*2.2.4 Heavy metal toxicity*

Heavy metals are inorganic, non-biodegradable compounds having atomic mass and density > 20 and > 5 g/cm3 , respectively. They cause mutagenic effects on plants through contaminating irrigation, food chain and environment [12]. Application of excessive quantity of water from contaminated source and fertilizers/pesticides results in accumulation of heavy metals in soil and from soil, plant absorbs them. In general, heavy metals (Ag, Cr, Cd, As, Sb, Pb, Se, and Hg) are non-essential and at higher concentrations can affect plant's normal functioning. Besides, some essential elements such as Zn, Cu, Ni, Fe, Co etc. at higher concentrations pose heavy metal toxicity in plant.
