Sediment quality Atlantic Ocean watershed: chapter 1
Lake Ontario, the most downstream of the Great Lakes, receives mainly the waters of the Niagara River and outflows into the St. Lawrence River. Mercury, used in several industrial processes during the 20th century, is considered as the major inorganic contaminant occurring in the sediments. Now, mercury concentrations have declined more than 25% over the last three decades in Lake Ontario following the implementation of abatement plans for the pollution from effluents. Despite this decline, it is still detected at relatively high concentrations. In addition to mercury, scientists detect other metals in Lake Ontario such as cadmium, lead and zinc.
As for polychlorinated biphenyls (PCBs), concentrations have declined 40% during the last thirty years to the point where they are lower than the probable effects level. Despite the fact that scientists also observe a decline in concentrations of dioxins and furans, as well as those of dichlorodiphenyltrichloroethane (DDT), a pesticide used in the 60’s, their concentrations still remain high in Lake Ontario’s sediments.
As for polybrominated diphenyl ethers, commonly known as PBDEs, concentrations in Lake Ontario’s sediments have more than tripled between 1983 and 2004. In 2004, concentrations are still significant at the mouth of some tributaries, namely near urban centers of Toronto and Hamilton.
Spatial distribution of PBDEs in lake Ontario
The figure shows the spatial distribution of the concentrations of PBDEs in surface sediment in Lake Ontario in 2004. They vary between 0 and 816 ng/g. High concentrations are measured near Hamilton and Toronto, with 430 and 149 ng/g, respectively. However, it is near Picton where the highest concentration was observed at 816 ng/g.
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