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8.12 Lethal Dose 50% (LD50)

7 min readjanuary 27, 2023

Riya Patel

Riya Patel


AP Environmental Science ♻️

252 resources
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What does LD50 mean?

LC50 stands for Lethal Concentration 50. It is a measure of the concentration of a chemical in air or water that causes death in 50% of a group of test animals in a specific time period (usually 4 hours for inhalation and 96 hours for water toxicity test). It is used to evaluate the toxicity of inhaled or ingested toxins and to evaluate the environmental hazard of a chemical in water. LC50 values are used to compare the relative toxicity of different chemicals and to guide the development of exposure limits and regulatory standards. This test is also used to evaluate the toxicity of a chemical in air, which is an important consideration for workers and communities exposed to air pollution or emissions from industrial sources.

Examples of LD50

LD50 values can vary widely depending on the chemical and the method of administration. Some examples of LD50 values for common chemicals are:
  • The oral LD50 for nicotine in rats is around 50 mg/kg.
  • The oral LD50 for caffeine in rats is around 190 mg/kg.
  • The oral LD50 for aspirin in rats is around 200 mg/kg.
  • The oral LD50 for ethanol (alcohol) in rats is around 7,000 mg/kg.
  • The oral LD50 for table salt (sodium chloride) in rats is around 3,000 mg/kg.
These are examples of LD50 values for different species of animals. The values represent the amount of a chemical that is required to kill 50% of the test animals in a specific route of administration. The values can vary greatly between species, indicating that different animals may have different sensitivities to the chemical. It is important to note that these values should not be directly applied to humans, as humans may have different sensitivities to the chemical. LD50 values are useful for identifying the relative toxicity of a chemical, and can be used to help determine safe exposure levels for humans, but it is important to consider other factors such as the chemical's potential for accumulation and long-term effects.

Why study LD50's?

LD50 values are useful for studying the toxic effects of chemicals because they provide a way to compare the relative toxicity of different chemicals. By determining the amount of a chemical required to cause death in 50% of a group of test animals, researchers can compare the toxicity of one chemical to another, regardless of the specific toxic effects caused. This information can be used to make informed decisions about the safety of chemicals used in industry, agriculture, and consumer products, and to guide the development of regulatory standards for chemical exposure. Additionally, the LD50 can be used to identify chemicals that may be particularly hazardous, and to inform the development of risk management strategies to protect human health and the environment.

Who invented the idea of an LD50?

The concept of LD50 (Lethal Dose 50) was first introduced by J.W. Trevan in 1927. He published a paper in the journal "British Medical Journal" in which he described the use of a single dose of a chemical that killed 50% of a group of test animals as a way to measure the toxicity of a chemical. This method quickly became widely accepted in the field of toxicology as a simple and efficient way to compare the relative toxicity of different chemicals. The concept was further developed and refined over the years by many other toxicologists, and is still widely used today as a standard method of toxicity testing.

What are some other toxicity dose terms in common usage?

There are several other toxicity dose terms that are used in addition to LD50:
  • LDlo: The lowest dose at which a chemical has caused death in a test population.
  • LD100: The dose at which a chemical has caused death in 100% of a test population.
  • ED50: The dose of a chemical that causes a specific effect, such as changes in behavior or organ damage, in 50% of a test population.
  • NOAEL: The No-Observed-Adverse-Effect Level is the highest dose at which there is no observed adverse effect in a test population.
  • NOEL: The No-Observed-Effect Level is the highest dose at which there is no observed effect in a test population.
  • POD: The Probable-Effect-Dose is a dose at which a certain effect is expected to occur in a certain percentage of the population.
  • TD50: The Therapeutic Dose is the dose of a chemical that causes a therapeutic effect in 50% of a test population.
  • EC50: The Effective Concentration is the concentration of a chemical in air or water that causes a specific effect, such as death or changes in behavior, in 50% of a test population.

How do I compare one LD50 value to another and what does it mean to humans?

To compare one LD50 value to another, you would need to take into account the species, route of administration, and conditions of the test. A lower LD50 value generally indicates a higher toxicity, but it is important to note that the LD50 value alone does not provide information about the long-term effects of a substance or the specific toxic effects it may cause. The LD50 value should be used in conjunction with other toxicity data to make a comprehensive assessment of the risk associated with a substance.

How are LD/LC50 tests done?

LD50 and LC50 tests are typically conducted using laboratory animals, such as rats or mice. The animals are divided into groups and are exposed to different concentrations or doses of the test substance. The substance can be administered by various routes such as oral, dermal, inhalation, and injection. The animals are observed for a specified period of time, usually for a period of about 4 days for oral and dermal exposure, and for a period of 4 hours for inhalation exposure. The number of animals that die or show signs of toxicity is recorded. From this data, the median lethal dose (LD50) or median lethal concentration (LC50) can be calculated. This is the dose or concentration at which 50% of the animals die or show signs of toxicity.
It's worth to mention that LD50/LC50 tests are considered to be controversial, as they cause harm and death to animals, and also there are alternatives methods that can be used to evaluate the toxicity of a substance without using animals.

Which LD50 information is the most important for occupational health and safety purposes?

For occupational health and safety purposes, the most important LD50 information would likely be the LD50 value and the route of administration (such as oral or dermal) that was used in the toxicity testing. This information can help to determine the potential for acute toxicity in the workplace, and can be used to set exposure limits and establish appropriate protective measures for workers. Additionally, information on the species and strain of animal used in the testing, as well as any observed symptoms of toxicity, may also be important for interpreting the relevance of the LD50 data to human health.

Can animal LD50 data be applied to humans?

LD50 data from animal studies can be used to provide a general estimate of a chemical's toxicity in humans, but it is important to keep in mind that there can be significant differences between species in terms of how they respond to a given chemical. Therefore, while animal LD50 data can provide useful information, it cannot be directly applied to humans without further research. Additionally, human data should be used whenever available.
LD50 data is generally used as a basis for determining a chemical's toxicity and establishing safe exposure levels for humans. However, it's important to note that the LD50 test only measures the dose at which 50% of the test population dies, and it does not provide information about other toxic effects that may occur at lower doses. Therefore, other toxicity testing should also be performed to get a complete picture of a chemical's potential effects on human health.

How should an LD50 value be used?

LD50 values should be used as a starting point for determining a chemical's toxicity. However, it is important to consider other factors such as the route of exposure, duration of exposure, and the population being exposed when interpreting the results.
LD50 values are used to determine a chemical's acute toxicity, which is the potential for harm from a single exposure or short-term exposure. These values are used to establish safe exposure levels for humans and to classify chemicals according to their potential hazard.
LD50 values can also be used to compare the relative toxicity of different chemicals. Chemicals with lower LD50 values are generally more toxic than those with higher values.
It is important to note that LD50 values should not be used to predict the effects of long-term exposure to a chemical or the effects of exposure to mixtures of chemicals. Other types of toxicity testing, such as chronic toxicity studies and subchronic toxicity studies, are needed to fully understand the potential effects of a chemical on human health.
Additionally, LD50 values are not always applicable or reliable indicator of toxicity in certain situations such as certain chemical are not lethal to certain population or certain chemical have long lasting chronic effect.

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