To identify the physical effects, behavioral changes, and gene expression profiles of the phase 1 detoxification-related gene (cyp 1a) and oogenesis-related gene (vg 1) induced by microplastics, high-density polyethylene microplastics of various sizes were used because of their dominance in coastal areas and effluent samples in Hong Kong. Adult zebrafish were used as the model organism to identify the upper and lower boundaries of microplastics ingestion and were exposed to individual polyethylene microplastics in five size ranges (10-22 mu m, 45-53 mu m, 90-106 mu m, 212-250 mu m, and 500-600 mu m) at a concentration of 2 mg/L for 96 h. To study behavioral changes and targeted gene expression profiles via real-time PCR (qPCR), a mixture of microplastics in three size ranges at effluent-related (11 particles/L), moderate (110 particles/L), and high concentrations (1,100 particles/L) were applied for 96 h. The zebrafish behavior was recorded by a video camera and by two observers (interrater reliability, > 85%). The results implied that the upper and lower size boundaries for microplastic ingestion were 558.4 +/- 26.2 mu m (yellow) and 19.7 +/- 3.1 mu m (red), respectively. In addition, 61 +/- 10% of fish in medium concentration treatments and 61 +/- 10% of fish in high concentration treatments were found with the microplastic ingestion and remaining in their intestine. In addition, 28 +/- 10% of fish in high concentration treatments were found with microplastic retaining in their gills (No. of fishes = 18 in each treatment). The presence of microplastics, which occupied 89 +/- 6% of intestine area, reduced the voids inside the intestine for feed. The expression of cyp1a in the intestine (medium concentration) and vtg1 in the liver (medium and high concentration) showed significant up regulation, and abnormal behavior (i.e., seizures and tail bent downward) was observed (medium and high concentration). In summary, the effects on the aryl hydrocarbon receptor (AHR) pathway, disruption of the oogenesis process, and neurotoxicity could be caused by acute exposure of adult zebrafish to microplastics.
