Can Hediste Diversicolor Speed Up the Breakdown of Cigarette Butts in Marine Sediments?

Cigarette butts (CBs) are non-biodegradable harmful residues of synthetic origin and are widespread in marine environments around the world. Although environmental factors are often primarily responsible for the fragmentation of microplastics in the marine environment, biotic factors have recently been shown to be equally important in plastic debris. This study evaluates the role of the Hediste diversicolor polychaete in the fragmentation of CBs in the marine environment. Polychaetes were exposed to three concentrations of CB (0 (as the control), 0.25, and 1 butt L−1) at two different temperatures (15 °C and 23 °C) for 28 days. At each temperature, aquaria without polychaetes were used to study the effect of the burrowing activity of the polychaete on CB fragmentation. Toxicants analysed from exposed sediments increased their concentration in a dose-dependent manner to the CB concentration at a temperature of 15 °C but not at 23 °C. CBs did not directly decrease Hediste survival, but prolonged elevated temperatures increased the polychaetes’ susceptibility. The negative effects of CBs on burial success and burrowing behaviour could not be offset by the reduced start time caused by elevated temperatures. Regardless of temperature, both the weight loss and physical fragmentation of CBs buried in polychaete-contaminated sediments were significantly higher than those without Hediste, with no differences between the two concentrations tested. FTIR-ATR analysis used to evaluate CB degradation in relation to cellulose acetate decomposition showed a greater degradation of this compound in treatments with Hediste than in those without polychaetes (~2.75 times), but these differences were not significant. This study is a promising initial step for future research, as any factor that facilitates the fragmentation of this prevalent and hazardous waste must be carefully studied to extract the maximum benefit to help to reduce CBs in the marine environment.