Assessment of metal contamination in Tecoma stans (L.) Kunth (Bignoniaceae) pollen samples from urban environments

Urbanization profoundly alters ecosystems, introducing various pollutants, including metals, which degrade environmental quality and pose risks to biodiversity, notably affecting pollinators like bees. Pollen, collected by bees during foraging, can serve as a bioindicator for assessing urban environmental quality, as it accumulates airborne and soil-derived contaminants. Studying metal concentrations in urban pollen is therefore critical, not only for monitoring pollution levels but also for understanding the potential toxicological impacts on bee populations, whose health is intrinsically linked to the quality of their food resources. This study aimed to assess the level of metal contamination in pollen samples of Tecoma stans (L.) Kunth, a plant species commonly found in urban settings and frequently visited by bees for foraging. Pollen samples were collected in the urban area of Uberlândia, MG, in 2023. Using spatial analysis of the city, sampling locations with distinct Bee Environmental Quality Index (BEQI) classifications — low, medium, and very high environmental quality — were selected to investigate the influence of environmental quality on metal concentrations. For this purpose, pollen samples from T. stans flowers were collected and analyzed at the designated sites, and the concentrations of aluminum (Al), calcium (Ca), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), and magnesium (Mg) were quantified using inductively coupled plasma optical emission spectrometry. Statistical analysis, including PERMANOVA, indicated no significant differences in overall metal profiles across locations with varying BEQI levels, suggesting widespread metal presence regardless of the perceived environmental quality for bees. Principal component analysis and cluster analysis revealed a strong positive association among Fe, Cd, Cr, and Mn, suggesting common origins, while Ca and Cu showed a negative association. Our findings highlight that bees in urban areas are exposed to widespread metal contamination, even in environments classified as having very high BEQI.