# Can _Hediste diversicolor_ Speed Up the Breakdown of Cigarette Butts in Marine Sediments?
## 1 Introduction  
Due to the difficulty in collecting and subsequently treating them, cigarette butts (CBs) are the most abundant and dispersed garbage in the world [1] and the most abundant type of litter on beaches [2; 3; 4]. CBs on beaches not only generate large economic costs but also serious environmental problems, which is why this waste is considered an important social problem [5]. The economic cost is determined by its impact on tourism, a value that can be reduced by up to 97% due to dirt [6; 7; 8]. Thus, most countries invest heavily in keeping their coasts clean. But CB cleaning is not only expensive, it is also ineffective (30% recovered) [9; 10], with CBs remaining in the environment even after cleaning, especially automatic cleaning, of the beaches [11]. The environmental cost is more difficult to determine. CBs represent a unique combination of physical and chemical contamination [12]; physical contamination because this trash sheds 100 small microfibrils per day [13], which marine organisms can feed on and transfer throughout the food chain [14; 15; 16] and chemical contamination because CBs can filter more than 7000 toxins into the environment, many of which have been shown to be dangerous for marine organisms (e.g., [17; 18; 19; 20; 21]). The effects ofthis chemical pollution are difficult to estimate in the marine environment, since CBs can not only leach toxicants into the seawater but can also adsorb toxicants from the ocean floor, depending on the concentrations available and relative to its degradation level (e.g., [22]).  
Our current knowledge about CB biodegradation mechanisms and their efficiency is quite limited [23]. CBs are generally made of cellulose acetate (CA), a chemically modified natural polymer [24] widely used in the textile, plastic film, and packaging industries [25]. CA degrades slowly since its high degree of acetylation makes its degradation difficult in the natural environment [26; 27]; thus, it remains in the environment for a long time. Although the decomposition of polymer material by physical forces of a mechanical nature is considered vital in the degradation process [28], recently, biotic factors have been considered equally important in this fragmentation [29; 30]. For example, some isopods and polychaetes create thousands of microfibres when digging blocks of expanded polystyrene over a short period (days) [31; 32]; thus, organisms can break down large polymers [33; 34; 35] at an even faster rate than abiotic processes [36] and/or can also alter their bioavailability by reducing their size and incorporating them into faeces and faecal matter [36; 37; 38; 39].  
_Hediste diverscolor_ ([PERSON], 1776) is a common and ecologically important polychaete burrowing species in estuarine sedimentary habitats of European and North American coasts, where it plays an essential role as a bioturbation species that greatly influences the flux of organic matter, oxygen, and bacterial diversity in sediments [40]. For the first time, here, we tested whether the bioturbation created by this polychaete in marine sediments, the most likely final fate of CBs, can directly or indirectly favour mechanical fragmentation of this type of litter. To do this, we determined not only if _Hediste_ can survive the different toxicants leached from CBs at summer and winter temperatures but also if CBs influence the burrowing activity of polychaetes and whether this activity influences directly or indirectly the mechanical fragmentation of CBs. We consider the broader definition of CB degradation that includes weight loss by the leaching of additives or part of the material with low molar mass [41].