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.