Heavy metals and pesticides in medicinal plants: environmental sources, plant responses, and human health risk assessment.

Medicinal plants have served as the foundation of healthcare across cultures for centuries, yet their safety is increasingly undermined by heavy metal and pesticide contamination driven by industrial growth, agrochemical misuse and environmental degradation. Despite widespread concern, the field remains fragmented. Contamination data are scattered across taxa and regions. The link between pollutant bioaccumulation and loss of medicinal potency is rarely explored mechanistically. Moreover, human health risk assessments tailored to herbal consumers remain largely absent from regulatory conversations. This review brings these threads together. It traces how heavy metals including Pb, Cd, As, Hg, Cr and Ni along with pesticide residues enter medicinal plants, disrupt their physiology, impair secondary metabolite production and ultimately reach human consumers. "Five widely consumed medicinal genera Ocimum, Mentha, Glycyrrhiza, Catharanthus and Withania are examined as illustrative models". Each offers a distinct perspective on species-specific bioaccumulation patterns, providing a comparative framework rarely found in existing literature. Crucially, this review connects plant level stress responses to real world health outcomes, critically evaluating risk assessment tools such as EDI, HQ, HI and Cancer Risk models within the underexplored context of habitual herbal product use. Detection technologies, regulatory standards and mitigation strategies are assessed with equal rigor. The need for this review is urgent. The absence of unified monitoring frameworks and taxon-specific safety thresholds leaves billions of herbal medicine users inadequately protected. This work provides a consolidated, actionable foundation for researchers, regulators and clinicians working toward safer, evidence-based herbal therapeutics.