Microplastics Contamination versus Inorganic Particles: Effects on the Dynamics of Marine Dissolved Organic Matter

Amedeo Boldrini,Luisa Galgani,Steven Arthur Loiselle,Marco Consumi

doi:10.3390/environments8030021

Abstract

Microplastic contamination has been linked to a range of impacts on aquatic environments. One important area that is only beginning to be addressed is the effect of microplastics on marine carbon cycling and how these compare to the effects related to inorganic particles typically present in ocean waters. The present study explores these impacts on dissolved organic matter dynamics by comparing three scenarios: a particle-free environment, a particle-enriched system with polystyrene microplastics, and a particle-enriched system with inorganic particles (water insoluble SiO2). Natural marine organic matter was obtained by culturing a non-axenic strain of Chaetoceros socialis in 2 L flasks under each of three scenarios. Following the diatom growth phase, filtered samples from the three flasks containing dissolved organic matter and bacteria were incubated separately in the dark for 5 days to monitor changes in dissolved organic matter. Chromophoric dissolved organic matter (CDOM), a bulk optical property, was monitored daily to examine changes in its quality and quantity and to compare degradation dynamics in the three systems. CDOM absorbance (quantity) remained higher in the control with respect to particle-enriched systems, suggesting that the presence of particles led to different rates of CDOM production and degradation. Using indicators for CDOM that could be related to microbial activity, results showed a higher CDOM alteration in the particle-enriched systems. These results indicate that microplastics have a potential role in modifying marine organic matter dynamics, on a similar magnitude to that of biogenic inorganic particles. Given their increasing concentrations of marine ecosystems, their role in marine microbial processing of organic matter needs to be better understood.

Highlights

From the synthesis of the first polymers, the production and use of plastics has grown constantly, largely due to their expanding range of application
As plastic is resistant to biological degradation, it accumulates in the environment and can be considered a persistent organic pollutant (POP) like many other compounds of anthropogenic origin [5,6]
In part 1, a diatom culture of Chaetoceros socialis was grown in three different treatments to obtain the dissolved organic matter to allow for microbial dark incubations in the second part of the experiment

Summary

Introduction

From the synthesis of the first polymers, the production and use of plastics has grown constantly, largely due to their expanding range of application. The global plastic production in 2019 reached 368 million tons [1]. The amount of plastic that reaches the ocean, as of 2010, was estimated between 4.7 and 12.7 million tons per year [2]. Most of this plastic comes from land-based sources through river discharge [3], evidenced by the high concentrations found in freshwater environments [4]. As plastic is resistant to biological degradation, it accumulates in the environment and can be considered a persistent organic pollutant (POP) like many other compounds of anthropogenic origin [5,6].

Methods

Results

Conclusion