WP16 Sediment Quality Assessment
Wednesday, 16 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(MCC-1117-834566) Sea urchin (Arbacia punctulata) embryo-larval assessment of dredged material elutriates - Implications of ammonia sensitivity.

McCulloch, W¹, Sohn, V¹, Derrick, P¹, Rees, S², ¹ EA Engineering, Science & Technology, Inc., Sparks, MD, USA² US Army Corps Engineers, Mobile Dist., Mobile, AL, USA

ABSTRACT- Elutriates prepared from proposed dredged material samples are assessed for chemical constituency, and are evaluated toxicologically by three test species: an invertebrate, a fish and a planktonic stage of a test species. The invertebrate and fish tests assess acute toxicity, and generate 96-hour LC50 values. The planktonic stage tests are typically performed with mussel (Mytilus sp.) or sea urchin (Arbacia or Stronglyocentrotus) embryos, and the test data generate an EC50 value based on percent normal development to a defined larval stage. In previous dredged material testing programs, the elutriate EC50s from the sea urchin tests have been significantly lower (< 10 percent elutriate), when compared to the LC50 values from the invertebrate and fish water column tests (generally > 50 percent elutriate). The goal of the present study was to determine if ammonia was a factor in the increased sensitivity of the sea urchin developmental test, and if so, to quantify ammonia's contribution to overall elutriate toxicity. Arbacia punctulata embryo-larval testing was performed with ammonium chloride to determine the 48-hour EC50 for un-ionized ammonia. Additionally, aliquots of dredged material elutriates were ammonia stripped by aeration at high pH (>11.0). Sea urchin embryo-larval tests were performed on pre- and post-ammonia stripped elutriates to quantify the toxicity removal through ammonia reduction. The test results indicate that the A. punctulata embryo-larval bioassay is very sensitive to the presence of ammonia, and that stripping ammonia from dredged material elutriates substantially reduces the toxicity of the samples being evaluated. This sensitivity can have a significant impact on the assessment of dredged material proposed for disposal in open water environments where ammonia can be rapidly dispersed and assimilated.

Key words: Arbacia, ammonia, elutriate, marine