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Microplastic Contamination in Coastal Regions of the Southern Gulf of Saint Lawrence

COINAtlantic is excited to share the following update from Krista Beardy, a University of New Brunswick Researcher, regarding the project, Microplastic Contamination in Coastal Regions of Southern Gulf of Saint Lawrence.


Microplastic contamination in the marine environment is a well-documented, but poorly understood concern. At a relatively low production cost, it offers a lightweight, airtight, waterproof, shatter resistant, corrosion resistant solution to a seemingly infinite number of consumer needs. However, this heavy consumer reliance on plastic products drives the increase in plastic production despite the limited capacity to successfully recapture and recycle this material once it has been used. These useful qualities, particularly the corrosion resistance, are why plastic pollution has been classified as a ‘contaminant of emerging concern’ (CEC) which describes anything that is not currently monitored but has shown the potential to cause harm to human health or to the environment. The reason for a CEC classification lies in a lack of research or gaps in that research that makes it difficult to reach a solid conclusion.

To address this issue in Atlantic Canada research began in 2017 in the coastal regions of the Bay of Fundy and continued in the southern Gulf of Saint Lawrence beginning in 2019. The Saint Lawrence River connects the central and eastern portions of the country with the Atlantic Ocean and receives freshwater run-off from 5 provinces essentially providing drainage for the Great Lakes system. With approximately 80% of marine plastics originating from land-based activities, the river’s banks wash through densely populated areas bringing with it this domestic and commercial debris. Included in this estimation is waste-water effluent which also continues downstream and into the marine environment. The Saint Lawrence River is also home to a heavily traveled commercial shipping route. Research has estimated that approximately 20% of marine plastics originate from at-sea industrial activities such as shipping, fishing and aquaculture. The Saint Lawrence River, like the Bay of Fundy, houses all three of these source industries. Both study regions contain critical habitats for a variety of fish species and benthic invertebrates. The shorelines and mudflats are an essential feeding area for both coastal mammals and shorebird populations who are at risk of mistaking plastic waste for their intended food source causing an increase in mortality. The seriousness of these effects are compounded by how effortlessly plastics are consumed with ingestion estimates as high as 44% for marine birds, 52% for sea turtles, 33% for oysters and 30% for macoma clams, one of the regions smallest bivalves. Other investigations into the effects of microplastics have shown neurotoxicity in nematodes and bivalves, reduced reproductive success in oysters and reduced byssal thread production in blue mussels.

The primary objective of this project was to address a knowledge gap in Atlantic Canada by assessing the current state of microplastic contamination in the southern Gulf of Saint Lawrence from northern New Brunswick, to Pictou Nova Scotia, and included the province of Prince Edward Island. Potential influences on the concentration of microplastics were also examined, such as tidal dynamics and the characteristics of the depositional environment including proximity to human activity. Environmental microplastic contamination was measured by the presence of microplastic (per gram of tissue) in the bivalve Mya arenaria (soft-shelled clam) and the adjacent sediment (50 gram sample) surrounding the bivalve harvest site.

Potential microplastics were found in both sediment and bivalves harvested from all sites in this study. When examining the full dataset, the concentration of potential microplastics in M. arenaria tissue was most strongly related to the weight of the individual itself. Smaller specimens consistently contained more microplastic per gram of tissue than larger specimens, a result that is consistent with other local studies performed Atlantic Canada (Beardy and Hunt, 2017; Fenech et. al., 2021) including one on freshwater mussels in the Saint John River (Doucet et al. 2021). The significance of this result lies in the potential effect of the microplastics on juvenile bivalves and whether juveniles are disproportionately affected by microplastic ingestion . In contrast, no significant relationship was observed when comparing the amount of microplastics in M. arenaria with the surrounding sediment. This lack of relationship extends to both the amount of shoreline debris observed at each site as well as the influence of regional tidal dynamics. Significant differences in potential microplastic concentration in M. arenaria were found between study sites in both the southern shore of the Northumberland Strait (NB) and the north shore of PEI, with the highest concentrations found in Cape Tormentine, NB and Tracadie, PEI (north shore). In contrast, the least amount of potential microplastics were observed on the south shore of PEI (north shore of the Northumberland Strait).

It was expected that higher concentrations of potential microplastics would be found in coastal areas that are close in proximity to highly populated areas, heavy marine traffic or industrial activities. However, a positive relationship was detected finding greater potential microplastic numbers with increasing distance from potential sources. This unexpected relationship may be due to local current activity or reflect the effects of the inflow of fresh water from Saint Lawrence River. This may be related to the ocean current diversion southward in the Gulf’s counterclockwise rotation, which would provide the south shore of PEI (where the concentration of potential microplastics in bivalves was less) with some measure of protection. This suggests that ocean current dispersion in southern coastal regions may contribute to the transport and subsequent deposition of microplastics where the influence of the corresponding current is strongest. The effects of dispersal by currents on localized microplastic distribution are difficult to measure because of the larger contribution from potential sources along the Saint Lawrence River as compared to the relatively small local sources in the Southern Gulf of St. Lawrence. This may make it difficult to assess the true source of contamination in this region and further study is required.

Very recent studies have shown that much of what has been reported as 'microplastic' has, upon confirmatory analysis, turned out to be cellulosic material that is resistant to procedural degradation. This may be due to the persistent nature of the cellulosic material, some of which may be highly processed natural fibers which contain preservative chemicals and pigments that become the root cause of visual misidentification. Despite the cost in both time and financial resources, it has been consistently recommended that microplastics undergo confirmatory analysis with such methods as Fourier Transform Infrared (FTIR) spectroscopy. Highly sensitive, FTIR can identify elements that are present in concentrations greater than approximately 3–5% of the total sample. This analysis showed that out of the subset of samples analyzed in this study, 23%

were correctly identified as ‘plastic’. Of these, 49% were fibers and 51% were fragments. From the fibers that were identified, 78% were Polyethylene (PET) and 4.8% as polyamide with a single occurrence each of polyvinylchloride (PVC) and polypropylene (PP). Of the fragments, 50% were identified as PVC, 14% as paint/coating components (urethane/polyurethane/epoxy), 5% acrylic with a single occurrence of polystyrene and polyisoprene. However, 21% of fragments were of uncommon or unknown polymers as were 9.7% of the fibers. Verifying which types of plastic are found in a specific area can narrow the focus of investigative studies that could determine the source of the contamination which, in turn, can lead to upstream intervention analysis. Our study results confirm that using FTIR spectroscopy can reduce the risk of misidentification which, has been shown to vary from 20 to 70% using visual identification methods alone.


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