An underestimated coastal threat: seasonal beach-scale assessment of cigarette butt accumulation in southern Brazil

Cigarette butts (CBs) are among the most recurrent forms of marine litter on urban beaches, yet their seasonal dynamics and spatial distribution remain underestimated in many coastal regions. This study investigates the spatiotemporal patterns of CB contamination on an urbanized beach in southern Brazil over 12 consecutive months. A total of 522 CBs were collected during the monitoring period, with a mean density of 0.020 ± 0.029 CBs m⁻². CB abundance varied significantly among seasons and beach sectors (p < 0.05), with summer and the central sector presenting the highest densities. The Cigarette Butt Pollution Index (CBPI) showed a mean value of 0.139 ± 0.206 over the 12-month monitoring period, while seasonal mean values ranged from 0.060 ± 0.103 in winter to 0.185 ± 0.228 in summer. All mean CBPI values fell within the lowest category (≤1.0) of the applied classification. Heatmap analyses revealed persistent hotspots in the central sector, an area of greatest recreational use and easiest access. The findings highlight the need for continuous management strategies, including awareness campaigns, enforcement mechanisms, and the integration of CB-specific policies into coastal management plans. Public health and tobacco control measures should also be considered, as reducing cigarette consumption is fundamental to decreasing the generation of cigarette butt waste. These actions, supported by monitoring tools such as the CBPI, can contribute to reducing CB inputs and improving the environmental quality of urban coastal environments.