Effects of combined exposure to polyethylene and oxidized polycyclic aromatic hydrocarbons on growth, development, and neurobehavior in Zebrafish

Abstract

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are a class of anthropogenic, persistent, and highly toxic PAH contaminants associated with developmental toxicity, 9-fluorenone (9-FLO) is a typical member of the OPAH family. Due to its ketone group, it has higher polarity, which results in increased solubility in water and greater potential for transport via atmospheric particles or water bodies. Polyethylene (PE), an amorphous polymer, is characterized by high diffusivity, high permeability, and a large internal molecular free volume, which confers a strong absorption capacity for organic pollutants. The effects of individual and combined exposures to these two common environmental pollutants on aquatic life remain unclear. In this study, we evaluated the effects of PE and 9-FLO exposure on growth, development, metabolism, and behavior using zebrafish as a model organism. We employed methods and techniques such as acridine orange staining, enzyme-linked immunosorbent assay (ELISA), video tracking, automated behavior analysis, microscopy imaging, and real-time fluorescence quantification. Zebrafish embryos at 2 h post-fertilization (hpf) were exposed to PE and 9-FLO, both individually and in combination. Our studies showed that exposure to PE or 9-FLO alone increases embryonic mortality and decreases hatchability compared to the control group. The 9-FLO group exhibited delayed hatching and inhibited larval length growth. The exposed groups showed a loose arrangement of telencephalic neurons, partial apoptosis, decreased dopamine (DA) content, increased serotonin (5-HT) content, decreased exercise capacity, reduced rhythmic amplitude, and increased rest time. The combined exposure group showed a slight alleviation of these effects compared to the single exposure groups but still exhibited significant differences from the control group. In summary, early exposure to PE and 9-FLO in zebrafish embryos, whether alone or in combination, affects growth, development, apoptosis, neurotransmitter release, and motor behavior of zebrafish neurons.