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Non-buoyant microplastic settling velocity varies with biofilm growth and ambient water salinity

Mendrik, Freija; Fernández, Roberto; Hackney, Christopher R.; Waller, Catherine; Parsons, Daniel R.


Freija Mendrik

Roberto Fernández

Christopher R. Hackney

Daniel R. Parsons


Rivers are the major conveyor of plastics to the marine environment, but the mechanisms that impact microplastic (<5 mm) aquatic transport, and thus govern fate are largely unknown. This prevents progress in understanding microplastic dynamics and identifying zones of high accumulation, along with taking representative environmental samples and developing effective mitigation measures. Using a suite of settling experiments we show that non-buoyant microplastic settling is influenced by a combination of biofilm growth, water salinity and suspended clay concentrations typically seen across fluvial to marine environments. Results indicate that biofilms significantly increased settling velocity of three different polymer types of non-buoyant microplastics (fragments and fibres, size range 0.02–4.94 mm) by up to 130% and significant increases in settling velocity were observable within hours. Impacts were both polymer and shape specific and settling regimes differed according to both salinity and sediment concentrations. Our results further validate previous statements that existing transport formula are inadequate to capture microplastic settling and highlight the importance of considering the combination of these processes within the next generation of predictive frameworks. This will allow more robust predictions of transport, fate and impact of microplastic pollution within aquatic environments.


Mendrik, F., Fernández, R., Hackney, C. R., Waller, C., & Parsons, D. R. (2023). Non-buoyant microplastic settling velocity varies with biofilm growth and ambient water salinity. Communications Earth & Environment, 4(1), Article 30.

Journal Article Type Article
Acceptance Date Jan 25, 2023
Online Publication Date Feb 11, 2023
Publication Date Dec 1, 2023
Deposit Date Feb 13, 2023
Publicly Available Date Feb 13, 2023
Journal Communications Earth and Environment
Print ISSN 2662-4435
Electronic ISSN 2662-4435
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 4
Issue 1
Article Number 30
Keywords General Earth and Planetary Sciences; General Environmental Science
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Copyright Statement
© The Author(s) 2023.<br /> Open Access. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit

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