Identification of microplastics and associated contaminants using ultra high resolution microscopic and spectroscopic techniques.

The present study establishes a new procedure to characterize micro(nano)plastics (MNPs) and identify contaminants adhered to the plastic particles in aquatic environments by applying ultra-high resolution microscopy and spectroscopy techniques. Naturally fragmented microplastics (MPs) were collected from Manzanillo and Santiago Bays, Mexico and analyzed using: Confocal Laser Scanning Microscopy (CLSM), Fourier-Transform Infrared Spectroscopy (FTIR), µ-RAMAN, Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and Environmental Electron Scanning Microscopy (ESEM). The information obtained from each of these techniques was integrated to produce a comprehensive profile of each particle. Sample preparation was tested by applying three different rinses (unrinsed, distilled water and alcohol) to untreated MPs collected from Manzanillo Bay, finding that when large impurities are present an alcohol rinse makes it easier to examine the associated contaminants. Based on this emerging methodology, polyethylene and polypropylene MPs were identified with associated contaminants such as arsenic, cadmium, aluminum, and benzene. This study demonstrates the presence of pollutants that may be linked to MNPs in aquatic ecosystems and proposes an accurate relatively fast procedure for their analysis that does not require chemical extraction.

Surface layer microplastic pollution in four bays of the central Mexican Pacific.

Surface microplastics were sampled monthly in four tropical bays (Manzanillo, Santiago, Navidad and Cuastecomates) of the central Mexican Pacific during March 2017 to February 2018. Microplastic concentrations ranged between 0.01 and 1.05 particles/m2 with a median per bay ranging between 0.26 and 0.40 particles/m2. Raman spectroscopy registered polypropylene (40%), polyethylene (40%) and polyester (20%) polymers. Fibers dominated all samples, except for Manzanillo where fragments numerically dominated during the rainy season (Jun-Oct). Fiber concentration was not significantly different among bays or seasons, likely associated with continuous wastewater discharge. Fragment concentrations were significantly higher in Bahía Manzanillo and Santiago than the other two bays. Non-metric multidimensional scaling showed distinct distribution of Manzanillo samples (which has important port activities) as compared to Santiago, Navidad, Cuastecomates (where tourism economic activities predominate). This first direct comparison of sea surface microplastic concentration among four bays in Mexico provides a baseline to study impacts on marine zooplankton in this tropical ecosystem.