pesticide
Meaning of pesticide: Grouped by what they are meant to kill rather than by what they are, which is why the class name predicts almost nothing.
Definition of pesticide
A pesticide is any substance made to kill, repel or control an organism treated as a pest. The group covers insecticides, herbicides aimed at plants, fungicides, rodenticides and several smaller classes, united by purpose rather than by chemistry. Because the chemistry differs completely from class to class, so do the effects on people, and nothing generalizes from one to another.
What are the main classes?
| Class | Target | Chemical groups within it |
|---|---|---|
| Insecticide | Insects | Organophosphates, carbamates, pyrethroids, neonicotinoids |
| Herbicide | Unwanted plants | Glyphosate, phenoxy compounds, bipyridyls |
| Fungicide | Molds and fungi | Dithiocarbamates, azoles |
| Rodenticide | Rats and mice | Compounds that block the vitamin K needed for clotting |
The rows describe the target organism, not the mechanism, and the chemistry within one row varies as much as it does between rows. Organophosphate insecticides block the enzyme that clears the nerve messenger acetylcholine, so signals never switch off; the same enzyme exists in people, and acute poisoning produces a distinctive picture of watering eyes, salivation, tiny pupils, vomiting and muscle twitching. Anticoagulant rodenticides act through vitamin K exactly as some prescribed blood thinners do. Pyrethroids, by contrast, are far more toxic to insects than to mammals. The boundary with treatment is not sharp either, since permethrin, a pyrethroid, is applied to skin as a medicine for scabies and head lice.
How does contact happen?
Occupational exposure is the heaviest, and it comes mainly through skin and inhaled spray during mixing and application rather than through swallowing. Residue on food is the route that reaches everyone else, at levels far lower and regulated against limits set for each compound. Household use, drift from nearby land, and contaminated dust and water fill in the rest. Deliberate swallowing of concentrated product remains a large cause of poisoning deaths worldwide, which is one reason several of the most acutely toxic compounds, the herbicide paraquat among them, have been restricted or withdrawn in many countries.
What is known about the health effects?
Acute poisoning is well characterized and specific to the chemical group involved, and antidotes exist for some groups and not others. Long-term low-level exposure is far harder to study, because the dose is rarely measured, exposures are mixed, and any effect takes decades to surface. Research has concentrated on certain cancers, on Parkinson disease, on the developing brain and on fertility, and the weight of evidence differs sharply between individual compounds rather than applying to pesticides as a whole. Regulators reassess compounds as evidence accumulates, and several once used widely have since been withdrawn on that basis.
Used in a sentence
The occupational history included questions about pesticide exposure as part of the evaluation.
Good to know
Because pesticides differ enormously in chemical structure and mechanism across classes such as insecticides, herbicides and rodenticides, their effects on the human body vary correspondingly and cannot be generalized from one class to another.
Word origin
Where “pesticide” comes from
Formed from pest, referring to a harmful organism, and the suffix -cide, from Latin caedere, meaning to kill.