The distribution and characterisation of microplastics in air, surface water and sediment within a major river system

Imogen E Napper; Anju Baroth; Aaron C Barrett; Sunanda Bhola; Gawsia W Chowdhury; Bede F R Davies; Emily M Duncan; Sumit Kumar; Sarah E Nelms; Md Nazmul Hasan Niloy; Bushra Nishat; Taylor Maddalene; Natalie Smith; Richard C Thompson; Heather Koldewey

doi:10.1016/j.scitotenv.2023.166640

The distribution and characterisation of microplastics in air, surface water and sediment within a major river system

Sci Total Environ. 2023 Nov 25:901:166640. doi: 10.1016/j.scitotenv.2023.166640. Epub 2023 Aug 28.

Authors

Affiliations

¹ International Marine Litter Research Unit, University of Plymouth, UK; School of Biological and Marine Sciences, University of Plymouth, UK. Electronic address: imogen.napper@plymouth.ac.uk.
² Wildlife Institute of India, Dehradun, Uttarakhand, India.
³ School of Biological and Marine Sciences, University of Plymouth, UK.
⁴ Department of Zoology, University of Dhaka, Dhaka 1000, Bangladesh; WildTeam, 69/1 New Circular Road, Malibagh, Dhaka 1217, Bangladesh.
⁵ Nantes Université, Institut des Substances et Organismes de la Mer, ISOMer, UR2160, Nantes, F-44000, France.
⁶ Centre for Ecology and Conservation, University of Exeter, Penryn Campus, UK.
⁷ Isabella Foundation, Dhaka, Bangladesh.
⁸ National Geographic Society, Washington, DC, USA; University of Georgia, Athens, GA, USA.
⁹ International Marine Litter Research Unit, University of Plymouth, UK; Plymouth Marine Laboratory, UK.
¹⁰ International Marine Litter Research Unit, University of Plymouth, UK; School of Biological and Marine Sciences, University of Plymouth, UK.
¹¹ Centre for Ecology and Conservation, University of Exeter, Penryn Campus, UK; Zoological Society of London, London, UK.

PMID: 37647965
DOI: 10.1016/j.scitotenv.2023.166640

Abstract

Rivers are key pathways for the transfer of microplastics (MP) to marine environments. However, there are considerable uncertainties about the amount of microplastics transported by rivers to the ocean; this results in inaccuracies in our understanding of microplastic quantity and transport by freshwater systems. Additionally, it has been suggested that rivers may represent long-term sinks, with microplastics accumulating in sediment due to their high density or other biological, chemical, and physical factors. The atmosphere is also an important pathway by which airborne microplastics may enter aquatic habitats. Here, we compare for first time microplastics type and concentration in these key environmental mediums (air, water and sediment) along a major river (Ganges), from sea to source to understand 1) the abundance, 2) the spatial distribution, and 3) characteristics. Mean microplastic abundance settling from the atmosphere was 41.12 MP m² day^-1; while concentrations in sediment were 57.00 MP kg^-1 and in water were 0.05 MP L^-1. Across all sites and environmental mediums, rayon (synthetically altered cellulose) was the dominant polymer (54-82 %), followed by acrylic (6-23 %) and polyester (9-17 %). Fibres were the dominant shape (95-99 %) and blue was the most common colour (48-79 %). Across water and sediment environmental mediums, the number of microplastics per sample increased from the source of the Ganges to the sea. Additionally, higher population densities correlated with increased microplastic abundance for air and water samples. We suggest that clothing is likely to be the prominent source of microplastics to the river system, influenced by atmospheric deposition, wastewater and direct input (e.g. handwashing of clothes in the Ganges), especially in high density population areas. However, we suggest that subsequent microplastic release to the marine environment is strongly influenced by polymer type and shape, with a large proportion of denser microplastics settling in sediment prior to the river discharging to the ocean.

Keywords: Air; Fibres; Freshwater; Microplastic; Sediment; Water.