Polychlorinated dibenzo-p-dioxins and dibenzofurans in Niagara River suspended sediments.

Niagara River archived suspended sediments were analyzed for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) to investigate temporal trends and to assess congener profiles as source indicators. In general, concentrations ranged from 6 to 35 pg g(-1) toxic equivalents (TEQs) and 1000-6000 pg g(-1) total PCDDs/Fs and reflected a slight decline in the 1980s, but with little apparent change since that time. This temporal trend was consistent with those observed in Lake Ontario environmental compartments. The observed levels generally reflected ambient background levels in the Niagara River; however, three samples were substantially above ambient levels and a fourth sample, while not elevated, had a profile that was distinctly different from those typically observed at Niagara-on-the-Lake at the mouth of the Niagara River. Event-based concentrations ranged from approximately 160-620 pg g(-1) TEQs; congener profiles for these samples were consistent with known source areas in the Niagara River watershed, including Pettit Flume and Bloody Run Creek. These qualitative and quantitative results indicated loadings of dioxins and furans from hazardous waste sites in the Niagara River are occurring episodically, and can be measured in suspended sediments downstream at the river mouth at Niagara-on-the-Lake.

Spatial distribution and trends of total mercury in waters of the Great Lakes and connecting channels using an improved sampling technique.

Environment Canada recently developed a clean method suitable for sampling trace levels of metals in surface waters. The results of sampling for total mercury in the Laurentian Great Lakes between 2003 and 2009 give a unique basin-wide perspective of concentrations of this important contaminant and represent improved knowledge of mercury in the region. Results indicate that concentrations of total mercury in the offshore regions of the lakes were within a relatively narrow range from about 0.3 to 0.8 ng/L. The highest concentrations were observed in the western basin of Lake Erie and concentrations then declined towards the east. Compared to the offshore, higher levels were observed at some nearshore locations, particularly in lakes Erie and Ontario. The longer-term temporal record of mercury in Niagara River suspended sediments indicates an approximate 30% decrease in equivalent water concentrations since 1986.