Butyltins in Sediments of the St. Lawrence River
Butyltins are organometallic compounds that have been used as biocides in antifouling paints for ship hulls; as fungicides, insecticides and wood preservation products; and as stabilizers in polyvinyl chloride since 1960. Butyltins can be measured in sediments in the form of tributyltin (TBT) and its degradation products, dibutyltin (DBT) and monobutyltin (MBT). These substances are persistent in the environment and bioaccumulate in aquatic organisms. Because TBT is highly toxic, the use of TBT paints for small vessels (less than 25 m) was regulated in Canada in 1989; however, it was still allowed for larger boats until 2002. In addition, the Prohibition of Certain Toxic Substances Regulations, 2012 prohibits the manufacture, use, sale, and offer for sale or import of TBT in Canada. As a part of a collaboration between monitoring and research programs on chemical contamina- tion in the St. Lawrence River, 250 sediment samples were analyzed in order to determine current butyltin concentrations in sediments along the St. Lawrence.
Overview of the Situation
St. Lawrence River
Surface sediment samples were collected between 2003 and 2010 in the three fluvial lakes, the fluvial section, Montreal harbour–both inside and outside of the port area–and the seaway locks and Lachine Canal. The results showed that 50% of samples contained one of the three forms of butyltin and that MBT was the form most frequently detected. The majority of stations (74%) had little or no contamination, with concentrations of less than 5 ng tin/g (5 ng Sn/g). The rest of the stations contained less than 100 ng Sn/g and can be considered as contaminated by butyltin. These stations are mainly located in the depositional basins of the fluvial lakes.
Sediment samples were collected in 20 marinas located between Cornwall and Trois-Rivières. All samples contained detectable concentrations of butyltins. The most common form was MBT in 95% of cases. Each quality class contains about one third of the stations (See section : Contamination Thresholds for Butyltins). Some stations had concentrations exceeding 200 ng Sn/g.
Port de Montréal
The Port of Montreal is located along the south shore of the Island of Montreal, between the Lachine Rapids and Pointe-aux-Trembles. Butyltins were present in 92% of surface sediment samples collected at 49 stations near the main piers. The basins of the maritime and Bickerdike terminals in the upstream section of the port are the most heavily contaminated, with values of 1341 ng Sn/g and 356 ng Sn/g, respectively. TBT was detected in over 75% of analyses and was the main form of butyltin.
More than half (51%) of all stations were contaminated, with values between 5 and 100 ng Sn/g, while 37% of stations had contamination levels exceeding 100 ng Sn/g.
The Contrecœur Islands sector, located in the fluvial section of the river between Montréal and Lake Saint-Pierre, is a natural environment that has been designated a National Wildlife Area. Surface sediments in this sector contained butyltins: 56% of sampling stations had sediments that were contaminated or heavily contaminated.
The two highest concentrations (2093 ng Sn/g and 982 ng Sn/g) are mainly in the form of TBT and could have an effect on benthic organisms. These concentrations greatly exceed the interim criteria of 800 ng Sn/g proposed for port areas in the Great Lakes (Bartlett et al. 2005). These concentrations are located in an area of slow-moving water a few kilometres downstream of a transshipment pier located on the river and used occasionally.
Seaway Locks and Lachine Canal
Some surface sediment samples collected in seaway locks (Saint-Lambert and Sainte-Catherine) showed the pres- ence of butyltins, with a median value of 76 ng Sn/g and a maximum value of 515.3 ng Sn/g.
Sediments of the Lachine Canal showed relatively low concen- trations (maximum 85 ng Sn/g) compared with those observed in the marina at the canal entrance (maximum 222 ng Sn/g), a potential source of butyltins in the Lachine Canal.
Table 1.1 Descriptive statistics of sediment quality in groups of stations
|Substance||n||Percentage of detection (%)||Minimum value (ng Sn/g)||Median value (ng Sn/g)||Maximum value (ng Sn/g)|
|River||MBT||136||40||< 0,7||< 0,7||89,2|
|DBT||136||17||< 0,5||< 0,5||9,1|
|TBT||136||23||< 0,4||< 0,4||66,0|
|Contre-coeur||MBT||16||50||< 0,7||< 0,7||12,1|
|Port of Montreal||MBT||49||47||< 0,7||< 0,7||170,0|
Table 1.2 Evaluation of sediment quality in groups of stations
|Quality classes*||Percentage of stations|
|River||Little or no contamination||74|
|Contre-coeur||Little or no contamination||44|
|Port of Montreal||Little or no contamination||12|
|Marinas||Little or no contamination||35|
|Locks||Little or no contamination||0|
|Lachine Canal||Little or no contamination||17|
Legend: BT – butyltin; DL – Detection limit, n – number of samples
*See section Contamination Threshholds for Butyltins
Contamination Thresholds for Butyltins
In the absence of Canadian quality criteria for assessing the quality of butyltin-contaminated sediments, we used as guideline values the quality criteria for tributyltin developed in Norway for sediments in saltwater (Bakke et al. 2010) and the “interim” criteria proposed for port areas in the Great Lakes (Bartlett et al. 2005). Taking the total of the three forms of butyltin into consideration, we established three categories of contamination (see legend), which were subdivided into colour subclasses to better present the results on concentration maps. It is important to specify that these quality classes are arbitrary and should not be considered as criteria or standards.
Figure 1: Distribution of butyltin concentrations in sediments of fluvial lakes
Figure 2: Location of sectors in the Port of Montreal showed in figure 3
Figure 3: Distribution of butyltin concentrations in sediments in the Port of Montreal
Figure 4: Distribution of butyltin concentrations in sediments of the fluvial section and Contrecœur sector
Figure 5: Distribution of butyltin concentrations in sediments of the seaway locks and the Lachine Canal
Results from various monitoring and research projects provide a picture of the state of butyltin contamination in the St. Lawrence River. In the three fluvial lakes and the fluvial section, with the exception of the Contrecœur Islands sector, sediments show little or no butyltin contamination. The Contrecœur Islands sector is a special case; it has very high concentrations of butyltins in surface sediments, thereby increasing the risk of effects on benthic organisms in the natural environment.
Sediments collected within the port (Port of Montreal) and navigation (channel and locks) infrastructure and in recreational activity areas such as marinas show much higher levels of butyltin contamination than in the river. This contamination occurs mainly in the form of DBT and TBT, particularly in the upstream sector of the Port of Montreal, which is the area with the highest level of contamination.The area downstream of Lake Saint- Pierre will be characterized for butyltins over the next few years.
State of the St. Lawrence Monitoring Program
Four government partners – Environment Canada, Fisheries and Oceans Canada, Parks Canada Agency, and the Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques – and Stratégies Saint-Laurent, a nongovernmental organization that works actively with riverside communities, are pooling their expertise and efforts to provide Canadians with information on the state of the St. Lawrence and its long-term evolution.
To this end, environmental indicators have been developed on the basis of data collected as part of each organization’s ongoing environmental monitoring activities. These activities cover the main components of the environment, namely water, sediments, biological resources, uses and shorelines.
For More Information
- Bakke T, Källqvist T, Ruus A, Breedveld GD, Hylland K. 2010. Development of sediment quality criteria in Norway. J Soils Sediments 10:172-178.
- Bartlett AJ, Borgmann U, Dixon DG, Batchelor SP, Maguire RJ. 2005. Toxicity and bioaccumulation of tributyltin in Hyalella azteca from freshwater harbour sediments in the Great Lakes Basin, Canada. Can J Fish Aquat Sci 62:1243-1253.
- 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 p.
- Regoli L, Chan HM, de Lafontaine Y, Mikaelian I. 2001. Organotins in zebra mussels (Dreissena polymorpha) and sediments of the Quebec City Harbour area of the St. Lawrence River. Aquat Toxicol 53(2):115-126.
- Magella Pelletier, Water Quality Monitoring and Surveillance, Environment Canada
- Mélanie Desrosiers, Centre d’expertise en analyse environnementale du Québec, Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques
- Serge Lepage, Environmental Protection Operations Division, Environment Canada (now retired)
- Yves de Lafontaine, Aquatic Ecosystem Protection Research Division, Environment Canada (now at the Maurice Lamontagne Institute, Fisheries and Oceans Canada)
We would like to thank Ms. Mylène Salvas of Parks Canada for the data on the Lachine Canal sector.
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Aussi disponible en franc?ais sous le titre: Les butyle?tains dans les se?diments du fleuve Saint-Laurent