Is the St. Lawrence full of microplastics?

The results are partially encouraging. The team found that microplastic concentrations were not statistically different between the various sites studied and were generally below 100 particles of plastic per million litres (PPML). At similar sites in urban rivers in China, concentrations have been found to exceed 2 million PPML. Professor Valérie S. Langlois from the INRS Eau Terre Environnement Research Centre agrees: Although sampling methods differ, the St. Lawrence River is less polluted with microplastics than other comparable rivers.

Surprisingly, however, the research team’s data contradicted its hypotheses. Since the majority of plastic waste comes from urban environments, the team predicted that the highest levels of microplastic contamination would be found in the waters near large population centres. Instead, contamination levels were highest in saline environments with less human impact. This is thought to be due to the salinity of the water, which has a direct impact on the coagulation of plastics and their solubility in water.

The sites chosen for sampling included areas affected by human presence, such as Quebec City and Trois-Rivières, as well as more isolated ones, such as Montmagny and La Malbaie. Salinity also varied between sites, ranging from the fresher waters of Varennes to the salty waters of Trois-Pistoles. The study sampled surface water at each of the 11 selected sites in the St. Lawrence Estuary using two different collection nets. Attached to the research vessel, these nets were passed through the water at a depth of 40 cm to collect three samples at each site. The samples were then analyzed to determine the quantity, size, and type of polymers detected in order to understand the composition of what can be found in our waters.

Realizing that the St. Lawrence is not immune to microplastic contamination is a step in the right direction. However, researchers agree: There is a serious lack of information on the impact these plastics can have on marine wildlife.

In 2022, the Université du Québec à Rimouski received funding to conduct research projects on the impact of microplastics, and according to Professor Zhe Lu, the data are beginning to come in! The team recently published an article on the impact of microplastics on benthic fish. These researchers are also working on microplastic photodegradation, the risks of microplastic contamination, and the impact of microplastics on the St. Lawrence food chain. Stay tuned!