, 2008) and induce an increased immune response at a molecular level. We need to clarify whether further kinds of physical effects may be observed, especially when transferred to organisms other than mussels. As BI 2536 price far as the microplastics’ size is concerned, filter feeders and other organisms near the bottom of the marine food chain may be primarily affected (Thompson et al., 2004 and Moore, 2008). This still needs to be validated, also by clarifying which levels of the food chain are most affected. Investigations on marine mammals also showed that plastic particles are transferred along the food chain by feeding on plastic-contaminated fish (Eriksson

and Burton, 2003). It will be essential to elucidate the underlying mechanisms

in order to find out whether enrichment or depletion occurs within the food chain and if microplastics can finally be found in marine top predators and in humans. Moreover, microplastics may serve as transport vectors for invasive micro-organisms to remote regions (Barnes, 2002 and Gregory, 2009). However, it is still unknown to which extent they contribute to changes in species assemblages and how they influence endemic species and ecosystems. Since plastics contain additives like plasticizers or organic pollutants, which have sorbed out of the marine environment into the plastic matrix (Carpenter et al., 1972 and Hale from et al., 2010), physical find protocol effects may be enhanced by chemical and toxic effects. In seabirds a positive relationship between pollutant concentration and plastic burden has already been observed (Ryan et al., 1988). First investigations, especially on plastics as passive samplers, reveal that equilibrium sorption of organic pollutants is about two orders of magnitude higher than to natural sediments and soils (Mato et al., 2001). Again, detailed knowledge on mechanisms is missing. It is neither investigated how pollutants sorb onto or into microplastics in comparison to natural particles

like suspended matter, detritus or phytoplankton, nor can we describe how material properties, additives or weathering influence the sorption behaviour. In order to decide whether uptake of microplastics and associated pollutants increase bioaccumulation of the pollutants in marine organisms, mechanisms like substance leaching out of the plastic matrix need to be quantified. Since plastic particles may settle from the water body to the sediment it also has to be clarified whether sediment represents a sink and, thus, a long-term source for microplastics and associated chemicals. Accumulation of larger plastic has been observed in ocean gyres (Moore et al., 2001), on beaches, and in sediments worldwide (Barnes et al., 2009).