What Does Lethal Concentration 50 (LC50) Mean?
Lethal concentration 50 (LC50) is the concentration at which an airborne chemical will kill 50% of laboratory animals exposed to it under proper testing conditions.
A chemical’s LC50 value is often used as a representation of its acute toxicity.
Safeopedia Explains Lethal Concentration 50 (LC50)
To determine the LC50 of a chemical, a sample group of test animals is exposed to a given concentration of the substance over a set period of time (typically one to four hours). This group undergoes a single exposure and is then kept under clinical observation for 14 days.
Exposure to toxic chemicals in the workplace takes place by three major routes - through the mouth (oral), skin (dermal), and lungs (inhalation). The acute toxicity of chemical agents is based on the number of deaths that occur following acute exposure in animal tests.
The LC50 value is expressed as the weight of a substance per standard volume of air (mg/l) for vapors, dust, or mists; or as volume parts per million (ppmV) for gasses. Values for inhalation toxicity are based on four-hour tests in laboratory animals. Experimental values from a one-hour exposure test can be converted into a four-hour equivalent period.
The equation used for converting mg/l to ppm is: mg/l = ppm × molecular weight (MW) / 24,450
Values for Acute Inhalation Toxicity
A substance which has a vapor pressure greater than 300 kPa at 50°C, or is completely gaseous at 20°C at a standard pressure of 101.3 kPa. LC50 (4 hours) is equivalent to LC50 (1 hour) divided by a factor of 2.
A vapor is the gaseous form of a substance released from its liquid or solid state. The test atmosphere for some substances will be a combination of liquid or gaseous phases - for others, it will be almost entirely gaseous phases. Classification should be based on the cutoff value for gasses in units of ppmV. LC50 (4 hour) is equivalent to LC50 (1 hour) divided by a factor of 2.
Dust and Mists
Dusts are solid particles suspended in gas, usually air. Mists are liquid droplets that are likewise suspended in a gas, usually air. In either case, LC50 (4 hour) is equivalent to LC50 (1 hour) divided by a factor of 4.
The Difference Between LC50 and LD50
Lethal concentration 50 (LC50) and lethal dose 50 (LD50) are both parameters used to quantify the toxicity of a substance. Both indicate the concentration that proved fatal for 50% of the exposed sample population during testing.
The primary difference between the two is the route of exposure. LC50 represents the toxicity of an airborne substance, while LD50 represents the toxicity of a substance that has been swallowed, injected, or absorbed through the skin.