Lethal Dosage (LD50) Values

An LD50 is a standard measurement of acute toxicity that is stated in milligrams (mg) of pesticide per kilogram (kg) of body weight. An LD50 represents the individual dose required to kill 50 percent of a population of test animals (e.g., rats, fish, mice, cockroaches). Because LD50 values are standard measurements, it is possible to compare relative toxicities among pesticides. The lower the LD50 dose, the more toxic the pesticide.

A pesticide with an LD50 value of 10 mg/kg is 10 times more toxic than a pesticide with an LD50 of 100 mg/kg.

The toxicity of a pesticide is related to the mode of entry of the chemical into an organism. Oral LD50 values are obtained when test subjects are fed pesticide-treated feed or water. Dermal LD50 values are obtained when the pesticide is applied to the skin of the animal. Inhalation LD50 values are obtained when the animal breathes the pesticide with a mask. Often the inhalation LD50 is lower (more toxic) than the oral LD50, which is in turn lower (more toxic) than the dermal LD50.

LD50 values are not always given on the pesticide label; rather, the relative toxicity of a pesticide product is reflected by one of three signal words: DANGER, WARNING, or CAUTION. The purpose of signal words is to alert the user to the level of toxicity of the product. The signal word is generally assigned based on the pesticide's inhalation, oral or dermal toxicity, whichever is the most toxic.

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