Analysing the influence of hydrodynamic and sedimentary factors on the microplastic distribution in the Ashtamudi estuary, India

K L Priya; Gubash Azhikodan; Katsuhide Yokoyama; K R Renjith

doi:10.1016/j.marpolbul.2025.117537

Analysing the influence of hydrodynamic and sedimentary factors on the microplastic distribution in the Ashtamudi estuary, India

Mar Pollut Bull. 2025 Jan 8:212:117537. doi: 10.1016/j.marpolbul.2025.117537. Online ahead of print.

Authors

K L Priya¹, Gubash Azhikodan², Katsuhide Yokoyama³, K R Renjith⁴

Affiliations

¹ Department of Civil Engineering, TKM College of Engineering, Kollam, India. Electronic address: klpriyaram@gmail.com.
² Department of Civil and Environmental Engineering, Tokyo Metropolitan University, Minami Osawa, Tokyo, Japan. Electronic address: gubash@tmu.ac.jp.
³ Department of Civil and Environmental Engineering, Tokyo Metropolitan University, Minami Osawa, Tokyo, Japan.
⁴ Ecology & Environment Research Group, Centre for Water Resources Development and Management, Kozhikode, India.

PMID: 39787909
DOI: 10.1016/j.marpolbul.2025.117537

Abstract

This study evaluates the influence of water current and suspended sediment concentration (SSC) on microplastic distribution in various mixing regimes of the Ashtamudi estuary, India. Microplastic abundance ranged from 3.2 to 53 items/L, with highest concentrations observed near the confluence of the river and the sea. Partially mixed regions exhibited elevated near-bottom microplastic concentrations, identifying these zones as potential settling areas. Microplastic abundance showed a direct relationship with SSC and an inverse relationship with current. A non-linear model developed to predict microplastic abundance based on SSC and current demonstrated good performance, achieving an R² value of 0.97. This model outperformed the SSC-only model, representing a significant advancement over previous studies. The findings highlight the critical roles of hydrodynamic and sedimentary factors in governing microplastic distribution within the water column. The developed model, after calibration, can be applied to other estuaries globally, supporting plastic monitoring programmes in implementing effective mitigation measures.

Keywords: Ashtamudi estuary, India; Microplastics; Silt and clay fraction; Stratification parameter; Suspended sediment concentration; Water current.