The earthworm bioassay was able to assess reductions in metal bioavailability and evaluate chemical immobilization amendment effectiveness. Using this approach, we concluded that LSB is an effective amendment for reducing metal bioavailability to earthworms in contaminated soil, although the effectiveness of LSB may be only temporary (Gradwohl, 1998).
Calcium nitrate–extractable metals appear to be a very promising surrogate measure of metal bioavailability for earthworms in soil. The large differences in the Ca(NO3)2–extractable metal concentrations of the lethal and nonlethal soils, as well as the similarity in lethal Ca(NO3)2–extractable Zn levels of the smelter soil and Zn-spiked artificial soil (Conder and Lanno, 2000) indicates the possibility of developing universal, soil-independent ILLs based on Ca(NO3)2–extractable metal levels. Testing field soils contaminated with metals other than predominantly Zn is needed to further validate the use of weak-electrolyte extractions as surrogate measures of metal bioavailability in soil. Correlation with metal residues in soil organisms (underway for earthworms used in this study) is also necessary.
Although Ca(NO3)2 extractions are easier to perform and better related to earthworm toxicity in soil, PRSs may be useful as an in situ screening tool, and may avoid possible physicochemical alterations of soil involved in weak electrolyte sampling techniques.
This research was made possible through a grant from the OSU Environmental Institute to R. Lanno and N. Basta. J. Conder received support in the form of a graduate research fellowship from the U.S. Environmental Protection Agency during part of this study. The authors are appreciative of R. Gradwohl, who provided the remediated soil–amendment combinations for this study. Thanks are due to A. Conder and K. Kejela for assistance with experimental procedures and K. Greer at Western Ag Innovations Inc. for his advice regarding the PRSs. The views expressed in this document do not necessarily represent those of the OSU Environmental Institute, USEPA, or Western Ag Innovations Inc.
J.M. Conder, current address: Inst. of Applied Science, Univ. of North Texas, Denton, TX 76203