What is the LD50?
- An inhaled concentration that disorients half of the exposed bees.
- A dose that causes the death of 50 % of the individuals tested.
- A dose that kills all animals exposed to a substance.
Show answer
Correct answer: 2.
A dose that causes the death of 50 % of the individuals tested.
Why?
The LD50, or median lethal dose, is a measure of acute toxicity. It indicates the dose of a substance that causes the death of 50 % of a tested population under precise experimental conditions.
It always depends on the species studied, the route of exposure and the period of observation. An oral LD50 in the rat, for example, does not transpose directly to a contact LD50 in the bee.
The lower the LD50 value, the more toxic the substance is in the short term for the organism and the route of exposure considered.
What to understand
The LD50 does not mean that a substance is “safe” below a certain dose. It describes only an acute lethal effect within a given experimental framework.
In bees, this concept is useful for comparing the acute toxicity of substances, in particular certain pesticides. But it is not sufficient to assess the whole risk to a colony.
A substance can cause significant sublethal effects without immediately killing the bees: disorientation, reduced foraging, learning impairments, weakening of the colony or interactions with other stress factors.
Key points
The LD50 is the dose that kills 50 % of the individuals tested under defined conditions.
It measures mainly acute toxicity. On its own it does not describe chronic effects, sublethal effects or effects at colony level.
For exposure by inhalation, one speaks rather of the LC50, that is, the median lethal concentration in the inhaled air.