Evaluation of Acute Toxicity of Cigarette Butt Leachates in Fish: Relationship with Nicotine Concentrations Monitored by Molecular Fluorescence

Cigarette butts are among the most abundant urban residues worldwide and constitute an emerging source of aquatic pollution due to the release of nicotine and other toxic compounds into the environment. In the present work, the acute toxicity of nicotine solutions and cigarette butt leachates was evaluated using fish, specifically juveniles of Poecilia reticulata, under controlled and standardized laboratory conditions. Acute toxicity assays of nicotine were performed, exposing fish to increasing concentrations ranging from 0.5 to 8.0 mg？L^？1 for 96 h. Mortality increased with nicotine concentration, obtaining an LC50 value of 2.0 mg？L^？1 for the studied species. Additionally, cigarette butt leachates were prepared under standardized laboratory conditions and tested at different dilution percentages (in a range of 2.5% to 20 %). The highest leachate concentrations produced elevated mortality and behavioral alterations, including severe mobility impairment in exposed organisms. Nicotine concentrations in the tested solutions were determined by a previously developed molecular fluorescence methodology based on the use of a luminescent metal-organic framework sensor. The analytical results demonstrated that nicotine concentrations in cigarette butt leachates were significantly lower than the LC50 experimentally determined for pure nicotine, suggesting that the observed toxic effects are associated not only with nicotine but also with the combined action of additional toxic substances released from cigarette residues. The present study highlights the ecotoxicological relevance of cigarette butt leachates as emerging aquatic pollutants and demonstrates the usefulness of combining biological models with fluorescence-based analytical methodologies for environmental monitoring applications.