Analysis of the elemental composition of marine litter by field-portable-XRF

• Marine litter represents a pervasive global environmental issue.
• We describe how FP-XRF may be used to measure the elemental content of litter.
• The method is applied to beached plastic, foam, cork, rope and painted surfaces.
• Accuracy, precision, thickness, heterogeneity and independent analyses are evaluated.
• High concentrations of Br, Cd and Pb in many litter samples are of concern.

Marine litter represents a pervasive environmental problem that poses direct threats to wildlife and habitats. Indirectly, litter can also act as a vehicle for the exposure and bioaccumulation of chemicals that are associated with manufactured or processed solids. In this study, we describe the use of a Niton field-portable-x-ray fluorescence (FP-XRF) spectrometer to determine the content of 17 elements in beached plastics, foams, ropes and painted items. The instrument was used in a ‘plastics’ mode configured for complex, low density materials, and employed a thickness correction algorithm to account for varying sample depth. Accuracy was evaluated by analysing two reference polyethylene discs and was better than 15% for all elements that had been artificially impregnated into the polymer. Regarding the litter samples, limits of detection for a 120 s counting time varied between the different material categories and among the elements but were generally lowest for plastics and painted items with median concentrations of less than 10 μg g−1 for As, Bi, Br, Cr, Hg, Ni, Pb, Se and Zn. Concentrations returned by the XRF were highly sensitive to the thickness correction applied for certain elements (Ba, Cl, Cr, Cu, Fe, Sb, Ti, Zn) in all matrices tested, indicating that accurate measurement and application of the correct thickness is critical for acquiring reliable results. An independent measure of the elemental content of selected samples by ICP spectrometry following acid digestion returned concentrations that were significantly correlated with those returned by the XRF, and with an overall slope of [XRF]/[ICP]=0.85. Within the FP-XRF operating conditions, Cl, Cr, Fe, Ti and Zn were detected in more than 50% and Hg and Se in less than 1% of the 376 litter samples analysed. Significant from an environmental perspective were concentrations of the hazardous elements, Cd, Br and Pb, that exceeded several thousand μg g−1 in many cases.

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