Antifouling paint particles (APPs), generated by coating degradation and ship-maintenance activities, are an emerging but poorly characterized source of marine pollution. APPs can release particle-associated and dissolved toxicants, yet their relative contributions to toxicity remain unclear. In this study, environmentally collected APPs were used to prepare two exposure media: an APP suspension containing suspended paint particles and dissolved constituents, and a corresponding membrane-filtered leachate representing the operationally defined dissolved fraction. Their toxic effects on the marine copepod Tigriopus japonicus were assessed using acute toxicity tests, chronic life-history assays, and comparative transcriptomic analyses. The APP suspension caused greater acute and chronic toxicity than the leachate under the test conditions. Transcriptomic profiling revealed 474 and 116 differentially expressed genes (DEGs) following APP suspension and leachate exposure, respectively, compared with the control. Gene Ontology (GO) enrichment and toxicity pathway analyses identified both shared and exposure-specific responses, with broader perturbations of toxicity-related biological processes following APP suspension exposure. Collectively, the greater phenotypic responses and distinct molecular profiles highlight the importance of considering multiple exposure forms when evaluating APP toxicity.
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