Diquat Herbicide Poses Health Risk

The Hidden Danger on Our Plates: The Banned Herbicide Contaminating US Food and Fueling Disease

Fresh scientific analysis reveals that a chemical employed as a substitute for glyphosate in popular weedkillers can inflict significant harm on human health. The substance, diquat, is known to damage internal organs and disrupt the delicate balance of bacteria in our gut. Despite being outlawed in major markets like the European Union, the United Kingdom, and China due to these risks, it sees extensive application throughout the United States.

In America, diquat is commonly sprayed in orchards and vineyards and its usage is expanding as more controversial herbicides like paraquat and glyphosate are phased out. This shift has led to the alarming situation where a chemical deemed too dangerous for many nations is now a common component in products like Roundup, appearing on shelves just last year. The US Environmental Protection Agency (EPA) has so far not acted on requests to follow the lead of other countries and prohibit its use.

A Cascade of Internal Damage

New research, drawing from over 100 studies, spotlights the gut as a primary target for diquat's toxic effects. Ingestion is the main route of poisoning, initiating a destructive process within the digestive system. The chemical's core mechanism involves creating oxidative stress, a state where harmful molecules called reactive oxygen species (ROS) overwhelm the body's defences. This not only directly harms the intestinal lining but also triggers wider inflammation and systemic toxicity.

The harm to the digestive system is multifaceted and severe. Diquat weakens the intestinal barrier, which is crucial for keeping pathogens and toxins out of the bloodstream. By harming the proteins that hold this barrier together, it allows harmful substances to leak from the gastrointestinal tract, causing an inflammatory response within the bowels that can radiate through the system. This process is often described as a "gut-organ axis," where local injury in the gut fuels damage in distant organs.

The Assault on Gut Bacteria

The human gut is home to a complex ecosystem of microorganisms, collectively known as the gut microbiome, which plays a vital role in overall health. Diquat disrupts this delicate balance, killing off beneficial bacteria. Specifically, it reduces the abundance of helpful bacteria like Lactobacillus while allowing harmful microbes to thrive. This imbalance further weakens the gut's defences and can interfere with the creation of vital compounds that fight disease.

This disturbance to the gut's microorganisms has far-reaching consequences. A healthy gut is essential for absorbing nutrients and for energy metabolism. By damaging the gut lining and altering its bacterial composition, diquat inhibits these crucial functions. The body's ability to repair itself is also compromised, creating a vicious cycle of damage and inflammation. This growing understanding of the gut's central role in health makes the impact of chemicals like diquat particularly concerning.

Irreversible Harm to Kidneys

The kidneys are another major target for diquat's toxicity. The chemical is known to cause permanent structural and operational harm to these vital organs. After ingestion, diquat accumulates in high concentrations in the kidneys, where it wreaks havoc. It attacks by destroying the membranes of kidney cells and interfering with the critical signals that cells use to communicate.

Studies show that diquat triggers acute kidney injury by damaging cell membranes and activating inflammatory pathways. This leads to scarring and a steady decline in kidney function. In severe cases of poisoning, the result can be acute renal failure, characterised by the shutdown of the kidneys. Autopsies in poisoning cases have revealed congested kidneys and necrotic, or dead, renal tubules.

Liver and Lungs Under Attack

The liver, the body's primary detoxification organ, is also severely affected by diquat. Similar to its consequences for the kidneys, the herbicide disrupts the mitochondria within liver cells, which are the powerhouses responsible for energy production. This leads to cell death and promotes inflammation and harm to that organ. The toxic impact on this organ can also trigger wider immune responses that harm tissues well beyond the gut.

The lungs do not escape diquat's destructive path. While perhaps less acutely toxic to the lungs than its chemical relative paraquat, diquat still generates harmful molecules that damage respiratory tissue. It triggers inflammation that can lead to significant injury. In some cases, exposure can lead to bronchopneumonia, with radiological images showing infiltrates and exudates similar to those seen in acute respiratory distress syndrome (ARDS).

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The Specter of Systemic Failure

The widespread bodily inflammation initiated by diquat can culminate in a life-threatening condition known as multiple organ dysfunction syndrome (MODS). This is a scenario where the body’s organ systems start to fail one by one. The systemic toxicity begins in the gut but spreads through the bloodstream, leading to a domino effect of organ damage that can be fatal.

The fundamental mechanism is oxidative stress, where the generation of reactive oxygen species overwhelms the body's antioxidant defences. This process damages biological macromolecules, induces lipid peroxidation in cell membranes, and ultimately leads to cell death. Although a large portion of the in-depth research has involved rodents, the evidence points to a significant threat to human health, prompting calls for further investigation into the effects of long-term, low-dose exposure.

A "Regrettable Substitution"

Critics describe the replacement of glyphosate with diquat in consumer products as a "regrettable substitution." This scientific term refers to the practice of replacing one toxic chemical with another which is similarly dangerous, sometimes even more so. Nathan Donley of the Center for Biological Diversity, an advocacy group, stated that from the viewpoint of human wellness, diquat is "considerably more dangerous than glyphosate."

This substitution gives the public and regulators the false impression of progress while continuing to put public health at risk. An analysis by the non-profit Friends of the Earth, based on EPA data, found diquat to be approximately 200 times more harmful than glyphosate when it comes to long-term contact. This highlights a systemic failure in the regulatory process, which allows hazardous chemicals to be swapped without adequate consideration of the risks posed by the replacement.

Links to Neurological Disease

Beyond the immediate organ damage, there are growing concerns about diquat's long-term neurological effects. The chemical is a suspected neurotoxin and is linked to Parkinson's disease. Research has identified diquat as one of ten pesticides that can directly damage the specific neurons that are lost in Parkinson's disease.

Its structural similarity to paraquat, another herbicide strongly linked to Parkinson's, has raised red flags for years. Studies suggest diquat can induce cell death in neural tissue through mechanisms that generate reactive oxygen species, a key factor in neurodegeneration. Exposure has been shown to cause brain tissue swelling and axonal degeneration in poisoned patients, reinforcing the connection to neurodegenerative changes.

A Carcinogenic Threat

The list of diquat's potential dangers also includes cancer. It is considered a potential cancer-causing agent, adding another layer of risk to its use. While the International Agency for Research on Cancer (IARC) designated glyphosate as a "probable" human carcinogen, leading to widespread litigation and the reformulation of Roundup, the replacement chemical, diquat, carries its own set of grave concerns.

After its 2018 acquisition of Monsanto, Bayer was confronted with almost 175,000 legal actions from users who alleged they developed cancer from glyphosate-based Roundup. The company's decision to switch to other active ingredients, including diquat, for its residential products was a direct response to this legal pressure. However, this move has been criticised as a toxic sleight of hand, replacing one hazard with another.

International Bans vs. US Inaction

The contrast between the regulatory stance in the United States and other major nations is stark. The European Union, the UK, Switzerland, and China have all banned diquat, citing unacceptable risks to human health and the environment. The EU's decision in 2018 was based on concerns over exposure risks for workers and the public, as well as dangers to wildlife.

Despite this global consensus on its dangers, the US EPA has not initiated a review of the chemical. Advocacy groups are currently tied up in battles over other pesticides like chlorpyrifos and paraquat, which are also prohibited in other places yet still see extensive use in America. This has left diquat "overshadowed," allowing its use to grow without sufficient regulatory scrutiny.

The Failure of US Pesticide Law

Advocates point to fundamental weaknesses in pesticide statutes in the United States as a key reason for the discrepancy. Nathan Donley of the Center for Biological Diversity remarked that the US is still contending with issues that European nations resolved two decades ago. He suggests the Environmental Protection Agency is hampered by a legal framework that makes it difficult to prohibit substances, even when the scientific evidence of harm is strong.

A prime example is the case of chlorpyrifos, a neurotoxic insecticide. The EPA banned its use on food crops in 2021, a decision hailed as a major public health victory. However, following a lawsuit by industry, a judicial ruling nullified the prohibition in 2023, arguing the agency had not adequately considered certain agricultural uses. This legal setback illustrates the immense power of industry and the high hurdles the EPA faces in implementing protective measures.

An Industry-Captured Agency?

Some critics have leveled accusations that the EPA is captured by the very industry it is meant to regulate. They argue that the agency's pesticides office appears to operate from a philosophical standpoint that toxic pesticides are a "necessary evil" for agriculture. This mindset, it is argued, limits the agency's willingness to take decisive action to protect public health and the environment.

This perceived reluctance to act allows for situations like the "regrettable substitution" of glyphosate with diquat. The non-profit Friends of the Earth has argued it is "unconscionable" that the EPA allows this toxic swap, comparing it to replacing aspirin in a pain reliever with a powerful opioid without warning consumers of the increased risks. This lack of transparent labeling leaves consumers in the dark about the potentially greater dangers in reformulated products.

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The Growing Use of Diquat

Diquat is a non-selective contact herbicide, meaning it kills all green vegetation it touches. In US agriculture, its largest single use is as a desiccant to dry out potato vines before harvest, but it is also used on other crops. Beyond farms, it is used to control aquatic weeds, including in areas that are sources for public drinking water.

The decision by Bayer to use diquat in combination with other chemicals in its new glyphosate-free Roundup products for the residential market has significantly expanded its potential for human exposure. These products combine systemic herbicides with diquat, which provides rapid, visible results by quickly burning down foliage. This increased use comes at a time when a growing body of evidence is detailing its severe toxicity.

The Path Forward: Beyond Chemical Swaps

The saga of diquat underscores a fundamental problem with pesticide regulation that focuses on banning single chemicals in isolation. This approach often leads to the cycle of regrettable substitution, where one hazardous product is simply replaced by another. Advocacy groups argue for a more holistic approach that moves away from a reliance on toxic pesticides altogether.

For consumers, the lack of clear warnings on reformulated products presents a significant challenge. For farmworkers and communities near agricultural areas, the risks of exposure are even greater. The ongoing use of a chemical banned across much of the developed world raises serious questions about the adequacy of US public health and environmental protections.

Seeking Safer Alternatives

In countries where diquat is now banned, farmers have had to adapt. For potato desiccation within the United Kingdom, for instance, growers have turned to a combination of mechanical flailing of the crop canopy followed by applications of alternative chemical desiccants known as PPO inhibitors. While these alternatives exist, the loss of diquat was seen as a major blow, often increasing costs and complexity for growers.

Other crops, like linseed, also relied on diquat for desiccation before harvest. Farmers in the UK now primarily use glyphosate or are trialling alternatives like carfentrazone and pyraflufen. These examples show that agriculture can adapt to the removal of hazardous chemicals, though it often requires new strategies and investment in alternative methods. The key is a regulatory framework that prioritizes safety over convenience.

The Unseen Human Cost

While regulatory bodies and corporations debate risk assessments and economic benefits, the human cost continues to mount. Every year, there are documented cases of acute poisoning from diquat. A US study covering 1998 to 2013 identified hundreds of such cases, including several fatalities. Many incidents were work-related, often resulting from inadequate protective equipment or equipment failure.

The long-term, chronic effects are harder to quantify but are potentially more widespread. The link to debilitating conditions like kidney disease and Parkinson's suggests a hidden public health crisis. Children are particularly vulnerable to the neurodevelopmental effects of pesticides. The continued presence of diquat within the United States food chain and environment represents a persistent and preventable threat to the health of the nation.