Pesticides come from three broad sources: plants and minerals found in nature, synthetic chemicals built from petroleum, and living microorganisms like bacteria and fungi. The balance between these sources has shifted dramatically over time. Today, roughly 99% of synthetic chemicals, including most pesticides on the market, are derived from fossil fuels.
The Oldest Pesticides Were Natural
Pest control is nearly as old as agriculture itself. Ancient Sumerians were using sulfur compounds to kill insects as far back as 2500 B.C. By the 1600s and 1700s, farmers across Europe and Asia had expanded their toolkit to include tobacco, arsenic, herbs, and other plant-based preparations. These early pesticides worked, but they were inconsistent in strength and limited in supply.
Several plants produce chemicals that are naturally toxic to insects, and humans figured this out long before anyone understood the chemistry involved. The pyrethrum daisy produces compounds called pyrethrins in its dried flowers that attack insect nervous systems on contact. Tobacco plants produce nicotine, which mimics a chemical messenger in insect brains and overstimulates their nerve cells. The roots of certain tropical legumes contain rotenone, which disrupts energy production in insect cells. Neem tree seeds contain a compound that stops insects from feeding and reproducing. All of these plant-derived pesticides are still used today, though most have been largely replaced by synthetic versions.
How Synthetic Pesticides Are Made
The synthetic pesticide era began in the late 1800s and early 1900s, when chemists developed the first organic compounds designed specifically to kill insects. The earliest were organochlorines, a family of chemicals made from organic molecules bonded to chlorine atoms. DDT, chlordane, and lindane all belong to this group. After World War II, pesticide production scaled up rapidly, drawing on the same industrial chemistry infrastructure that had been built for wartime chemical manufacturing.
Most synthetic pesticides start as hydrocarbons pulled from petroleum. These hydrocarbon feedstocks are then combined with other elements, including chlorine, oxygen, sulfur, phosphorus, nitrogen, and bromide, to create chemical intermediates. Those intermediates are further processed into the active ingredients found in finished pesticide products. Major petroleum companies like ExxonMobil, ChevronPhillips Chemical, and Shell all produce pesticides or their chemical precursors.
Over the decades, chemists developed several distinct chemical families, each designed to attack pests in a different way:
- Organophosphates are built around a central phosphorus atom. They account for roughly half of all insecticides used worldwide and work by blocking an enzyme that insect muscles need to relax, causing paralysis.
- Carbamates have a similar mechanism but use a carbamate group instead of phosphorus. About 50 different chemicals belong to this family, and they’re used not just as insecticides but also as fungicides and herbicides.
- Pyrethroids are synthetic versions of the pyrethrins found in chrysanthemum flowers. The first one, allethrin, was created in 1949 by modifying the natural pyrethrin structure to make it more potent and longer lasting.
- Neonicotinoids are the newest major class, chemically similar to nicotine. They target the same nerve receptors in insects that nicotine does. One neonicotinoid, imidacloprid, is among the most widely used insecticides in the world today.
Biopesticides: A Third Category
Not all modern pesticides come from petroleum or plant extracts. Biopesticides are derived from natural materials like bacteria, fungi, viruses, minerals, and even common food ingredients. Canola oil and baking soda both have pesticidal applications and qualify as biopesticides. Insect sex pheromones, which are synthetic copies of the scent chemicals insects use to find mates, can be used to lure pests into traps or disrupt their breeding.
The most widely used biopesticide is a soil bacterium called Bacillus thuringiensis, or Bt. Different strains of Bt produce proteins that are toxic to specific groups of insects when eaten. One strain kills caterpillars, another kills mosquito larvae, another targets beetle grubs. Because each strain is highly targeted, Bt generally leaves beneficial insects unharmed. It’s used in both organic and conventional farming and has even been engineered directly into certain crop varieties.
What’s Actually in a Pesticide Product
A bottle of pesticide from the hardware store or a commercial farm supply isn’t pure active ingredient. Every pesticide product contains two types of components: the active ingredient that actually kills or repels the pest, and “inert” ingredients that do everything else. Inert ingredients can include solvents that help the active ingredient dissolve, surfactants that help it stick to plant surfaces, stabilizers that keep it from breaking down in the bottle, and carriers that make it easier to spray.
The term “inert” is misleading. It’s a legal designation, not a safety claim. Inert ingredients can include common food commodities like edible oils, spices, and herbs, but they can also be synthetic chemicals. Under federal law, manufacturers must list the active ingredient by name and percentage on the label. For inert ingredients, only the total combined percentage is required. The specific identity of each inert ingredient is considered confidential business information and doesn’t have to be disclosed.
How Pesticides Enter the Environment
Regardless of their source, pesticides rarely stay exactly where they’re applied. They move into the broader environment through three main pathways. Spray drift carries dust or droplets through the air during or shortly after application, depositing pesticide on unintended areas like neighboring fields, waterways, or homes. Runoff washes pesticides off treated surfaces during rain or irrigation, carrying them into streams, rivers, and drainage systems. Volatilization turns certain pesticides into vapor after application, allowing them to travel through the atmosphere for hours or even days before settling elsewhere.
These pathways mean that even pesticides applied carefully on a single field can end up in soil, water, and air well beyond the target area. The degree of spread depends on the pesticide’s chemical properties, the weather, the application method, and the landscape.
How Pesticides Get Approved
Before any pesticide can be sold in the United States, the EPA must evaluate it and grant a registration, which functions as a license for distribution, sale, and use. The company seeking approval must submit studies covering product chemistry, human health hazards, risks to animals and wildlife, environmental fate (how quickly the chemical breaks down in soil and water), residue levels on food, exposure risks for the people applying it, and spray drift potential. These requirements are codified in federal regulations and form the scientific basis for determining whether a pesticide meets safety standards for both people and the environment.