Locomotor behavior of Neocaridina palmata: a study with leachates from UV-weathered microplastics

Toxicity and potential underlying mechanism of Karenia selliformis to the fish Oryzias melastigma

Karenia selliformis can produce toxins such as gymnodimines, and form microalgal blooms causing massive mortality of marine life such as fish and shellfish, and resulting in serious economic losses. However, there are a few of studies on the toxic effects of K. selliformis on marine organisms and the underlying mechanisms, and it is not clear whether the toxins produced by K. selliformis affect fish survival through the food chain. In this study, a food chain was simulated and composed by K. selliformis-brine shrimp-marine medaka to investigate the possibility of K. selliformis toxicity transmission through the food chain, in which fish behavior, histopathology and transcriptomics changes were observed after direct or indirect exposure (through the food chain) of K. selliformis. We found that both direct and indirect exposure of K. selliformis could affect the swimming behavior of medaka, manifested as decreased swimming performance and increased "frozen events". Meanwhile, exposure to K. selliformis caused pathological damage to the intestine and liver tissues of medaka to different degree. The effect of direct exposure to K. selliformis on swimming behavior and damage to fish tissues was more severe. In addition, K. selliformis exposure induced significant changes in the expression of genes related to energy metabolism, metabolic detoxification and immune system in medaka. These results suggest that toxins produced by K. selliformis can be transferred through the food chain, and that K. selliformis can destroy the intestinal integrity of medaka and increase the absorption of toxins, leading to energy metabolism disorders in fish, affecting the metabolic detoxification capacity of the liver. Our finding provides novel insight into the toxicity of K. selliformis to marine fish.

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.