Differential photoaging behaviors of different colored commercial polyethylene microplastics in water: The important role of color characteristics

Upon entering the environment, plastics would undergo photoaging and forming microplastics (MPs). However, information on the photoaging behavior of colored MPs and how the color characteristics (wavelength, lightness, and saturation) influence their photoaging process is still lacking. Thus, attention was paid to comparing the photoaging process of transparent and five-colored MPs. To reveal the degree of photodegradation and photooxidation, physicochemical changes (e.g., surface morphology, functional groups, and the leaching of intermediates) of transparent and five-colored MPs were explored. Photodegradation rates and photooxidation degrees ranked transparent > yellow > red ≈ orange > green > blue. However, transparent and five-colored MPs exhibited a different photoaging sequence and eluted different photodegradation products from each other. Pearson correlation analysis was used to describe the relationships between color characteristics (wavelength, lightness, and saturation) and their photoaging properties, and the results indicated that MPs (yellow, red, and orange) with longer color wavelength, higher lightness, and lower saturation are more susceptible to UV light than MPs with shorter color wavelength, lower lightness and higher saturation (green and blue). The findings demonstrate that the photoaging process of colored MPs is correlated to their color characteristics, highlighting the important role of color in MPs' environmental fate.