Pyrolysis GC-MS Characterization of Plastic Debris from the Northern Gulf of Alaska Shorelines

Abstract

Plastics and their breakdown components are accumulating at alarming rates in global ecosystems, including the Gulf of Alaska. Obtaining knowledge of the chemical composition of plastics is important because different types of plastics are manufactured using different types of polymers and copolymers for specialized applications. We employed pyrolysis GC-MS for the chemical characterization of 115 plastic debris samples of different physical and optical properties nonrandomly collected from shorelines in the northern Gulf of Alaska. A twotier approach of peak fingerprinting and mass spectral data of marker peaks provided higher confidence in the data. The analyses did not appear to be compromised by the physical properties, optical properties, or weathering conditions of the debris. Polyethylene and polypropylene, the low-density floating plastics possibly of oceanic origins, were some of the most frequently detected polymers in the Katmai National Park and Preserve and Kenai Fjords National Park. Interestingly, a more diverse composition of polyethylene, polypropylene, polystyrene, poly(ethylene terephthalate), and poly(vinyl chloride) was detected in Western Prince William Sound shorelines, possibly of oceanic as well as terrestrial origins. Additional benefits of the pyrolysis GC-MS method included the detection of copolymers and plastic additives in the same analytical runs.

Environmental Markers of Plastics and Microplastics

“…Thermal reactions at temperatures above 300 °C in the absence of oxygen (pyrolysis) have been used to identify micro- and nanoplastics in environmental samples from the gas phase distributions and intensities and products detected by pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS). − The pyrolysis of PE, for example, generates alkanes and alkenes, PS releases benzene, styrene, and styrene oligomers, while PVC generates benzene and chlorobenzene, among other aromatic compounds. , In the presence of oxygen and temperatures below 300 °C, thermal oxidation leads to the formation of low molecular weight volatile aldehydes, ketones, and carboxylic acids for PE and PS and to HCl and aromatic compounds for PVC. ,,− ,− The thermal-oxidation process and products of PE, PS, and PVC under environmental conditions (<100 °C) are poorly explored, in part due to the low reaction rates expected for the temperature ranges found under environmental conditions. Nonetheless, PE and PS are reported to undergo thermal decomposition at temperatures near 100 °C or below, , but little is known about the products released under these conditions …”