Production of methane and ethylene from plastic in the environment

[Howard Dryden]

03/08/2018 Production of methane and ethylene from plastic in the environment

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0200574 1/8

Abstract

Mass production of plastics started nearly 70 years ago and the production rate is expected to double over the next two decades.

While serving many applications because of their durability, stability and low cost, plastics have deleterious effects on the

environment. Plastic is known to release a variety of chemicals during degradation, which has a negative impact on biota. Here, we

show that the most commonly used plastics produce two greenhouse gases, methane and ethylene, when exposed to ambient

solar radiation. Polyethylene, which is the most produced and discarded synthetic polymer globally, is the most prolific emitter of

both gases. We demonstrate that the production of trace gases from virgin lowdensity

polyethylene increase with time, with rates

at the end of a 212day

incubation of 5.8 nmol g d of methane, 14.5 nmol g d of ethylene, 3.9 nmol g d of ethane and 9.7

nmol g d of propylene. Environmentally aged plastics incubated in water for at least 152 days also produced hydrocarbon gases.

In addition, lowdensity

polyethylene emits these gases when incubated in air at rates ~2 times and ~76 times higher than when

incubated in water for methane and ethylene, respectively. Our results show that plastics represent a heretofore unrecognized

source of climaterelevant

trace gases that are expected to increase as more plastic is produced and accumulated in the

environment.

Citation: Royer SJ,

Ferrón S, Wilson ST, Karl DM (2018) Production of methane and ethylene from plastic in the

environment. PLoS ONE 13(8): e0200574. https://doi.org/10.1371/journal.pone.0200574

Editor: P. PardhaSaradhi,

University of Delhi, INDIA

Received: December 21, 2017; Accepted: July 1, 2018; Published: August 1, 2018

Copyright: © 2018 Royer et al. This is an open access article distributed under the terms of the Creative Commons

Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author

and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information file.

Funding: This research was supported by National Science Foundation (CMORE,

DBI0424599

to DMK and OCE1260164

to Matthew J. Church and DMK), the Simons Foundation (SCOPE Award ID 329108 to DMK), the Balzan Prize for

Oceanography (awarded to DMK) and the Gordon and Betty Moore Foundation’s Marine Microbiology Initiative (grant #3794

to DMK). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the

manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Over the past 50 years, polymer manufacturing has accelerated, from 2x10 metric tonnes (Mt) per year in 1950 to 381x10 Mt per

year in 2015, and is expected to double in the next 20 years [1]. The total global production of plastics to date is estimated at

8300x10 Mt, with polyethylene being the most common polymer [2,3], accounting for approximately 36% of all plastic types [1]. In

the environment, plastics are vulnerable to weathering and degradation processes, caused by environmental factors such as light,

heat, moisture, chemical oxidation and biological activity that are responsible for physical and chemical changes in the structure of

the polymer [4].

Polyethylene, like other plastics, is not inert and is known to release additives and other degradation products into the environment

throughout its lifetime. For example, the additive bisphenolA

used in the manufacture of many plastic products [5] is leached as

plastics age, and hydrocarbon gases are produced during hightemperature

decomposition (>202°C) [6]. These chemicals vary

amongst different types of plastic and, once released, some can be toxic and have adverse effects on the environment and human

health [7–9]. Degradation processes not only affect the chemical integrity of the plastic but also ultimately results in the

fragmentation of the polymer into smaller units increasing the surface area exposed to the elements.

Most plastic is synthesized from natural gases [10] and leaching is expected to occur during the aging processes. However, to the

best of our knowledge, no previous study has reported hydrocarbon gas emissions from plastics under natural conditions. This

study seeks to investigate this phenomenon and its potential environmental consequences.

Our research investigated the production of hydrocarbon gases from polyethylene and other plastics at ambient temperature, with

an emphasis on methane (CH ), one of the most potent atmospheric greenhouse gases [11–13] and ethylene (C H ), which reacts

with OH in the atmosphere and increases carbon monoxide concentrations [14,15]. Given the substantial rise in plastic production

worldwide, understanding the extent of CH and C H emissions from plastic is essential. In addition, we report production rates of

ethane (C H ), the second most abundant hydrocarbon in the atmosphere after CH , known to enhance the level of tropospheric

ozone and carbon monoxide [14,16], and propylene (C H ), also a hydrocarbon pollutant in the atmosphere [17]. Since plastics

come in different compositions and morphologies, we conducted a series of experiments to evaluate gas production under a variety

of environmental conditions. We show that solar radiation initiates the production of these gases for the polymers tested.

Materials and methods

Published: August 1, 2018 https://doi.org/10.1371/journal.pone.0200574

Production of methane and ethylene from plastic in the environment

SarahJeanne

Royer , Sara Ferrón, Samuel T. Wilson, David M. Karl

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