The tides condition the distribution of microplastics emitted by the treatment systems in the Vigo estuary

Researchers from the Marine Research Center of the University of Vigo, conducted a study on the transport and accumulation of micropollutants emitted from wastewater treatment systems (WWTPs) in the Vigo estuary. Using a particle simulation model, they verified how the distribution of microplastics depends to a great extent on the tidal stage at the time of discharge from the treatment systems.

The results demostrate that “in the case of the Vigo estuary, the highest concentration of microplastics modelled was observed on the south coast of the estuary, in the vicinity of the city of Vigo, specifically near Samil, and was practically non-existent in areas in the interior of the estuary”. Regarding the analysis of the emission of microplastics attending the tides, the work shows that in the case of spring tides, around 20% of the microplastics emitted in the interior of the estuary would reach the open ocean, a similar fraction (around 24%) would remain in the vicinity of the Cíes Islands and the rest would be distributed throughout the entire estuary. In neap tidal conditions, the amount of microplastics exported to the open ocean and to the Cíes Islands would be “negligible”.

According to the authors of the work, “It is estimated that wastewater treatment systems are the main source of microplastics (<5 mm) in coastal areas due to the washing of garments with a high content of plastic fibers such as PET or nylon “. In their study, they detail that they used a Lagrangian module of the Delft3D hydrodynamic programme to simulate with virtual particles the trajectories followed by microplastics from the seven wastewater treatment plants in the estuary, Lagares EDAR being the most important one. The model developed was previously calibrated with field data on the concentration of microplastics in rock mussels in different areas of the estuary, which gives the work “a considerable degree of confidence in the results obtained”, according to those responsible for the study. When evaluating the work carried out, they also point out how the behavior of the particles is “practically independent” of the particular characteristics of microplastics (size and density), which makes the study achieve “an important degree of generality, without depend on the specific type of microplastic poured”.

The work was published in the magazine Marine Pollution Bulletin in an article titled Modelling the distribution of microplastics released by wastewater treatment plants in Ria de Vigo (NW Iberian Peninsula). It is signed by Maite de Castro, Marisela Des, José Luis Gómez Gesteira and Moncho Gómez Gesteira, from the Ephyslab group (CIM, University of Vigo); Magda Sousa, Américo Ribeiro and Joao Dias, from the University of Aveiro (Portugal), and Jesús Gago, from the Vigo Oceanographic Center (IEO).

Source: DUVI