Toxicological effects of micro/nanoplastics and benzo[a]pyrene on cellular and molecular responses of Apostichopus japonicus (Selenka, 1867) during intestinal regeneration

Micro(nano)plastics (M/NPs) are pervasive in marine environments. Benzo[a]pyrene (B[a]P), a typical polycyclic aromatic hydrocarbon (PAH), possesses teratogenic, mutagenic, and carcinogenic properties. B[a]P can accumulate on M/NPs, altering their toxicity. This study investigated individual and combined effects of M/NPs and B[a]P on the intestinal regeneration of the benthic invertebrate Apostichopus japonicus. Eviscerated sea cucumbers were exposed to 0.1 mg L M/NPs (80 nm [NP80] or 20 μm [MP20]) and/or 0.03 μg L B[a]P for 28 days. Cell proliferation, antioxidant and immunoenzyme activity, gene expression, and microbial community in the regenerated intestine were assessed. It demonstrated that combined exposure prolonged regeneration process, leading to increased oxidative stress and intestinal damage. Differential gene expression analysis revealed that co-exposure and single NP80 exposure both significantly changed translation-related processes, while single MP20 exposure primarily affected lipid metabolism. All treatments significantly altered the intestinal microbiota. Under the MP20+B[a]P treatment, Ralstonia abundance significantly increased, while Cobetia and Paracoccus abundances decreased. In general, co-exposure exerted more detrimental effects on intestinal regeneration than any single exposure, with MP20+B[a]P demonstrating more severe impacts. This study provides novel insights into the biotoxicity of M/NPs and B[a]P, contributing to better understanding of the detriments of microplastics and PAHs on marine benthic invertebrates.