Filtered threats: The impact of cigarette butt leachate on marine life.

Cigarette butts (CBs) are the most littered waste item globally and represent a significant yet underrecognized source of chemical contaminants in aquatic ecosystems. This study assessed the toxicological effects of CB leachate on the tropical mussel Mytella charruana, focusing on lysosomal membrane stability (LMS) and the bioaccumulation of trace metals and polycyclic aromatic hydrocarbons (PAHs). Mussels were exposed to serial dilutions (0.01-10%) of CB leachate for 24 and 120 h in controlled laboratory conditions. The leachate contained detectable levels of copper (53 μg L-1), iron (45 μg L-1), zinc (60 μg L-1), and a total PAH concentration of 2149 ng L-1, predominantly low molecular weight compounds such as naphthalene. The Neutral Red Retention Time (NRRT) assay revealed significant LMS impairment at nearly all tested concentrations, with time-dependent effects observed particularly at low dilutions. Despite low metal accumulation, organisms exposed to the leachate bioaccumulated naphthalene and phenanthrene. The findings demonstrate that even minimal concentrations of CB leachate (equivalent to one CB per 2500 L of water) can induce sublethal cellular effects in M. charruana within 24 h. These results highlight the underestimated ecotoxicological risk of cigarette waste in coastal environments and underscore the need for stricter regulation and management of this pervasive pollutant.