"Heavy Metals" are chemical metal elements that have a specific gravity not less than five times that of the specific gravity of water; water having a specific gravity of 1. For ease of understanding "Specific gravity' is a measurement of density compared to an equal amount of water.
A healthy life is reliant on small amounts of organic heavy metals and they are nutritionally essential. Termed trace elements, zinc, iron, copper and manganese are metals that fall into this category. The nutritionally essential elements are formed naturally in foods such as fruit and vegetables.
When the body is unable to metabolise heavy metals it starts to deposit them in the fatty tissue of your body. These metals then accumulate and become toxic. Heavy metals are adapt at entering the body through the air, food, water and even transdermal (through the skin).
There are 35 metals that are common and 23 of those metals are termed "Heavy Metals". From any and all of these metals toxicity may result. The metals we are most likely to come in contact with are:
Lead
Lead can be absorbed by the body through inhalation, ingestion or placental transfer. In adults, approximately 10% of ingested lead is absorbed but in children this figure can be 4 to 5 times higher. After absorption, the lead is distributed in soft tissue such as the kidney, liver and bone marrow where it has a biological half-life in adults of less than 40 days and in skeletal bone where it can persist for 20 to 30 years. more
In humans, lead is a cumulative poison that can severely affect the central nervous system. Infants, foetuses and pregnant women are most susceptible. Placental transfer of lead occurs in humans as early as the 12th week of gestation and continues throughout development.
Arsenic
Arsenic is a naturally occurring element which can be introduced into water through the dissolution of minerals and ores (where it exists mainly in the sulfide form), or from industrial effluent, atmospheric deposition (through burning of fossil fuels and waste incineration), drainage from old gold mines, or the use of some types of sheep dip. Natural sources can make a significant contribution to the arsenic concentration in drinking water. Pentavalent arsenic (As(V)) is generally the most common form in well oxygenated surface waters but under reducing conditions, such as those found in deep lake sediments or ground waters, the trivalent form (As(III)) predominates.
Although the results of studies indicate that arsenic may be essential for a number of animal species, there is no evidence that it is essential for humans.
Soluble arsenic salts are readily absorbed by the gastro-intestinal tract. After absorption inorganic arsenic binds to haemoglobin, and is deposited in the liver, kidney, lungs, spleen and skin. Inorganic arsenic does not appear to cross the blood-brain barrier but can cross the placenta. Approximately 45 - 85% of ingested arsenic is excreted in the urine within 1 to 3 days.
Extensive reviews and summaries of the human and animal toxicity data for arsenic are available (IPCS, 1981: WHO 1988).
Mercury
Mercury is generated naturally in the environment from the degassing of the earth's crust, from volcanic emissions. It exists in three forms: elemental mercury and organic and inorganic mercury. Mining operations, chloralkali plants and paper industries are significant producers of mercury (Goyer 1996). Atmospheric mercury is dispersed across the globe by winds and returns to the earth in rainfall, accumulating n aquactic food chains and fish in lakes. (Clarkson 1990).
Contamination can result from industrial emission or spills. Mercury compounds fall into two categories: iroganic mercury salts, many of which are very insoluble in water, and organics mercury compounds, the most notable being methylmercury. Inorganic mercury can be converted into methylmercury, possible by the action of bacteria in sediments, and can then readily enter the food chain.
Mercury is used widely in electrical components including cells, lamps arc rectifiers, and swtiches. It is also used in dental amalgams, fungicides, antiseptics, preservatives and pharmaceuticals.
Food is the main route of exposure, with highest concentrations found in fish and fish products. The average Australian adult dietary intake of mercury is approximately 0.004mg per day. Drinking water is likely to constitute only a small fraction of total intake.
Cadmium
Contamination by cadmium may occur as a result of impurities in the zinc of galvanized pipes or in solders used in fittings, water heaters, water coolers and taps. Cadmium can also be released to the environment in waste water, through contamination of fertilizers and by metallurgical industries.
Cadmium metal is used as an anti-corrosive coating on steel but its use is being phased out. Cadmium compounds are commonly used as pigments in plastics, in batteries and in some electrical components.
It can be found in soils due to insecticides, fungicides, sludge and commercial fertilizers that use cadmium in agriculture.
Food is the main source of cadmium intake. The estimated average Australian adult dietary intake of cadmium is approximately 0.03mg per day. Smoking is a significant additional source of cadmium.
