7. Microelements and Their Role in Human Health

Microelements viz. zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), molybdenum (Mo), boron (B), chlorine (Cl) and nickel (Ni) have been recognized as essential and silicon (Si), sodium (Na), cobalt (Co), and strontium (Sr) as beneficial or quasi-essential for plants. In addition to these plant essential microelements, human beings and animals require chromium (Cr), iodine (I) and selenium (Se). Microelements are used in relatively small amounts and constitute less than 0.1% of dry plant tissue. Some of the microelements may be toxic when consumed at high amounts. Soil is the main source of microelements for plants, except in situations of large atmospheric deposition or from flooding by contaminated waters. The microelements in soils undergo several transformations and their availability to plants depends on the chemical form and distribution between soil’s solid and liquid phases, which is influenced by soil conditions, particularly pH, texture and soil aeration status. Microelements perform a variety of functions in plants. Besides being component of enzymes, certain microelements are involved in activation of enzymes and play a role in oxidation-reduction reactions of plant metabolism. Micronutrient deficiencies in plants not only limit agricultural production but also affect human nutrition as plant food is the main source of dietary intake. Microelements in humans play several physiological functions including synthesis of enzymes, hormones and other substances, helping to regulate growth, development and functioning of the immune and the reproductive systems. Deficiencies of microelements in soil and plants can be corrected by applying chemical fertilizers either alone or in combination with organic manures. Micronutrient level in humans can be optimized through dietary diversification, mineral supplementation, food fortification, or increasing their concentrations and/or bioavailability in food products. Correction of deficiencies and optimization of micronutrient levels in humans depends on several factors including current dietary intake, food habits and the nutrient content of the food items consumed, metabolic pathway of a nutrient, current body stocks, age, gender, and body weight. In this chapter, we discuss sources of microelements, their transformations in soil, functions in plants and humans, effects of their deficient and excessive uptake on plants and humans, and the approaches to optimize their levels in plants and humans.