Aline Reis de Carvalho, PhD student at Softmat, has defended her thesis on microplastic pollution in the Garonne river

27 Oct 2021 | Thesis defence, Events, SMODD team

Aline carried out her research in the SMODD team at the Softmat laboratory, in collaboration with the laboratory EDB.

On 27th October, she defended her thesis entitled: “patio-temporal monitoring of microplastic pollution in the Garonne catchment and potential trophic transfer”

It was estimated that 4 to 13 million tonnes of plastic were dumped into the oceans in 2010 (Jambeck et al., 2015). After carrying out numerous studies in the marine environment, it is only fairly recently that the scientific community has realized the importance of understanding and identifying the origins of this pollution. The assessment of the level of plastic pollution in inland waters has only recently been discussed (Wagner, 2014). The general objective of this thesis was to carry out a spatio-temporal monitoring of the pollution of large microplastics (size 700 µm-5 mm) in the Garonne watershed as well as the consumption of these particles by aquatic organisms.

The first objective was to quantify the spatial and temporal variations in the concentrations of microplastics in the water of the Garonne and in its main tributaries and to assess the determinants of this variation. We found a significant effect of the level of urbanization on the concentration of microplastics, with the concentration of microplastics increasing with the level of urbanization. The concentration of microplastics was significantly different between sampling campaigns with higher microplastic concentrations in warm periods with poor hydrology.

The second objective was to understand the dynamics of microplastic pollution in water during a flood episode and to analyze the impact of urbanization on this dynamic. A greater increase in the concentration of microplastics was observed at the downstream site for the two flood events monitored and was due to the increased flow of the river. The flooding resulted in an increase in polyethylene particles and white polystyrene particles only in the downstream site. Urbanization has regulated the variation of microplastic pollution in the studied freshwater ecosystem during a flood event.

The third objective was to analyze the potential presence of microplastics in fishing groundbaits, potential sources of contamination of freshwater. Recreational fishing, where many fishermen throw manufactured groundbaits into freshwater ecosystems, is a widespread activity with significant socio-economic implications in Europe. It also represents a potential pathway for microplastics in freshwater that has not yet been quantified. Accordingly, we analyzed three different categories of industrially produced primers (“flour”, “boilies” and “pellets”) for their microplastic contamination (particles 700 µm to 5 mm). Out of 160 samples, 28 microplastics were identified in the flours and boilies. We reveal that microplastics in primers can be introduced accidentally during manufacturing and / or from contaminated raw materials and can be transferred to freshwater.

For the fourth and final objective, we investigated whether there is a transfer in the food web of microplastics (macro-invertebrates and fish) by analyzing the relationship between the trophic position of organisms and plastic contamination in their system digestive. Initial analyzes revealed that there was no significant correlation between microplastic pollution in water and the environment and microplastic contamination in macroinvertebrates and fish, respectively. The results of the contamination of microplastics and trophic niche of individuals, measured using stable isotopes, indicate, for the species studied, a mainly direct and accidental ingestion of microplastics composed of the densest polymers when they feed on the bottom of streams.

Highlight of the thesis:

  • In 2020, Aline was a finalist in the “Ma thèse en 180s” competition, at the regional level. Watch her peformance.
  • The research carried out during her thesis was the subject of a national press release.

Congratulations to Aline for the quality of her work!