Our study evaluated surface interactions of arsenic (As) and uranium (U) with commercial microplastics by integrating field sampling and experiments in laboratory-controlled conditions. Multiple freshwater bodies close to mining sites on Native American lands contain As and U above the allowed maximum contaminant levels while also containing plastic waste contamination due to the lack of access to standardized waste management practices. A mixture of elevated concentrations of heavy metals and microplastics can potentially transport these contaminants through various trophic levels. We sampled water sources in various water bodies nearby the Jackpile Mine of Laguna Pueblo, NM, and the Rio Grande to determine the occurrence of microplastics and the accumulation of heavy metals on their surface. Water samples were filtered, digested, and subsequently analyzed using Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS), and Transmission Electron Microscopy (TEM). We carried out sorption batch experiments at pH 3 and 7 to evaluate the chemical surface interactions of As and U with polyethylene (PE), polystyrene (PS), and poly(methylmetacrylate) (PMMA) microplastics. Our results confirmed microplastic contamination in the freshwater bodies sampled, particularly in bodies of water used for recreational activities. Experiments carried out at pH 3 and pH 7 showed no sorption or interaction of As with any type of commercial microplastics. On the other hand, SEM/EDS and TEM analyses of the experiments supplied with U at pH 7 revealed that U precipitates deposited onto the PMMA microplastic surface; however, the soluble fraction of U showed less affinity to the microplastic surface. Our initial results suggest that microplastics may serve as a nucleation site for U complexes and precipitates. Currently, our work is focused on further understanding the chemical interactions of U with polyethylene and polystyrene microplastics.

Understanding the surface interactions of uranium and arsenic with commercial microplastics

ACS Spring 2022

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