Issue :
Since the 1900's, the water and sediments of the St. Lawrence River have been contaminated by many different toxic substances (metals, PAHs, PCBs) from industrial, agricultural and urban sources. With the implementation of pollution remediation measures in the 1980's, sediment contaminant concentrations have declined considerably and today are below the threshold concentrations that can have effects on aquatic organisms (EC and MDDEP 2007).

At the turn of the 21 st century, the development of new technologies resulted in the use of a number of organic contaminants, such as PBDEs, coming from urban wastewater. Little is known about their harmful effects on aquatic fauna, and the development of quality criteria is still at an early stage.

The results of current and past characterizations were analyzed in order to assess the quality of Lake Saint-Pierre sediments and identify emerging trends. Since the 1970's, surface sediments in Lake Saint-Pierre have been sampled four times:

• The first study, which was carried out in 1976, primarily in the upstream part of the lake, namely the area around the Berthier-Sorel Islands, focused largely on metal contamination of sediment (Sérodes 1978).
• The work done in 1986 produced an initial status report on a number of organic substances in sediment, including polychlorinated biphenyls (PCBs), in most of the northern part of the shipping channel (Hardy 1990).
• Lastly, sediments in the entire northern part of the lake were sampled in 2003 and 2013 by Environment Canada and analyzed for PCBs, chlorinated dioxins and furans, polycyclic aromatic hydrocarbons (PAHs), PBDEs and metals, including mercury. This fact sheet focuses on those recent results.

Key measures

Sediment quality criteria and indices

The sediment quality criteria used in this document (TEL: threshold effect level; OEL: occasional effect level) are taken from EC and MDDEP (2007). They are defined on the basis of observed biological effects on benthic and pelagic organisms and contaminant concentrations measured in sediment.

The quality indices are calculated by dividing the measured concentration of each substance in each sample by the TEL quality criterion for the substance in question. An index higher than 1 indicates that the concentration exceeds the criterion and biological effects may be observed, whereas an index lower than 1 indicates that sediment quality is good.

Mean quality indices were calculated for metals (except mercury) and PAHs:

The metals index is the average of the quality indices calculated for the respective concentrations and criteria for the following seven metals: copper, zinc, lead, nickel, chromium, arsenic and cadmium. The OEL is used for nickel because there is no defined TEL.
 
The PAH index is the average of the indices calculated for the respective concentrations and criteria for the following 12 substances: acenaphthylene, acenaphthene, anthracene, benzo[a]anthracene, benzo[a]pyrene, chrysene, dibenzo[a,h]anthracene, fluoranthene, fluorene, naphthalene, phenanthrene, pyrene.

The overall indicator status is based on the proportion of uncontaminated sites and contaminated sites relative to the total number of sites characterized. This proportion defines an overall status that ranges from good to poor.

Toxic contaminants in the 20 th century

Status in 2013: The overall sediment quality status of Lake Saint-Pierre is classified as good in 2013. The concentrations of metals and mercury are below the TEL criterion in almost every case, which indicates very good sediment quality. For PCBs, PAHs and chlorinated dioxins and furans, a number of sampling sites, particularly in the area of the Berthier-Sorel Islands, show concentrations higher than the TEL. However, for the lake as a whole the mean concentrations of these substances are below the TEL (Table 1).

Long description

Figure 2 presents the northern sector of Lake Saint-Pierre. The colours correspond to the level of sediment contamination by mercury for four years: 1976, 1986, 2003 and 2013. For 1976, the area is predominantly green, corresponding to concentrations between 0.09 and 0.17 µg/g. Red areas corresponding to concentrations above 0.3 µg/g are concentrated in the channels of the Berthier-Sorel Islands. For 1986, most of the downstream area is green, corresponding to concentrations between 0.09 and 0.17 µg/g. Yellow and red zones corresponding to concentrations above 0.17 µg/g are concentrated upstream in the area of the channels of the Berthier-Sorel Islands. For 2003, the area is predominantly blue and green, corresponding to concentrations below 17 µg/g. Small yellow and red areas corresponding to concentrations above 0.17 µg/g remain in the channels of the Berthier-Sorel Islands. For 2013, the area is entirely blue and green, corresponding to concentrations below 0.17 µg/g.

Figure 3. Change in the metals index in Lake Saint-Pierre surface sediments in 1976, 1986, 2003 and 2013.

Long description

Figure 3 presents the northern sector of Lake Saint-Pierre. The colours correspond to the index of sediment contamination by metals for four years: 1976, 1986, 2003 and 2013. For 1976, the area is predominantly orange and red, corresponding to contamination indices above 1.6. For 1986, the area is mainly orange, corresponding to indices of approximately 1.6. For 2003 and 2013, the area is almost entirely blue and green, corresponding to indices below 1, except for small yellow areas in the channels of the Berthier-Sorel Islands.

Figure 4. Change in PCB concentrations in Lake Saint-Pierre surface sediments in 1986, 2003 and 2013. 

Long description

Figure 4 presents the northern sector of Lake Saint-Pierre. The colours correspond to the level of sediment contamination by PCBs for three years: 1986, 2003 and 2013. For 1986, the area is almost entirely orange and red, corresponding to concentrations above 79 ng/g. For 2003 and 2013, the area is mainly blue and green, corresponding to concentrations below 34 ng/g. Small yellow and red zones corresponding to concentrations above 34 ng/g remain in the channels of the Berthier-Sorel Islands.

Figure 5. PAH index and dioxin and furan concentrations in Lake Saint-Pierre surface sediments in 2013.

Long description

Figure 5 presents the northern sector of Lake Saint-Pierre. The colours correspond to the index of sediment contamination by PAHs in 2013. The downstream area is primarily green and blue, corresponding to an index below 1, whereas the upstream area in the channels of the Berthier-Sorel Islands, where the index is above 1, is predominantly yellow and red. The figure also presents the index of sediment contamination by dioxins and furans in 2013. The downstream area is largely green and blue, corresponding to an index below 0.85, whereas the upstream area in the channels of the Berthier-Sorel Islands is predominantly yellow, with an index above 0.85.

Table 1. Average concentrations and variation of toxic substances measured in sediment of Lake Saint-Pierre between 1986 and 2013

Changes since the 1980s

Changes since the 1980s: 1986 was used as a reference year for calculating the percentage change in contaminant concentrations in sediment, since the highest levels of most substances were recorded that year (Table 1).

The mean concentrations of metals (including mercury) and PCBs declined by about 75% and 82% respectively between 1986 and 2013. This decline appears to be continuing since concentrations decreased by 15 to 25% between 2003 and 2013. A comparison of sampling years is not possible for dioxins and furans and for PAHs because these substances were not analyzed. However, it appears that the mean concentrations of dioxins and furans and PAHs in the sediment samples collected in 2013 were below the TEL except in the area of the Berthier-Sorel Islands which remains contaminated.

Contaminants of emerging concern: PBDEs

PBDEs are a group of 209 brominated organic compounds which are used as flame retardants in plastics. Once they enter the aquatic environment. they are persistent and bind to sediment particles. The most harmful PBDEs are those with five bromine atoms (pentaBDEs); BDE-99 and BDE-100 are among those commonly monitored. It should be noted that these contaminants are excluded from the calculation of the overall indicator status.

Figure 6. Change in BDE-99 concentrations in Lake Saint-Pierre sediments in 2003 and 2013. 

Long description

Figure 6 presents the northern sector of Lake Saint-Pierre. The colours correspond to the level of sediment contamination by BDE-99 in 2003 and 2013. For 2003, the area is almost entirely orange and red, corresponding to concentrations above 0.8 ng/g. For 2013, the downstream area is predominantly blue and green, corresponding to concentrations below 0.5 ng/g. The upstream area is primarily yellow and red, corresponding to concentrations above 0.8 ng/g in the channels of the Berthier-Sorel Islands.

Status in 2013: The guideline value of 0.4 ng/g of BDE-99 established by the federal government for the protection of aquatic wildlife (EC, 2011) was exceeded by 42% of surface sediment samples collected in 2013 in the northern part of Lake Saint-Pierre. Nearly half of these samples contained concentrations that were two times higher than the guideline (Figure 6). The highest concentrations were found in the area of the Berthier-Sorel Islands.

Changes since 2003: The mean concentration of pentaBDEs in Lake Saint-Pierre surface sediments declined by 59% between 2003 and 2013 and a marked decrease of 75% was observed in the area of the Berthier-Sorel Islands (Table 1). Despite this decline, close to 60% of the highest concentrations were found in the channels around those islands.

Figure 7. Temporal profiles of BDE-99. BDE-100 and BDE-209 concentrations in Lake Saint-Pierre sediments.

Long description

Figure 7 presents a graph of BDE-99, BDE-100 and BDE-209 concentrations measured at various depths in a 32-cm sediment core, corresponding to various years from 1992 to 2012. BDE-100 concentrations ranged from 0.1 to 0.3 ng/g over the entire period. The quality criterion is 0.4 ng/g. BDE-99 concentrations ranged from 0.4 to 0.9 ng/g, except in 2006 and 2007, when concentrations were approximately 1.1 ng/g and 1.2 ng/g, respectively. BDE-209 concentrations are below 5 ng/g, except in 2006, 2007 and 2008, when they reached roughly 14 ng/g, 7 ng/g and 6 ng/g, respectively.

The temporal profiles (Figure 7) show a peak in the concentrations of two pentaBDEs (BDE-99, BDE-100) and of decaBDE (BDE-209) measured in 2006 and 2008. At that time, there was an increase in the manufacture and use of PBDEs immediately preceding the adoption of regulatory measures respecting these substances. The first set of regulations aimed at prohibiting the manufacture of these substances and restricting their use was adopted by the federal government in 2008 (Prohibition of Certain Toxic Substances Regulations (2012)).

Since 2010, the BDE-99 concentration has hovered around the federal guideline of 0.4 ng/g and the BDE-100 concentration has remained below the guideline.  The BDE-209 concentration has remained well below the guideline of 18.9 ng/g. These results suggest that PBDE concentrations should continue to decline but that monitoring remains critical.

Toxic substances such as PCBs. mercury and other metals, PAHs and dioxins and furans in Lake Saint-Pierre surface sediments—a legacy of the industrial expansion of the mid-1900s—have declined significantly to levels below the sediment quality guidelines for the protection of aquatic life. Substances of emerging concern such as PBDEs which are associated with recent uses continue to be monitored despite the decline in their concentrations since 2006.

The entire northern part of Lake Saint-Pierre can be considered relatively unaffected by legacy toxic contaminants with the exception of the area of the Berthier-Sorel Islands. Emerging contaminants such as PBDEs (BDE-99) will continue to be monitored for some time to identify long-term trends. The development of analysis techniques for the detection of organic substances of emerging concern will help provide a more complete picture of sediment quality in the future.

Bibliography:

Environment Canada, 2011. Polybrominated diphenyl ethers in the Canadian environment. Environmental Monitoring and Surveillance in Support of the Chemicals Management Plan Factsheet 10 pages.

Environment Canada and Ministère du Développement durable de l’Environnement et des Parcs du Québec. 2007. Criteria for the Assessment of Sediment Quality in Quebec and Application Frameworks:Prevention. Dredging and Remediation. 39 pages.

Sérodes, J.B., 1978. Qualité des sédiments de fond du fleuve Saint-Laurent entre Cornwall et Montmagny, Direction régionale des eaux intérieures.

Hardy, B., Bureau, J., Champoux, L., et Sloterdijk, H., 1990. Caractérisation des sédiments de fond du lac St-Pierre, fleuve Saint-Laurent. Environnement Canada, Centre Saint-Laurent.

Pelletier, M., 2008. Évolution spatiale et temporelle de la dynamique et de la géochimie des sédiments du lac Saint-Pierre. Environnement Canada – Direction générale des sciences et de la technologie, Monitoring et surveillance de la qualité de l’eau au Québec. Rapport scientifique et technique ST-240, 94 p. + annexes.

Prepared by:

Magella Pelletier
Fresh Water Quality Monitoring and Surveillance - St. Lawrence and Atlantic Coastal
Environment and Climate Change Canada