Mission Tara Microplastics: a holistic set of protocols and data resources for the field investigation of plastic pollution along the land-sea continuum in Europe

Abstract

The Tara Microplastics mission was conducted for 7 months to investigate plastic pollution along nine major rivers in Europe-Thames, Elbe, Rhine, Seine, Loire, Garonne, Ebro, Rhone, and Tiber. An extensive suite of sampling protocols was applied at four to five sites on each river along a salinity gradient from the sea and the outer estuary to downstream and upstream of the first heavily populated city. Biophysicochemical parameters including salinity, temperature, irradiance, particulate matter, large and small microplastics (MPs) concentration and composition, prokaryote and microeukaryote richness, and diversity on MPs and in the surrounding waters were routinely measured onboard the French research vessel Tara or from a semi-rigid boat in shallow waters. In addition, macroplastic and microplastic concentrations and composition were determined on river banks and beaches. Finally, cages containing either pristine pieces of plastics in the form of films or granules, and others containing mussels were immersed at each sampling site, 1 month prior to sampling in order to study the metabolic activity of the plastisphere by meta-OMICS and to run toxicity tests and pollutants analyses. Here, we fully described the holistic set of protocols designed for the Mission Tara Microplastics and promoted standard procedures to achieve its ambitious goals: (1) compare traits of plastic pollution among European rivers, (2) provide a baseline of the state of plastic pollution in the Anthropocene, (3) predict their evolution in the frame of the current European initiatives, (4) shed light on the toxicological effects of plastic on aquatic life, (5) model the transport of microplastics from land towards the sea, and (6) investigate the potential impact of pathogen or invasive species rafting on drifting plastics from the land to the sea through riverine systems.

Keywords: Land-sea continuum; Microplastics; Plastisphere; Scientific expedition; Toxicology.

Fig. 1

Sampling strategy in the land-sea continuum. Left: Example of sampling strategies in the Tiber River (Italy) along the salinity gradient from the sea (station 1), the outer estuary (station 2), intermediate salinity (station 3) to downstream (station 4), and upstream (station 5) of the first heavily populated city (Roma). Samples were taken on land (using transect and quadras), in the river (using Niskin bottle, Manta net, and cages with PE pellets or with mussels), and at sea (using Niskin bottle and Manta net only). Right: The route of the research vessel Tara for 7 months crossing 9 of the major rivers in Europe

Fig. 2

Photographs of the 330-µm mesh size manta trawl (left) and the following microplastic sorting with sterilized forceps (right) (credit to Noélie Pansiot, Tara Ocean Foundation)

Fig. 3

Sketch of the sampling protocol for macro-, meso-, and microplastics on beaches (left) and river bank (right). Squares are the five quadrats of 0.50 m length sides (0.25 m.²) along the high tide (dotted line)

Fig. 4

Schematic diagram of the water sampling system, showing the setup of the various parameters analyzed from the same sampling station. CULT, microbial culture; NUT, nutrients; FCM, flow cytometry; PM, particulate matter; S023, sequencing on DNA extracted from 0.2-µm filters after 3-µm prefiltration; S325, sequencing on DNA extracted from 3-µm filters after 25-µm prefiltration

Fig. 5

Illustration of microbial life on plastics (left; credit to Christian Sardet) and complementary set of studies performed during the Mission Tara Microplastics to investigate the microbial life on plastics and in the surrounding waters (right, related methodologies are indicated in italic)