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Read the ACS privacy policy. Other durations of exposure versus the traditional 4 hours may apply depending on specific laws. Chemicals can have a wide range of effects on our health. Depending on how the chemical will be used, many kinds of toxicity tests may be required. Since different chemicals cause different toxic effects, comparing the toxicity of one with another is hard.
We could measure the amount of a chemical that causes kidney damage, for example, but not all chemicals will damage the kidney. We could say that nerve damage is observed when 10 grams of chemical A is administered, and kidney damage is observed when 10 grams of chemical B is administered. However, this information does not tell us if A or B is more toxic because we do not know which damage is more critical or harmful. Therefore, to compare the toxic potency or intensity of different chemicals, researchers must measure the same effect.
One way is to carry out lethality testing the LD 50 tests by measuring how much of a chemical is required to cause death. This type of test is also referred to as a "quantal" test because it is measures an effect that "occurs" or "does not occur". In , J. Trevan attempted to find a way to estimate the relative poisoning potency of drugs and medicines used at that time. He developed the LD 50 test because the use of death as a "target" allows for comparisons between chemicals that poison the body in very different ways.
Since Trevan's early work, other scientists have developed different approaches for more direct, faster methods of determining the LD Acute toxicity is the ability of a chemical to cause ill effects relatively soon after one oral administration or a 4-hour exposure to a chemical in air. In nearly all cases, LD 50 tests are performed using a pure form of the chemical. Mixtures are rarely studied. The chemical may be given to the animals by mouth oral ; by applying on the skin dermal ; by injection at sites such as the blood veins i.
Researchers can do the test with any animal species but they use rats or mice most often. Other species include dogs, hamsters, cats, guinea-pigs, rabbits, and monkeys. In each case, the LD 50 value is expressed as the weight of chemical administered per kilogram body weight of the animal and it states the test animal used and route of exposure or administration; e.
If the lethal effects from breathing a compound are to be tested, the chemical usually a gas or vapour is first mixed in a known concentration in a special air chamber where the test animals will be placed. When an LC 50 value is reported, it should also state the kind of test animal studied and the duration of the exposure, e. Inhalation and skin absorption are the most common routes by which workplace chemicals enter the body.
Thus, the most relevant from the occupational exposure viewpoint are the inhalation LC 50 and skin application tests LD 50 -skin. Despite this fact, the most frequently performed lethality study is the oral LD It is absorbed and transported into the body causing typical effects on the central nervous system and on other organs.
Target organs The degree of the toxic effect is not the same in all organs. Usually there are one or two organs which show the major toxic effect. These are referred as target organs of toxicity of the particular substance.
The central nervous system is the target organ of toxicity most frequently involved in systemic effects. The blood circulation system, liver, kidneys, lungs and skin follow in frequency of systemic effects. Muscle and bones are the target organs for a few substances.
The male and female reproduction systems are vulnerable to many substances. Skin is the largest organ in the human body, 1. It provides a protective cover to the body but can fail if the load is overwhelming. A number of substances can penetrate healthy intact skin and enter the blood circulation. Phenol is a substance that may even result in death after exposure and penetration through the skin.
The vast majority of work-related skin diseases are contact eczemas, irritation and inflammation of the skin. This condition can be either a non-allergic or allergic reaction to exposure to chemical substances. Examples of common contact sensitizers are several colorants and dyes, metals such as nickel and its salts, chromium and cobalt salts and organomercuric compounds, monomers of a number of acrylates and methacrylates, rubber additives and pesticides.
In practice chemical skin injury is also influenced by environmental conditions such as humidity and heat. The lung is the major route through which toxic substances in the workplace enter the body. It is also the first organ to be affected by dusts, metal fumes, solvent vapours and corrosive gases.
Allergic reactions may be caused by substances such as cotton dust, TDI toluene diisocyanate, used in the manufacture of polyurethane plastics , and MIC methylisocyanate, used in production of carbaryl insecticide.
In a catastrophic chemical accident in Bhopal, India, in , more than people died from exposure to MIC. When dust particles of a certain size of some substances are inhaled the lungs are unable to remove them. They become embedded in the lung causing a condition called pneumoconiosis. Pneumoconiosis is mainly a problem for workers exposed to the dust of silica quartz and asbestos, and is the commonest non-malignant occupational lung disease throughout the world.
Other substances, such as formaldehyde, sulphur dioxide, nitrogen oxides and acid mists may cause irritation and reduce the breathing capacity. Some metals affect the nervous system, especially heavy metals such as lead, mercury and manganese. Organophosphate insecticides such as malathion and parathion interfere severely with information transmission chemical neurotransmitter function in the nervous system, leading to weakness, paralysis and sometimes death.
The blood circulation is a target for the adverse effects of solvents. Blood cells are mainly produced in the bone marrow. Benzene affects the bone marrow; the first sign is mutation in the blood cells called lymphocytes. To study mutation, lymphocytes are cultured in the laboratory to observe specific types of cellular changes.
Lead, in the form of the metal or its compounds, is another classic example of a chemical that may cause blood problems. Lead in the blood may inhibit certain enzyme activities involved in the production of hemoglobin in red blood cells.
Chronic lead poisoning may result in a reduced ability of the blood to distribute oxygen through the body, a condition known as anaemia. The liver is the largest of the internal organs in the body and has several important functions. It is a purification plant which breaks down unwanted substances in the blood.
The liver has a considerable reserve capacity; symptoms of liver disorder appear only in serious diseases. Solvents such as carbon tetrachloride, chloroform and vinyl chloride, as well as alcohol, are hazardous to the liver.
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