Any chemical substance is toxic if it is ingested or absorbed in excessive amounts. Table salt, for example, if consumed in excess, can be toxic. The degree of danger or hazard when using a pesticide is determined by multiplying toxicity by exposure.
Every pesticide has a LD50 value. The LD50 value identifies the dosage rate necessary to kill 50 percent of a test animal population. Lethal dose is expressed in milligrams of chemical per kilogram of body weight of the test population. The lower the LD50 value, the more toxic the material.
Pesticides that are dangerous in one exposure or a few exposures in a short period of time are considered to have acute toxicity. Acute pesticide exposure to a person can often result in pesticide poisoning.
Other pesticides that are dangerous in repeated smaller exposures throughout an extended amount of time are considered to have chronic toxicity. Long term exposure to a pesticide with chronic toxicity can result in health problems such as tumors, cancer, reproductive disorders, nerve damage, birth defects, endocrine system interference, and respiratory issues.
Signal words are written on every pesticide label to indicate relative toxicity to the user. The signal word is important as a toxicity indicator, but the route and length of exposure are other factors that also impact the risk of any pesticide.
CAUTION is the signal word for pesticides that are slightly toxic, and indicates two or more tablespoons are lethal.
WARNING is the signal word for pesticides that are moderately toxic. This signal word indicates it would take one teaspoon to two tablespoons to be lethal.
DANGER is the signal word for highly hazardous pesticides. When this word appears on the label, it indicates the pesticide is so highly toxic that only a few drops to one teaspoon full ingested orally is lethal to a human.
Pesticide labels contain safety information and other valuable information you must read and understand before using any product. You are required by law to follow pesticide label instructions and following instructions will help minimize the overall risk to you and the environment.