Association of metals with expanded polystyrene in the marine environment
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Expanded polystyrene (EPS) has characteristics distinctively different to many thermoplastics that strongly influence its behaviour in the marine environment. However, the extent and nature of its interactions with metals are poorly understood. In the present study, fragments of beached EPS have been retrieved from an urban harbour and an open sandy beach in southwest England and the concentrations, locations and availabilities of various metals (and metalloids) of geochemical importance and anthropogenic significance determined. Total (aqua regia-digestible) metal concentrations at the surface (normalised to a depth of 0.5 cm) were considerably greater than surface concentrations reported for polyolefins retrieved from the same region and, with the exception of Cd, Sb and Zn, were significantly greater than those in unweathered EPS packaging material. Median surface concentrations of Al, As, Co, Fe, Mn, Ni and Sb were significantly greater at the open beach than the harbour, but concentrations of Cu and Pb were significantly greater at the latter. Where measured, concentrations of all metals were similar at the surface and subsurface (0.5 to 1 cm), and availability to 0.7 M HCl ranged from <20 % for Al and Fe to >60 % for Mn and Pb. These results, coupled with visible characteristics, suggest that aqueous and particulate metals are able to interact with the EPS surface via a number of mechanisms (adsorption, precipitation, entrapment) and migrate through the weathered, porous structure to within the polymer matrix. Enrichment factors normalised to Al as a granulometric proxy and relative to a regional baseline indicate "moderately severe" contamination with respect to Cd, Cu, Pb, Sb and Zn in at least one of the environments studied, suggesting that EPS might be a significant carrier and means of exposure for these metals in the marine environment.
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