From litter distribution to bioaccumulation: assessing cigarette butt-derived metal uptake by south Caspian Sea...

Cigarette butts (CBs) contain numerous pollutants that pose risks to the environment. Although global prevalence and detrimental effects of CBs have been documented, data on their abundance, spatial distribution, and ecological impacts along the southern Caspian Sea coast remain scarce. This study assessed the abundance and spatial distribution of CBs at 12 tourist beaches along the southern coast of the Caspian Sea. Furthermore, to investigate ecological effects, the uptake of metals from the leachate of discarded CBs by the macroalga Cladophora glomerata of the southern Caspian Sea was examined using a microcosm system. The average abundance of CBs was 0.39 ± 0.06 CBs/m², and based on the Cigarette Butt Pollution Index (CBPI), most beaches were categorized as significant or high pollution, with Ramsar beach reaching severe pollution (CBPI = 15.6). Additionally, the microcosm experiment showed that CB exposure increased macroalgal biomass. After 30 days, dry weight was 365.4 ± 6.4 g in the control, compared with 394 ± 6.1 g (15 CBs/aquarium), 416.7 ± 8.08 g (30 CBs/aquarium), and 449.5 ± 10.65 g (45 CBs/aquarium). Furthermore, concentrations of all studied metals increased with the number of CBs (p < 0.05). These findings highlight the interlinked roles of beach pollution, CB-derived metal leachates, and macroalgal responses, thereby underscoring the need for integrated shoreline management and ongoing monitoring to mitigate ecological risks along the southern Caspian Sea coast.