Author: PARIMAL RAMESH UDGAVE
Fertilization of crops is the application of fertilizers to stimulate germination, growth, and development of crops. It is the important input in farming. Fertilizers can be divided into two types- 1. Organic 2. Inorganic. Organic fertilizers are eco-friendly fertilizers made up from animal, vegetable and degradable matter. Organic fertilizer poses no risk of soil or water pollution. However, it doesn’t make big difference when it comes to crop yield or production. For higher crop yields, inorganic fertilizers are the best choice. However, when it comes to soil, water, and environmental pollution it contributes a large percentage. Inorganic fertilizers are the results of chemical reactions and synthetic chemicals. Examples of inorganic fertilizers are Phosphate, nitrate, ammonium and potassium salts. Inorganic fertilizers are a potential source of heavy metals and radionuclides. Heavy metals are toxic materials having a density of 6.0 g/cm3 or more. The potential hazardous heavy metals include arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb) and zinc (Zn). Natural radionuclides are the atoms which are of unstable nature due to the high nuclear energy. Unplanned or sudden high exposure of radionuclides results in harmful effects on different living systems specifically microbiota, plants, and animals. However, lower levels of radionucleotides don't make harm to living systems. But, the biggest problem is depletion and enrichment of radionuclides.
Table No. 1: Effects of heavy metal accumulation or exposure to living systems
| Sr. No. | Heavy Metal | Aquatic animals | Human |
| 1 | Cadmium (Cd) | Damage Nervous system, Reproductive system, Changes tissue structure, Affect survival and growth | Carcinogenic, Heart, kidney problems, Reproductive infertility problems |
| 2 | Chromium(Cr) | Growth is inhibited, Changes or destroys gills of fish, Affected embryo survival in catfish. | Carcinogen, Cancer |
| 3 | Copper (Cu) | Toxic destroys gills and kidney, | Liver diseases (Liver cirrhosis), lethal effects |
| 4 | Lead (Pb) | muscular and neurological degeneration, growth inhibition, mortality, reproductive problems and paralysis | Carcinogen, Failure of cardiovascular, kidney, nervous system, circulatory systems |
| 5 | Mercury (Hg) | Damages Gills, kidney, and brain, Inhibits hormone production and transportation | Damage nervous system, brain, and kidney, |
| 6 | Nickel (Ni) | Damages gills and leads to lethal effects also inhibits growth and development | Different types of cancer (Nose, Larynx, Prostate), Defects in newborn children |
| 7 | Zinc (Zn) | Gills and Kidney damage, Reduce growth and development | Respiratory problems, Skin irritation |
| 8 | Uranium (U) | Damages body tissues, Kidney, and Gills | Cancer and Kidney disease or failure |
Bioaccumulation of Heavy metals and Radionuclides:
Bioaccumulation of Heavy Metals and Radionuclides in the future crisis of safe food chain system. The problem with metals and radionuclides is the biomagnification. Biomagnification is the process by which the concentration of toxic materials increases in living organisms or systems. According to the latest market research conducted by Ameri Inc, the global market of inorganic fertilizer consumption market in 2014 was 185 Million metric tons which are 193 million metric tons in 2017 and predicted to be 215 million metric tons in 2024 (Ameri Research Inc. 2017). Pressure on agricultural activities stimulates the fertilizer consumption which means there will be no decline in future for consumption of fertilizers. It will lead to the step by step enrichment of the heavy metals in soil.
Bioavailability of Metals for Bioaccumulation
There are some factors which affect bioaccumulation of metals. Factors are physiochemical form and speciation. Furthermore, hard water makes difficult for metals to mix or solubilize. It also competes with Calcium and Magnesium ion for binding on cell membranes.
Bioaccumulation of metals in Animal systems
Bioaccumulation of metals in organisms and animals occurs through ingestion of food/water, Respiration using gills and by adsorption on body or skin. However, feeding or ingestion of food is the primary reason for bioaccumulation of metals in animal bodies. Water bodies are likely to be easily polluted with these metals. Even if metals don’t mix with water it can go through water in animal organelles. Some heavy metals can react with fats, feeding of this fat can also lead to bioaccumulation of metals in animal systems.
Aquatic animals are also at risk because of the bioaccumulation of heavy metals. Edible aquatic animals which also poses and links heavy metals to animal food chain system.
Bioaccumulation of metals in Plant systems
Uptake of these metals in soil and water bodies helps plants to absorb metals in its plant parts. Plants normally act in two days when they are exposed to heavy metals, one is accumulators and second is excluders. Accumulators plants normally tolerate and survive upon accumulation of metals in plant parts which starts from roots to shoot, shoot to branches, branches to leaves and fruits. Accumulator plants normally bio-transform or biodegrade metals. However, there is plenty of plants which cannot bio-transform or degrade heavy metals. This poses an environmental risk. Heavy metals often transported to the leaves and fruits. This is dangerous because at this stage it can easily transport to food chain of animals. Excluder plants normally inhibit entry of heavy metals into roots, however, there are some plants which does not survive because of blockage in cell wall or organelles. There are some conditions which do an effect on uptake of heavy metals to plants including plant species, plant root system, type of soil/medium, chelating agents and vegetative uptake.
Conclusion:
Plants growing in heavy metal contaminated soil show reduction in their growth and development. However, some plants tolerate specific amounts of heavy metals. If these plants are ingested by animals/human, heavy metals enter into Environmental Food Chain system. Therefore, controlling heavy metals transportation is very essential. Fertilizers in agriculture can act as a potential source of heavy metals. Therefore, organic farming can save us from soil toxicity of heavy metals and radionuclides. It can act as a best alternative.
About Author / Additional Info:
I am working as Asst. professor. My scientific interests include Nano-biotechnology, Soil toxicology, Eco-toxicology and Environmental science