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.

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Direct air capture (DAC) is critical for achieving stringent climate targets, yet the environmental implications of its large-scale deployment have not been evaluated in this context. Performing a prospective life cycle assessment for two promising technologies in a series of climate change mitigation scenarios, we find that electricity sector decarbonization and DAC technology improvements are both indispensable to avoid environmental problem-shifting. Decarbonizing the electricity sector improves the sequestration efficiency, but also increases the terrestrial ecotoxicity and metal depletion levels per tonne of CO2 sequestered via DAC. These increases can be reduced by improvements in DAC material and energy use efficiencies. DAC exhibits regional environmental impact variations, highlighting the importance of smart siting related to energy system planning and integration. DAC deployment aids the achievement of long-term climate targets, its environmental and climate performance however depend on sectoral mitigation actions, and thus should not suggest a relaxation of sectoral decarbonization targets.

With rapid global development, the amount of food waste is increasing, which has seriously affected the environment. Usually, food waste is composted with sawdust to prevent environmental pollution as a result of the loss of N and S. Unfortunately, the quality of the compost of food waste and sawdust (CFS) is poor, and the material is hard to handle. Torrefaction, a process of slow pyrolysis under anoxic conditions, can be used to improve the properties of a fuel sample. This study investigated the fuel properties of CFS samples subjected to torrefaction at five different temperatures (250, 300, 350, 400, and 450 °C) and a residence time of 30 min. Physicochemical analyses of the samples were carried out according to standard methods, and the combustion characteristics of the samples were studied by thermogravimetric analysis. Torrefaction has great impact on proximate and ultimate analyses, chlorine contents, energy and mass yields, and grindability and combustion characteristics. The grindability and combustion properties of CFS were also improved by torrefaction. At a torrefaction temperature (300 °C), the higher heating value reached its maximum value (19 334 kJ/kg), meaning that the torrefied CFS contained up to 63.89% of its original energy content and the combustion characteristics were optimal at this torrefaction temperature.