Short CommunicationA first estimation of uncertainties related to microplastic sampling in rivers
Graphical abstract
Introduction
Over the last decade, considerable attention has been paid to plastic pollution in the marine environment (Li et al., 2018; Li et al., 2016). Yet rivers, which are one of the major pathways for plastics entering the ocean, have not been investigated to the same extent despite the fact that in the past five years, an increasing number of studies have focused on river plastic contamination. Data are still scarce and sampling methods need to be improved and harmonised (Dris et al., 2018; Eerkes-Medrano et al., 2015; Wagner et al., 2014). Moreover, there is a major need to set up networks for measuring microplastics in inland waters to monitor the evolution of their contamination over time and to set up databases at regional scales, in line with regional regulations, like the Water Framework Directive in Europe (although microplastics are not included as an indicator of good environmental status in its current version).
Only easy to implement methodologies can be considered. However, they have to be representative of the water bodies. The 200-year long experience in river monitoring suggests that fluctuations in usual water quality parameters occur at much larger time scales than those of sampling, and as a consequence, for instance, sampling 1 L of water is often enough to measure both dissolved and particulate water quality parameters. Such an experience is missing for microplastic contamination, in particular, for low concentration contamination, taking into account that the dynamics of such particles in the water column is up to now badly known. To the best of our knowledge, only two articles address small-scale temporal and spatial variability of microplastics found in rivers (Dris et al., 2018; Liedermann et al., 2018). Dris et al. (2018) analysed the temporal and spatial variability of fibre concentrations in the Seine and Marne Rivers (France), using a 80 μm mesh net. They showed that the longer the net deployment time, the lower the variability between consecutive samples. They also assessed fibre distribution variability throughout the river cross-section and observed that concentrations are similar across the water column and tend to increase near the banks. Liedermann et al. (2018) studied microplastics distribution, using a 500 μm mesh net, within the Danube River and also detected a slight tendency towards higher concentrations nearer the banks.
On the basis of the sampling of 16 successive replicates and 3 sampling durations, in a river in Southwestern France, we investigate the microplastic concentration fluctuations and assess the corresponding uncertainties, and their variation with both the number of replicates and the time exposure.
Section snippets
Study site and sampling methodology
This study was conducted on April 6th, 2018 between 11 am and 2 pm in the Gave de Pau River, downstream of the Pau city centre yet still within the conurbation (Southwestern France, lat.: 43.304828°, long.: −0.436492°). At this location, the river is 87 m wide with a maximum depth of about 2 m. The flow is torrential with an annual mean discharge of 69.1 m3/s (average over the period February 2000–July 2018 at station Q5231010 - Gave de Pau at Artiguelouve - Pont de Lescar; Banque hydro
Results
In total, 3191 microplastics were found within the 950 m3 of filtered water. 11.88 m3 of water were filtered per minute of exposure. Exposure times of 3, 5 and 7 min allowed filtering 35.6, 59.4 and 83.2 m3 of water, respectively. No macroplastic was caught in the net.
The microplastic concentrations varied between 2.64 and 4.24 MPs/m3, with a median value of 3.26 MPs/m3.
The shapes and colours of microplastic particles are presented in Table S1. The microplastic shape and colour variability
Discussion and conclusion
The median concentration of microplastics in the Gave de Pau River (3.26 ± 0.21 MPs/m3) was ten times higher than concentrations measured in the Danube River between Vienna and Bratislava (0.32 MPs/m3; Lechner et al., 2014; exposition time and volume of water filtered not mentioned) and in the Seine River downstream of the heavily-populated Paris Basin (0.35 MPs/m3, mesh size: 330 μm, net towed behind a motor boat for 15 min at about 2 m/s for a volume of filtered water ranging from 182 to 200 m
CRediT authorship contribution statement
Antoine Bruge: Conceptualization, Methodology, Software, Formal analysis, Writing - original draft. Marius Dhamelincourt: Methodology, Investigation, Formal analysis, Data curation, Visualization, Writing - original draft. Laurent Lanceleur: Conceptualization, Methodology, Resources. Mathilde Monperrus: Conceptualization, Methodology, Resources. Johnny Gasperi: Formal analysis, Data curation, Visualization, Writing - review & editing. Bruno Tassin: Formal analysis, Data curation, Visualization,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This study was funded by the French Ministry of Ecology and Solidary transition and the Direction Inter-Régionale de la Mer Sud-Atlantique. The authors would also like to thank Lauren Meshako from the Surfrider Foundation Europe and Robert Sachs for proofreading this article.
References (14)
- et al.
Synthetic and non-synthetic anthropogenic fibers in a river under the impact of Paris megacity: sampling methodological aspects and flux estimations
Sci. Total Environ.
(2018) - et al.
Microplastics in freshwater systems: a review of the emerging threats, identification of knowledge gaps and prioritisation of research needs
Water Res.
(2015) - et al.
The Danube so colourful: a potpourri of plastic litter outnumbers fish larvae in Europe’s second largest river
Environ. Pollut.
(2014) - et al.
Plastic waste in the marine environment: a review of sources, occurrence and effects
Sci. Total Environ.
(2016) - et al.
Microplastics in freshwater systems: a review on occurrence, environmental effects, and methods for microplastics detection
Water Res.
(2018) - Banque Hydro. Available online: http://www.hydro.eaufrance.fr/ (accessed on 9 August 2018)...
- et al.
Microplastic contamination in an urban area: a case study in greater Paris
Environ. Chem.
(2015)
Cited by (32)
Retention efficiency for microplastic in a landscape estimated from empirically validated dynamic model predictions
2024, Journal of Hazardous MaterialsAn analytical approach to confidence interval estimation of river microplastic sampling
2023, Environmental PollutionPreservation, storage, and sample preparation methods for freshwater microplastics - a comprehensive review
2023, Environmental Science: AdvancesExperimental uncertainty assessment of meso- and microplastic concentrations in rivers based on net sampling
2023, Science of the Total EnvironmentEnvironmental fate of microplastics in an urban river: Spatial distribution and seasonal variation
2023, Environmental Pollution