Interactive effects of microplastics and selected pharmaceuticals on red tilapia: Role of microplastic aging.

The present study used red tilapia (Oreochromis niloticusas) as the model fish to compare the interactive effects between aged and virgin microplastics (MPs) with the antibiotic sulfamethoxazole (SMX) and the ß-blocker propranolol (PRP). To this end, the ultraviolet irradiation was used to simulate the MP aging in the environment. The accumulations of MPs and pharmaceuticals, and changes in enzyme activities and genes expressions in tilapia were also evaluated. Some physical properties of MPs changed during the aging process, reflected by 0.27- and 0.16-fold increases in the specific surface area and average pore volume, respectively. And more carbonyl formation was observed on the surface of aged MPs. Compared to the 14-d coexposure with virgin MPs, the MP aging increased the accumulation of PRP by 82.3% in the brain, whereas decreased the concentration of SMX by 46.1% in the gills. The stress on tilapia caused by the MPs and PRP was alleviated by the aging process, largely related to the lower neurotoxicity and reduced lipid peroxidation damages. However, the coexposure to aged MPs and SMX would result in higher inhibitions of cytochrome P450 enzymes activities. The results of the transcriptomics showed that the MP aging mainly influenced the expression of genes related to the metabolic process, immune system process, and the genetic information process in tilapia under the coexposure to MPs and pharmaceuticals. Collectively, our results suggest that the MP aging could induce complex changes in the interactive effects between MPs and pharmaceuticals on aquatic organisms.

Toxicological effects of nano- and micro-polystyrene plastics on red tilapia: Are larger plastic particles more harmless?

Nanoplastics (NPs) and microplastics (MPs) are a heterogeneous class of pollutants with diverse sizes in aquatic environments. To evaluate the hazardous effects of N/MPs with different sizes, the accumulation, oxidative stress, cytochrome P450 (CYP) enzymes, neurotoxicity, and metabolomics changes were investigated in the red tilapia exposed to three sizes of polystyrene (PS) N/MPs (0.3, 5, and 70 - 90 µm). After 14-d exposures, the largest particles (70 - 90 µm) showed the highest accumulation levels in most cases. Exposures to PS-MPs (5 and 70 - 90 µm) caused a more severe oxidative stress in red tilapia than PS-NPs. The activity of CYP3A-related enzyme was obviously inhibited by PS-NPs, whereas the CYP enzymes in the liver may not be sensitive to MP exposures. In the brain, only 5 µm PS-MPs significantly inhibited the acetylcholinesterase activity. After exposures, the treatments with 0.3, 5, and 70 - 90 µm N/MPs resulted in 31, 40, and 23 significantly differentially expressed metabolites, respectively, in which the pathway of tyrosine metabolism was significantly affected by all the three PS-N/MP exposures. Overall, the PS particles within the µm size posed more severe stress to red tilapia. Our results suggest that the toxicity of N/MPs may not show a simply monotonic negative correlation with their sizes.