Toxicity of Pesticides

Hazard Indicator Categories

Most toxic/hazardous < > Least toxic/hazardous
I II III IV
Oral LD501=
0-50 mg/kg2

50-500 mg/kg

500-5,000 mg/kg

>5,000 mg/kg
Inhalation LC503=
0-0.2 mg/l4

0.2-2 mg/l

2-20 mg/l

>20 mg/l
Dermal (skin) LD501=
0-200 mg/kg

200-2,000 mg/kg

2,000-20,000 mg/kg

>20,000 mg/kg
Eye effects:
Corrosive: Corneal opacity not reversible within 7 days.

Corneal opacity reversible within 7 days. Irritation.

No corneal opacity. Irritation reversible within 7 days.

No irritation.
Skin effects:
Corrosive.

Severe irritation at 72 hours.

Moderate irritation at 72 hours.

Mild or slight irritation at 72 hours.
Signal words:
DANGER/POISON: in large boldfaced letters on the label and usually accompanied by skull and crossbones symbol.

WARNING: in large boldfaced letters.

CAUTION: in large boldfaced letters.

CAUTION: in large boldfaced letters.
Acute (single) oral dosage lethal to human adults:
Few drops to 1 teaspoon.

1 teaspoon to 2 Tablespoons.

1 ounce to 1 pint.

>1 pint


The Environmental Protection Agency has established four toxicity categories based on the LD50 and Eye and Skin effects of the various pesticides. The user's key to these toxicity categories is the signal words present on the front panel of the pesticide label. The following table summarizes these toxicity categories.

Toxicity is usually expressed as the acute oral LD50. "Acute oral" refers to a single dose taken by mouth or ingested. "Acute dermal" refers to a single dose applied directley to the skin (skin absorption). "Inhalation" refers to exposure through breathing or inhaling.

1 LD50= Abbreviation for the amount of toxicant (poison) needed to kill 50% of a test animal population. It is expressed in terms of weight of chemical per unit of body weight. LD50 is used to measure the acute oral and dermal toxicity of a chemical. The lower the LD50 value, the more poisonous the chemical. LD50 is not a measure of environmental hazard.

2 mg/kg = mg of chemical per kg of test animal body weight.

3 LC50 = Abbreviation for the amount of toxicant (poison) present in air or water. It is expressed in terms of parts per million (ppm) (mg/l). The lower the LC50 value, the more poisonous the chemical. LC50 is not a measure of environmental hazard.

4 mg/l = mg of chemical per liter of air or water.

Revised Sept 96

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