Many people worry about pesticides in foods.
Pesticides are used to reduce damage to crops from weeds, rodents, insects and germs. This increases the yield of fruits, vegetables and other crops.
This article focuses on pesticide residues, or the pesticides found on the surface of fruits and vegetables when they are purchased as groceries.
It explores the most common types of pesticides used in modern farming and whether their residues affect human health.
What Are Pesticides?
In the broadest sense, pesticides are chemicals used to control any organism that might invade or damage crops, food stores or homes.
Because there are many kinds of potential pests, there are several kinds of pesticides. The following are some examples:
- Insecticides: Reduce destruction and contamination of growing and harvested crops by insects and their eggs.
- Herbicides: Also known as weed killers, these improve crop yields.
- Rodenticides: Important for controlling destruction and contamination of crops by vermin and rodent-borne diseases.
- Fungicides: Especially important for protecting harvested crops and seeds from fungal rot.
Developments in agricultural practices, including pesticides, have increased crop yields in modern farming by two to eight times since the 1940s (1).
For many years, the use of pesticides was largely unregulated. However, the impact of pesticides on the environment and human health has been under greater scrutiny since the publication of Silent Spring by Rachel Carson in 1962.
Today, pesticides are under much greater scrutiny from governmental and non-governmental organizations.
The ideal pesticide would destroy its target pest without causing any adverse effects to humans, non-target plants, animals and the environment.
The most commonly used pesticides come close to that ideal standard. However, they are not perfect, and their use does have health and environmental effects.
Summary: Pesticides aim to destroy pests without negatively affecting humans and the environment. Pesticides have gotten better over time, but none are perfect at providing pest control without side effects.
Types of Pesticides
Pesticides may be synthetic, meaning they’re created in industrial labs, or organic.
Organic pesticides, or biopesticides, are naturally occurring chemicals, but they may be reproduced in labs for use in organic farming.
Synthetic pesticides are designed to be stable, have a good shelf life and be easy to distribute.
They are also designed to be effective at targeting pests and have low toxicity to non-target animals and the environment.
Classes of synthetic pesticides include the following (2):
- Organophosphates: Insecticides that target the nervous system. Several of them have been banned or restricted due to toxic accidental exposures.
- Carbamates: Insecticides that affect the nervous system similarly to organophosphates, but they’re less toxic, as their effects wear off more quickly.
- Pyrethroids: Also affect the nervous system. They’re a laboratory-produced version of a natural pesticide that’s found in chrysanthemums.
- Organochlorines: Including dichlorodiphenyltrichloroethane (DDT), these have been largely banned or restricted due to negative effects on the environment.
- Neonicotinoids: Insecticides used on leaves and trees. They’re currently under scrutiny by the US EPA for reports of unintended harm to bees.
- Glyphosate: Known as a product called Roundup, this herbicide has become important in farming genetically modified crops.
Organic or Biopesticides
Organic farming makes use of biopesticides, or naturally occurring pesticide chemicals that have evolved in plants.
There are too many types to outline here, but the EPA has published a list of registered biopesticides.
Also, the US Department of Agriculture maintains a national list of approved synthetic and restricted organic pesticides.
Here are a few examples of important organic pesticides:
- Rotenone: An insecticide used in combination with other organic pesticides. It’s naturally produced as a beetle deterrent by several tropical plants and notoriously toxic to fish.
- Copper sulfate: Destroys fungi and some weeds. Although it’s classified as a biopesticide, it’s industrially produced and can be toxic to humans and the environment at high levels.
- Horticultural oils: Refers to oil extracts from various plants with anti-insect effects. These differ in their ingredients and potential side effects. Some can harm beneficial insects like bees (3).
- Bt toxin: Produced by bacteria and effective against several kinds of insects, Bt toxin has been introduced into some types of genetically modified organism (GMO) crops.
This list is not comprehensive, but it illustrates two important concepts.
First, “organic” does not mean “pesticide-free.” Rather, it refers to specialized kinds of pesticides that occur in nature and are used instead of synthetic pesticides.
Second, “natural” does not mean “non-toxic.” Organic pesticides can also be harmful to your health and the environment.
Summary: Synthetic pesticides are created in labs. Organic or biopesticides are created in nature, but may be reproduced in labs. Although natural, these are not always safe for humans or the environment.
How Are Pesticide Levels in Foods Regulated?
Multiple kinds of studies are used to understand what levels of pesticides are harmful.
Some examples include measuring levels in people who were accidentally exposed to too much pesticide, animal testing and studying the long-term health of people who use pesticides in their jobs.
This information is combined to create limits of safe exposures.
For example, the lowest dose of a pesticide causing even the most subtle symptom is called the “lowest observed adverse effect level,” or LOAEL. The “no observed adverse effect level,” or NOAEL, is also sometimes used (4).
Organizations like the World Health Organization, European Food Safety Authority, US Department of Agriculture and US Food and Drug Administration use this information to create a threshold for exposure that is considered safe.
To do this, they add an extra cushion of safety by setting thresholds 100–1,000 times lower than the LOAEL or NOAEL (4).
By being very cautious, regulatory requirements on pesticide use keep the amounts of pesticides on foods well below harmful levels.
Summary: Several regulatory organizations establish safety limits for pesticides in the food supply. These limits are very conservative, restricting pesticides to many times lower than the lowest dose known to cause harm.
How Reliable Are the Safety Limits?
One criticism of pesticide safety limits is that…