Pesticide toxicology: organochlorines, botanicals and herbicides

How insect and weed killers such as DDT, pyrethrins, glyphosate and paraquat harm people, and why pesticide poisoning matters so much in Colombia.

Updated Nov 12, 2026

Pesticides are designed to kill living things, so many are toxic to people too. Insecticides are generally more toxic to humans than herbicides, but the herbicide paraquat is one of the deadliest poisons in agriculture. This page covers organochlorine and botanical insecticides and the main herbicides; organophosphates and carbamates are covered with the cholinergic toxidrome.

Key points

Organochlorines such as DDT keep sodium channels open, causing tremor and seizures; they persist for years and build up in fat and food chains.
Pyrethrins and synthetic pyrethroids act on nerve ion channels and can cause seizures if enough is absorbed; they are strong irritants; rotenone mainly irritates.
Chlorophenoxy herbicides (2,4-D) have low acute toxicity but can cause coma and muscle weakness in large ingestions; old 2,4,5-T was contaminated with dioxin.
Glyphosate is the world's most used herbicide; poisoning is mostly from its surfactant formulations, and IARC classifies it as probably carcinogenic (group 2A).
Paraquat concentrates in the lung and generates free radicals, causing delayed, often fatal lung fibrosis; extra oxygen can worsen the injury.
In Colombia, pesticides caused most deaths from acute chemical poisoning in 2024, and paraquat was the leading agent in completed suicides.

Organochlorine insecticides (DDT and relatives)

The group includes DDT and its analogues, benzene hexachlorides such as lindane, and the cyclodienes. They slow the closing of sodium channels in nerve membranes, so neurons fire repeatedly; the result is central nervous system stimulation. With DDT, tremor is often the first sign and seizures may follow; with the other compounds seizures can come first. There is no specific antidote, so treatment is supportive. These compounds are fat-soluble, slowly broken down and persistent in soil and water, and they accumulate up food chains; DDT's metabolite DDE is still found in people decades after most countries banned DDT. They are also endocrine disruptors (see persistent environmental pollutants).

Botanical insecticides

Pyrethrum is a flower extract with six insecticidal esters (pyrethrins); synthetic pyrethroids such as permethrin are now a large share of world pesticide use.
Absorbed in large amounts, by inhalation or ingestion, they act on the central nervous system through sodium, calcium and chloride channels, causing excitation, seizures and paralysis; treatment is symptomatic, and they are strong irritants.
Rotenone, from Derris and Lonchocarpus roots, irritates the gut, eyes, skin and airways when swallowed or contacted; treatment is symptomatic.
Nicotine stimulates and then blocks nicotinic receptors; neonicotinoids are related synthetic insecticides used in agriculture.

Chlorophenoxy herbicides

2,4-D and 2,4,5-T are weed killers. Their acute human toxicity is relatively low, but a large ingestion of 2,4-D can cause coma and marked, sometimes weeks-long, muscle weakness. 2,4,5-T was a component of Agent Orange and was contaminated with TCDD, the most potent dioxin, which is why its use was cancelled. Some studies link chlorophenoxy herbicides to non-Hodgkin lymphoma.

Glyphosate

Glyphosate is absorbed through the leaves and roots and kills plants non-selectively, which is why crops engineered to resist it are grown widely. It is now the most widely used herbicide in the world. Poisoning by ingestion of commercial products is common in low- and middle-income countries; much of the toxicity comes from the surfactants added to the formulation. Features include eye and skin irritation, oesophageal erosion, aspiration pneumonia and kidney failure; treatment is supportive. In 2015 IARC classified glyphosate as probably carcinogenic to humans (group 2A), mainly for non-Hodgkin lymphoma; IARC stresses that this is a hazard classification, not an estimate of risk at a given exposure.

Paraquat

Paraquat is a bipyridyl herbicide that accepts a single electron and then hands it to oxygen, generating free radicals over and over. The lung takes it up actively, so after swallowing it the first signs are bleeding from the gut (vomiting blood, bloody stools), and days later come pulmonary oedema, alveolitis and progressive fibrosis; liver, kidney and heart can also fail, and death may come weeks later. Because the lung injury is delayed, the priority is binding the poison in the gut early with adsorbents such as activated charcoal or Fuller's earth. Gastric lavage is avoided because it risks aspiration, and oxygen is given cautiously, only for real hypoxaemia, because it can feed the radical injury. Once absorbed, treatment succeeds in fewer than half of patients.

Pesticide poisoning in Colombia and the region

Colombia's 2024 national surveillance report on acute chemical poisoning found that pesticides were the third most frequent group overall but caused 41.3% of the deaths. Chlorpyrifos, paraquat and glyphosate were the pesticides most often involved, more than half of the pesticide cases were suicide attempts, and paraquat was the agent in 29.3% of completed suicides. Most pesticide poisonings happened at home, which points to easy access. WHO aims to ban the most toxic and most persistent pesticides, and the Stockholm Convention restricts persistent organic pollutants such as DDT.

Test yourself

Think of the answer, then tap the question to see it.

How do organochlorine insecticides such as DDT cause tremor and seizures?

They slow the closing of sodium channels in nerve membranes, so neurons fire repeatedly and the brain is stimulated.

Why is oxygen given cautiously in paraquat poisoning?

Paraquat generates free radicals by passing electrons to oxygen, so extra oxygen can worsen the lung injury; it is kept for real hypoxaemia.

In glyphosate product ingestion, what part of the formulation causes much of the toxicity?

The surfactants added to help the herbicide enter plants; they contribute to irritation, oesophageal injury and systemic effects.

Why was the herbicide 2,4,5-T withdrawn?

It was contaminated with TCDD, the most potent dioxin, and was part of Agent Orange.

Which herbicide was the leading agent in completed suicides by poisoning in Colombia in 2024?

Paraquat, according to the national surveillance report of the Instituto Nacional de Salud.

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Sources: Pesticide residues in food (World Health Organization, 2026); IARC Monograph on Glyphosate (International Agency for Research on Cancer (WHO), 2026); Informe de Evento 2024 Intoxicaciones Agudas por Sustancias Químicas (Instituto Nacional de Salud (Colombia), 2025).

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