Monitoring the State of the St.Lawrence River: Toxic
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WATER SEDIMENTS SHORELINES BIOLOGICAL RESOURCES USES TOXIC CONTAMINATION IN SEDIMENTS Lake Saint-Louis: Where Two Rivers Meet Background three metres (m) over more than half its area, the lake forms an immense ake Saint-Louis, formed by the 148-km2 triangle stretching for more Photo: Nathalie Gratton, Environment Canada Lconfluence of the Ottawa and St. than 25 km. The water mass of the Shipek corer Lawrence rivers, is one of Quebec’s Great Lakes extends throughout most popular lakes with pleasure almost the entire lake, while that of Montreal Island before reaching the boaters. With an average depth of the Ottawa River flows alongside Lachine Rapids. The St. Lawrence ship channel cuts through Lake Saint-Louis, allowing commercial ship traffic to move on through the Beauharnois Canal into Lake Saint-François and up the St. Lawrence to the Great Lakes. With the opening of the St. Lawrence Seaway in the late 1950s and the construction of hydroelectric dams, the area upstream of Lake Saint-Louis became heavily industrialized, especially along the Saint-Louis River. This industrializa- tion has inevitably had repercussions on the aquatic environment, because of discharges of numerous contami- Photo: Martin Jean, Environment Canada Aerial view of Lake Saint-Louis Islands nants of varying degrees of toxicity. SEDIMENTS Figure 1. Location map of Lake Saint-Louis Île de Montréal Pointe-Claire Dorval Lachine QUEBEC ONTARIO Beaconsfield Baie ATLANTIC Sainte-Anne- d’Urfé OCEAN de-Bellevue UNITED STATES Kahnawake Indian Reserve Pincourt L’Île Perrot Notre-Dame- Châteauguay de-l'Île Perrot Léry r e iv Îles de R y la Paix a Pointe-des- u ug Cascades ea ât Ch r Maple Grove e l a iv Melocheville n R a Beauharnois s C i is u o o n r -L a t 0 1 2 3 4 5 km h n u i a a e B S Source: Modified from Fortin et al., 1994. The waters and sediments of Lake between the Îles de la Paix island Subsequently, the loadings of toxic Saint-Louis became increasingly group and the shore, there is another substances were reduced considerably contaminated with toxic substances sedimentary basin containing particles through steps taken to reduce emis- such as mercury and polychlorinated from the St. Lawrence River, the sions of hazardous wastes under the biphenyls (PCBs). Because of the dif- erosion of the Îles de la Paix, and the St. Lawrence Action Plan and the fering sources of the inflows of water Saint-Louis River. Quebec government’s Programme de and sediment particles, the northern réduction des rejets industriels (program to part of Lake Saint-Louis presents a Overview of the Situation reduce industrial wastes). Hence, the different sedimentary and geochemi- concentrations of the various organic cal picture than the southern part. As Quebec’s population grew and substances in the sediments have A high proportion of the suspended its industry developed during the gradually diminished, and the concen- particles from the Ottawa River settle mid-20th century, the waters and sedi- trations of metals are now close to the on the bottom of the lake off ments of Lake Saint-Louis became values observed in the early 1970s. Beaconsfield, thus forming muddy increasingly contaminated with toxic Though these concentrations still sediment beds several kilometres substances such as mercury and slightly exceed the levels considered wide. On the south side of the lake, polychlorinated biphenyls (PCBs). likely to have effects on benthic State of the St. Lawrence River Toxic Contamination in Sediments Lake Saint-Louis: Where Two Rivers Meet SEDIMENTS organisms, improved wastewater Table 1. Average concentration of different toxic substances treatment must be seen as having in surficial sediment in Lake Saint-Louis done much to improve the quality of the aquatic environment. Average concentration (µg/g) As Cd Cr Cu Ni Pb Zn Hg PCB Northern Part of the Lake SAMPLING YEAR In the northern part of Lake Saint- 1976 Louis, the sediment loadings from the Entire lake ––68 33 43 28 169 3.68 – Ottawa River cause accumulations of about 1 cm of muddy sediment per Northern part ––61 27 47 32 194 0.42 – year over an area of more than 20 km2. Southern part ––74 39 40 25 148 6.38 – At some locations, the sediment is at 1986 least 2 m deep, reflecting the great Entire lake 5.9 – 95 33 33 33 211 1.11 0.132* stability of this part of the lake. Northern part 5.9 – 101 36 35 42 258 0.27 0.138* Ancient sediments sampled in this Southern part 6.0 – 89 31 30 33 151 2.09 0.121* sedimentary basin show a relatively rapid increase in mercury (Hg) 2003 concentrations in the environment. Entire lake 7.8 0.83 68 26 38 29 153 0.30 0.020** Northern part 9.6 0.93 73 27 40 33 180 0.11 0.017** Southern part 4.8 0.66 59 26 33 23 110 0.60 0.023** Figure 2. Distribution of mercury PERCENT CHANGE (Hg) concentrations in From 1976 to 2003 sediment in the nothern part of Lake Saint-Louis Entire lake ––021 13 -4 10 92 – Mercury (µg/g) Northern part ––-20 2 15 -4 7 74 – Ê 00.20.40.60.80.1 0.3 0.5 0.7 Ê Southern part ––20 33 7726 91 – 0 From 1986 to 2003 10 Entire lake -31 – 29 21 -14 23 27 73 85 Northern part -64 – 28 24 -16 22 30 60 87 20 Southern part 20 – 34 17 -9 28 28 71 81 30 SEDIMENT QUALITY CRITERIA 40 TEL 5.9 0.6 37 36 – 35 120 0.17 0.034 50 PEL 17 3.5 90 200 – 91 310 0.49 0.280 Depth (cm) * The average PCB concentration in 1986 is the sum of Aroclors 1242, 1254 and 1260. 60 ** Congeners were used to calculate the approximate value of the average concentration of Aroclors 1242, 1254 and 1260. 70 TEL: Threshold Effect Level. PEL: Probable Effect Level. 80 TEL PEL 90 TEL: Threshold Effect Level. PEL: Probable Effect Level. Photo: Nathalie Gratton, Environment Canada Photo: Nathalie Gratton, Environment Canada State of the St. Lawrence River Toxic Contamination in Sediments Lake Saint-Louis: Where Two Rivers Meet SEDIMENTS This increase, which is also observed Figure 3. Spatial distribution of mercury (Hg) in sediment for metals (copper [Cu], zinc [Zn], lead in Lake Saint-Louis in 1985 and 2003 [Pb], and nickel [Ni]) and PCBs, is caused by the use of these substances 1985 Île de Montréal in various industrial processes. In the more recent sediments, the concentra- tions are lower, with values close to the Threshold Effect Level (TEL) for benthic organisms. For the northern part of the lake as a whole, mercury concentrations fell St. Lawrence Seaway by 75% from 1976 to 2003, while those Île Perrot for PCBs fell by 85% from 1985 to 2003, Châteauguay except for the sediments confined r e iv within the Dorval marina, which still R y a u g show high concentrations of PCBs, u a te â possibly associated with older sedi- h C ments. The majority of the metals (chromium [Cr], Cu, Pb and Zn) show Beauharnois 0 4 km an approximately 30% decrease in con- Saint-Louis River centration from 1985 to 2003. This Île de Montréal decrease must be regarded as relative- 2003 ly small and insignificant compared with those measured in the other lakes along the St. Lawrence, especially because the concentrations of arsenic (As) and Ni have increased while near- ly 50% of the current average concen- trations of the various metals still St. Lawrence Seaway exceed the TEL for benthic organisms. Île Perrot Châteauguay r e iv R y a u g u a te â h C Beauharnois 0 4 km Saint-Louis River Hg concentrations Sampling station 0.0 0.094 0.17 0.25 0.49 0.87 µg/g State of the St. Lawrence River Toxic Contamination in Sediments Lake Saint-Louis: Where Two Rivers Meet SEDIMENTS Figure 4. Spatial distribution of polychlorinated biphenyls (PCBs) Southern Part of the Lake in sediment in Lake Saint-Louis in 1986 and 2003 On the south side of the lake, the sediment particles from the Saint- 1985 Île de Montréal Louis River settle almost exclusively in a small basin between an island group called the Îles de la Paix and the lake’s south shore. Sediment accumulation here is fairly substantial, but more unstable. High water levels in the St. Lawrence in spring and fall cause St. Lawrence Seaway heavy erosion of the muddy bottoms and the contours of the islands, thus Île Perrot Châteauguay causing large amounts of material to move downstream. r e iv R y Geochemical data on sediment a u g u a samples gathered in 1976, 1985 and te â h C 2003 show that the mercury concentra- tions measured in the southern part of Beauharnois 0 4 km Lake Saint-Louis have decreased by Saint-Louis River about 90% over nearly 30 years. But even so, the concentrations of contam- 2003 Île de Montréal inants in the sediment around the Îles de la Paix remain above the Probable Effect Level (PEL) for benth- ic organisms. The concentrations of PCBs have decreased by about 85% since 1985, as the result of improved wastewater St. Lawrence Seaway treatment in the region and a general decrease in PCBs in the St. Lawrence Île Perrot Châteauguay over the past 20 years. However, the r e iv highest concentrations of PCBs are R y a u still found at the mouth of the Saint- g u a te Louis River, upstream from the Îles de â h C la Paix.