User talk:Chitranshu pandey

Heavy metals are natural components of the Earth's crust which cannot be degraded or destroyed. To a small extent they enter our bodies via food, drinking water and air. As trace elements, some heavy metals (e.g. copper, selenium, zinc) are essential to maintain the metabolism of the human body. However, at higher concentrations they can lead to poisoning. Its poisoning could result, for instance, from drinking-water contamination (e.g. lead pipes), high ambient air concentrations near emission sources, or intake via the food chain. Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater. The term “Heavy Metal” refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. Examples of heavy metals include cadmium (Cd), arsenic (As), chromium (Cr), thallium (Tl) and lead (Pb). Heavy metals tend to accumulate in an organism over time, thus increasing the concentration in the organism. This is called as bioaccumulation. Cadmium (Cd), one of the toxic heavy metal has been classified as a human carcinogen by the International Agency for Research on Cancer (IARC) (ATSDR1999). It was discovered by German scientist as a by-product of the zinc refining process during the year 1817. Its name has been derived from the Latin word cadmia and the Greek word kadmeia ( Duruibe et al, 2007). Cadmium having atomic no.48, a soft bluish white metal, and chemically similar to in group 12, Zn and Hg. The most common forms of cadmium found in the environment exist in combinations with other elements. Hydrochloric acid (HCl), sulphuric acid (H2SO4) and nitric acid (HNO3) dissolve cadmium by forming cadmium chloride (CdCl2), Cadmium Sulphate (CdSO4) or Cadmium Nitrate (Cd(NO3)2). Most cadmium used in this country is obtained as a by-product from smelting (melting) zinc, lead, or copper ores. The cadmium by-product is mostly used in metal plating and to make pigments, batteries, and plastics. Prolonged exposure to Cd will cause toxic effect due to its accumulation over time in a variety of tissues, including kidneys, liver, and central nervous system (CNS) and peripheral neuronal systems. 1.1 Distribution and absorption: Natural cadmium level in the atmosphere and earth’s crust are 0.1 to 5 ng/m3 and 0.1 to 0.5 µg/g respectively. It is estimated that for every 10 million parts of earth’s crust containing about 2 parts of cadmium.Cadmium is a rare element and is present in the natural environment in form of its various compounds, at a relatively low level. It is widely and increasingly used in industries for corrosion- protection coating, nickel-cadmium batteries and several other applications, it easily absorbs neutrons and is used to make control rods for nuclear reactors. Cadmium is found throughout the environment from natural sources and processes such as the erosion and abrasion of rocks and soils, and from singular events such as forest fires and volcanic eruptions. Some typical levels of the natural occurrence of cadmium are as follows: Atmosphere                            0.1 to 5.0 nanograms per cubic meter (ng/m3) Earth’s Crust                          0.1 to 0.5 micrograms per gram (mg/g) Marine Sediments                  1 microgram per gram (mg/g) Sea Water                              0.1 micrograms per litre (mg/L)

This metal derives its toxicological properties from its chemical similarity to zinc an essential micronutrient for plants, animals and humans. It is bio persistent and, once absorbed by an organism, remains resident for many years (over decades for humans) although it is eventually excreted. Cadmium plays a critical role in neurobiology; a growing number of clinical investigations have pointed to Cd intoxication as a possible etiological factor of neurodegenerative diseases, including Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease (Okuda B. et.al., ) Many individuals in Europe and Asian already exceed these exposure levels, and the margin is very narrow for large groups. Human exposure to cadmium occurs through ingestion of contaminated food or water, inhalation as well. Most of that arises from the uptake of cadmium by plants from fertilizers, sewage sludge, manure and atmospheric deposition. Main source of cadmium exposure to humans are use of (Assche V et al., 1998) phosphate fertilisers (41.3%), Fossil Fuel Combustion (22.0%), Iron & Steel Production (16.7%), Natural Sources (8.0%), Non-ferrous Metals (6.3%), Cement Production (2.5%), Cadmium Products (2.5%) and Incineration (1.0%). 1.2 Cadmium neurotoxicity Toxicity of cadmium has been demonstrated in several organs. Cadmium leads to injury of tissue by creating oxidative stress, epigenetic changes in DNA. Among various organs in the body, brain is a soft target of cadmium. Cadmium has a very detrimental effect on the nervous system. A no of studies shows cadmium induced decrease in attention and memory in humans (Caciari T et al., 2012). This is likely to because of cadmium induces neuron cell death. Cadmium is well-known to cross the placenta and to accumulate in fetal tissues. Prenatal exposure is a threat to the developing brain and results in reduced birth weight and birth (Gundacker C et al., 2012). In humans, long-term exposure is associated with renal dysfunction and hepatic disorders. High exposure can lead to obstructive lung disease and has been linked to lung cancer, although data concerning the latter are difficult to interpret due to compounding factors. Cadmium may also produce bone defects (osteomalacia, osteoporosis) in humans and animals. In addition, the metal can be linked to increased blood pressure and effects on the myocardium in animals, although most human data do not support these findings. The major issues of concern related to cadmium may be summarized as follows: •	Atmospheric deposition seems continuously to cause the content of cadmium in agricultural top soil to increase, which by time will be reflected in an increased human intake by foodstuffs and therefore in an increased human risk of kidney damages and other effects related to cadmium. •	In the marine environment levels of cadmium may significantly exceed background levels causing a potential for serious effects on marine animals and in particular birds and mammals. •	Significant quantities of cadmium are continuously stockpiled in landfills and other deposits and represent a significant potential for future releases to the environment. Being such a high exposure of cadmium to environment at present there is a need to develop the strategic management to reduce its environmental toxicity of cadmium in the environment and its health implications. The average daily intake for humans is estimated as 0.15µg from air and 1µg from water. Smoking a packet of 20 cigarettes can lead to the inhalation of around 2-4µg of cadmium, but levels may vary widely. .