Toxicity and Reactions

Maggie Scarbrough

Pesticides’ ability to cause harmful effects is toxicity. It is dependent on the type and amount of active ingredients, type and amount of carrier and solvent ingredients, type and amount of inert ingredients and the type of formulation.


To test toxicity, lab animals are exposed to different amounts of chemicals for different periods of times. Effects on humans are estimated based on these results, although effects will vary according to the individual. Some people will be highly sensitive and some are sensitive to particular groups of chemicals.


When you have a choice of pesticides, consider toxicity and the population that will be exposed.


Acute, delayed and allergic effects are all harmful effects of pesticides. An acute effect is an illness or injury that occurs immediately after exposure, usually within a day. Delayed effects are more difficult to measure than those that appear directly after exposure. Acute effects are simpler to treat and more easily recognizable. There are four types of acute effects: acute oral, acute inhalation, acute dermal and acute eye.


Once a pesticide is consumed the acute effect will either be the burning of your mouth, throat and stomach or absorption by your blood stream that will carry the chemical to all parts of your body. Just a few drops of some pesticides can make it difficult to eat and drink.


Acute inhalation effects are similar to oral effects. They can burn your respiratory system, making it difficult to breath and they can be carried by your blood throughout your body.


Harm to your skin may include cracking, blistering, itching and color change. Dermal effects may also include entrance of chemicals into your bloodstream after being absorbed through the skin.


Acute eye effects include permanent or temporary blindness. Chemicals again can enter your bloodstream, by way of your eyes.


The onset of delayed effects occurs after 24 hours. Some delayed effects are considered chronic. Repeated exposures to certain pesticides over extended periods of time may cause delayed effects. Other times a single exposure to a particular pesticide may cause a delayed effect.


Sometimes a large amount of pesticide may cause an acute effect while smaller amounts of the same chemical over a period of time will cause a delayed effect. The smaller exposure can show no symptoms at first, but a build up in the body of the chemical will cause a delayed, and often chronic, effect.


If a person is exposed to two different chemicals, they may become ill due to the effect of those two chemicals combined. This may happen even though one of those chemicals may not cause specific harm on its own.


Sometimes one chemical may cause damage after a single exposure and a period of time has passed. Some herbicides can destroy lung cells as long as 3 to 14 days after exposure. Other times a particular set of circumstances is necessary to make a chemical cause a particular harmful effect. Those delayed effects include chronic effects, developmental and reproductive effects, and systemic effects.


Illnesses or injuries that appear after a long period of time are known as chronic effects. Tumors, cancer and changes in genes or chromosomes are some of the delayed effects linked to chronic toxicity. Pesticide labeling will include precautionary statements that specifically address these possibilities.


Illness or injury to a fetus still in the womb of a woman exposed to pesticides is considered a developmental effect. They also include birth defects and illness or death. Infertility, sterility, and impotence are reproductive effects experienced when an injury occurs to the reproductive system of an exposed man or woman.


Developmental and reproductive effects are usually immediate, though may not be apparent for some time. For example, a birth defect may not be detected until after delivery. Repeated exposures over time may also cause developmental or reproductive effects. Labeling will also warn of these consequences.


An illness or injury to a bodily system that does not appear in the first 24 hours is a delayed systemic effect. These can include nerve and/or brain disorders like paralysis, tremor, and blindness, blood disorders like anemia, lung or respiratory disorder like asthma, skin disorders like rash and discoloration and liver or kidney disorders like jaundice. Again, labels will warn of these specific effects.


Delayed effects are difficult to determine for a variety of reasons including the time between exposure and onset, and the possibility of other exposures. Also, lab testing still doesn’t accurately reflect all human effects. If there is clear evidence of specific delayed effects, the Environmental Protection Agency will take steps to help reduce these. They might remove a particular pesticide from the market, require dosage changes, require specific protective gear for application, require new warning labels or restrict use to certified applicators.


While the EPA and research scientists strive to reduce known risks, all risks of pesticide applications cannot be fully known. Therefore it is essential to take any and all possible precautions and heed pesticide labels