Microplastics at the ocean-atmosphere interface in Mexican coastal areas of two major oceans

The rapid increase in global plastic production has accelerated the dissemination of microplastics (MP), impacting urban and coastal environments. This study quantifies and categorizes MP in two major Mexican ports: Veracruz (Gulf of Mexico) and Manzanillo (Pacific Ocean). Nine polymer types were identified through micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) analysis of air and seawater samples. Polyester (PES) was the most prevalent polymer, followed by acrylic polymers (ACR) and polyethylene (PE). At Veracruz, the airborne MP concentrations were 3.9 (1.9) MP m^-3 in the morning and 2.2 (1.4) MP m^-3 in the afternoon. In Manzanillo, morning and afternoon concentrations were 3.2 (1.8) MP m^-3 and 2.6 (1.6) MP m^-3, respectively. Surface concentrations of marine MP were elevated near the coast, averaging approximately 14.4 (1.4) MP m^-3. Additionally, artificial non-plastic particles (ANPP) were identified and were even more abundant than MP in both matrices. In all locations and matrices, fibers constituted at least 70 % of detected MP, while fragments comprised the remainder. Identified MP ranged in size (equivalent diameter) from 82 μm to 160 μm. The observed variations in MP composition and concentrations across sites, depths, and sampling times underscore the significant influence of proximity to port activities and local meteorological conditions. Furthermore, these findings provide compelling evidence supporting the transfer of MP from the ocean to the atmosphere via ocean-atmosphere interactions. These baseline data will inform targeted management and risk-assessment frameworks for Mexican coastal regions.