Cigarettes are the most littered item in the world. In total, 4.5 trillion are discarded annually, and their filters can introduce toxic chemicals and plastics into waterbodies. Therefore, assessing the ecotoxicological effects of smoked and non-smoked cigarette filters is necessary. Using the freshwater organism Daphnia, this study analyses the toxicity and sublethal effects caused by these two types of filters with New Approach Methodologies, such as effect-based bioassays and enzymatic biomarkers. Toxicity was assessed by measuring mortality following exposure to increasing concentrations of filters. The study also analysed survival and growth rates and quantified enzyme activities.
After 48 hours, only smoked cigarette filters were toxic from 100 ml extract/L with an EC50 value of 397 ml/L. In contrast, exposure of 21 days reduced survival at lower concentrations, with smoked filters decreasing median survival to 4 days at 200 ml/L, corresponding to four filters per litre of water. The growth rate of daphnids was most affected after 7 days of exposure to concentrations of 5-70 ml/L. Size changes observed at 7 days were reduced at 14 and 21 days of exposure, suggesting possible acclimation. Enzymatic activity was also altered after 21 days from concentrations of 15-45 ml/L, with significant increases in acid phosphatase and decreases in alkaline phosphatase, peptidase, and β-galactosidase.
Given the observed effects in Daphnia, cigarette filters may have the potential to impact other freshwater organisms. This is supported by evidence that some psychoactive substances can elicit comparable responses in daphnids and vertebrate models. Furthermore, negative effects on these primary consumers may lead to cascading effects, such as higher trophic levels and loss of biodiversity. Lastly, the limited availability of data on environmentally relevant concentrations of filters also underscores the importance of this study, highlighting the need to consider this emerging contaminant in environmental risk assessment frameworks.
