# Can _Hediste diversicolor_ Speed Up the Breakdown of Cigarette Butts in Marine Sediments?
## 4 Discussion  
It is now well established that CBs represent a significant source of pollutants in the environment. Upon contact with water, various organic and inorganic compounds are released from these CBs [12; 17; 18; 19; 52; 53; 54; 55; 56], rendering them bioavailable to aquatic life. The highest variability in terms of toxicant concentrations analysed in sediment occurred between treatments at 15 \({}^{\circ}\)C and 23 \({}^{\circ}\)C. Except for naphthalene at the highest concentration of CB studied (1 CBL\({}^{-1}\)), all contaminants increased their concentration in the sediment in a dose-dependent manner to the CB concentration at 15 \({}^{\circ}\)C. However, this relationship was disrupted at 23 \({}^{\circ}\)C, where the highest CB concentration consistently exhibited pollutant concentrations similar to that of the control or lower than those analysed in the 0.25 CBL\({}^{-1}\) treatment (nicotine). While potentially toxic element leachates from CBs have been studied in various types of water [18; 56], no studies have investigated the potential differences in leachates from this type of litter in seawater at different temperatures. The only experiment conducted aimed to determine the influence of temperature and relative humidity on the airborne chemicals emitted by CBs [57], showing that increased temperature led to the faster release of nicotine, triacetin, and other chemicals. However, temperature may also play a crucial role in determining the phase transfer and mobility of these pollutants, such as PAHs [58]. Although it would be interesting to determine whether temperature effectively affects the release of CB contaminants or their mobility, given the substantial increase in the CB presence on beaches in summer, this is not the primary focus of this study. In this study, CB did not directly decrease the survival of _H. diversicolor_, but both time and temperature did increase its effects. While the survival of this polychaete upon exposure to different CB concentrations has not been previously studied, it has been shown that the lowest concentration at which the burrowing of _H. diversicolor_ is affected by toxic CB leachates in seawater is 2 CBL\({}^{-1}\) (LOEC for 96 h = 172 \(\mathrm{\SIUnitSymbolMicro L}^{-1}\) nicotine), with higher concentrations causing growth retardation and extensive DNA damage [59]. However, this work also found that this lower concentration was higher (LOEC for 96 h = 8 CBL\({}^{-1}\); 694 ngmL\({}^{-1}\) nicotine) when polychaetes were exposed to CB microfibres in sediment, with no effect on the relative growth rate after 96 h and 28 days of exposure. Therefore, it is unsurprising that the concentrations tested in this study, 0.25 and 1 CBL\({}^{-1}\), did not influence _H.disite_ survival. However, summer temperatures did affect the survival of CB-exposed polychaetes, particularly at the highest concentration. Elevated temperatures could increase the susceptibility of marine invertebrates to contamination [60; 61; 62; 63]. Although little is known about the effect of increased temperature on pollutant toxicity in polychaetes, higher temperatures have recently been shown to exacerbate the negative effects of marine acidification on _H. diversicolor_ survival [40]. CBs can cause significant sublethal effects, such as behavioural changes and/or alterations in the reproductive performance of marine invertebrates [15]. Limited current data on the effect of CB on sediments indicate a reduction in benthic copep reproduction of _Nitobra_ sp. (0.1 and 0.01 CBL\({}^{-1}\)) [64], as well as decreased burrowing activity and growth of the polychaete _H.disteriscolor_[59]. Similarly, our results show that CBs within sediment significantly prolonged the time taken by _H. diversicolor_ to initiate burrowing (\(p<0.05\)), with an initial difference of 6 days compared with the controls at 15 \({}^{\circ}\)C and 9 days at 23 \({}^{\circ}\)C (after 14 exposure days).