Propolis: Biological Activity and Its Role as a Natural Indicator of Pollution in Mining Areas

Pollution in mining areas represents a major environmental issue, significantly impacting ecosystems and human health. This study highlights propolis as an efficient natural bioindicator for detecting and assessing the degree of contamination in these areas. The objective of this study is to determine the levels of metals (Pb, Cd, As, Cr, Fe, Mn, Cu, and Zn) in propolis from mining exploitation areas in Romania, specifically in the counties of Alba, Hunedoara, Maramureș, and Caraș-Severin. Although mining operations are closed, the anthropogenic impact varies due to differences in the surface areas of the zones affected, the areas occupied by waste heaps, local hydrological conditions, and partial ecological rehabilitation efforts. To highlight the impact of contamination, a reference area considered unaffected by anthropogenic activities was used as a benchmark for each county. The values obtained in the investigated area were compared with those from this control zone to determine the differences and the specific impact of pollution. Maximum values were recorded in Roșia Montană for Pb (9.27 mg·kg−1), Cd (0.17 mg·kg−1), and As (0.87 mg·kg−1); in Băile Borșa for Fe (150.23 mg·kg−1) and Zn (2.9 mg·kg−1); in Certeju de Sus for Cu (6 mg·kg−1) and Cr (7.01 mg·kg−1); and in Moldova Nouă for Mn (25.43 mg·kg−1). The maximum content values of phenols (189.49 mg·kg−1 in Alba County) and flavonoids (88.06 mg·kg−1 in Caraș-Severin) were recorded, as well as the minimum IC50 antioxidant activity (0.33 µg·mL−1). Propolis from these areas showed antimicrobial activity against five bacterial strains (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, and Streptococcus mutans) and five fungal strains (Candida albicans, Aspergillus niger, Aspergillus flavus, Cryptococcus neoformans, and Penicillium chrysogenum), although such antimicrobial and antifungal activities were more intense in unpolluted areas. The present study reveals that propolis is a natural indicator of heavy metal pollution in mining areas. These data support the usefulness of propolis due to its high capacity to accumulate and reflect environmental contaminants.