EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Controls on microplastic flux mechanisms in a large river

Freija Mendrik1, Daniel Parsons1, Christopher Hackney1, Cath Waller1, Vivien Cumming2, Robert Dorrell1, and Grigorios Vasilopoulos1
Freija Mendrik et al.
  • 1Energy and Environment Institute, University of Hull, United Kingdom of Great Britain and Northern Ireland (
  • 2Science Stories Limited

The majority of marine plastic pollution originates from land-based sources with the dominant transport agent being riverine. Despite many of the potential ecotoxicological consequences of plastics being well known, research has only just recently begun to explore the source to sink dynamics of plastics in the environment. Despite the widespread recognition that rivers dominate the global flux of plastics to the ocean, there is a key knowledge gap regarding the nature of the flux, the behaviour of microplastics (<5mm) in transport and its pathways from rivers into the ocean. Additionally, little is presently known about the role of biota in the transport of microplastics through processes such as biofilm formation and how this influences microplastic fate. This prevents progress in understanding microplastic fate and hotspot formation, as well as curtailing the evolution of effective mitigation and policy measures.


As part of the National Geographic Rivers of Plastic project, a combined-laboratory and field investigation was conducted. Fieldwork was undertaken in the Mekong River, one of the top global contributors to marine plastic pollution with an estimated 37,000 tonnes of plastic being discharged from the Mekong Delta each year. This flux is set to grow significantly in accordance with the projected population increase in the basin. The results presented herein outline a suite of laboratory experiments that explore the role of biofilms on the generation of microplastic flocs and the impact on buoyancy and settling velocities. Aligned fieldwork details the particulate flux and transport of microplastic, throughout the vertical velocity profile, across the river-delta-coast system, including the Tonle Sap Lake. The results also highlight potential areas of highest ecological risk related to the dispersal and distribution of microplastics. Finally, pilot data on the levels of microplastics within fish from the Mekong system are also quantified to explore the potential impact of biological uptake on the fate and sinks of plastics within the system.

How to cite: Mendrik, F., Parsons, D., Hackney, C., Waller, C., Cumming, V., Dorrell, R., and Vasilopoulos, G.: Controls on microplastic flux mechanisms in a large river , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8116,, 2020.

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  • CC1: Comment on EGU2020-8116, Winnie Courtene-Jones, 05 May 2020

    I'd be really interested to know more about the ADCP and field experiments - did you find different flow rates through the river?  were the stacked nets deployed in the centre of edge of the river - as flow dynamics will vary. Can you comment on the microplastic distribution through the water column?  

    Also, are you doing lab based experiements with the corals? As in the natural environment there are many stressors which could inflience coral health and so it would be difficult to attribute this to microplastics.

    Thank you

    • AC1: Reply to CC1, Freija Mendrik, 05 May 2020

      Thanks for your questions! The nets are deployed in the centre of the river and yes there are different flow rates vertically. At the moment I can't comment on the vertical distribution of microplastics in the water column as I have collected the samples but haven't been able to process them due to lockdown. I expect there will be variation in the types of microplastics seen though such as less dense polymers being found at the surface. 

      I have previously done lab based experiments with corals which will support this work (hopefully being published this year). I realise there are lots of other factors that need to be taken into consideration and these will be accounted for but it will still be interesting to see if there is a difference in microplastic concentration on the reefs compared to other aquatic environments. 

      • CC2: Reply to AC1, Winnie Courtene-Jones, 05 May 2020

        Thank you for your response, looks like you are taking a comprehensive approach. All the best for getting back into the lab once we are out of lockdown - a difficult time for all.