A normally distributed sigmoid curve such as this one approaches a response of 0% as the dose is. Interpret frequency (normal distribution) and dose - of most exposures in toxicology. Dosage - response mathematical relationship. (positive sigmoid curve. The dose–response relationship, or exposure–response relationship, describes the change in Dose–response curves are generally sigmoidal and monophasic and can be fit to a classical Hill equation. they apply to endocrine disruptors argues for a substantial revision of testing and toxicological models at low doses.
The dose-response relationship or curve allows one to establish causality that a chemical has induced the observed effects, helps establish the lowest dose at which toxicity occurs if there is a threshold, and determines the rate or slope for the dose response.
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There may or may not be a threshold, a dose below which no observable effect is expected. Within a species or population, the majority will respond similarly to a given toxicant; however, a wide variance of responses may be encountered, some individuals are susceptible and others resistant. As demonstrated in Figure 2. A large standard deviation indicates great variability of response.
The shape and slope of the dose-response curve is helpful in predicting the risk or toxicity of a substance at specific dose levels.
Major differences among toxicants may exist not only in the dose at which the toxicity is seen but also in the percent of population responding per unit change in dose i.
Dose–response relationship - Wikipedia
As illustrated in Figure 4 below, Toxicant A has a higher threshold but a steeper slope than Toxicant B, the implication being that comparatively, Toxicant B is more toxic at lower dosages and Toxicant A more toxic at higher dosages.
A threshold for toxic effects occurs at the point where the body's ability to detoxify a xenobiotic or repair toxic injury has been exceeded. For most organs there is a reserve capacity so that loss of some organ function does not cause decreased performance. Figure 5, below, see http: Given the larger number of subjects needed to observe an unlikely phenomenon one usually cannot afford to study sufficient numbers of subjects at very low doses to accurately portray the dose response relationship at the lowest dose ranges.
Hence laboratory animals are typically studied at dosages which are orders of magnitude higher than human beings are expected to be exposed and conclusions of risk in human settings are derived from extrapolations of observed data at higher ranges to the lower ranges at which humans might be exposed. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer uct. One of the more commonly used measures of toxicity is the LD The LD50 says nothing about non-lethal toxic effects though.
A chemical may have a large LD50, but may produce illness at very small exposure levels. It is incorrect to say that chemicals with small LD50s are more dangerous than chemicals with large LD50s, they are simply more toxic.
The danger, or risk of adverse effect of chemicals, is mostly determined by how they are used, not by the inherent toxicity of the chemical itself. The LD50s of different poisons may be easily compared; however, it is always necessary to know which species was used for the tests and how the poison was administered the route of exposuresince the LD50 of a poison may vary considerably based on the species of animal and the way exposure occurs.
Some poisons may be extremely toxic if swallowed oral exposure and not very toxic at all if splashed on the skin dermal exposure.
The potency of a poison is a measure of its strength compared to other poisons. The more potent the poison, the less it takes to kill; the less potent the poison, the more it takes to kill.
The potencies of poisons are often compared using signal words or categories as shown in the example in table 2. The designation toxic dose TD is used to indicate the dose exposure that will produce signs of toxicity in a certain percentage of animals.
The TD50 is the toxic dose for 50 percent of the animals tested. The larger the TD the more poison it takes to produce signs of toxicity.
General Principles of Toxicology - Page 2 of 6
The toxic dose does not give any information about the lethal dose because toxic effects for example, nausea and vomiting may not be directly related to the way that the chemical causes death. The toxicity of a chemical is an inherent property of the chemical itself. It is also true that chemicals can cause different types of toxic effects, at different dose levels, depending on the animal species tested.