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What are signal words?
Signal words are found on pesticide product labels, and they describe the acute(short-term) toxicity of the formulated pesticide product. The signal word can be either:DANGER, WARNING or CAUTION. Products with the DANGER signal word are themost toxic. Products with the signal word CAUTION are lower in toxicity.1 The U.S. EnvironmentalProtection Agency (EPA) requires a signal word on most pesticide productlabels. They also require it to be printed on the front panel, in all capital letters,to make it easy for users to find. The only pesticide products that are not required todisplay a signal word are those that fall into the lowest toxicity category by all routesof exposure (oral, dermal, inhalation, and other effects like eye and skin irritation).2,3See the table below titled "Toxicity Category."
CAUTION means the pesticide product is slightly toxic if eaten, absorbed throughthe skin, inhaled, or it causes slight eye or skin irritation.2,4
WARNING indicates the pesticide product is moderately toxic if eaten, absorbedthrough the skin, inhaled, or it causes moderate eye or skin irritation.2,4
DANGER means that the pesticide product is highly toxic by at least one route of exposure. It may be corrosive, causing irreversibledamage to the skin or eyes. Alternatively, it may be highly toxic if eaten, absorbed through the skin, or inhaled. If thisis the case, then the word "POISON" must also be included in red letters on the front panel of the product label.2,4
| TOXICITY CATEGORY (Signal Word)2 | ||||
|---|---|---|---|---|
| High Toxicity (DANGER/Danger-Poison) Category I | Moderate Toxicity (WARNING) Category II | Low Toxicity (CAUTION) Category III | Very Low Toxicity (Optional Signal Word = CAUTION) Category IV | |
| Acute Oral LD50 | Up to and including 50 mg/kg (≤ 50 mg/kg) | Greater than 50 through 500 mg/kg (>50-500 mg/kg) | Greater than 500 through 5000 mg/kg (>500-5000 mg/kg) | Greater than 5000 mg/kg (>5000 mg/kg) |
| Inhalation LC50 | Up to and including 0.05 mg/L (≤0.05 mg/L) | Greater than 0.05 through 0.5 mg/L (>0.05-0.5 mg/L) | Greater than 0.5 through 2.0 mg/L (>0.5-2.0 mg/L) | Greater than 2.0 mg/L (>2.0 mg/L) |
| Dermal LD50 | Up to and including 200 mg/kg (≤200 mg/kg) | Greater than 200 through 2000 mg/kg (>200-2000 mg/kg) | Greater than 2000 through 5000 mg/kg (>2000-5000 mg/kg) | Greater than 5000 mg/kg (>5000 mg/kg) |
| Primary Eye Irritation | Corrosive (irreversible destruction ofocular tissue) or corneal involvement orirritation persisting for more than 21 days | Corneal involvement or othereye irritation clearing in 8 -21 days | Corneal involvement or othereye irritation clearing in 7days or less | Minimal effects clearing in less than 24 hours |
| Primary Skin Irritation | Corrosive (tissue destruction into thedermis and/or scarring) | Severe irritation at 72 hours(severe erythema or edema) | Moderate irritation at 72hours (moderate erythema) | Mild or slight irritation at72 hours (no irritation orerythema) |
How are signal words chosen?
Before the EPA can determine the appropriate signal word for a pesticide product, the manufacturer performs research onlaboratory animals to determine the toxicity of the formulation. Required studies include oral exposure (eating the product),inhalation exposure (breathing in the product), dermal exposure (spreading the product on the skin) and exposures to theskin and eyes to check for irritation. The study that shows the highest toxicity is used to determine the signal word.3 For example,if a product demonstrated low toxicity when eaten, moderate toxicity when inhaled, and high toxicity when appliedto skin, the EPA would assign the signal word DANGER, based on the most sensitive route of entry. In this example it was theskin.1
See the text box on LD50/LC50 for more details about the requiredtoxicity tests.
LD50/LC50: A commonmeasure of acute toxicity is the lethal dose (LD50) orlethal concentration (LC50) that causes death (resultingfrom a single or limited exposure) in 50 percent of the treatedanimals. LD50 is generally expressed as the dose inmilligrams (mg) of chemical per kilogram (kg) of bodyweight. LC50 is often expressed as mg of chemical pervolume (e.g., liter (L)) of medium (i.e., air or water) the organismis exposed to. Chemicals are considered highly toxic when theLD50/LC50 is small and practically non-toxicwhen the value is large. However, the LD50/LC50does not reflect any effects from long-term exposure (i.e., cancer,birth defects or reproductive toxicity) that may occur at levels belowthose that cause death.
How are signal words useful?
Signal words help alert users to special hazards of a pesticide product.The signal word can be used by shoppers to select the leasttoxic product(s) of those that are sufficiently effective.4
Regardless of the signal word on the pesticide product, it is importantto remember that every product still has the potential to poison(i.e., is harmful at high doses). Special care should be taken tocarefully follow all of the directions on the label, each time a pesticideproduct is used.
