High temperature depended on the ageing mechanism of microplastics under different environmental conditions and its effect on the distribution of organic pollutants.

Microplastics, as an emerging class of pollutants has become a global concern, and is receiving increasing attention. Interestingly, microplastics are always in their ageing process when they enter the real environment. Our study investigated the ageing properties of polystyrene (PS) plastics in air, pure water and seawater environments at 75 °C. A two-dimensional (2D) Fourier transform infrared (FTIR) correlation spectroscopy (COS) analysis was used to better understand the ageing mechanism of the PS plastics. Based on the 2D-COS analysis, different ageing mechanisms were identified under different ageing conditions, such as an ageing sequence of aged-PS particle functional groups in air: 1601(CC) > 1050(C-O)>1453(C-H)>1493(C-H)>1375(C-OH)>1666(CO). Among the functional group changes, O-functional groups (C-O, C-OH and CO) were introduced during the ageing process. Moreover, for pristine PS particles, hydrophobicity was a major factor for the interaction between the microplastics and organic pollutants. For aged-PS particles, their adsorption capacities were significantly enhanced as the degree of ageing increased. The ageing degree of PS was highly responsible for increasing of the specific surface area and the increase in oxygen-containing surface groups. Furthermore, there was a significant enhancement in the adsorption affinity for antibiotic contaminants than for polycyclic aromatic hydrocarbon contaminants. Aged PS particles had little adsorption of polycyclic aromatic hydrocarbons, because the presence of oxygen-containing surface groups on the aged PS plastics might allow the formation of hydrogen bonds with the surrounding water molecules. Overall, a 2D-COS analysis was an effective method for understanding the ageing process of microplastics under different environmental conditions at high temperature. These results also clearly demonstrated the characteristics and mechanisms of the interaction between aged-microplastics and organic pollutants, which could be useful for understanding the environmental behavior of co-existing pollutants.