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

Sunlight transforms plastic into water-soluble products,the potentialtoxicity of which remains unresolved, particularly for vertebrateanimals. We evaluated acute toxicity and gene expression in developingzebrafish larvae after 5 days of exposure to photoproduced (P) anddark (D) leachates from additive-free polyethylene (PE) film and consumer-grade,additive-containing, conventional, and recycled PE bags. Using a worst-casescenario, with plastic concentrations exceeding those found in naturalwaters, we observed no acute toxicity. However, at the molecular level,RNA sequencing revealed differences in the number of differentiallyexpressed genes (DEGs) for each leachate treatment: thousands of genes(5442 P, 577 D) for the additive-free film, tens of genes for theadditive-containing conventional bag (14 P, 7 D), and none for theadditive-containing recycled bag. Gene ontology enrichment analysessuggested that the additive-free PE leachates disrupted neuromuscularprocesses via biophysical signaling; this was most pronounced forthe photoproduced leachates. We suggest that the fewer DEGs elicitedby the leachates from conventional PE bags (and none from recycledbags) could be due to differences in photoproduced leachate compositioncaused by titanium dioxide-catalyzed reactions not present in theadditive-free PE. This work demonstrates that the potential toxicityof plastic photoproducts can be product formulation-specific. Photoproduced water-soluble productsfrom consumer plasticsdisrupt the gene expression of developing zebrafish with plastic formulationspecificity.

Automated summary

Sunlight can transform plastic into water-soluble products, which may have potential toxicity for vertebrate animals. In this study, we exposed zebrafish larvae to photoproduced and dark leachates from different types of polyethylene bags and films, and evaluated their acute toxicity and gene expression. While we observed no acute toxicity, RNA sequencing revealed differences in the number of differentially expressed genes for each leachate treatment. Gene ontology analysis suggested that the additive-free polyethylene leachates disrupted neuromuscular processes, particularly for the photoproduced leachates. We also found that the composition of photoproduced leachates from conventional bags differed due to titanium dioxide-catalyzed reactions, which may explain the fewer differentially expressed genes elicited by these leachates. This study highlights the product formulation-specific potential toxicity of photoproduced plastic products on gene expression in zebrafish larvae.