4.2 Signal Words, Toxicity Categories & Precautionary Statements

4.2 Signal Words, Toxicity Categories & Precautionary Statements

Quick Answer: EPA assigns every pesticide product a signal word based on its acute toxicity. The four toxicity categories (I–IV) drive the signal word — DANGER (or DANGER-POISON with a skull & crossbones for highly toxic products), WARNING, or CAUTION — and the specific precautionary statements on the front panel. Knowing the table is one of the most heavily tested label topics on the Michigan pesticide applicator exam.

The Basis: LD50 and LC50

EPA's toxicity categories are built on acute toxicity studies — the harm a single, short exposure causes. Two metrics drive the classification:

• LD50 (Lethal Dose 50) — the dose, in milligrams of substance per kilogram of test animal body weight (mg/kg), that kills 50% of a test population. Lower LD50 means higher toxicity.
• LC50 (Lethal Concentration 50) — the concentration in air or water, in milligrams per liter (mg/L), that kills 50% of a test population.

Six modes of acute exposure drive the category: oral, dermal, inhalation, primary eye irritation, primary skin irritation, and skin sensitization. The product's overall category is the most severe (lowest Roman-numeral) category across any of these modes — a product that is Category I by inhalation but Category III by oral route is labeled Category I.

The EPA Toxicity Category Table

Exam tip: Category I corrosive products (severe eye/skin damage) carry DANGER without the skull & crossbones; the skull & crossbones and the word POISON appear only when the product is highly toxic by oral, dermal, or inhalation route.

Signal Words in Detail

DANGER-POISON (Category I, highly toxic)

Used for products in Toxicity Category I by oral, dermal, or inhalation route. The label must display the word DANGER, the word POISON, and a skull-and-crossbones symbol. The first-aid statement on these labels is typically extensive — these products can cause serious injury or death from a single exposure.

DANGER (Category I, corrosive)

Used for products in Toxicity Category I because of corrosive eye or skin effects (irreversible damage). The label says DANGER but does not include the skull & crossbones. The statement may read "Corrosive — causes irreversible eye damage and skin burns."

WARNING (Category II, moderate)

Used for products in Toxicity Category II. The label must say WARNING, and the product is considered moderately toxic. The first-aid statement is required but shorter than for Category I.

CAUTION (Category III or IV)

CAUTION is used for Toxicity Category III (mildly toxic) and Toxicity Category IV (very low toxicity). Some Category IV products may have no signal word depending on the route. "Caution" is the lowest signal word.

Child Hazard Warning

The phrase "Keep Out of Reach of Children" is required on the front panel of essentially every pesticide product, under 40 CFR 156.66 — not only Category I and II products. EPA allows an exception only in the narrow case of a product whose packaging and marketing make exposure to children implausible, which almost never applies to products a certified applicator handles. A common exam distractor pairs the child hazard statement with a toxicity category; the statement is not category-dependent, while the signal word is.

Precautionary Statements

Precautionary statements expand on the signal word by describing the specific hazards and the actions that reduce them. EPA organizes precautionary statements into three groups:

1. Hazards to Humans and Domestic Animals

Describes the specific harm to people and pets and the PPE or practices that prevent it. Examples: "Causes skin irritation. Do not get on skin or clothing. Wear long-sleeved shirt, long pants, shoes, socks, and chemical-resistant gloves."

2. Environmental Hazards

Describes risks to non-target organisms — wildlife, aquatic organisms, bees, and endangered species. Examples: "This pesticide is toxic to fish and aquatic invertebrates. Do not apply directly to water, or to areas where surface water is present, or to intertidal areas below the mean high water mark."

In Michigan, environmental hazard statements interact with the Great Lakes watersheds — drift and runoff protection statements are particularly important given the state's extensive surface water.

3. Physical or Chemical Hazards

Describes flammability, explosivity, oxidizing potential, or corrosivity. Examples: "Do not use or store near heat or open flame," or "Corrosive — store in original corrosive-resistant container."

Statement of Practical Treatment (First Aid)

Also called the first-aid statement, this gives the immediate action for each exposure route — typically swallowed, inhaled, on skin, in eyes, and notes for a physician. For Category I products, the statement often includes a specific antidote note. Always call a poison control center (1-800-222-1222 nationwide) or a physician for any significant exposure, and have the label in hand when you call.

Reading Signal Words in the Field

Signal words tell you, at a glance, how much care a product demands:

• DANGER / DANGER-POISON — highest caution; consider substituting a lower-toxicity product, use full PPE, and have spill and emergency response ready.
• WARNING — moderate caution; standard PPE; careful mixing and loading.
• CAUTION — lowest acute toxicity; still follow all label PPE and use directions.

A common exam trap is to assume the signal word tells you about chronic (long-term) toxicity, environmental fate, or efficacy — it does not. The signal word reflects acute toxicity only. A Category IV product can still have chronic or environmental concerns that appear in the precautionary statements and environmental hazards sections.

Why This Matters for Michigan Applicators

Michigan's Part 83 of NREPA incorporates federal label law, so a signal-word violation is enforceable by MDARD as a state violation. MDARD inspectors routinely verify that applicators carry and use the PPE specified in the precautionary statements — the signal word is the trigger that tells you which PPE category applies. The exam tests the category table directly: expect questions like "Which signal word is used for Toxicity Category II?" and "Which category requires the skull-and-crossbones symbol?"