Degradation Rates of Plastics in the Environment

TLDR

Plastic waste is produced at roughly 400 Mt yr⁻¹ and its environmental accumulation is rapidly increasing, yet knowledge of its persistence remains limited. The perspective reviews literature on environmental degradation rates and pathways of major thermoplastic polymers. The authors introduce the specific surface degradation rate (SSDR) metric to harmonize measurements and extrapolate polymer half‑lives. SSDR values vary widely across environments, with marine HDPE SSDRs ranging 0–11 μm yr⁻¹ and extrapolated half‑lives from 58 yr for bottles to 1200 yr for pipes, while HDPE and PLA show similar marine rates yet PLA degrades ~20× faster on land, underscoring the need for standardized experimental conditions and reporting.

Abstract

Plastic waste is currently generated at a rate approaching 400 Mt year–1. The amount of plastics accumulating in the environment is growing rapidly, yet our understanding of its persistence is very limited. This Perspective summarizes the existing literature on environmental degradation rates and pathways for the major types of thermoplastic polymers. A metric to harmonize disparate types of measurements, the specific surface degradation rate (SSDR), is implemented and used to extrapolate half-lives. SSDR values cover a very wide range, with some of the variability arising due to degradation studies conducted in different natural environments. SSDRs for high density polyethylene (HDPE) in the marine environment range from practically 0 to approximately 11 μm year–1. This approach yields a number of interesting insights. Using a mean SSDR for HDPE in the marine environment, linear extrapolation leads to estimated half-lives ranging from 58 years (bottles) to 1200 years (pipes). For example, SSDRs for HDPE and polylactic acid (PLA) are surprisingly similar in the marine environment, although PLA degrades approximately 20 times faster than HDPE on land. Our study highlights the need for better experimental studies under well-defined reaction conditions, standardized reporting of rates, and methods to simulate polymer degradation using.