Dispersal of Contaminants from Municipal Discharges as Evidenced from Sedimentary Records in a Great Lakes Coastal Wetland, Cootes Paradise, Ontario

Cootes Paradise is a coastal wetland, at the western end of Lake Ontario. The marsh, which is an important spawning ground for fish and a crucial habitat for other species, has been considerably degraded by excessive contaminant inputs from wastewater treatment plants (WTPs), marsh tributaries, and Combined Sewer Overflows (CSOs). These discharges are not only major sources of nutrients (e.g., phosphorus) to the marsh, but are also the main contributors of pharmaceuticals, hormones, and other wastewater contaminants. Studies have shown that many of these compounds are toxic and have estrogenic effects on organisms living in the vicinity of these sources. This study investigates dispersal of contaminants from nearby point sources, as determined from sediment contamination, both spatially and stratigraphically. This was accomplished by establishing the trends and utilizing the relationships between limiting nutrient phosphorus, estrogenic alkylphenols, and faecal sterols, specifically, coprostanol. High levels of phosphorus (1,655–1,987 mg TP kg−1) and alkylphenolics (2.51–4.89 mg kg−1) were measured in sediments near the discharge outlets. Statistical analysis revealed a close relationship between investigated pollutants and the molecular marker coprostanol, and provides evidence of significant sediment contamination near the discharge points, suggesting deposition of most contaminants within a short distance from the points of entry and limited dispersal of pollutants within the wetland. The stratigraphic distribution of pollutants, which reflects the historical trends, reveals major spikes in pollutant concentrations near point sources that could be attributed to episodic events of major significance and shows a long persistence of the investigated contaminants in sedimentary environments.