There is an inverse relationship between product toxicity and LD50 value. Products with lower LD50 values are more hazardous and pose a greater risk than products with higher LD50 values Figure 1. For most ready-to-use products, such as most granules, baits, and dusts, the MSDS-reported LD50 is for the product in its useable form because these products can be used when purchased i.
For products that must be diluted in water, the resulting LD50 increases considerably upon dilution. Consider the insecticide Premise 0. In its concentrated form, it is 5. However, the results of oral studies are important for drug studies, food poisonings, and accidental domestic poisonings. Oral occupational poisonings might occur by contamination of food or cigarettes from unwashed hands, and by accidental swallowing.
In general, the smaller the LD 50 value, the more toxic the chemical is. The opposite is also true: the larger the LD 50 value, the lower the toxicity. The LD 50 gives a measure of the immediate or acute toxicity of a chemical in the strain, sex, and age group of a particular animal species being tested. Changing any of these variables e. The LD 50 test was neither designed nor intended to give information on long-term exposure effects of a chemical. Once you have an LD 50 value, it can be compared to other values by using a toxicity scale.
Confusion sometimes occurs because several different toxicity scales are in use. These tables differ in both the numerical rating given to each class and the terms used to describe each class. It is important to reference the scale you used when classifying a compound. It is also important to know that the actual LD 50 value may be different for a given chemical depending on the route of exposure e.
For example, some LD 50 s for dichlorvos, an insecticide commonly used in household pesticide strips, are listed below:. Differences in the LD 50 toxicity ratings reflect the different routes of exposure. The toxicity rating can be different for different animals.
The data above show that dichlorvos is much less toxic by ingestion in pigs or dogs than in rats. Using Table 1, dichlorvos is moderately toxic when swallowed oral LD 50 and extremely toxic when breathed inhalation LC 50 in the rat. Using Table 2, dichlorvos is considered very toxic when swallowed oral LD 50 by a rat. In general, if the immediate toxicity is similar in all of the different animals tested, the degree of immediate toxicity will probably be similar for humans.
When the LD 50 values are different for various animal species, one has to make approximations and assumptions when estimating the probable lethal dose for man. Tables 1 and 2 have a column for estimated lethal doses in man. Special calculations are used when translating animal LD 50 values to possible lethal dose values for humans. Safety factors of 10, or are usually included in such calculations to allow for the variability between individuals and how they react to a chemical, and for the uncertainties of experiment test results.
The LD 50 is only one source of toxicity information. For a more thorough picture of the immediate or acute toxicity of a chemical, additional information should be considered such as the lowest dose that causes a toxic effect TDLO , the rate of recovery from a toxic effect, and the possibility that exposure to some mixtures may result in increasing the toxic effect of an individual chemical. Add a badge to your website or intranet so your workers can quickly find answers to their health and safety questions.
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.
The kidneys are part of the body's urinary system. They have the task of excreting the waste products that the blood has transported from various organs of the body, of keeping the fluids in balance and of ensuring that they contain an adequate blend of various necessary salts.
They also maintain the acidity of the blood at a constant level. Solvents may irritate and impair kidney function. The most hazardous to the kidneys is carbon tetrachloride. Other well-known kidney- damaging substances are lead and cadmium. Allergic reactions An allergic reaction, or sensitization as it is also called, may appear after repeated contact to a substance.
Once the sensitization has bee produced, even very low doses can provoke a reaction. The different allergies are numerous, varying from minor skin irritation to very severe or even fatal reactions. The pattern of sensitization varies according to the species. In humans, the skin and the eyes are the most common areas of allergic response, whereas, for example, in the guinea pigs reactions are more common in the respiratory system. Organophosphate pesticides, such as dialiphos, naled and parathion, are examples of chemicals where the combined effect is the sum of the effects observed when the chemicals act individually.
The effect can be more than the sum of the individual effects of two chemicals e. An example of an increase in risk is with asbestos fibres and cigarette smoking. They act together: the risk of developing lung cancer after exposure to asbestos fibres is forty times greater for a smoker than for a non-smoker. Another pair of the chemicals where the combined risk is greater than a mere additive effect are the solvents, trichloroethylene and styrene.
This effect is used to find an antidote to a poison. For example, two commonly used solvents isopropanol and carbon tetrachloride have this kind of joint effect. Isopropanol, at concentrations which are not harmful to the liver, increases the liver damage caused by carbon tetrachloride. In some cases, when the exposure to a substance is repeated the body may decrease its sensitivity to the substance, i. However, some substances are resistant to decomposing processes.
The adverse effects increase with the concentration of these substances and their accumulation in foodchains. In the natural environment, large numbers of potentially toxic substances are present. In some cases, when the substance is on its own it would cause no harm but it may interact with other toxic substances or under specific conditions it may be concentrated or transformed to a more dangerous compound.
An example of an air pollution reaction is the production of photochemical smog. Chlorinated hydrocarbons such as DDT and dieldrin have similar chemical and biological effects. When present together they lead to more serious effects than when acting separately. To assess the effects of toxic substances in the environment some indicators of ecotoxicity are used.
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