Residual Monomer Content Affects the Interpretation of Plastic Degradation

Franziska Klaeger,Matthias Bienmüller,Alexander S Tagg,Stefan Otto,Ingo Sartorius,Matthias Labrenz

doi:10.1038/s41598-019-38685-6

Franziska Klaeger, Matthias Bienmüller + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-38685-6

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Abstract

Plastic degradation rates in the marine environment are essential to understand. This study demonstrates that in plastic-microbial interaction experiments, residual monomeric and oligomeric content of PA6 significantly influences the development of dissolved organic carbon. While it is well recognized that additives in plastics should be considered during the inception of plastic-exposure experiments, residual monomers have yet to be prominently considered in the same light. As such, in degradation studies where residual contents of monomers and/or oligomers are not considered, degradation of synthetic polymers could be significantly overestimated. The substantial conversion of these monomeric and oligomeric leachates also has implications for plastic-biofilm development studies and microplastic-biota-based ingestion experiments.

Highlights

There are well-established and worldwide concerns about plastic pollution
In order to understand the effect that residual monomers and oligomers (rM) content could have on the interpretation of plastic degradation, exposure tests investigating differing monomer contents were designed where dissolved inorganic carbon (DIC = [CO2] + [HCO3−] + [CO32−]) was selected as the indicator by which biological degradation is chemically measured
To ensure that the measured carbon came from the plastic, the 14C content was determined in the DIC of the ABW following incubation

Summary

Introduction

There are well-established and worldwide concerns about plastic pollution. As such, it is essential to understand the potential for degradation of plastics in the environment, especially the marine environment. Plastic degradation results in fragmentation of larger plastic pieces into smaller plastic particles by a combination of abiotic (such as UV irradiation) and biotic factors (extracellular enzymatic action resulting in biodeterioration/ biofragmentation). PA6 (commonly referred to as nylon-6) is produced by ring-cleavage polymerization During this process, some molecules fail to polymerize and remain as oligomers and monomers within the structure of the polymer. In order to understand the effect that rM content could have on the interpretation of plastic degradation, exposure tests investigating differing monomer contents were designed where dissolved inorganic carbon (DIC = [CO2] + [HCO3−] + [CO32−]) was selected as the indicator by which biological degradation is chemically measured

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Conclusion