Distribution and characteristics of microplastics in urban waters of seven cities in the Tuojiang River basin, China.

Microplastics pollution presents an increasing concern worldwide due to the large amount and potential risks. However, data on microplastics in the freshwater environment are still limited, especially in southwest China. This study investigated the microplastics distribution, characteristics and risks in urban water of different cities in the Tuojiang River basin in southwest China. Microplastics were found in all seven cities of the Tuojiang River basin and the concentrations varied from 911.57 ± 199.73 to 3395.27 ± 707.22 items/m3, among which Ziyang urban water had the highest microplastics concentration. Fiber (34.88-65.85%) was a typical and abundant microplastic type. The small size (0.5-1 mm) (27.27-66.67%) was predominant, and white (23.30-54.29%) was the dominant color among all samples. Polypropylene was identified as the main polymer type by Fourier transform infrared spectroscopy. The morphological analysis by scanning electron microscopy indicated that the surfaces of the microplastics had many cracks and a multitude of particles were adsorbed onto it. According to correlation analysis, there was a significant positive correlation between gross domestic product(P=0.015<0.05) and gross domestic product of the secondary industries(P=0.014<0.05) of cities in the Tuojiang River basin and microplastics concentrations, demonstrating impacts of the secondary industries on the microplastics pollution. In addition, water bodies with lower oxidation-reduction potential tended to have higher microplastics abundance. In the Tuojiang River basin, microplastics pollution was more serious in location where water quality was poor. The polymer risk index (H) was calculated to assess the environmental risk of microplastics in different cities, and the results showed that Fushun sites had the highest risk in regard to microplastics. This study provides a valuable reference for a better understanding of the microplastics level and source identification in southwest China.