Degradation Rates of Plastics in the Environment

Plastic waste is currently entering the natural environment at a rate of over 300 Mt year-1. Coupled with the long lifetimes of common plastics, this input is already resulting in rapid accumulation, yet our understanding of plastic persistence in the environment is very limited. This review summarizes the existing literature on environmental degradation rates and pathways for the major types of thermoplastic polymers. It also highlights the need for better experimental studies of polymer degradation under well-defined reaction conditions, and standardized reporting of rates. 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 variability due to degradation studies conducted in different natural environments. For example, SSDRs for HDPE in the marine environment range from essentially 0 to ca. 11 μm year-1. Using a mean SSDR for HDPE in the marine environment a...