Case study 6.27: Toxicity identification evaluation of solid-phase sediment from San Francisco Bay, California, USA

Amphipod toxicity was periodically observed in sediment from Grizzly Bay, a site that is tested as part of the San Francisco Bay Regional Monitoring Program. This site is contaminated by a complex mixture of trace metal and organic chemicals at moderate concentrations. Toxicity was observed in solid-phase sediments but not in porewater, making it necessary to employ solid-phase TIE techniques to characterize causes of toxicity (e.g., Lebo et al. 1999; Burgess et al. 2000; Ho et al. 2002). Reductions in sediment toxicity were observed following all 3 solid-phase TIE treatments, but additions of both coconut charcoal (to sorb organics) and cation exchange resin beads (to bind metals) reduced toxicity only to the extent observed following the addition of an equal volume of control sediment. Thus, toxicity reduction may have been the result of simple dilution, a situation that made it difficult to characterize causes of toxicity. Weak acid rinsing (0.5N hydrochloric acid) reduced sediment toxicity to a greater extent than did rinsing with seawater alone, perhaps implicating trace metals, but other possibilities need further examination before conclusive characterizations can be made based on this technique.