Meishe River is the longest urban river in Haikou. The level of microplastics pollution in this river may affect the ecological balance, and can have an adverse effect on human health. Thus, it is essential to gain a comprehensive understanding of the microplastics pollution in the river to ensure safety of the human living environment. Microscopic examination and Micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) were used to investigate the distribution and characteristics of microplastic pollution in surface water and sediments of the Meishe River. The results revealed that microplastics extracted from Meishe River mainly consisted of polyethylene (PE) and poly octadecyl acrylate (POA), and the abundance of microplastics in the surface water and sediments lay in the range of 3–10 items/L and 61–205 items/100 g dry weight, respectively. With respect to shapes and colors of microplastics, among the micro plastics found in the surface water, 74% were fiber and 57% were white colored, while among those in the sediments, 88% were fiber and 55% were of white colored. In terms of particle size, microplastics with the particle size of 0.1–0.5 mm were the most abundant (49% approximately) in surface water, while the microplastics with particle size 1.0–5.0 mm were dominant (74%) in the sediments. The results clearly showed that the Meishe River was polluted by microplastics, which may eventually flow into the nearby sea and adversely affect the sea environment. Consequently, some organisms in the urban river may be adversely affected.

Microplastics and heavy metal pollution frequently co-occur in the marine environment, raising concerns about their potentially harmful impacts on marine fish. This study undertook a comprehensive evaluation of the individual and combined stress effects of polylactide microplastics (PLA-MPs) and chromium (Cr) on marine medaka larvae. Following a 14-day exposure to PLA-MPs (100 μg/L) and Cr (50 μg/L), both individually and in combination, significant increases in heart rate and body length were observed. Notably, the combined exposure to PLA-MPs and Cr caused marked histopathological alterations, including shedding, atrophy, and lysis of the intestinal tissues. Furthermore, both individual and combined exposure induced oxidative stress in fish larvae, leading to changes in various enzyme activity indices. Individual exposure to either PLA-MPs or Cr led to anxious behavior in the larvae, whereas combined exposure not only caused anxious behavior but also altered swimming patterns. These findings suggest that combined exposure to PLA-MPs and Cr can exacerbate the toxic effects on marine medaka larvae.