Polystyrene foam as a source and sink of chemicals in the marine environment: An XRF study

Polystyrene foam (expanded and extruded polystyrene: EPS and XPS, respectively) is a ubiquitous and pervasive type of marine plastic whose physical properties, transport and fate are distinctly different to those of other common (unfoamed) types of thermoplastic litter. In this study, a range of fragments of EPS and XPS retrieved from three beaches in southwest England have been characterised by energy-dispersive X-ray fluorescence (XRF) spectrometry in order to examine the chemical makeup and potential biological and geochemical impacts and interactions of this type of plastic waste. Analyses performed through sample faces and, in some cases and after dissection, through the material core, revealed variable concentrations of Fe, Ti and Zn among the fragments and, in many instances, within the same sample. This likely reflects the presence of reaction residues and pigments arising from the manufacture of polystyrene, and, for Fe and Ti, significant and heterogeneous ion and mineral acquisition from the environment during transport in suspension or while beached. Acquired oxides of Fe are partly responsible for the chemical fouling observed on the face of most samples and are able to act as an adsorbent for other metals, like Pb. Detection of Br in many fragments up to concentrations of 11,500 mg kg^-1 likely results from the incorporation of the flame retardant, hexabromocyclododecane, in EPS and XPS designed for (but not necessarily limited to) the construction sector. These observations suggest that EPS and XPS can act as both a source and sink for contaminants in the marine environment that merit further investigation.