Lethal Dose 50% (LD50)
Introduced| English | Meaning |
|---|---|
| LD50/ˌel diː ˈfɪfti/ | The dose that kills half a test population. |
| dose/dəʊs/ | An amount of a substance or radiation received by an organism or material. |
Measuring how poisonous
- How do we say one chemical is more toxic than another?
- We need a fair, standard number.
- The most common one is the LD50 半数致死剂量.
- It stands for "lethal dose, 50%".
What LD50 means
- LD50 is the dose 剂量 that kills half a test population.
- It is measured per kilogram of body weight.
- That way it is fair across animals of different sizes.
- A lower number means a smaller dose is deadly.
LD50 is the dose that kills half of a test population
LD50 is the dose of a substance that…
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LD50 (lethal dose, 50%) is the dose that kills half of a test group — a standard measure of toxicity.
The inverse rule
- Here is the tricky part: low LD50 means high toxicity.
- A tiny lethal dose (low LD50) is a very dangerous poison.
- A huge lethal dose (high LD50) is fairly safe.
- So the number and the danger run in opposite directions.
More toxic or less toxic?
Sort each substance by its LD50 - remember, a lower LD50 means more toxic.
A substance with a lower LD50 is…
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Lower LD50 = more toxic: it takes only a tiny dose to kill. The relationship is inverse.
LD50 is given per kilogram of body weight, so it works for animals of different ____.
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By measuring dose per kg of body weight, LD50 compares fairly across animals of different sizes.
Comparing chemicals
- LD50 lets scientists rank chemicals by toxicity.
- A nerve toxin might have an LD50 of about 1 mg/kg.
- Table salt has an LD50 of thousands of mg/kg.
- The salt is far safer, and its high LD50 shows it.
A higher LD50 means a chemical is more toxic.
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False. LD50 is the dose that kills half a test population, so a higher LD50 means more of it is needed: the chemical is less toxic.
Select all true statements about LD50.
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LD50 measures toxicity; lower means more toxic. The last option reverses the relationship.
The one thing to get right: lower LD50 = more toxic. It feels backwards, so read it carefully. LD50 is the amount needed to kill — if only a tiny amount is needed (a low number), the substance is deadly; if a huge amount is needed (a high number), it's relatively safe. Number down, danger up.
Two substances compared:
- A nerve agent has an LD50 of about 1 mg/kg — a pinprick's worth can kill. Its low number screams "extremely toxic".
- Table salt has an LD50 of roughly 3000 mg/kg — you'd have to eat huge amounts to be poisoned. Its high number says "relatively safe".
- Same measure, opposite meaning: the smaller LD50 is the deadlier chemical.
LD50 (lethal dose, 50%) is the dose that kills half of a test population, measured per kg of body weight so it is fair across sizes. The key rule is inverse: a lower LD50 means a substance is more toxic (a tiny dose kills), and a higher LD50 means it is safer. It lets scientists rank chemicals by toxicity.