Metal fractionation and mobility in medicinal plants near industrial emission sources

In areas influenced by industrial emissions, the total metal content in medicinal plants provides limited insight into toxicological risks, as herbal preparations mobilize different chemical forms of elements with varying bioavailability. A key scientific challenge is the lack of knowledge regarding the fractional composition and extractability of potentially toxic metals from plant tissues, particularly for Cr, Ni, Cu, and Mn, which are widely emitted by combustion-based industries. Despite their environmental relevance, information on how these metals partition across operationally defined fractions and how readily they transfer into decoctions and tinctures remains scarce. This gap hampers accurate assessment of human exposure through herbal products and limits the broader understanding of metal mobility under technogenic pressure. This study investigated the distribution and mobility of Cr, Ni, Cu, and Mn in medicinal plants collected from 28 monitoring sites located in both background and impact territories surrounding the Thermal Power Station. A sequential extraction scheme was applied to differentiate the metals into Fraction I (FI, distilled H₂O), Fraction II (FII, 40% C₂H₅OH), Fraction III (FIII, 10% HCl), and Fraction IV (FIV, concentrated HNO₃ + 30% H₂O₂), while the residual insoluble fraction was considered Fraction V (FV). The results demonstrated that, compared to background conditions, metal concentrations increased across all fractions in the impact zone, with the greatest enrichment observed in the most mobile and easily extractable forms. In both aboveground parts and roots, the hydrochloric-acid-soluble fraction predominated, while the proportion of water- and alcohol-extractable forms increased with intensifying anthropogenic pressure. For decoctions and tinctures derived from aboveground plant tissues, substantially higher extractability was recorded relative to roots, indicating a greater potential risk associated with herbal raw materials harvested within the impact territory. For background plants, this pattern was weaker and not consistently expressed across all species. Among the studied elements, Mn and Cu showed the highest proportions in aqueous and alcoholic extracts. These findings highlight the importance of assessing not only the total metal content but also the fractional composition of pollutants in medicinal plants collected near industrial facilities, as changes in metal mobility under technogenic influence directly affect the safety of herbal preparations.