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Executive Summary

Most chemical contaminants entering the marine environment have an affinity for particles and tend to accumulate to elevated concentrations in sediments, creating the potential for toxicity to benthic or demersal organisms. Physical and chemical processes within sediments such as resuspension and diffusion can result in the transport of contaminants to other areas. A principal concern of the SCBPP, therefore, was the evaluation of various indicators of sediment quality that could be used to evaluate the health of benthic environments. This report presents the results of sediment toxicity tests conducted on SCBPP sediment samples.

Sediment samples were collected from 72 stations during SCBPP sampling cruises. Station locations ranged from Point Conception to the Mexican border in depths of 10-200 meters. These stations represented a subset of SCBPP sites selected for benthic chemistry analysis. Sediments were collected using a 0.1 m² Van Veen grab during July and August, 1994. Sediment samples were stored under refrigeration for up to four weeks before testing. Each sample was evaluated using two toxicity tests, enabling the toxicity of both sediment and interstitial water to be measured.

The toxicity of whole sediment was evaluated by measuring the survival of the tube dwelling amphipod Ampelisca abdita following a 10 day exposure. Interstitial (pore) water was tested for toxicity using a sea urchin embryo development test. Interstitial water was obtained by centrifuging sediment. The supernatant was diluted with seawater to produce test concentrations of 100, 50, and 25%. Embryos of the purple sea urchin (Strongylocentrotus purpuratus) were exposed to the test samples for 72 hours and then evaluated for the percentage of normal development using a microscope.

Amphipod survival was high in all samples tested, ranging from 80-98%. Statistically significant reductions in survival were identified for six samples. None of the 72 samples were identified as toxic, however, as amphipod survival was ³80% of the control for all samples.

In contrast to the amphipod survival data, sea urchin embryo development was adversely affected by interstitial water from many sediment samples. Most of the 100 and 50% samples produced less than 80% of the control development in embryos, with many samples producing less than 5% normal development. Even a majority of the samples diluted to 25% interstitial water were toxic.

Many of the interstitial water samples contained elevated ammonia concentrations that were sufficient to cause embryo toxicity. The elevated ammonia concentrations were likely caused by sediment handling and storage procedures. A regression model for ammonia toxicity was applied to the data for 25% interstitial water in order to distinguish between toxicity due to ammonia and other factors. Fifteen samples were identified as having toxicity not caused by ammonia.

Nine of the 15 toxic interstitial water samples were located in the northern part of the SCB, distant from large point source waste discharges. The remaining toxic samples were located near POTW discharges in the central and southern parts of the study area.

Though limited comparable data are available, the SCBPP sediment toxicity results are generally consistent with prior research in selected areas of the SCB. Previous measurements of whole sediment toxicity at contaminated sites in Santa Monica Bay and off Palos Verdes have also shown a lack of toxicity to amphipods in 10-day tests. Ammonia toxicity has also been identified as an important factor in sea urchin embryo tests of interstitial water from southern California bays and estuaries. Previous measurements of interstitial water toxicity off Palos Verdes have also identified toxicity at stations located near a POTW discharge.