# Can _Hediste diversicolor_ Speed Up the Breakdown of Cigarette Butts in Marine Sediments?
## 4 Discussion
The earthworm _Eisena fetida_ avoided soil contaminated with CBs, and the avoidance rate positively correlated with CB concentration but negatively correlated with exposure time [65]. Burial success, like other energy-intensive activities, is favoured by warmer temperatures, as it activates metabolism in ectothermic animals [66], including _H.diste diversicolor_[67]. In fact, increased temperature altered the burrowing behaviour, shortening the time taken by the polychaete to initiate burrowing (Figure 3A control). Ref. [59] reported that burrowing times of _H. diversicolor_ were more than 10 times longer when exposed to CB leachates with concentrations <2 CBL\({}^{-1}\) but found no significant differences in the burial rate when exposed to CB microfibres in sediment. Occasionally, the negative effects of certain stressors, such as water acidification, on marine animals' energetic activities or foraging can be offset by elevated temperatures [68]. However, if thenegative impact of the stressor outweighs the increase in or acceleration of metabolism due to the temperature increase, a negative effect will be observed in the organism. Thus, the negative impact of CBs on the _H. diverscolor_ burrowing behaviour at 23 \({}^{\circ}\)C was such that it was not only uncompensated for by the increase in temperature but also accompanied by a significantly decreased burial success rate (up to 66% in 1 CBL\({}^{-1}\)). Polychaetes that successfully buried themselves took longer to start the burying process as the CB concentration in sediment increased. A similar trend was observed with the burial rate at the two tested temperatures, although this was not significant. Similarly, [40] found that increased temperature potentiated the adverse effect of marine acidification on the initiation of _H. diverscolor_ burrowing activity. However, in this study, burial rate increased with decreasing pH levels, especially at 25 \({}^{\circ}\)C; however, regardless of pH, a higher burial rate was observed at 25 \({}^{\circ}\)C compared with 15 \({}^{\circ}\)C.  
Reduced burrowing activity not only affects the survival of the _Hediste_ population, as they are exposed to predators for longer durations, but also affects the ecosystem due to the crucial ecological role of this polychaete in sediment bioturbation (i.e., [69; 70; 71]). However, until now, the potential role of this bioturbation in the fragmentation of residues as long-lasting in the environment as CBs had not been studied. Our results indicate that, regardless of temperature, both the weight and physical degradation of CBs buried in polychaete sediments exhibit significantly higher levels of fragmentation than those in contaminated sediments without _H. diverscolor_. No differences were observed between the weight loss or degradation levels of CBs at the two CB concentrations tested, which is likely due to polychaete mortality and the reduced burial success at 1 CBL\({}^{-1}\) and 23 \({}^{\circ}\)C. Studies on CA degradation in different aqueous environments have also found that the effect of temperature is insignificant and that most of the weight loss occurs in the initial degradation steps [23]. Our data confirm that the initial step of the CB decomposition process (\(\sim\)30 days) involves mass loss (\(\sim\)15-20%; [72]), but the percentage of this loss was significantly higher in treatments with _H. diverscolor_, with many CBs losing 20-30% of their weight. In the only study conducted on the CB degradation status on tropical beaches, this mass loss corresponded approximately to degradation level I (0% mass loss with tobacco residues and preserved filter and paper coating;), II (15% mass loss without tobacco residues, preserved filter and paper coating, and manufacturer's identification), and III (26% mass loss, no tobacco remains, and filter with paper coating but considerably worn and discoloured, without manufacturer's identification) [49].