Environmental exposure to heavy metals in Miniopterus schreibersii (Kuhl, 1819) from polluted and reference sites: blood cell impairment as a biomarker of pollution.

Heavy metals are persistent environmental pollutants with well-documented toxic, genotoxic, and bioaccumulative effects across ecosystems. This study evaluates blood cell morphology as a potential biomarker of environmental pollution in Miniopterus schreibersii (Kuhl, 1819), a migratory bat species. Individuals were captured from a contaminated site (Dardagani underground quarry) and a reference site (Mokra Megara Cave) in Bosnia and Herzegovina. Environmental sampling included guano, soil, and water. Guano was analyzed for nine heavy metals (Cr, Cu, Mn, Fe, Co, Ni, Cd, Pb, Zn) to assess site-specific contamination. Distinct spatial differences in metal accumulation were observed. Elevated Cu and Mn concentrations in guano from the contaminated site indicated anthropogenic input, whereas higher Fe, Ni, and Pb at the reference site reflected natural lithogenic enrichment. Hematological and cytological examinations revealed morphological alterations in blood cells of bats from the contaminated site, including neutrophil hypersegmentation, polychromatophilia, atypical granulation, and nuclear abnormalities in lymphocytes. The total lymphocyte count differed significantly, and these qualitative changes suggest early physiological adjustments or potential indicators of sublethal toxic exposure. By integrating environmental (soil and guano) and biological (blood morphology) parameters, this study demonstrates a non-lethal and ecologically relevant approach to biomonitoring. Blood cell alterations, combined with metal analyses in guano, provide a sensitive tool for detecting potential chronic environmental stress. M. schreibersii is reaffirmed as a valuable sentinel species for ecological monitoring in karst and other vulnerable habitats; however, the limited number of high-quality blood smears obtainable under field conditions still remains a constraint to broader generalization of the findings.