what is LD50?

In many Material Safety Data Sheets we see LD50 , What is LD50 ?

Definition of LD50 given in IMDG Code is “LD50 (median lethal dose) for acute oral toxicity is the statistically derived single dose of a substance that can be expected to cause death within 14 days in 50 per cent of young adult albino rats when administered by the oral route. The LD50 value is expressed in terms of mass of test substance per mass of test animal (mg/kg).”

The hazard symbol for toxic/highly toxic subst...
The hazard symbol for toxic/highly toxic substances according to directive 67/548/EWG by the European Chemicals Bureau. (Photo credit: Wikipedia)

Which means the amount of a substance required to kill at least 50% test animal when administered orally (in above case) with respect to their body weight.

LD50 is issued for toxicity in oral and dermal route and LC50 is used for toxicity in inhalation route.

Let us see some examples of LD50 which can kill 50% of adult albino rats compared to humans

LD50 for paracetamol is 1.944g , over dosage may cause death due to liver failure.

However this is not an absolute figure some may be killed with much less dosage than LD50 and some may survive much higher dosage.  These LD50 figures assist the experts in predicting toxicity giving a safe margin in practical applications.

LC50 – Lethal Concentration is also measured in same way for inhalation toxicity.

Skull and crossbones
Skull and crossbones (Photo credit: Wikipedia)


LD50 for acute dermal toxicity is that dose of the substance which, administered by continuous contact for 24 hours with the bare skin of the albino rabbit, is most likely to cause death within 14 days in one half of the animals tested. The number of animals tested shall be sufficient to give a statistically significant result and be in conformity with good pharmacological practices. The result is expressed in milligrams per kilogram body mass.


LC50 for acute toxicity on inhalation is that concentration of vapour, mist or dust which, administered by continuous inhalation to both male and female young adult albino rats for one hour, is most likely to cause death within 14 days in one half of the animals tested. A solid substance shall be tested if at least 10% (by mass) of its total mass is likely to be dust in the respirable range, such as the aerodynamic diameter of that particle fraction is 10 microns or less. A liquid substance shall be tested if a mist is likely to be generated in a leakage of the transport containment. For both solid and liquid substances, more than 90% (by mass) of a specimen prepared for inhalation toxicity testing shall be in the respirable range as defined above. The result is expressed in milligrams per litre of air for dusts and mists or in millilitres per cubic metre of air (parts per million) for vapours.

Toxicity Classification for Sea Transport

Refer IMDG Code chapter 2.6 for classification criteria of toxic substances for sea transport.