Accelerating microplastic contamination in 210Pb dated sediment cores from an urbanized coastal lagoon (NW Mexico) since the 1990s

The ubiquity of microplastics (MP) across all ecosystems raises concerns about their potential harm to the environment and living organisms. Sediments are a MP sink, reflecting long-term accumulation and historical anthropogenic impacts. Three ²¹⁰Pb-dated sediment cores were used to understand the temporal variations of MP abundances (particles kg^-1) and fluxes (particles m^-2 year^-1) within the past century in Estero de Urías Lagoon, an urbanized coastal lagoon in the Mexican Pacific. MP particles, extracted from sediments by density separation (saturated NaCl solution) were counted using a stereomicroscope, under visible and ultraviolet light on Nile red (NR) stained filters. The polymer composition was determined in ∼10 % of the suspected MP particles using Fourier Transform Infrared spectrometry. Fibers (66 to 89 % of the total particles) predominated over fragments (11 to 34 %). Before 1950, no MP particles were detected. Polyethylene terephthalate (PET) was the prevalent synthetic polymer (up to 50 % of the particles), while semisynthetic cellulosic fibers were predominant, underscoring the broader scope of anthropogenic contamination. Suspected MP abundances (NR stained filters) were highest in the core collected at the innermost area, which was attributed to the lagoon's hydrodynamics, since current velocities decrease from the proximal to the distal area to the sea. From the regression between MP fluxes and time elapsed since sediments deposited, the cores showed consistent accelerated increases of MP burial since mid-20th century, most likely because of the increasing availability of plastic products and population growth, with the consequent increment in plastic waste and wastewater releases. Our findings emphasize the growing MP pollution challenges at EUL, which may directly impact subsistence fishing and shrimp aquaculture activities, threatening local livelihoods and food sources; and also highlight the need for improved waste management and pollution control strategies in rapidly industrializing regions, to protect both aquatic ecosystems and human populations dependent on fishing products.