Paraquat poisoning is a severe, often fatal condition caused by exposure to paraquat, one of the most toxic herbicides in the world. As little as 10 to 15 milliliters of a concentrated solution (roughly two to three teaspoons) can kill an adult. There is no antidote, and the mortality rate climbs steeply with the amount ingested and the time before treatment begins.
Why Paraquat Is So Dangerous
Paraquat is a fast-acting weedkiller used on farms across the United States and in more than 100 countries. Its lethal dose in humans is approximately 3 to 5 mg per kilogram of body weight. Commercial liquid products contain 20% to 50% paraquat, meaning a single swallow of concentrated product can deliver a fatal dose. Ingestion of more than 30 mL of a 20% solution is generally considered unsurvivable.
What makes paraquat uniquely destructive is how it behaves once inside the body. It generates massive amounts of oxygen free radicals, molecules that tear apart cell membranes and damage DNA. The lungs are especially vulnerable because they actively concentrate paraquat from the bloodstream, pulling it in at levels far higher than anywhere else in the body. This is why lung failure is the most common cause of death in paraquat poisoning, even when the chemical was swallowed rather than inhaled.
How People Get Exposed
The vast majority of serious paraquat poisoning cases involve swallowing the liquid, whether accidentally or intentionally. In many countries where paraquat is sold without strict controls, it is a leading method of self-harm, and this accounts for most hospital admissions worldwide.
Skin contact with diluted field-strength solutions (0.07% to 0.14%) rarely causes systemic poisoning on its own, but prolonged contact, especially on broken or abraded skin, can allow enough absorption to cause harm. Concentrated paraquat will chemically burn skin on contact. Inhalation of spray droplets during normal agricultural application is not typically associated with severe poisoning, though it can irritate the nose, throat, and airways.
Symptoms and How They Progress
Paraquat poisoning unfolds in stages over hours and days, and the timeline depends heavily on how much was ingested.
The first signs appear within minutes to hours and center on the mouth and digestive tract:
- Pain, swelling, and redness in the mouth and throat
- Difficulty swallowing or choking
- Severe stomach pain
- Vomiting, sometimes with blood
- Diarrhea, which may also be bloody
- Nosebleeds
Within hours, the chemical spreads through the bloodstream and begins damaging organs. At this stage, symptoms can include confusion, muscle weakness, a dangerously fast heart rate, seizures, and shock from plummeting blood pressure. Some people lose consciousness.
Over the following days, organ damage becomes the primary threat. The lungs, kidneys, liver, and heart are most affected. In the lungs, paraquat triggers a cascade of inflammation followed by scarring (fibrosis) that progressively destroys the ability to exchange oxygen. Kidney failure often develops within the first 48 to 72 hours. In cases involving large ingestions, multi-organ failure and death can occur within one to three days. With smaller but still significant doses, lung fibrosis may progress over one to three weeks before becoming fatal.
Diagnosis
Doctors can confirm paraquat exposure with a simple bedside urine test. A chemical called sodium dithionite is mixed with the patient’s urine sample. If paraquat is present, the urine turns a distinctive dark blue or green color. This test can detect paraquat roughly 24 to 48 hours after ingestion, and the intensity of the color change gives a rough indication of how much paraquat is in the body. Blood and urine samples can also be sent to a lab for precise concentration measurements, which help predict survival odds.
Treatment Options and Survival
There is no antidote for paraquat. Treatment focuses on removing as much of the chemical as possible before it reaches the organs and then supporting the body through the damage.
If someone arrives at a hospital quickly after swallowing paraquat, the first step is usually administering activated charcoal or a clay-based absorbent called Fuller’s earth to bind the chemical in the stomach before it enters the bloodstream. Speed matters enormously here. Blood-filtering procedures like hemodialysis may help if started within about two hours of ingestion and before the lungs are involved, but their effectiveness drops off sharply after that window closes.
Beyond decontamination, treatment is largely supportive: IV fluids for dehydration and shock, medications for pain, and monitoring for organ failure. One critical and counterintuitive rule is that supplemental oxygen is avoided whenever possible in the early stages. Paraquat’s toxicity is driven by oxygen-dependent chemical reactions, and giving extra oxygen can actually accelerate lung damage.
Survival depends almost entirely on how much was ingested. Small accidental exposures, particularly to diluted field-strength solutions, are generally survivable with prompt care. Ingestion of even moderate amounts of concentrated product carries a mortality rate above 50%, and large ingestions (more than 30 mL of a 20% solution) are almost universally fatal regardless of treatment.
Regulatory Restrictions in the U.S.
Paraquat is banned outright in over 60 countries, including the entire European Union, but it remains legal in the United States under tight restrictions. The EPA classifies all paraquat products as Restricted Use Pesticides, meaning only trained, certified applicators can purchase or apply them. Workers operating under a certified applicator’s supervision are specifically prohibited from handling paraquat themselves.
In 2021, the EPA finalized additional safety measures. Paraquat must now be sold in closed-system packaging that prevents anyone from pouring it into other containers, a direct response to poisoning cases involving the chemical being stored in unlabeled bottles. Aerial applications are capped at 350 acres per applicator per day for most crops. Pressurized handgun and backpack sprayers are banned entirely. Applicators treating more than 80 acres in a day must work from an enclosed cab, and those treating smaller areas must use either an enclosed cab or a high-level respirator.
Fields treated with paraquat also have mandatory waiting periods before workers can re-enter: 48 hours for most crops and seven days for cotton that has been desiccated with the chemical.
Long-Term Health Concerns
People who survive paraquat poisoning often face lasting organ damage, particularly in the lungs. Pulmonary fibrosis, the scarring process that paraquat triggers, is irreversible. Survivors may have permanently reduced lung capacity and chronic breathing difficulties. Kidney and liver damage can also persist, depending on how severe the initial injury was.
Separately from acute poisoning, long-term occupational exposure to paraquat has drawn attention for a possible link to Parkinson’s disease. Epidemiological studies have found that farmworkers with years of paraquat exposure develop Parkinson’s at higher rates than the general population, and the chemical is known to damage the same type of brain cells that degenerate in Parkinson’s. This association has fueled ongoing litigation and is one of the reasons several countries have moved to ban the herbicide entirely.