Heavy Metals in Air, Soil, and Water: Major Sources, Soil Health Impacts, and Mechanisms Underlying Uptake, Toxicity, and Tolerance in Plants

Abstract

Characterized by their high atomic weight and a density of at least 5 g/cm 3 , heavy metals can be categorized as essential (harmless) metals and nonessential (toxic) metals. Compared to natural sources, anthropogenic (man-made) activities are the major contributors of heavy metals to various environmental compartments like air, water, and soil. This chapter aims to: (i) provide an overview of essential and non-essential heavy metals and their sources of entry into air, water, and soil; (ii) highlight the major impacts of heavy metals on the health characteristics of soil; (iii) evaluate important transporters involved in the uptake of different heavy metals in plants; (iv) discuss key aspects involved in the phytotoxicity of selected heavy metals such as arsenic, cadmium, chromium, cobalt, copper, iron, lead, mercury, nickel, and zinc; and (v) emphasize important heavy metal tolerance-mechanisms (mentioning the role of nitric oxide as an example) in plants. The outcomes of the discussion may assist in guiding future research in this direction.