New insights on metal ions accelerating the aging behavior of polystyrene microplastics: Effects of different excess reactive oxygen species.

Microplastics (MPs) will coexist with various pollutants in the environment, but it is not clear whether these pollutants will affect the aging process of MPs. The aging process of polystyrene microplastics (PS-MPs) mediated by Cu2+ and Pb2+ was investigated in this study. The results showed that the aging rate of PS-MPs mediated by Cu2+ and Pb2+ were significantly higher than that of ultrapure water (After 7 days of light irradiation, the CI values of aging PS-MPs mediated by ultrapure water, Cu2+ and Pb2+ increased from 0.030 of original PS-MPs to 0.034, 0.048 and 0.086 respectively). This process may be related to the generation of a large amount of reactive oxygen species, because OH were detected in PS-MPs suspension mediated by Cu2+, which were significantly higher than those in ultrapure water, while 1O2 mediated by Pb2+ were more. However, these photo-aging effects were significantly inhibited by reactive oxygen species (ROS) quencher, which indicated that excessive ROS production was the main reason for metal ions to promote the photo-aging of PS-MPs. In addition, this study reported that excessive ROS will accelerate the formation of carbonyl group on the surface of PS-MPs, and lead to the change of physical and chemical properties of PS-MPs. This study provides new insights for the environmental behavior of MPs under the condition of combined pollution.

Photo-transformation of microplastics and its toxicity to Caco-2 cells.

In recent years, microplastics (MPs) pollution, as a global environmental problem, has been widely concerned by countries all over the world. However, the research on the impact of MPs on human health is still limited. In this study, we studied the photo-transformation behavior of polystyrene microplastics (PS-MPs) under ultraviolet light and its toxicity to Caco-2 cells. Our results showed that the surface of PS-MPs was roughened by light, and cracks and pits appeared. UV-vis spectra showed that the opening of phenyl ring and the formation of carbonyl group might exist in this process. Based on FTIR and 2D-COS analysis, we observed the formation of carbonyl group and hydroxyl group, and preliminarily determined that the order of photo-transformation of PS-MPs was 698 (CH) > 752 (CH) > 1030 (CO) > 3645 (OH/OOH) > 1740 (CO). XPS showed that the photo-transformation of PS-MPs was a process in which carbon-containing functional groups were gradually partially transformed into oxygen-containing functional groups. Finally, the toxicity results showed that with the increase of PS-MPs concentration and the extension of light irradiation time, the survival rate of Caco-2 cells gradually decreased and the integrity of cell membrane was destroyed. The increased cytotoxicity can be explained at least in part by the fact that the toxicity of oxygen-containing functional groups is greater than that of carbon-containing functional groups, but how these functional groups affect the cytotoxicity of cells still needs sustained research in the future. This study can provide new insights for understanding the environmental behavior and ecological effects of PS-MPs in the environment.

The occurrence and effect of altitude on microplastics distribution in agricultural soils of Qinghai Province, northwest China.

Microplastic (MPs) is a new type of environmental pollutant that has been widely detected in recent years. It is one of the main environmental problems faced by the global ecosystem and has attracted widespread attention. However, few studies have focused on the occurrence and distribution of MPs in agroecosystems. Therefore, Qinghai Province, a typical northwest region of China, was selected as the research area to study the distribution characteristics of MPs in agricultural soils in the low-altitude areas. The results indicated that MPs were detected in all soil samples. The abundance of MPs in agricultural soils in Qinghai Province ranged from 240 to 3660 items·kg-1. MPs with size less than 0.5 mm dominated, accounting for 50% of the total MPs. The main types of MPs were film and fiber, accounting for 67% and 29% respectively. It was proved that the use of mulching film and sewage irrigation are the main sources of MPs, and the recovery and treatment of agricultural waste can reduce MPs pollution. At the same time, the spatial distribution characteristics of MPs in the soil of Qinghai Province were analyzed, and the results showed that the heavily polluted areas of MPs were mainly concentrated in the densely populated areas in the east of the province. In addition, the influence of altitude on MPs abundance was investigated, and there was a negative correlation between altitude and MPs abundance, and ultraviolet light may accelerate the aging and degradation of MPs. This study revealed the distribution characteristics of farmland soil pollution in typical northwest China, and provided an important theoretical basis for the subsequent study of MPs in agricultural ecosystems.

Aging mechanism of microplastics with UV irradiation and its effects on the adsorption of heavy metals.

Microplastics are formed by the degradation of plastic wastes under the action of physicochemical mechanisms in environment, and they are becoming a new type of pollutant that is attractings global attention. However, research on the aging characteristics and mechanism of microplastics is limited. The aging mechanism of Polystyrene (PS) with UV irradiation under different conditions (air, pure water and seawater) and the effect of aging on heavy metal adsorption were studied. The results show that PS have different characteristics with UV irradiation under different conditions, and the aging of PS is the most obvious in air. Based on the 2D-COS analysis, different aging mechanisms were identified under different aging conditions, aging sequence of aged PS functional groups in air and water were clearly definited. An isothermal adsorption model shows that aging can significantly increase the adsorption of heavy metals by PS. The adsorption of heavy metals is also affected by different aging methods. Over all, a 2D-COS analysis was an effective method for understanding the aging process of PS. These results further clarify the aging mechanism of PS, and provides a theoretical basis for the assessment of environmental behavior and ecological risk when microplastics and heavy metals coexist.

Fenton aging significantly affects the heavy metal adsorption capacity of polystyrene microplastics.

Microplastics released into the environment undergo a variety of aging processes, however, information about the influence of aging on the adsorption behavior of microplastics is limited. In order to better understand the effect of aging polystyrene (PS) on the ability to adsorb heavy metal, H2O2 and Fenton reagent were used to investigate the aging properties of PS. Aging PS with these two different aging agents at pH = 4 and room temperature for the same time. Physical and chemical characterization indicated that aging caused oxidation of the surface of PS and the formation of surface micro-cracks. Based on the 2D-COS analysis, the aging process of PS functional groups could occur in the following sequence: 1375 (C-OH) > 1739 (C=O) > 1182 cm-1 (C-O-C) > 1716 (O-C=O). The adsorption experiments for Cd2+ with two different concentrations were carried out by PS with different aging time at room temperature. The adsorption data showed that the adsorption capacity of Cd2+ was significantly enhanced after aging compared with pristine PS, and the adsorption capacity of PS after Fenton aging treatment is much stronger than that after H2O2 aging treatment. The kinetic analysis of the adsorption data indicates that the adsorption process is more consistent with the second-order kinetics than the first-order kinetics, and it is further concluded that the adsorption of Cd2+ by PS is a relatively complicated process. According to the fitting results of adsorption isotherms, the adsorption process of pristine PS mainly occurs on the surface, but with the continuous aging, more adsorption sites may be exposed on the surface of PS, so it can be concluded that the adsorption mechanism of Cd2+ by PS is the coexistence of physics and chemistry. This study indicates aging microplastics may have a significant impact on the destination and migration of metal contaminants, which deserves to be further concerned.