Paraquat

Paraquat is a widely used commercial herbicide that is highly effective at killing weeds and grasses. It’s especially used to kill plants that are resistant to Roundup and its main ingredient glyphosate. Paraquat is sold in concentrated form and is mixed with water and sprayed on crops.

About 377 companies manufacture paraquat products worldwide. Syngenta’s product Gramoxone is one of the most well-known brands in the United States.

Paraquat is highly toxic and can cause short-term and long-term health effects, some of which may be fatal. Research also links long-term paraquat exposure to the development of Parkinson’s disease, an terminal neurological brain disorder that affects muscle movement and communication.

Commercial farmers and other agricultural workers in the United States have been using paraquat to control invasive weeds and grasses since 1964. It is an important tool for the control of weeds in many commercial agricultural and non-agricultural settings worldwide. It is also used for desiccation (process of removing water and drying out plants) of crops, like cotton, prior to harvest.

Paraquat is highly poisonous, and the U.S. Environmental Protection Agency says just “one sip can kill.” Because of its toxicity, the EPA limits the herbicide’s use to licensed applicators for commercial use. There are no paraquat products licensed for homeowner use.

People who are licensed paraquat applicators are at the greatest risk for exposure, but anyone who works in areas where paraquat is used may be exposed. This includes groundskeepers, farmers, growers, pickers and other agricultural workers, as well as their close contacts.

All brands of paraquat marketed in the United States contain dyes, sharp odors and chemicals that help prevent people from accidentally drinking the weed killer. Paraquat products also include an agent that induces vomiting.

Symptoms of paraquat exposure vary depending on the concentration of the chemical and the route someone was exposed through, such as inhalation, ingestion or skin contact. For example, ingesting a large amount of paraquat causes acute poisoning and symptoms appear immediately. Licensed applicators and other agricultural workers exposed to smaller amounts of the chemical over a long period may not manifest symptoms for years.

Short-Term Exposure Symptoms

The first symptoms of acute poisoning through ingestion are immediate. Short-term exposure symptoms can occur within seconds to several weeks after exposure and can be fatal.

Pain and swelling in the mouth and throat are typically the first signs. When the chemical enters the stomach, it causes gastrointestinal problems such as diarrhea, vomiting and nausea.

Long-Term Exposure Symptoms

People who survive acute paraquat poisoning typically have long-term health problems that affect various organs.

Licensed applicators, farmers and agricultural workers that have been exposed to paraquat for years may not suffer acute symptoms of poisoning. But they can still have long-term effects from exposure such as an increased risk for developing Parkinson’s disease.

Paraquat Poisoning

Acute paraquat poisoning occurs through ingestion, inhalation or skin exposure. Most cases of poisoning occur because of accidental ingestion. Poisoning is usually fatal and there is no antidote.

The majority of the damage by paraquat is through the pathological process of inflammation (activation of inflammatory cells, fluid induction leading to swelling, cell death). Small to medium amounts of paraquat can damage the mouth, stomach, lungs or intestines. Swallowing large amounts can damage multiple organs and lead to death within hours.

Paraquat toxicity is most severe in the lungs and leads to acute lung inflammation (swelling of the lung bulbs that exchange oxygen and carbon dioxide, thereby impairing airflow) and lung cell damage. The patient typically develops increasing signs of respiratory distress over three to seven days and ultimately dies of severe breathing impairment up to five weeks later.

Ingestion of large amounts of paraquat concentrate results in organ failure, pulmonary edema (swollen lungs), cardiac, kidney, and liver failure and seizures due to nervous system involvement. Death results from multiple organ failure within several hours to a few days.

Ingestion of smaller quantities usually leads to toxicity in kidneys and lungs developing over the next two to six days. Mortality in this group is still over 50%. 

Kidney failure develops quite rapidly after ingestion exposure to paraquat. Some liver toxicity (jaundice, rise in liver enzymes) is also common in these patients. However, neither kidney nor liver damage contribute to mortality. No long-term effects on these organs have been reported in patients that recover.

Gastrointestinal (digestive system) toxicity is universal in those ingesting paraquat. Lesions of the mouth and the tongue begin to appear within the first few days and may become ulcerated with bleeding. These can occur even in those who spit paraquat out without swallowing. Lesions in the pharynx (throat), esophagus, and stomach are very common and much more deadly. The contribution of this direct effect to mortality is under-estimated.

Several studies link long-term paraquat exposure to developing Parkinson’s disease. These studies propose that paraquat creates oxidative stress that damages and kills neurons that produce dopamine in the brain, increasing the risk of the disease.

Parkinson’s disease is an terminal neurological brain disorder. Researchers theorize the loss of neurons that produce dopamine may cause the condition to develop.

The possible scientific link to Parkinson’s disease has led several people to file paraquat lawsuits against herbicide manufacturers, including Syngenta. Lawsuits claim paraquat is defective and led farmers to develop Parkinson’s disease. Plaintiffs say that manufacturers failed to warn the public about the risk.

Sampling of Studies

An ecological study published in December 2022 examined the association between paraquat exposure and end-stage renal disease. The study found that people who experienced paraquat poisoning had rapid damage to their organs. The findings included acute kidney injury, which is associated with an increased risk of death.

A National Institutes of Health, National Institute for Occupational Safety and Health and the EPA Agricultural Health Study examined the health of U.S. farmers over several years. Researchers found that paraquat use increased the risk of developing Parkinson’s disease.

People exposed during their teen or young adult years had an increased Parkinson’s disease risk of 200% to 600%, according to studies from The Unified Parkinson’s Advocacy Council.

The EPA’s Position

The EPA reviewed studies connecting paraquat to Parkinson’s disease. In 2019 the agency released a memorandum saying the evidence was insufficient to determine a link between them.

However, in September 2022, the EPA cancelled the registrations for several products containing paraquat at the request of manufacturers. Among the registrations cancelled include Syngenta Corp.’s Gramoxone SL 2.0 and Amvac Chemical Corporation’s Parazone 3SL Herbicide.

There is no antidote for paraquat poisoning and it’s usually deadly. People who ingested paraquat should seek emergency care.

Hospital treatment consists of removing paraquat from the body using Fuller’s earth or activated charcoal, according to the Centers for Disease Control and Prevention. If the patient arrives at the hospital within an hour of ingesting paraquat, nasogastric suction may be used.

People who may have gotten paraquat on their skin should wash themselves with soap and water. Flush eyes with plain water for 10 to 15 minutes. Seek medical care immediately.

Roundup and paraquat are both herbicides, but are not the same. Roundup’s active ingredient is glyphosate.

Paraquat is more poisonous than glyphosate and is 28 times more acutely toxic, according to a Pesticide Action Network report. Because of its toxicity, paraquat is banned in several countries and is a restricted use herbicide in the United States.

Unlike paraquat, Roundup has no restrictions on use and anyone can purchase and use it, including homeowners. The EPA considers glyphosate’s toxicity to humans to be low, though the World Health Organization’s International Agency for Research on Cancer has stated that glyphosate is “probably carcinogenic to humans.” People who have developed cancers such as non-Hodgkin lymphoma after using Roundup have sued its manufacturer.

Despite being banned or phased out in the European Union, Brazil and China, paraquat is more popular than ever in the United States. Paraquat use in the U.S. has increased and continues to rise, according to the National Water-Quality Assessment (NAWQA) Project.

From 2006 to 2017, the estimated amount used jumped from about 3 million pounds to 11 million pounds. The increase in the use of paraquat is linked to its use on weeds that are resistant to Roundup, according to the Center for Biological Diversity.

Every 15 years, the EPA reevaluates the use of certain pesticides. In October 2020, the EPA reapproved paraquat for restricted use. In July 2021, after receiving and considering public comments on the paraquat proposed decision, the EPA released the interim decision for registration review. The agency is also requiring strict safety measures to reduce human health and environmental risks associated with paraquat.