Pesticide User's Guide

Bulletin 745

Relative Toxicity of Pesticides

The toxicity of pesticides is based upon the LD50s (lethal dose required to kill 50 percent of the test population within 14 days after an exposure to the concentration of chemical) of the pesticide formulation related to oral, dermal, and inhalation exposure (See Table 1). The required warning words and signs and precautionary statements or acceptable modifications mandatory on all labels relative to the toxicity category of the pesticide formulation are listed in Table 2. Every pesticide must be labeled "Keep Out of Reach of Children." Additional information required on the label denotes environmental hazards and physical or chemical hazards.

Table 1. Toxicity Categories for Pesticides
Hazard Indicators	I	II	III	IV
Oral LD50	Up to and including 50 mg/kg.	From 50 through 500 mg/kg	From 500 through 5,000 mg/kg.	Greater than 5,000 mg/kg.
Inhalation LC50: (a) Dust or mist	Up to and including 2.0 mg/l.	From 2.0 through 20 mg/l.	From 20 through 200 mg/l.	Greater than 200 mg/l.
Inhalation LC50: (b) Gas or vapor	Up to and including 200 p/m.	From 200 through 2,000 p/m.	From 2,000 through 20,000 p/m.	Greater than 20,000 p/m.
Dermal LD50	Up to and including 200 mg/kg.	From 200 through 2,000 mg/kg.	From 2,000 through 20,000 mg/kg.	Greater than 20,000 mg/kg.
Eye effects	Irreversible corneal opacity at 7 days.	Corneal opacity reversible within 7 days or irritation persisting for 7 days.	No corneal opacity irritation reversible within 7 days.	No irritation.
Skin irritation	Severe irritation or damage at 72 hours.	Moderate irritation at 72 hours.	Mild or slight irritation at 72 hours.	No irritation at 72 hours.

The organophosphate type of insecticides (examples parathion and malathion) vary greatly in their toxicity and hazard to man. Many of the most toxic insecticides belong to this group. Because they are more readily broken down in the environment, some phosphate insecticides such as parathion are now being used to replace many of the more persistent organochlorine (or chlorinated hydrocarbon) insecticides. Likewise, the carbamate insecticides (examples - Temik and Sevin) are similar to the organophosphates in their toxicity range.

Organochlorine insecticides are generally less hazardous to handle but, due to their greater stability, may create more of an environmental pollution and residue problem than the organophosphates or the carbamates.

In general, herbicides and fungicides are less toxic than many of the other types of pesticides. However, because of current concern about the possibilities of chronic health problems and environmental effects, including ground water contamination, many of those that have been commonly used in the past are now under EPA review. Some herbicides such as the arsenicals are not particularly hazardous by skin contact, but are very toxic stomach poisons. Paraquat, which is a widely used herbicide in minimum tillage systems, must be considered highly toxic when ingested, with the potential of causing respiratory failure. It can also enter the body via skin exposure if skin openings or lesions permit excessive penetration. Paraquat requires the use of protective clothing and equipment, including protective gloves and boots, apron, goggles, respirator or approved mask, close woven coveralls or a rubber spray suit and a suitable head covering. Any oral ingestion of paraquat requires that the recipient receive immediate medical attention.

Poisonings due to fungicides are uncommon, although there is some concern by EPA of the long time chronic effects. Most incidents of poisoning from fungicides involve the misuse of treated seed as a feed. Earlier incidents associated with the misuse of organic mercury compounds are no longer encountered because of the suspension of registration and use of such materials in the early 1970s.

Know the pesticides you use and follow carefully the precautions listed on the pesticide product label. Table 3 gives the relative acute toxic exposure hazards to the applicator of some of the more common pesticides. They could be classified quite differently, if we considered the hazard from accidental ingestion, a potential problem often resulting from improper storage, or the Risk Evaluations based upon EPA's review of the registration.

Table 2. Required Signal Words and Precautionary Statements by Toxicity Category
Toxicity Category	Signal Word	Oral, Inhalation, or Dermal Toxicity	Skin and Eye Irritation
I	DANGER POISON (In Red) and Skull and Crossbones (if toxicity category based on oral, dermal, or inhalation)	Poisonous if swallowed (inhaled or absorbed through skin). Do not get in eyes, on skin, or on clothing. (Front panel statement of practical treatment required.)	Corrosive, causes eye and skin damage (or skin irritation). Do not get in eyes, on skin, or on clothing. Wear goggles or face shield and rubber gloves when handling. Harmful or fatal if swallowed. (Appropriate first aid statement required. )
II	WARNING	May be fatal if swallowed (inhaled or absorbed through the skin). Do not breathe vapors (dust or spray mist). Do not get in eyes, on skin, or on clothing. (Appropriate first aid statement required.)	Causes eye (and skin) irritation. Do not get in eyes, on skin, or on clothing. Harmful if swallowed. (Appropriate first aid statement required.)
III	CAUTION	Harmful if swallowed (inhaled or absorbed through the skin). Avoid breathing vapors (dust or spray mist). Avoid contact with skin (eyes or clothing). Appropriate first aid statement required.)	Avoid contact with skin, eyes, or clothing. In case of contact immediately flush eyes or skin with plenty of water. Get medical attention if irritation persists.
IV	CAUTION	(No caution statement required.)	(No caution statement required.)
Child hazard warning "KEEP OUT OF REACH OF CHILDREN" required on the front panel of every pesticide label unless circumstances warrant waiver by EPA Administrator.