Heavy Metal Accumulation and Its Effect on Phytochemical Constituents of Medicinal Plants Growing Near Thermal Power Stations

Abstract

Thermal power stations, including other anthropogenic sources, release high levels of potentially toxic heavy metals, including Cadmium (Cd), Lead (Pb), Chromium (Cr), Nickel (Ni), Arsenic (As) and Mercury (Hg), into the environment via fly ash, water plumes, and wastewater effluents. Persistent metal deposition alters the actual properties and increases metal bioavailability, facilitating plants' uptake from the industrial peripheries. Medicinal plants collected from areas around thermal power stations have therefore taken up these metals to a greater level of toxicity than the permissible limit, giving rise to apprehensions regarding consumer safety. Contrastingly, an increasing body of evidence has pointed toward the impact of heavy metal stress on plant primary and secondary metabolism that leads to important changes in the quantity and quality of bioactive phytochemicals. E.g., phenolics, flavonoids, alkaloids, and terpenoids, thereby determining the therapeutic abilities they boast. The present review merges research works published between 2019 and 2025 on (i) heavy metal contamination in the soil and water bodies around thermal power plants, (ii) accumulating patterns in medicinal plants. (iii) mechanistic associations between metal-induced oxidative stress and the modulation of phytochemical pathways, and (iv) implications on pharmacological quality and human health. Field and experimental studies indicate that necessary antioxidant phenolic and flavonoid biosynthesis are often promoted by oxidative stress responses caused by heavy metals, thereby suppressing or modifying other metabolite classes according to metal type, concentration, species, and organ constraints. The review stresses the ongoing urgent need for systematic monitoring of heavy metals and phytochemicals in the medicinal plants collected around power plant complexes, stringent regulation of allowable limits for herbal commodities, and the integration of phytoremediation-based landscape management for lessening environmental and human health risks.