Survey of Sediment Quality in the Duluth/Superior Harbor: 1993 Sample Results

The Duluth/Superior Harbor has been designated as part of the St. Louis River Area of Concern (AOC) by the International Joint Commission (IJC). Contaminated sediments contribute to impaired uses in this AOC. The degree of sediment contamination in depositional areas outside the shipping channels is not well documented in the harbor, which has a long history of industrialization. In order to obtain a cohesive dataset, a sediment quality assessment was conducted in the St. Louis River estuary during September 1993. This study was designed to support the assessment goals of the Phase I sediment strategy for the St. Louis River Remedial Action Plan (RAP). This survey included the collection of sediment cores from 40 sites suspected to exhibit contamination (Table 1, Figure 1). The U.S. EPA Research Vessel, the Mudpuppy, was used to collect sediment samples between the Fond du Lac Dam and Duluth/Superior entries during September 1993. A vibracore sampler (10 cm diameter) was used for collecting up to 3-m deep cores. The surficial (0-30 cm) layer was analyzed for the following contaminants: 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), thirteen pesticides, mercury (Hg), lead (Pb), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn), total organic carbon (TOC), and ammonia. Up to five sections per core (at 30 cm increments) were analyzed for mercury, PCBs (congeners and Aroclors), PCB immunoassay, PAH fluorescence screen, and TOC. Six of the 40 vibracore samples were sectioned in 2 to 5 cm increments and dated using the radioisotopic tracer 137 Cesium. In addition, surface gravity cores were collected from six sites, selected by their proximity to commercial, private or public shipyards, boat docks, and loading facilities; these samples were analyzed for tributyltin and three other butylated forms of tin (i.e., mono-, di-, tetra-). Surficial sediments, collected with a Ponar, were evaluated for acute toxicity to two benthic invertebrates: the amphipod, Hyalella azteca (H. azteca), and midge, Chironomus tentans (C. tentans). The Ponar samples were alsoevaluated for acute toxicity to the bacterium Photobacterium phosphoreum (MicrotoxR test) and genotoxicity to the bacterium Vibrio fischeri (MutatoxR). All analytical and toxicity test methods followed the data quality objectives of the Quality Assurance Project Plan.