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 MP from organic matrices. Selected methodologies were tested on spiked samples and optimized before being applied to feces collected from three sites in Mexico City (n=10 samples per site). MP were extracted using a digestion process with 50% hydrogen peroxide and analyzed by microscopy and FTIR spectroscopy. 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%), and the polymers identified included polystyrene and polyethylene. 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 MP 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 bioindicators of local contamination.