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.

Abstract

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.

Citation

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. https://doi.org/10.1038/s43247-023-00690-z

• 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
• DOI: https://doi.org/10.1038/s43247-023-00690-z
• Keywords: General Earth and Planetary Sciences; General Environmental Science
• Public URL: https://hull-repository.worktribe.com/output/4200423