Molybdenum is an essential trace element that is important for both animals and plants and that is also essential for humans. Molybdenum is an important constituent of xanthine oxidase and other redox enzymes in animals. Complexes of molybdenum with thiosemicarbazone and semicarbazone ligands have been found to be active against various types of tumors.
In plants, at the start of protein synthesis, it is essential for the fixation of nitrogen present in the atmosphere. It is an important constituent of certain enzymes that are present in plants and thus plays an important role in the metabolism of carbon, nitrogen, and sulfur. Thus, molybdenum plays an important role in crop development and nitrogen metabolism through the activation of nitrate reductase enzymes and nitrogenase enzymes. For healthy plant growth, routine control of Mo is therefore highly recommended.
Excess molybdenum emanating from industrial effluents may cause hazardous effects on animals. The disease molybdenosis, found in domestic animals, particularly bovine species, occurs due to a high dietary intake of molybdenum. A high concentration of molybdenum is also harmful for ruminants because it decreases copper adsorption by the liver. Severe gastrointestinal irritation occurs due to molybdenum poisoning and eventually it results in death due to cardiac failure in animals. High intake of molybdenum results in bone deformation teeth vulnerable and malfunctioning in fats and protein metabolism.
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When the concentration of molybdenum is higher than 5µg/g , it becomes toxic for most animals. Molybdenum is also known as a biological antagonist. It is added in trace amounts to fertilizers to start and enhance plant growth. Low levels of molybdenum in plants result in a decrease in the number of flowering plants. It also causes a hindrance in the formation and development of reproductive organs, like pollen. In acidic soil, molybdenum is present in an immobile state, causing a deficiency of molybdenum in plants growing in these conditions. In the soil, molybdenum is mainly present in oxyanion form, which is found chemisorbed on iron oxide, non-crystalline aluminosilicates, organic matter, and sometimes silicate clays. It forms soluble thiomolybdates, e.g., that are easily accessible in terms of biodegradation under reducing conditions. In soil solutions, the predominant dissolved species of molybdenum is the molybdate anion. Its protonation occurs at low pH. Thus, the bioavailability of molybdenum is totally dependent on the presence of its anionic species. In addition, aluminum and iron oxides are used for the determination of the sorption of molybdate into soils. The highest values of sorption are obtained when the pH is higher than 4.
