Publication Summary

Studies near the Post Point Wastewater Treatment Plant outfalls found sediment toxicity ascribed to sulfides. This study was to determine if this toxicity warranted detailed cleanup investigations.

Sediments were collected from 8 locations in September 2007 and tested using 4 bioassays. Sulfide levels in sediment, porewater, and during bioassays were also measured. Only 2 samples had minor toxicity, but they were among the highest sulfide levels measured, and a dose-response relationship was suggested. Sulfides levels near Post Point were not different from levels in other inner Bellingham Bay areas.

Recommendations include no detailed studies, limited monitoring for sediment toxicity, and new sampling and toxicity test methods.

Previous studies near 2 Post Point Wastewater Treatment Plant outfalls in Bellingham Bay, Bellingham, Washington, have suggested sediment toxicity related to sulfides. The purpose of this study was to determine if the incidence and severity of toxicity near the outfalls warrants more detailed cleanup investigations.

During 2007, the Washington State Department of Ecology tested surface sediment from 8 locations for toxicity using 4 bioassay protocols. Levels of total sulfides in sediment and porewater were measured in the same samples. Results showed little observable toxicity despite elevated sulfides in both sediment and porewater of some samples. Only the Microtox luminosity test results for 2 samples exceeded the Sediment Quality Standards.

Results indicated a possible dose-response relationship between total sulfides and Microtox toxicity, but different from relationships calculated using previous results. Levels of total sulfides also explained some of the variability in amphipod and larval test toxicity results. Losses of sulfides from porewater appeared to occur during setup procedures and tests themselves more than during sample storage.

As a result of this study, it is recommended that future monitoring of sediment toxicity in the Post Point area be limited. Results also suggest that improved sample handling and toxicity testing protocols should be developed for evaluating areas of high sediment sulfide.

Link to EIM data for User Study ID PPTox07