Degradation and lifetime prediction of plastics in subsea and offshore infrastructures

Ibukun Oluwoye; Laura L Machuca; Stuart Higgins; Sangwon Suh; Tamara S Galloway; Peter Halley; Shuhei Tanaka; Mariano Iannuzzi

doi:10.1016/j.scitotenv.2023.166719

Degradation and lifetime prediction of plastics in subsea and offshore infrastructures

Sci Total Environ. 2023 Dec 15:904:166719. doi: 10.1016/j.scitotenv.2023.166719. Epub 2023 Sep 4.

Authors

Ibukun Oluwoye¹, Laura L Machuca², Stuart Higgins³, Sangwon Suh⁴, Tamara S Galloway⁵, Peter Halley⁶, Shuhei Tanaka⁷, Mariano Iannuzzi²

Affiliations

¹ Curtin Corrosion Centre, Western Australian School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, Perth, Australia; Graduate School of Global Environmental Studies, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, Japan. Electronic address: Ibukun.Oluwoye@Curtin.edu.au.
² Curtin Corrosion Centre, Western Australian School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, Perth, Australia.
³ Curtin University, GPO Box U1987, Perth, WA 6824, Australia.
⁴ Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA.
⁵ College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QD, UK.
⁶ School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia.
⁷ Graduate School of Global Environmental Studies, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto, Japan.

PMID: 37673242
DOI: 10.1016/j.scitotenv.2023.166719

Abstract

Engineering and civil developments have relied on synthetic polymers and plastics (including polyethylene, polypropylene, polyamide, etc.) for decades, especially where their durability protects engineering structures against corrosion and other environmental stimuli. Offshore oil and gas infrastructure and renewable energy platforms are typical examples, where these plastics (100,000 s of metric tonnes worldwide) are used primarily as functional material to protect metallic flowlines and subsea equipment against seawater corrosion. Despite this, the current literature on polymers is limited to sea-surface environments, and a model for subsea degradation of plastics is needed. In this review, we collate relevant studies on the degradation of plastics and synthetic polymers in marine environments to gain insight into the fate of these materials when left in subsea conditions. We present a new mathematical model that accounts for various physicochemical changes in the oceanic environment as a function of depth to predict the lifespan of synthetic plastics and the possible formation of plastic debris, e.g., microplastics. We found that the degradation rate of the plastics decreases significantly as a function of water depth and can be estimated quantitatively by the mathematical model that accounts for the effect (and sensitivity) of geographical location, temperature, light intensity, hydrostatic pressure, and marine sediments. For instance, it takes a subsea polyethylene coating about 800 years to degrade on ocean floor (as opposed to <400 years in shallow coastal waters), generating 1000s of particles per g of degradation under certain conditions. Our results demonstrate how suspended sediments in the water column are likely to compensate for the decreasing depth-corrected degradation rates, resulting in surface abrasion and the formation of plastic debris such as microplastics. This review, and the complementing data, will be significant for the environmental impact assessment of plastics in subsea infrastructures. Moreover, as these infrastructures reach the end of their service life, the management of the plastic components becomes of great interest to environmental regulators, industry, and the community, considering the known sizeable impacts of plastics on global biogeochemical cycles.

Keywords: Coatings; Contaminants; Decommissioning; Flowlines; Microplastics; Offshore energy infrastructure; Plastics; Underwater cables.

Publication types

Review