CEU Series: Take Into Account The Toxicity Of Pesticides

Farmers use pesticides as one means of controlling the weeds, diseases and insects that threaten their crops. It is estimated that is many instances, food production would fall by some 40% without pest control products. Pesticides are an important part of making sure Americans have access to an abundant supply of safe and healthy foods and agriculture will be able to meet the challenge of feeding a growing world population.

While farmers and consumers benefit from the use of crop protection products, pesticides do pose potential risks to users and consumers if not used correctly.

A pesticide may be defines as any substance used to control pests. Target pests may be insects, weeds, diseases, etc. Most pesticides control the pests by poisoning them. Pesticides can also be toxic (poisonous) to desirable plants and animals, including humans.

Some pesticides are so highly toxic that very small quantities can kill a person, while others are relatively non-toxic and almost any pesticide can make people ill if they are exposed to a sufficient amount. Because even fairly safe pesticides can irritate the skin, eyes, nose, or mouth, it is a good idea to understand how pesticides can be toxic so you can follow practices designed to reduce or eliminate your exposure and the exposure of others to them.

The most important thing to remember is that you should always use caution whenever you work with any pesticide!

Goals of This Module

  • Understand what toxicity is and how it affects humans.
  • Learn the three routes of entry (how pesticides enter the body) and the importance of each.
  • Be familiar with how toxicity is measured and what is meant by label warning statements.
  • Distinguish between acute and chronic toxicity.
  • Realize that the RISK posed by a pesticide is a function of TOXICITY X EXPOSURE

Toxicity refers to the ability of a substance to produce adverse effects or injury to a living system including the human body, or organs or metabolic systems of the body, such as the lungs or respiratory system. These adverse effects may range from slight symptoms such as headaches to severe symptoms like coma, convulsions, or death. Poisons work by altering normal body functions. Most toxic effects are naturally reversible and do not cause permanent damage if prompt medical treatment is sought. Some poisons, however, can cause irreversible (permanent) damage.

Toxicity represents the kind and extent of damage that can be done by a chemical. In other words, if you know the toxicity of a pesticide, you know “how poisonous” it is.
The effect of a pesticide is dependent on a number of factors. The most important factor is the dose-time relationship. Dose is the quantity of a substance that a human, plant, or animal is exposed to. Time means how often the exposure occurs.

Toxicity is usually divided into two types, acute or chronic, based on the number of exposures to a poison and the time it takes for toxic symptoms to develop. Acute toxicity is due to short-term exposure and happens within a relatively short period of time, whereas chronic exposure is due to repeated or long-term exposure and happens over a longer period. It is important that pesticide applicators know and understand the difference between acute and chronic toxicity.

Acute toxicity refers to how poisonous a pesticide is to a human, animal, or plant after a single short-term exposure. Acute toxicity is used to describe effects which appear right away or within 24 hours of exposure. A pesticide with a high acute toxicity may be deadly even when a very small amount is absorbed by the body. Acute toxicity levels are used as a way to assess and compare how poisonous pesticides are. The acute toxicity of a pesticide is used as the basis for the signal words (DANGER, WARNING, and CAUTION) which appear on every pesticide label. Acute toxicity may be measured as acute oral toxicity, acute dermal toxicity, and acute inhalation toxicity.
Chronic toxicity is the delayed poisonous effect from exposure to a substance. Chronic toxicity of pesticides concerns the general public, as well as those working directly with pesticides because of potential exposure to pesticides on/in food products, water, and the air. It is measured in experimental conditions after three months of either continuous or occasional exposure.

Label Identification Of Acute and Chronic Toxicity

To alert pesticide users to the acute toxicity of a pesticide, the Environmental Protection Agency requires signal words to be placed on the label. Signal words are used to tell the user whether the chemical is highly toxic (DANGER), moderately toxic (WARNING), slightly toxic, or relatively non-toxic (CAUTION). These label warnings are based on the chemical’s acute toxicity. Pesticide products classified as toxicity category I based on acute oral, acute dermal, or acute inhalation toxicity studies will have the signal word DANGER on the label plus the word “POISON” and the skull and crossbones symbol. If the chemical is highly likely to cause severe skin or eye irritation, the label will bear the signal word DANGER but will not display the word POISON or the skull and crossbones symbol.Danger_poison_sign

In some cases, the acute oral and acute dermal toxicity of a pesticide may be in the slightly toxic category. But if the acute inhalation toxicity is in the highly toxic category, the pesticide label will have the signal words for a highly toxic pesticide. The degree of eye or skin irritation caused by the pesticide also influences the signal word.

The following table indicates the four categories of pesticide toxicity:

Categories of Acute Toxicity
*Not used for skin and eye irritation effects
LD50 LD50 LC50
Category Signal Word Required on Label Oral  mg/kg Dermal mg/kg Inhalation mg/l Oral lethal dose
I. Highly toxic DANGER [Poison +  Skull & Crossbones] * 0 to 50 0 to 200 0 to 0.2 A few drops to 1 teaspoonful [or a few drops on the skin]
II. Moderately Toxic WARNING 50 to 500 200 to 2,000 0.2 to 2 More than a teaspoonful to one ounce
III. Slightly Toxic CAUTION 500 to 5,000 2,000 to 20,000 2.0 to 20 More than one ounce to one pint or one pound
IV. Relatively Non-toxic CAUTION 5,000 + 20,000 + Greater than 20 + More than one  pint or one pound

For chronic toxicity, there is no comparable set of signal words like those used for acute toxicity. Instead, a statement identifying the specific chronic toxicity problem is sometimes used on the label. Such a statement might read “This product contains (name of chemical), which has been determined to cause tumors or birth defects in laboratory animals.” Chronic toxicity warning statements may be accompanied by label directions to wear certain kinds of protective clothing when handling or working with the pesticide to minimize or eliminate exposure to the pesticide.

It is important to read the label to look for signal words identifying the product’s acute toxicity and for statements identifying any chronic toxicity problem. A pesticide may be low in acute toxicity (signal word CAUTION), but it may have a label statement identifying potential chronic toxicity.

A material that has high acute toxicity does not necessarily have high chronic toxicity. Conversely, a chemical with low acute toxicity does not necessarily have low chronic toxicity. For many pesticides, the toxic effects following single acute exposures are quite different from those produced by chronic exposure.

For example, large amounts of the pesticide cryolite are eaten by rats at one time little or no harmful effects will be observed. It quickly passes through the intestinal tract and is eliminated without harmful effects. However, if rats are fed small amounts of cryolite every day in their feed, they become ill and die. Cryolite is a very insoluble compound, meaning that it does not readily dissolve. The small amount of chemical that is absorbed from a one-time exposure is not sufficient to cause illness, but absorption of the same small amount every day, day after day, can cause chronic illness and death. The effects of both acute toxicity and chronic toxicity are dose-related; the greater the dose, the greater the effect.

The hazard posed by pesticides or risk of harm from pesticide exposure is equal to how poisonous the pesticide is, multiplied by the amount and route of exposure to the pesticide, or: RISK = TOXICITY X EXPOSURE

While you cannot change the inherent toxicity of pesticides, an applicator or handler can limit the possibility of poisoning by preventing and/or limiting exposure.

Pesticide users can limit exposure by using the personal protective equipment (PPE) proscribed by the label. Washing hands and exposed skin frequently when using pesticides especially before, eating, drinking, smoking or using the restroom. It is also important that pesticide applicators and handlers, change their clothing and shower immediately after working with pesticides to reduce the amount of time they may be exposed to pesticides.

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4 comments on “CEU Series: Take Into Account The Toxicity Of Pesticides

  1. I am not a big fan of using dogs for experiments. rodents are a different story. I am rather enjoying these articles.

  2. i have relearned a lot about absorbing chemicals through the skin, i must be very careful and cover all areas of exposed skin on my arms and legs due to unhealthy skin condition. i enjoyed this articles very much

  3. this was a lot of information to absorb, however it was very informative and reminded me how important it is to use PPE and make sure to follow the label.

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