Toxic Metal in Plant-Based Therapeutics: Contamination Pathways, Oxidative Stress Induction, and Onset of Disease

Widespread environmental contamination by heavy metals from anthropogenic sources has raised significant concerns about their accumulation in plant based therapeutics and the associated risks to human health. With reported exceedances of permissible limits in approximately 20%-80% of plant based therapeutics across different geographical regions where over 30%-50% of the samples collected from high-risk environments, particularly areas adjacent to industrial, mining, and intensive agricultural activities. The samples contain elevated concentrations of toxic metals, frequently exceeding World Health Organization (WHO) safety thresholds. This study elucidates the mechanisms through which toxic metals infiltrate plant-based therapeutics and trigger oxidative stress, resulting in cellular dysfunction and disease progression. Under physiological conditions, reactive oxygen species (ROS) generated during normal metabolism are efficiently scavenged by endogenous antioxidants such as glutathione and superoxide dismutase, thereby preserving redox equilibrium. Exposure to redox-active metals disrupts this balance by catalyzing cyclic reactions-such as Fenton chemistry-that result in excessive ROS generation. This elevated ROS production overwhelms endogenous antioxidant defenses, leading to oxidative stress characterized by lipid peroxidation, protein oxidation, and DNA damage. Such molecular damage triggers various cell death pathways, including apoptosis, necrosis, necroptosis, and ferroptosis. The contamination of herbal drugs by toxic metals occurs in two primary stages. During the herb development phase, plants absorb metals from contaminated soils. The efficiency of this uptake is quantified by the transfer coefficient (TC) and the translocation factor (TF), which indicate the accumulation of metals in the roots relative to the soil and the movement from roots to aerial parts, respectively. Soil metal availability is influenced by factors such as parent material, atmospheric deposition, agrochemicals, organic waste, and inorganic pollutants, while being modulated by processes like crop removal, leaching, and volatilization. In the manufacturing phase, the metal burden is further augmented by both intentional additions (e.g., metal bhasma with purported therapeutic benefits) and unintentional sources (e.g., post harvest processing, transportation, storage conditions, equipment interactions, and cross-contamination). This comprehensive analysis underscores the urgent need for rigorous quality control measures throughout the herbal drug production process to mitigate metal-induced oxidative stress and its deleterious health effects.