Formulation Controls the Potential Neuromuscular Toxicity of Polyethylene Photoproducts in Developing Zebrafish

Sunlight transforms plastic into water-soluble products, the potential toxicity of which remains unresolved, particularly for vertebrate animals. We evaluated acute toxicity and gene expression in developing zebrafish larvae after 5 days of exposure to photoproduced (P) and dark (D) leachates from additive-free polyethylene (PE) film and consumer-grade, additive-containing, conventional, and recycled PE bags. Using a "worst-case" scenario, with plastic concentrations exceeding those found in natural waters, we observed no acute toxicity. However, at the molecular level, RNA sequencing revealed differences in the number of differentially expressed genes (DEGs) for each leachate treatment: thousands of genes (5442 P, 577 D) for the additive-free film, tens of genes for the additive-containing conventional bag (14 P, 7 D), and none for the additive-containing recycled bag. Gene ontology enrichment analyses suggested that the additive-free PE leachates disrupted neuromuscular processes via biophysical signaling; this was most pronounced for the photoproduced leachates. We suggest that the fewer DEGs elicited by the leachates from conventional PE bags (and none from recycled bags) could be due to differences in photoproduced leachate composition caused by titanium dioxide-catalyzed reactions not present in the additive-free PE. This work demonstrates that the potential toxicity of plastic photoproducts can be product formulation-specific.