Studies Show How Pesticides May Lead to Brain Cancer

A new meta-analysis published in the journal Nucleus identifies studies showing that pesticides can overwhelm cells’ defenses against them and interfere with cell communication in the brain. The authors review what is known at the molecular level about pesticides’ role in brain cancer.

With the strong associations established in epidemiologic studies and a dearth of evidence on the actual mechanisms by which pesticides inflict their damage on the brain, a new meta-analysis identifies studies showing that pesticides can overwhelm cells’ defenses against them, interfere with cell communication in the brain, and disrupt the epigenetic (gene function) regulation of gene expression.

In the journal Nucleus, Bilal Ahmad Mir, Ph.D., and colleagues at the University of Kashmir in Srinagar, India, review what is known at the molecular level about pesticides’ role in brain cancer.

Brain cancer is a heavy burden for its victims and their families, and attributing a cause is, as with many diseases, fraught with difficulty. But there are strong clues: For example, farming is a known risk factor.

In a 2021 meta-analysis of epidemiologic studies between 1998 and 2019, analyzed here by Beyond Pesticides, farming was associated with a 13% increase in the risk of brain cancer.

For farmers whose specific exposure to pesticides was documented in the studies, the increase jumped to 20%. So there is some reason to point a finger at synthetic chemicals.

But agricultural workers are not the only ones at risk. According to a systematic review, in 2019 brain cancer was the 10th leading cause of death in the general population. For men ages 20 to 39, brain cancer was the leading cause of cancer deaths.

This was about twice the rate for women. For children it is even worse: central nervous system tumors, which have a high mortality rate, are the most common childhood cancer; these and leukemia comprise more than half of all malignancies in children.

In 2023, Beyond Pesticides analyzed a review finding that, for children ages 0 to 14, the brain tumors classed as astrocytomas were more strongly associated with maternal and et al. exposures to pesticides during pregnancy than with children’s postnatal direct exposure.

Importantly, most exposures occurred at home, not in agricultural settings, and brain tumors in children under five have been linked to flea and tick products. However parental exposure to pesticides at work also poses a risk to children.

The brain, only 2% of the body’s mass, uses 15-20% of all the energy the body generates via aerobic metabolism, so oxygen homeostasis is of utmost importance. It is clear that pesticides induce the production of reactive oxygen species (ROS), which are implicated in many diseases.

In the brain, two important communication pathways can be disrupted by ROS: gap junctions, which are direct connections between cells allowing for the transfer of molecules such as neurotransmitters, and synapses, where electrical signals travel between neurons.

The brain is especially vulnerable because it needs both significant amounts of oxygen and higher levels of iron and copper than the rest of the body. These metals easily react with oxygen, and their balance must also be carefully maintained. Dysregulated iron is implicated in cancer metastasis.

Too much copper also fosters cell proliferation and metastatic potential. A further concern is that pesticides are easily and rapidly fat-soluble, leading to their accumulation in the brain’s high levels of polyunsaturated fatty acids.

Many pesticide families have been demonstrated to produce ROS: organophosphates (chlorpyrifos, quinalphos, dichlorvos); organochlorines (paraquat, dieldrin); and pyrethroids (permethrin), for example.

Many have multiple ways of harming cells. For example, the authors note that paraquat crosses the blood-brain barrier, creates ROS in the intercellular fluid and induces oxidative damage in the hippocampus region of the brain and neurons. It crosses the placenta, where it severely damages the fetal dopamine system.

The weed killer paraquat also interferes with the nicotinamide adenine dinucleotide, or NAD+ and NADH, process, which involves enzymes crucial for regulating mitochondrial energy generation, the oxygen-iron and oxygen-copper reactions, signal transduction, genomic stability, gene expression regulation, circadian clock management, immunity and inflammation.

Paraquat is still registered in the U.S. for farm use but banned in more than 70 other countries. In addition to its connection with brain cancer, it is strongly implicated in Parkinson’s disease.

In October, Beyond Pesticides called for the U.S. Environmental Protection Agency to ban paraquat using the same reasoning the agency employed to ban dacthal in August.

Epigenetics presents another route for pesticides to damage brain cells. The term refers to ways that gene expression can be controlled by non-gene molecules that attach to the DNA double helix and wrap it around structures called histones.

Methyl molecules are a powerful means of preventing gene expression, and the dysregulation of methylation is a primary process in cancer induction. Pesticides generating ROS can lead to hypermethylation, preventing detoxification and allowing the formation of tumors.

According toMir and colleagues, “Taken together, pesticide-induced ROS production may significantly alter the epigenome by targeting various enzymes involved in regulating the expression of various genes involved in detoxification and metabolic processes.” These epigenetic changes can have multigenerational effects.

“The excessive use of pesticides,” write Mir and colleagues, has led to “grave health consequences to humans.” The authors conclude that “the sale and usage of carcinogenic pesticides should be completely banned.”

Considered by itself, the epidemiologic evidence of pesticide harm demands that these chemicals be eliminated. The links between pesticides and brain cancer demonstrate this.

The combination of epidemiologic evidence and the emerging molecular, mechanistic evidence of pesticides’ influence on cancers, including brain cancer, make it clear that our food system should stop clutching at the crutch of synthetic chemicals and shift to organic agriculture as soon as possible.

In the meantime, you can reduce your exposure to pesticides. See, for example, Lawns We Can Live With — Caution: Children at Play, a factsheet from the Safer Pest Control Project.

See also Beyond Pesticides’ Action of the Week Archive for the latest concrete actions you can take to affect policy, along with our deep archive of research on pesticides’ human and ecosystem health effects and information about both buying organic and organic farming.

Originally published by Beyond Pesticides.