These experimental results indicated that UV irradiation and oxygen were important factors in the initiation of the photo-oxidative degradation of polymers.Observations and comparisons of the degradation of identical plastic pellets in three different environments revealed that the level of chemical weathering of plastic pellets was in the following order: air environment > ultrapure water environment > simulated seawater environment.The level of chemical weathering of the plastic pellets increased with the exposure time in all three environments, indicating that the UV exposure time and the environmental differences associated with the differences in the utilization rate of UV light, the salinity and the exposure level of oxygen were the important factors that affected the degradation degree of plastic pellets.Because smaller polymers formed by photo-oxidative degradation are more susceptible to biodegradation, abiotic degradation is expected to precede biodegradation.Thus, more investigations on the degradation processes of plastic particles in the environment are needed; this would help increase our understanding of the source of microplastics, predict the fate of microplastics in the environment, and evaluate the potential environmental hazards to organisms.