Trophic Transfer of Differentially Hydrophobic Nanoplastics along Marine Food Chains and Related Toxicity

Nanoplastics (NPs) with different hydrophobic properties are widely present in marine environments. However, the role of surface hydrophobicity in the bioaccumulation of NPs in the ecosystems is largely unknown. This study explores the role of surface hydrophobicity in trophic transfer of NPs along marine microalgae (Phaeodactylum tricornutum), mysids (Neomysis awatschensis), and fish (Sebastes schlegelii). For this, two types of Pd-doped polystyrene (PS) NPs (100 nm) were successfully synthesized, including hydrophobic PS1 NPs (octanol-water partition coefficients (K_ow), 11.14) and hydrophilic PS2 NPs (K_ow, 0.16). After 24-h dietary (algae-mysids) exposure (nominal concentrations, 1.0, 10.0 mg/L), hydrophobic PS1 NPs had higher accumulation in mysids than hydrophilic PS2 NPs due to much higher internalization of free PS1 NPs in seawater by mysids. Along NPs transfer (nominal concentrations, 1.0, 10.0 mg/L) from algae to mysids, and then fish, the contents of PS1 NPs in fish bodies (especially, gills, stomach, skin, blood, intestine, and liver) were also significantly higher than those of PS2 NPs. After dietary exposure, bioaccumulation factors (BAFs) of the two PS NPs in mysids and fish were 44-76 and 1-40 L/kg, respectively; and biomagnification factors (BMFs) along algae-mysids and algae-mysids-fish were 0.20-0.46 and 0.08-0.62, respectively. For PS1 NPs, both BAFs and BMFs were higher than those of PS2 NPs. Additionally, due to higher accumulation in fish brains, hydrophilic PS2 NPs exhibited more pronounced adverse effects on swimming and feeding behaviors of fish than hydrophobic PS1 NPs during dietary exposure. These findings highlight the importance of surface hydrophobicity on trophic transfer and the ecological risk of NPs in marine environments.