in Lake Simcoe and its Tributaries
In 2015, a study was undertaken to investigate levels of chemical contaminants in the surface water and sediments of Lake Simcoe and its tributaries. The contaminants included in this study were chosen based on historical use within the watershed, previous research undertaken (such as the LSRCA 2004 study), and literature from similar areas in the Great Lakes Region. As such, this study included: petroleum hydrocarbons (or PHCs); polycyclic aromatic hydrocarbons (PAHs); phenols; metals, including chromium and mercury; organochlorine pesticides (OCPs), including DDT and its metabolites; neutral chlorinated compounds (NCCs), and polychlorinated biphenyls (PCBs).
In terms of PHCs, none were detected in surface waters of the lake or tributaries, but sediments had some high values related to Fraction 4G. No PHC guideline values currently exist but one site in Mill Creek (Orillia) had a concentration that was 11 times higher than the average of other tributary sites. In the lake, high PHCs were present in the lower East Holland River and in shallow water off Barrie. PAHs were not often detected in surface waters, but high results were found in sediments at Mill Creek in Orillia, the outlet of the Holland Marsh, and the East Holland River downstream from Aurora and Newmarket. In Lake Simcoe, high PAHs in sediment were found in the shallow and deeper water off Barrie. Although no NCCs were detected at our study sites, phenols exceeded guideline values at Colbar Marsh and the deepwater lake site near Barrie. At the shallow water site off Barrie, PCB concentrations exceeded guideline values.
Of more concern were the presence of OCPs and metals in the Lake Simcoe Watershed. OCPs were mostly found in, and downstream of, areas of intense agricultural use (e.g. Holland Marsh and other polders) where they were used extensively as pesticides in the mid-20th century. Among OCPs, the presence of DDT, and its metabolites DDD and DDE, are of concern in that the highest concentrations recorded in Ontario were found. DDT, DDD, and DDE are very persistent and can have large impacts to foodwebs, especially to top-level predators. Heavy metals (esp. cadmium, copper, arsenic, and zinc) were found in areas with heavy industrial uses (particularly Mill Creek in Orillia), but the presence of chromium is of special concern in the East Holland River, linked to the locations of former leather tanneries in Aurora and Newmarket.
Generally, the contaminants recorded in the Lake Simcoe Watershed are the result of non-point anthropogenic sources (e.g. automobile exhaust, fossil fuel combustion) and specific areas of industrial, urban, and agricultural land-use activities (e.g., pesticides). Although some contaminants may be linked to current uses (e.g. PHCs, PAHs, phenols), others are likely legacy contaminants (i.e. DDT and chromium) from historical activities. Overall, it is recommended that regular monitoring of specific contaminants (e.g. DDT and metabolites, chromium, heavy metals) be undertaken more frequently. Sampling should target areas of guideline exceedances such as urban centres (Aurora, Barrie, and Newmarket) and intensive agricultural areas (Holland Marsh and other polders). More frequent and targeted sampling will aid in better evaluating our understanding of changes in chemical contaminants, including decreases or increases in concentration, movement through the watershed, and the potential risks to aquatic organisms or human health.