Abundance, Distribution, and Drivers of Microplastic Contamination in Urban River Environments

Joseph Tibbetts,Iseult Lynch,Gregory Sambrook Smith,Stefan Krause

doi:10.3390/w10111597

Abstract

Given the persistence of microplastics in the environment and their potential toxicity to ecosystems, understanding of likely microplastic accumulation ‘hotspots’ in rivers is urgently needed. To contribute to this challenge, this paper reports results of a microplastic survey from a heavily urbanised catchment, the River Tame and four of its tributaries, which flows through the city of Birmingham, UK. All sediment sampled was found to contain microplastics with an average abundance of 165 particles kg−1. While urban areas generally have a greater abundance of microplastics as compared with rural, there is no simple relationship between microplastic numbers and population density or proximity to wastewater treatment sites. The greatest change in microplastic abundance was due to the presence of a lake along the course of the River Tame—i.e., flow velocities are reduced on entering the lake, which promotes the deposition of fine sediment and potentially microplastics. This suggests that the greatest concentrations of microplastics will not be found in-channel but rather on the floodplain and other low velocity environments such as meander cutoffs. We also identified a new mechanism of microplastic fixation in freshwater environments through ecological engineers, specifically caddisflies, that incorporated microplastics into their casing. These results highlight the need to explore further hydrodynamic and ecological impacts on microplastics fate and transport in rivers.

Highlights

Microplastics are recognised as a pervasive pollutant within marine environments, with the first evidence of their wide spread accumulation in freshwater and terrestrial environments recently published [1,2,3]
Microplastic particles were evident at all sampling sites with a total of 1507 plastic particles found throughout the upper River Tame and its tributaries
While this study has reported a general trend of higher abundance of microplastics in more urbanised parts of the catchment, providing an unequivocal explanation for microplastic abundance at each site is less straightforward

Summary

Introduction

Microplastics are recognised as a pervasive pollutant within marine environments, with the first evidence of their wide spread accumulation in freshwater and terrestrial environments recently published [1,2,3]. While it is acknowledged that river environments provide an important conduit for microplastics between inland terrestrial inputs and marine environments, there is still very little research on the abundance, patterns, and characteristics of microplastic particles in freshwater environments that would allow us to better understand their fate and transport as well as where microplastics may accumulate [7,8,9,10,11]. This is of concern given the growing evidence of the impacts of microplastics on ecosystem and public health. An adequate assessment of microplastic risks to the environment and public health critically requires more detailed field-based evidence of microplastic types and properties within river corridors in order to benchmark regional variations in exposure to microplastics and their associated pollutants, and identify at risk ecosystems

Objectives

Results

Conclusion