Heavy Metal Pollution and Medicinal Plants: An Overview

Anthropogenic activities like the unbalanced use of fertilizers, agricultural chemicals like pesticides, and other industrial activities such as drilling, steelmaking, and burning of fossil fuels as well as the use of untreated wastewater from different industries have resulted in soil pollution with heavy metals (HMs). This important ecological restriction has contributed to reduced agricultural production and decreased nutritional quality due to the bioaccumulation of HMs in the plant body. Medicinal plants are being recommended for alternative products with non-food staple crops in potentially toxic elements contaminated environments. Despite their ability to bioaccumulate higher concentrations of HMs in their plant body, the plant parts used for medicinal purposes are transferring HMs into the food chain and have ultimately resulted in biomagnification through bioaccumulation in the food chain. Under HM stress, there is an increased production of reactive oxygen species, which pose oxidative stress on the membranous organelles, resulting in lipid peroxidation, protein denaturation, and nucleic acids destruction, damaging their structure and function and ultimately disrupting various metabolic processes involved in growth and development. In order to combat oxidative stress, medicinal plants activate the antioxidant system, which includes the secretion of enzymatic (ascorbate peroxidase, dehydroascorbate reductase, catalase, glutathione S-transferase, superoxide dismutase, glutathione reductase, and glutathione peroxidase) and non-enzymatic (carotenoids, glutamate, ascorbate, phenolics, or tocopherol) antioxidants. Chapter 8 summarizes the effects of HMs on the growth and physiological functions of medicinal plants and defence mechanisms against HM stress at morphological and molecular levels, both of which can contribute to improved bioactive compound yields.