Long-term storage of sediments: Implications for sediment toxicity testing

Juvenile Nereis (Neanthes) arenaceodentata survival and growth were used to evaluate the effect of storage time on the toxicity of sediments with moderate PAH and metal contamination. Seven San Francisco Bay area sediments and a clean control sediment were stored (4 degrees C) and then periodically evaluated (up to two years after collection). During each test, juvenile worms (2-3 weeks post emergence) were exposed for 21 days. Test endpoints were survival and growth rate (mg dry weight/day). In general, survival was high (>75%) and long-term cold storage (740 days) did not significantly alter growth or survival. In half of the sediments a cyclical phenomenon was observed associated with the appearance of ammonia in the overlying water of bioassay beakers. The periodicity of this phenomenon was approximately one year. It was not associated with any geophysical characteristic of the test sediments (i.e. grain size, % TOC, % TKN). Significant mortality (0% survival on day 427) was associated with the largest of these peaks in overlying water ammonia concentration. Results of this study suggest that ammonia in stored sediments is an important, potentially confounding factor in sediment toxicity tests.