Elemental analysis by neutron activation analysis and synchrotron x-ray fluorescence microscopy of ocean plastics ingested by pelagic seabirds

We report the combined use of Neutron Activation Analysis (NAA) for bulk measurement of marine plastics ingested by wildlife, with a more detailed analysis of individual plastics at different stages of degradation using synchrotron X-ray fluorescence microscopy (S-XFM). On average, Sable Shearwaters (n = 9) ingested 4.16 ± 4.62 g of plastics (50 ± 35 items), most of which were high-density polyethylene (47.4 %) and polypropylene (42.6 %) as determined by attenuated total reflectance Fourier transform infrared spectroscopy. Using NAA, the most abundant elements (Ti, Zn, Cd, Cu, Cr, Sr) were those commonly associated with plastic additives that confer UVC resistance, mechanical properties, or colouration. S-XFM revealed that visually and structurally near identical plastics may not only contain different chemical elements, but that the internal spatial distribution of these elements can vary substantially. S-XFM also detected the presence of lead (Pb) which may indicate prior recycling history of the plastic feed stock. A consistent finding was the accumulation of iron (Fe) and bromine (Br) at the surface of the degrading plastics, attributable to biofilm formation. Our observations highlight that bird populations ingesting marine plastics are exposed to an unpredictable profile of chemical elements, the degradation-dependent release rate of which is unknown in the acidic and enzymatically-active stomach environment. Based on the variability of their elemental content, we propose to regard marine plastics as ‘mixed waste’. We speculate that plastics more generally could be doped with complex elemental ‘fingerprints’ for the purpose of traceability and establishment of an unbroken chain of custody.