Heavy Metal Contamination of Environment and Crop Plants

Abstract

Heavy metal contamination is a prime environmental concern that threatens plants productivity, animal, and human health. Heavy metals occur in the earth’s crust, but due to their persistent and stable character, they cannot be degraded or destroyed. Various natural and anthropogenic processes release these heavy metals into the environment and contaminate the agricultural soils which is further associated with health hazard due to dietary intake of contaminated vegetables. The modern agricultural practices i.e. prolonged application of fertilizers, pesticides has resulted in the degradation of the ecosystem and accumulation of heavy metals especially in crop plants. Vegetable crops are vital for the human diet and in particular provide the nutrients to maintain normal health. The exposure of plants to heavy metals results in accumulation of metal content inside the plant cell via specific transport mechanisms. This alters the physiological and biochemical process that negatively affects the growth and development of plants. Heavy metals consequently alter the electron transport chain and generate ROS; singlet oxygen (1O2), hydroxyl radical (HO•), superoxide radical (O2•−), and hydrogen peroxide (H2O2). Albeit, ROS at low concentrations serves the role as important signalling molecules that are generally in equilibrium with antioxidant molecules but at higher concentrations impose adverse effect by interacting with macromolecules. Besides this, heavy metals also down-regulate the specific genes that are involved in the stress responses. Thus introduction of heavy metals in food chain and consumption of contaminated vegetables and its toxicity is a serious concern. Furthermore, strategy and policy are required to control the limits of accumulation in crop plants and vegetables.