Influences of different functional groups on the toxicity of pyrene derivatives to Skeletonema costatum: Interactive effects with polystyrene microplastics

Polycyclic aromatic hydrocarbons (PAHs) and microplastics, as persistent contaminants in the marine environment, have attracted significant attention for their potential risks. However, the toxicology of substituted PAHs (S-PAHs) in marine microalgae and the modulation of their toxicity by microplastics remain underexplored. Here, the toxicity of pyrene (Pyr) and derivatives of pyrene (S-Pyr), including 1-methylpyrene (P-CH), 1-hydroxypyrene (P-OH), 1-aminopyrene (P-NH), 1-pyrenecarboxylic acid (P-COOH) on the marine diatom Skeletonema costatum, both in the absence and presence of polystyrene microplastics (micro-PS) was investigated. Compared to Pyr, the P-CH, P-OH, and P-NH derivatives showed higher toxicity, whereas P-COOH exerted lower toxicity, as revealed by multiple physiological indices including growth inhibition rate, photosynthetic activity, and superoxide dismutase activity, and malondialdehyde content. Micro-PS could alleviate the toxicity of Pyr/S-Pyr toward S. costatum to varying degrees. Transcriptome analysis revealed a larger number of differentially expressed genes in the micro-PS combined with PAH treatment than in the corresponding PAH single treatment after 96 h of exposure. Furthermore, although Pyr/S-Pyr and micro-PS stress affect S. costatum to different degrees at the molecular level, genes related to metabolic pathways were primarily affected. This study provides valuable insights into the potential toxicity of S-PAHs and microplastics to marine microalgae, thereby enhancing our understanding of their environmental risks in marine ecosystems.