Fire-exposed polypropylene as a potential source of nanoplastics in aquatic environments

Worldwide, mismanaged plastic waste from developing countries is increasing, with a significant proportion of this waste being exposed to fire. As a result, fire-exposed plastics are increasingly entering natural environments. This study aims to enhance the understanding of nanoplastics (NPs) leaching from fire-exposed plastics in water. We selected polypropylene (PP), a widely used polymer that can contaminate the water environment. PP was exposed to fire with a torch at temperatures between 950 and 1150 °C for varying durations (10-30 s). An electronic balance, vernier calipers, Raman spectroscopy, XPS, SEM, and HRTEM were used to analyze the characteristics of plastics exposed to fire. A shaking incubator was used to simulate the physical impacts of water flow in a water environment. The NPs concentration was analyzed using DLS and TOC. After 24 h of shaking, no NPs were detected for pristine PP. However, the 30 s of fire-exposed PP released NPs with 1.33 × 10¹² ± 3.64 × 10¹¹ particle count kg^-1 within just 1 h. This study also found that stronger physical conditions (fire exposure time, shaking time, shaking rate) led to an increase in NPs release. Likewise, as the pH increased from 5 to 9, the absolute zeta potential increased, resulting in a gradual rise in NPs release. These findings underscore the urgent need to assess and manage the environmental risks posed by plastic residues resulting from campfire, wildfire, open burning, or container ship burning, as these residues have the potential to act as sources of NPs in water.