Spatial Characterization of Trace Metal Concentrations and Biomarkers of Exposure in Feral Pigeons (Columba livia) from a Highly Industrialized Metropolis in Mexico.

This study examined the geographical distribution of cadmium (Cd), copper (Cu), mercury (Hg), and lead (Pb) in the Monterrey Metropolitan Area (MMA), Mexico, using feral pigeons (Columba livia) as bioindicators. Trace metals were quantified in tail feathers collected from 74 individuals in nine municipalities using Anodic Stripping Voltammetry (ASV). Copper showed the highest concentrations (maximum mean 21.3 µg/g), followed by Pb (5.2 µg/g), Hg (0.7 µg/g), and Cd, which was detected in a few samples (< 0.6 µg/g). A consistent center-to-periphery gradient was observed for Cu, Hg, and Pb. Cluster analysis identified four spatially distinct groupings based on bioaccumulation, with the highest concentrations occurring in central municipalities characterized by higher human population density, suggesting heterogeneous exposure and increased combined risk from trace metals in more urbanized areas. Leukocyte frequencies varied across municipalities, suggesting site-specific physiological responses associated with differences in trace metal concentrations. Genotoxicity biomarkers showed spatial trends similar to trace metal levels, although differences were not statistically significant, indicating limited genotoxic effects at the observed exposure levels. The concordant spatial patterns between environmental and biological indicators highlight trace metal exposure as a relevant risk in the MMA and support the use of feral pigeons as effective bioindicators of trace metal pollution, with implications for human health in industrial and highly urbanized areas.