Modeling Microplastic Transport in the Marine Environment: Testing Empirical Models of Particle Terminal Sinking Velocity for Irregularly Shaped Particles

Róisín Coyle; Matthew Service; Ursula Witte; Gary Hardiman; Jennifer McKinley

doi:10.1021/acsestwater.2c00466

Modeling Microplastic Transport in the Marine Environment: Testing Empirical Models of Particle Terminal Sinking Velocity for Irregularly Shaped Particles

ACS ES T Water. 2023 Mar 22;3(4):984-995. doi: 10.1021/acsestwater.2c00466. eCollection 2023 Apr 14.

Authors

Róisín Coyle¹, Matthew Service², Ursula Witte³, Gary Hardiman^{4

5}, Jennifer McKinley⁶

Affiliations

¹ Civil Engineering, School of Natural and Built Environment, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, U.K.
² Agri-Food and Biosciences Institute, 18a Newforge Lane, Belfast BT9 5PX, Northern Ireland, U.K.
³ School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3FX, U.K.
⁴ School of Biological Sciences, Institute for Global Food Security (IGFS), Queen's University Belfast, 19 Chlorine Gardens, Belfast BT9 5DL, Northern Ireland, U.K.
⁵ Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, United States.
⁶ Geography, School of Natural and Built Environment, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, U.K.

Abstract

Microplastic (mP) pollution has been indicated as an area of concern in the marine environment. However, there is no consensus on their potential to cause significant ecological harm, and a comprehensive risk assessment of mP pollution is unattainable due to gaps in our understanding of their transport, uptake, and exchange processes. This research considers drag models that have been proposed to calculate the terminal settling velocity of regularly and irregularly shaped particles to assess their applicability in a mP modeling context. The evaluation indicates three models that predict the settling velocity of mPs to a high precision and suggests that an explicit model is the most appropriate for implementation in a mP transport model. This research demonstrates that the mP settling velocity does not vary significantly over time and depth relevant to the scale of an ocean model and that the terminal settling velocity is independent of the initial particle velocity. These findings contribute toward efforts to simulate the vertical transport of mPs in the ocean, which will improve our understanding of the residence time of mPs in the water column and subsequently their availability for uptake into the marine ecosystem.