An infographic describing how the signal word tells you if a pesticide product
is low, medium, or high in toxicity. Also available in Spanish.
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 the
most toxic. Products with the signal word CAUTION are lower in toxicity.1
The U.S. Environmental
Protection Agency (EPA) requires a signal word on most pesticide product
labels. 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 to
display a signal word are those that fall into the lowest toxicity category by all routes
of exposure (oral, dermal, inhalation, and other effects like eye and skin irritation).2,3
See the table below titled "Toxicity Category."
CAUTION means the pesticide product is slightly toxic if eaten, absorbed through
the skin, inhaled, or it causes slight eye or skin irritation.2,4
WARNING indicates the pesticide product is moderately toxic if eaten, absorbed
through 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 irreversible
damage to the skin or eyes. Alternatively, it may be highly toxic if eaten, absorbed through the skin, or
inhaled. If this
is the case, then the word "POISON" must also be included in red letters on the front panel of the product
label.2,4
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 of
ocular tissue) or corneal involvement or
irritation persisting for more than 21 days
Corneal involvement or other
eye irritation clearing in 8 -
21 days
Corneal involvement or other
eye irritation clearing in 7
days or less
Minimal effects clearing in less than 24 hours
Primary Skin Irritation
Corrosive (tissue destruction into the
dermis and/or scarring)
Severe irritation at 72 hours
(severe erythema or edema)
Moderate irritation at 72
hours (moderate erythema)
Mild or slight irritation at
72 hours (no irritation or
erythema)
How are signal words chosen?
Before the EPA can determine the appropriate signal word for a pesticide product, the manufacturer performs
research on
laboratory 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 the
skin 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
applied
to skin, the EPA would assign the signal word DANGER, based on the most sensitive route of entry. In this
example it was the
skin.1
See the text box on LD50/LC50 for more details about the required
toxicity tests.
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 least
toxic product(s) of those that are sufficiently effective.4
Regardless of the signal word on the pesticide product, it is important
to remember that every product still has the potential to poison
(i.e., is harmful at high doses). Special care should be taken to
carefully follow all of the directions on the label, each time a pesticide
product is used.
LD50/LC50: A
common measure of acute toxicity is the lethal dose (LD50) or lethal concentration
(LC50) that
causes death (resulting from a single or limited exposure) in 50 percent of test animals.
LD50
is generally expressed as the dose in milligrams (mg) of chemical per kilogram (kg) of body
weight. LC50 is often expressed as mg of chemical per volume (e.g., liter (L)) of
medium (i.e.,
air or water) the animal is exposed to. Chemicals are considered highly toxic when the
LD50/LC50
is small and less toxic when the value is large.
Where can I get more information?
NPIC aims to use the best scientific resources available at the time fact sheets are written. NPIC does not have the resources to keep all of its fact sheets entirely up to date. All NPIC documents indicate when the material was last updated. For more information on how NPIC selects scientific resources, visit our web page Writing NPIC Fact Sheets.
Whitford, F. The Complete Book of Pesticide Management: Science, Regulation, Stewardship, and
Communication;
Wiley & Sons: New York, 2002; pp 450-452.
National Pesticide Applicator Certification Core Manual; Randall, C., Hock, W., Crow, E.,
Hudak-Wise, C., Kasai, J.,
Eds.; National Association of State Departments of Agriculture Research Foundation: Washington, DC,
2006.
Label Review Manual; U.S. Environmental Protection Agency, Office of Prevention,
Pesticides,
and Toxic
Substances, Office of Pesticide Programs, U. S. Government Printing Office: Washington, DC, 2007.
https://www.epa.gov/sites/default/files/2018-04/documents/chap-07-mar-2018.pdf (accessed June 2008),
updated
Aug 2007.
Labeling Requirements for Pesticides and Devices. Code of Federal Regulations, Part
156.64,
Title 40, 2007.
NPIC fact sheets are designed to answer questions
that
are
commonly
asked by the public about pesticides that are regulated by the
U.S. Environmental Protection Agency (US EPA). This document is
intended to be educational in nature and helpful to consumers for
making decisions about pesticide use.
