Cigarette filter fibres as a source and sink of trace metals in coastal waters

Cellulose acetate fibres from cigarette filters represent a form of microplastic that has received little attention in the environment. In this study, a ground composite of spent, smoked filter material (FM) has been used to investigate the role of cellulose acetate fibres as a source and a sink of trace metals (Cd, Co, Cu, Ni, Pb and Zn) in coastal waters. FM suspended in river water and seawater and mixtures thereof representative of an estuarine gradient resulted in the leaching of pre-existent metals derived from the combustion of tobacco, with mean percentages of release ranging from about 40 for Pb to nearly 90 for Cd, Co and Zn. Addition of 40 μg L^-1 of each metal to FM suspensions incubated for 48 h yielded mean partition coefficients (K_Ds) ranging from <10 L kg^-1 for Co to > 100 L kg^-1 for Cu, Pb and Zn, with Cu and Ni displaying a net increase in K_D with increasing salinity. Adsorption is interpreted in terms of hydrophobic interactions between metal-organic complexes and the cellulose acetate surface, and in support of this assertion K_Ds exhibited a significant, positive relationship with published metal-humic acid binding constants. The findings of this study improve our understanding of the role of cellulosic microfibres more generally in transporting trace metals in aquatic systems.