Environmental Assessment of Benthic Impacts Associated with Pulp Mill Discharges. II. Distribution of Sediment EOX in Relation to Environmental Factors

Between 1991 and 1992, comprehensive toxicological, chemical, and benthic community structure surveys were conducted at Jackfish Bay, Lake Superior, Ontario, to assess sediment quality below a bleached kraft mill effluent (BKME) outfall. In this report, we describe the spatial distribution and concentration of extractable organic chlorines (EOX) in sediments below the outfall in relation to effluent discharge patterns, sediment deposition, and bioaccumulation potential. Triplicate sediment samples were collected by Ekman grab from 29 and 44 stations in 1991 and 1992, respectively, and from 15 stations in three reference areas not exposed to the effluent. For each sample, organic carbon content, dry weight, and sediment-associated EOX were determined. In addition, sediment traps were used to determine sediment deposition along two tangents transecting the effluent plume and at a reference station located approximately 4,200 m from the outfall. The spatial distribution of sediment EOX consisted of two distinct concentration gradients, each linked to effluent discharge patterns from Blackbird Creek and dominant circulatory patterns in Jackfish Bay: a north–south gradient, extending along the west shore of Jackfish Bay, and a east–west gradient. Sediment EOX ranged from 7,000 mg/kg organic carbon (oc) (2,050 mg/kg dry solids (ds)) in depositional sediments of Moberley Bay to nondetectable at some stations in eastern and outer Jackfish Bay. Reference (background) concentrations ranged from nondetectable to 3,000 mg/kg oc (1–15 mg/kg ds). The attenuation of EOX was significantly correlated with the rate of sediment deposition (r2 = 0.57; p ≤ 0.001). Although the concentration of sediment EOX was strongly correlated with toxicity to some invertebrates (Sibley et al.[1997] Arch Environ Contam Toxicol 32:274–284), bioaccumulation factors were typically <2 based on analysis of oligochaete tissues. The results of this study demonstrate that the spatial distribution of sediment-associated contaminants adjacent to pulp mill effluent outfalls are determined primarily by hydrodynamic and depositional characteristics of the receiving waters and that EOX can be used to accurately delineate areas of contamination.