Microplastics in Urban Bird Feces: A Methodological Approach and Case Study in Mexico City

Microplastics (MP) are ubiquitous contaminants in diverse environmental matrices, including biota. Urban birds, such as pigeons (Columba livia), are particularly vulnerable to MP exposure due to their scavenging habits and proximity to human activities. This study developed and applied a methodology to assess MP presence in pigeon feces, starting with a review of existing methods for extracting MPs from organic matrices. Of all the methodologies investigated, a method was established to be tested, varying the reagent, using pigeon feces collected from the Universidad Autónoma Metropolitana, Azcapotzalco Unit (UAM-A) and 15 virgin microplastics of five different types. Of both reagents, it was found that the method with 50% H2O2 presented better results (degradation of almost all organic matter and recovery efficiency of 93.33%). The selected method was optimized before being applied to feces collected from three sites in Mexico City (n = 10 samples per site). MPs were extracted using a digestion process with 50% hydrogen peroxide, flotation test with CaCl2, staining with red Nile dye and vacuum filtration and analyzed by microscopy and FTIR. Concentrations ranged from 16.4 to 27.8 MP/g dry feces, with fragments (80%) and fibers (20%) being the predominant shapes. The most common colors were black (32%) and white (22%), the polymers identified included polystyrene and polyethylene and the most common size was < 1 mm (54%). These findings suggest that pigeons ingest MP during feeding, likely due to confusion with organic matter, highlighting the risks of urban plastic pollution to avian health. The ingestion of MPs could lead to malnutrition, organ damage, and ecosystem imbalances, underscoring the need for improved waste management in urban areas. This study provides evidence of the pervasive impact of plastic pollution in non-marine environments, demonstrating the potential of urban birds as bio-indicators of local contamination.