| Popis: |
Microcosm laboratory experiments assessed the impact of floatable materials and associated contaminants transported to the surface millilayer (SMIL) after sediments composed of potential dredged materials were disturbed. Urban bay sediments collected from the Everett Harbor, WA, and clean sediments from Sequim Bay, WA, were mechanically disturbed and the resulting floatable fractions transported to the SMIL during a 48-h period were removed for analysis. Sediment, water and SMIL concentrtaions oforganic carbon, suspended solids, a suite of hydrocarbons, metals, sulfides and extractale mtaerials were quantified and compared to EPA's water quality criteria. Bioassay experiments examined the effects produced by exposing sea urchin embryos to these impaired SMIL samples. Contaminants transported to the surface layer within 48h were 0% to 0·2% of the total mass of contaminants in the test sediments. These experimental results were compared with those predicted by a computer model with reasonably close agreement. Contaminant concentrations in one SMIL impacted by Everett Harbor sediments exceeded EPA water quality criteria limits established for Cu, Zn, Pb, Hg and PAH. The other Everett Harbor sediment sample exceeded the water quality standards for Cu and Pb. Both of these samples were toxic to the developmental phases of sea urchins as shown by the bioassay. According to the numerical model, these SMIL contaminant concentrations would require high dilution ratios before background concentrations could be achieved. The experimental results suggest that dredged material disposal may influence the chemistry and biology of the ocean's surface layer. |
