Cigarette butts: A hidden toxic time bomb for aquatic metabolism and behavior.

Cigarette butts (CBs) are rapidly emerging as a burgeoning threat to marine ecosystems, posing substantial risks to aquatic life. This study systematically investigated the effects of CBs fibers and leachate on the behavior, metabolism, and mitophagy of the marine rotifer Brachionus plicatilis. The results indicated that exposure to CBs significantly inhibited the motility and feeding behavior of rotifers. Further studies found that CB exposure caused metabolic stress on rotifers and significantly interfered with their energy metabolism, which was specifically manifested as a biphasic dose-effect of amylase activity (increase at low concentrations and inhibition at high concentrations) and a decrease in triglyceride and neutral lipid content. CB exposure elicited oxidative stress and disrupted mitochondrial fission-fusion homeostasis (increased in ATG3, FUNDC1, FIS1, and Mfn2; decreased in Drp1/DNM1L, VPS35, and STOML2), lowering mitochondrial membrane potential and ATP levels while activating mitophagy and culminating in mitochondrial dysfunction. Addition of the antioxidant N-acetylcysteine effectively alleviated CB-induced mitochondrial dysfunction and metabolic disorders. Notably, the study revealed that the residual ash from smoked CB exerted the most pronounced toxic effect on rotifers, with distinct mechanisms between fibers and leachates. Fiber caused chronic toxic effects through continuous contact, while leachate quickly caused acute damage by dissolving substances. Rotifer health declined dose-dependently with CB concentration, with lipid-metabolic disorder serving as the central driver of the CB toxicity network.