity was consistently greater to embryos exposed at the SWI to intact (u nhomogenized) sediment samples relative to homogenized samples. Measurement of selected trace metals indicated considerably greater fluxes of copper, zinc, and cadmium into overlying waters of intact sediment samples. Inhibit ion of sea urchin embryo development was generally greater in sediment pore waters relative to SWI exposures. Pore water toxicity may have been due to elevated unionized ammonia concentrations in some samples. The results ind icate that invertebrate embryos are amenable to SWI exposures, a more ecolo gically relevant exposure system, and that sediment homogenization may crea te artifacts in laboratory toxicity experiments. (C) 2001 Elsevier Science Ltd. All rights reserved.