Biofilm-enhanced adsorption of strong and weak cations onto different microplastic sample types: Use of spectroscopy, microscopy and radiotracer methods. (1st July 2019) - Johansen, Mathew P.
Abstract: The adsorption of metals and other elements onto environmental plastics has been previously quantified and is known to be enhanced by surface-weathering and development of biofilms. However, further biofilm-adsorption characterisation is needed with respect to the fate of radionuclides. This study uses spectroscopy, microscopy and radiotracer methods to investigate the adsorption capacity of relatively strong and weak cations onto different microplastic sample types that were conditioned in freshwater, estuarine and marine conditions although marine data were limited. Fourier-transform infrared spectroscopy confirmed that surface oxidation chemistry changes induced by gamma irradiation were similar to those resulting from environmental exposures. Microscopy elemental mapping revealed patchy biofilm development, which contained Si, Al, and O, consistent with microbial-facilitated capture of clays. The plastics+biofilm of all sample types had measurable adsorption for Cs and Sr radiotracers, suggesting environmental plastics act broadly as a sink for the key pervasive environmental radionuclides of 137 Cs and 90 Sr associated with releases from nuclear activities. Adsorption onto high-density polyethylene plastic types was greater than that on polypropylene. However, in most cases, the adsorption rates of all types of plastic+biofilm were much lower than those of reference sediments and roughly consistent with their relative exchangeable surface areas. Graphical abstract: Image 1 Highlights: Differing types of microplastics were deployed in various aquatic systems. Surface weathering by gamma irradiation simulated environmental exposures. Microscopy revealed patchy biofilm development on microplastic surfaces. The elements associated with biofilm were dominated by the clay indicators Al, Si, and O. The plastics+biofilm adsorbed Cs and Sr cations, but not as strongly as sediments.