When we discuss the risks of pesticide exposure, it’s important to clarify that environmental toxins do not “cause” diseases per se. Rather, they are a risk factor, just like one’s genetics, family history, etc. That doesn’t mean we shouldn’t minimize our exposure.
Even if there’s not a simple causal link between pesticides and disease, we must consider the effects of these chemicals on people who are already susceptible. If exposure is the “straw that broke the camel’s back,” it’s worth investigating — and eliminating, if possible.
But why do pesticides raise one’s risk of developing Parkinson’s, autoimmune disorders, and cancer? How do they interact with our bodies’ inherent functions?
Answering these questions is critical to pushing for lasting change, from industry regulations to safer agricultural and domestic practices. For too long, pesticide manufacturers such as Monsanto have absolved themselves by saying “there’s no clear link.” However, just because the link isn’t simple doesn’t mean it isn’t there.
How Do Pesticides Work?
A pesticide includes any chemical meant to kill insects, fungus, or weeds. For the purposes of this article, we’ll be using “pesticide” as a generic term for all insecticides, fungicides, and herbicides. Pesticides typically contain an ingredient that stops or derails a key metabolic process.
For example, glyphosate, the active ingredient in Roundup, disrupts the shikimate pathway in plants, fungi, and bacteria. This metabolic process creates key amino acids for tissue growth. Glyphosate inhibits the enzyme that catalyzes this pathway. Although shikimate does not occur in animals, glyphosate still affects them, as we’ll discuss in a moment.
Pesticides may also work by disabling organisms’ nervous systems. For example, pyrethroids (e.g. permethrin in mosquito control products) are excitotoxins that prevent nerves’ sodium channels from closing. This permanently paralyzes insects. While mammals aren’t as vulnerable, they often develop rashes after contact with pyrethroids.
Understanding these modes of action is crucial for understanding how these pesticides interact with human bodies. There’s a reason they contribute to diseases rather than outright killing us: their disruption of metabolic and neurological pathways has ripple effects.
Pesticides as a Risk Factor for Neurological Disorders
Neurological disorders are chronic health conditions in which nerve cells cannot function well. This category includes neurodegenerative diseases (e.g., ALS, Alzheimer’s, Parkinson’s) and autoimmune disorders targeting the nervous system (e.g. myasthenia gravis, Guillain-Barré Syndrome).
A higher incidence of Parkinson’s has been observed in farmworkers, who are regularly exposed to pesticides. Parkinson’s disease is a degenerative disorder that affects the central nervous system, primarily motor functions. It causes tremors, slow movement, and rigidity in the limbs. This happens as nerve cells in the basal ganglia’s movement center die, evidently as proteins misfold into Lewy bodies.
Research has pinpointed paraquat, an herbicide, and rotenone, an insecticide, as the two key environmental risk factors for Parkinson’s. Paraquat’s lethal effects are well-known to the point that it has been banned in several countries. It works by stimulating oxidation that results in cell damage. Rotenone disrupts the electron transport chain in mitochondria, forcing free radicals to build up in cells’ powerhouses. Neurons are particularly susceptible to this effect, as shown by animal studies in which rotenone created Parkinson-like symptoms.
Guillain-Barré Syndrome (GBS), in which immune cells attack the peripheral nervous system, has also been linked to pesticide exposure. While considerably rarer than Parkinson’s, Guillain-Barré incidence seems to be higher in rural areas.
Myasthenia gravis (MG) is another autoimmune disorder linked to pesticide exposure. In MG, the immune cells attack the nerves that stimulate skeletal muscle movement, particularly around the face and neck.
Both these disorders are functionally similar to organophosphate toxicity, a condition that arises upon frequent contact with insecticides. This fact further suggests that chronic exposure is a risk factor for GBS and MG.
It’s important to note that, except for paraquat, none of these pesticides are directly harmful to humans. Rather, they disrupt key metabolic processes, primarily in neurons. Those who are genetically predisposed to Parkinson’s, MG, or other conditions may be less resilient to this damage, however small.
Moreover, chronic exposure adds up over time. That’s because our genomes are not set in stone from birth. They can and do change over time as our genes are expressed in different ways. Chronic exposure to toxic chemicals creates epigenetic effects that alter this gene expression.
Pesticides as a Risk Factor for Cancer
Many pesticides work by creating oxidative stress in cells. As mentioned above, rotenone prevents oxygen electrons from leaving the cells. These free radicals, aka Reactive Oxygen Species (ROS), eagerly attach to any molecule they can. This oxidation process prevents normal cell respiration and damages tissue.
You likely know that cancer is associated with unchecked oxidation. The key word there is “unchecked.” Our bodies can normally expel any ROS, and any damaged cells are simply replaced through apoptosis (programmed cell death). Many of our foods have antioxidant properties that sustain this balance.
In cancer, apoptosis becomes dysfunctional and unhealthy cells proliferate, creating tumors and disrupting normal cells. Pesticides that promote ROS beyond what our body can expel are therefore a key risk factor for cancer. They compound the problem if we’re also exposed to other carcinogens and/or genetically predisposed to develop cancer.
The most infamous pesticide, glyphosate, has been described as carcinogenic. Found in Monsanto’s widely used Roundup products, glyphosate disrupts the shikimate pathway. As noted above, this does not exist in animals. However, it does in microorganisms, including many species that compose our gut microbiome. These beneficial bacteria are crucial to our immune defense.
Chronic exposure to glyphosate evidently harms our microbiome and increases our risk of immunodeficiency. And in the case of glyphosate, that seems to indirectly contribute to an increased risk of non-Hodgkin lymphoma, a cancer of the body’s white blood cells (a critical component of our immune systems). (Glyphosate may lead to neurological disorders as well.)
So, do pesticides cause cancer or neurological disorders? Yes and no. As companies like Monsanto will eagerly tell you, the chemicals are “harmless when used as directed.” By that, they mean spraying your weed-killer or mosquito control according to the label’s instructions. Acute exposure will only hurt you if you intentionally ingest it.
The problem is that pesticides are used long-term, and all those tiny interactions with your body add up over time. So while a single use won’t suddenly make you grow a tumor, continual exposure creates epigenetic effects that could make tumors more likely.
Also, it is true that not everyone who is chronically exposed to glyphosate will develop non-Hodgkin lymphoma. Long-term use of rotenone won’t always cause Parkinson’s. There are many factors at play. We cannot simply state that Chemical X causes Disease Y.
However, we can and should raise concern about the chemicals that significantly increase our risk of that disease. If it’s a key risk factor that we could eliminate, why wouldn’t we? It is ultimately a public health issue, as many people are exposed to pesticides without ever touching a bottle of Roundup. These substances linger in our environment and our food. Over time, all those short-term incidents create long-term exposure.
We must regulate or ban chemicals that evidently raise the likelihood of developing cancer, Parkinson’s, and other serious health conditions. Until then, we live in a world with an extra set of risk factors — one we can avoid by finding sustainable, safer alternatives to pesticides.
This article was inspired by an interview with Jack Quinn, former U.S. Congressman and an advocate for Parkinson’s awareness since his diagnosis in 2014.