Poisoning may be acute or chronic. Actuate poisoning is the poisoning having a short and relatively severe course. Poisoning persisting over a long period of time is known as chronic poisoning.
Common metallic poisons include Arsenic, Mercury and Lead. These metals have extensive uses in industries, agricultural, commercial and for domestic purposes. As exposure to these metals is unavoidable, particularly in urban, semi- urban and industrial areas, some amounts are constantly absorbed and remain accumulated in the body. Thus, incidents of chronic poisoning by these are far more than the incidents of acute poisoning.
Arsenic: Arsenic is a persistent, bio- accumulative and toxic substance also classified as a carcinogen and is among the top 20 most toxic substances. WHO guideline value for arsenic in drinking water is 0.01 mg/1. Arsenic has been discovered in ground water in several countries in all five continents, but the worst is recorded from West Bengal in India and Bangladesh. This happens because arsenic is also a natural part of the Earth’s crust in some parts of the world and seeps into water, which has flowed through arsenic-rich rocks.
Arsenic poisoning is common in persons working in industries manufacturing sheep-dips, weed killers, insecticides, dyes, paints, cosmetics and in those using these products.
The commonly encountered signs and symptoms of chronic arsenic poisoning are loss of appetite, indigestion, nausea, vomiting, constipation, diarrhoea, loss of weight and brownish pigmentation of skin. It also causes hypertension and neurological effects. It can also cause about half a dozen types of cancers, including cancer of the skin, bladder, lung, liver and kidney. In China it has been found to cause a severe disease of the blood vessels leading to gangrene. It is called ‘black foot disease’.
Chronic arsenic poisoning is very different from acute poisoning. Immediate symptoms of acute poisoning include vomiting, Oesophagal and abdominal pain and bloody ‘rice water’ diarrhoea. Chelation therapy may be effective in acute poisoning.
Lead: Lead is a highly toxic metal that was used for many years in products found in and around our homes. Lead may cause a range of health effects from behavioral problems and learning disabilities, to seizures and death. Children of 6 years old and under are most at risk, because their bodies are under quick growth phase. The Primary sources of lead exposure are deteriorating lead based paint, lead-contaminated
dust and lead-contaminated residential soil. If not detected early lead poisoning can lead to damage to the brain and nervous system, behavioral and learning problems (such as hyperactivity), delayed growth and impaired hearing in children. Lead is also harmful to adults and may cause reproductive problems in both men and women. Symptoms of poisoning also include, high blood pressure, digestive problems, nervous system disorders, memory loss and muscle and joint pain.
Mercury: Mercury occurs naturally and is also released by human activities. Mercury has been commonly used in dental amalgam, and other medical devices, light switches, fluorescent lights, batteries and paints. Mercury is also used in industrial process such as chlorine production, cement manufacturing and copper and lead smelting. Because there is such devastating health risk associated with mercury and organic mercury compounds, widely used in industry as catalysts and in agriculture, the WHO has placed limits on the allowed mercury content in food. Important signs and symptoms of chronic mercury poisoning are : gingivitis, salivation, constipation, diarrhoea, anaemia, loss of weight, loosening of teeth, restricted field of vision, insomnia, anxiety, irritability and tremors of hand and tongue. Mercury chelating compounds remain the first line of treatment.
Phytofiltration
Recent research reveals that ‘Pteris vittata’, a fern, can readily purify water poisoned with arsenic. In other words water contaminated with arsenic can be cleaned by growing ferns in it. This particular fern species reduces the concentration to below the safety limit. The procedure, called ‘phytofiltration’, could provide a cheap way to remove arsenic from water supplies. The ferns would be grown directly in the water, similar to the reed-bed systems currently used to remove organic waste.
Arsenic pollution of drinking and irrigation water has emerged as a massive health threat in India and Bangladesh, where wells drilled into aquifers have turned out to be tapping poisoned water. When the water is used to irrigate rice paddies, arsenic also accumulates in the crops. According to one estimate, 3000 people may be dying in Bangladesh each year because of arsenic contamination.
Bioremediation
It is often used to describe a variety of quite different microbial processes that occur in natural ecosystems, such as mineralization, detoxification, co-metabolism or activation. It can be defined as breakdown of organic compounds in nature by the action of micro organisms, such as bacteria, actinomycetes and fungi. Since bioremediation uses naturally occurring microorganisms to transform harmful substances to non-toxic compounds, its role in restoring the contaminated soils to their original health and thus serving the environment from pollution is highly significant. Some of the more common genera involved in bioremediation of oil products include Nocardia, Pseudomonas, Acetobacter, Flavobacterium, Micrococcus and Arthrobacter.
Features of Bioremediation
Remediate means to solve a problem, and "bio- remediate" means to use biological organisms to solve an environmental problem such as contaminated soil or groundwater. In a non- polluted environment, bacteria, fungi, protists, and other microorganisms are constantly at work breaking down organic matter.
An ecologically sound, natural process; residues are usually harmless products.
Instead of merely transferring contaminants from one environmental medium to another (e.g. from water to the air or to land) bioremediation completely eliminates the target chemicals.
Bioremediation is far less expensive than other technologies that are often used to clean up hazardous waste.
Bioremedition can often be accomplished where the problem is located (in-situ). This eliminates the need to transfer large quantities of contaminated waste off-site, and the potential threats to human health and the environment that can arise during such transportation.