2.6. Heavy and Non Heavy Metals

Heavy and non heavy metals occur naturally in the environment from pedogenetic processes (erosion, volcanic activities, etc.) and anthropogenic activities (mining, refining ores, tanneries, batteries, paper industries, pesticides and fertilizer industries, etc.). These metals essentially become contaminants in the soil and water environment because of their excess generation by natural and man-made activities. These pollutants are of specific concern due to their toxicity, bio-accumulation tendency and persistency in nature for long periods of time. The main heavy and non heavy metal contaminants are:

Antimony occurs naturally in the ground and is often used in the flame retardant industry. It is also used in ceramics, glass, batteries, fireworks and explosives. Drinking water gets contaminanted through natural weathering of rock, industrial production, municipal waste disposal or manufacturing processes.

Arsenic (As) is a semi-metal element which is odorless and tasteless. Agricultural and industrial practices cause arsenic contamination in drinking water.

Asbestos is naturally occurring mineral. Six minerals (chrysotile, crocidolite, anthophyllite, tremolite, actinolite and amosite) have been characterized as asbestos. It is used in the production of cements, floor tiles, paper products, paint, and caulking; in transportation-related applications; and in the production of textiles and plastics. Most of the asbestos pollute the environment by extensive opencast mining, generating enormous amount of mine waste and host rocks.

Barium (Ba) occurs naturally in some aquifers that serve as sources of ground water. The major uses of barium are in oil and gas drilling muds, automotive paints, bricks, tiles and jet fuels. It generally pollutes drinking water after disolving from naturally occurring minerals in the ground and unconventional drilling practices.

Beryllium (Be) occurs naturally in the ground and is often used in electrical equipment and mechanical industries. It generally gets into water from run-off during mining operations, discharge from processing plants and improper waste disposal from industrial applications.

Boron (B) Boron is a naturally occurring element. In nature it is found combined with oxygen and other natural elements forming several different compounds called borates. Anthropogenic boron contamination in aquifers has been attributed to leaking septic systems and borate mining.

Cadmium (Cd) is a contaminant in the metals used to galvanize pipe. Corrosion of galvanized pipes or improper waste disposal causes water pollution . The other source of Cd is PVC-window frames, plastics and plating on steel.

Chromium (Cr) occurs naturally in the ground. It is often used in the electroplating of metals. It generally gets into water from run-off during old mining operations and improper waste disposal from industrial application (plating, metallurgy, pigments, and leather tanning.

Chlorine (Cl) is naturally occurring substance. It gets in to the groundwater mostly by human activities (road salt, fertilizers, industry waste or sewage)

Cyanide (CN) is used in electroplating, steel processing, plastics, synthetic fabrics, metal recovery processes and fertilizer products. Improper waste disposal causes water pollution.

Copper (Cu) is found naturally in sand stones and in minerals such as malachite and chalcopyrite. Increased levels of Cu are due to uses in fertilizers, building materials, rayon manufacture, pesticide sprays, agricultural and municipal wastes and industrial emissions.

Fluoride (F) occurs naturally in some water supplies. Improper waste disposal and mining activities cause water pollution.

Lead (Pb) occurs naturally (weathering of parent rocks and ore deposits) and man-made (mining, industrial emission; smelting, waste water irrigation and application of fertilizers) sources. Mining activities and industrial activities (plastics, finishing tools, cathode ray tubes, ceramics, solders, pieces of lead flashing and other minor product, steel and cable reclamation) cause environmental pollution.

Mercury (Hg) occurs naturally in the environment and can be found in metallic, inorganic, and organic forms. It is used in metal processing industries, medicinal, cosmetic, and spiritual purposes. It usually contaminates the water as a result of improper waste disposal.

Nickel (Ni) occurs naturally in the ground. It is generally used in electroplating, stainless steel and alloy products. Mining, industrial application (nickel plating, colored ceramics, batteries, furnaces used to make alloys or from power plants and trash incinerators) and refining operations (trash cause environment pollution.

Nitrate (NO3) occurs naturally in soil and water. It is used in fertilizer and is found in sewage and wastes from human and/or farm animals and generally gets into drinking water from those activities .

Selenium (Se) is generally found in food and soils. It is widely used in electronics, TV cameras, computer cores, photocopy operations, the manufacture of glass, chemicals, drugs, and as a fungicide and a feed additive. Mining and retorting activities can cause environment contamination.

Silver (Ag) occurs naturally in elemental form and as various ores. Ag is generally used in industry, photographic chemicals, water distillation equipment, mirrors, silver plating equipment, special batteries, table cutlery, jewelery, dental medical and scientific equipment including amalgams. The main source of silver contamination of environment (air, soil and water) is by natural and anthropogenic sources (photographic developing solutions that photofinishers discard directly to sewers.

Sodium (Na) occurs naturally in food and drinking water. Drinking water contributes only a small fraction to the overall Na intake. The main sources of Na contamination are near coastal areas, windborne sea spray and domestic, commercial and industrial discharges. In general, sodium salts are not acutely toxic substances because of the efficiency with which mature kidneys excrete sodium. High concentrations of Na tend to increase the corrosive action of water, give it unpleasant taste, and tend to hamper the operation of ion exchange softeners in the removal of hardness.

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