The Invisible Burden: Environmental Toxins and Cancer Risk
I’ve been thinking a lot about this topic lately. Not just as a clinician… but as a father. As someone who drinks water, who buys groceries at the local market, who breathes the air. We all do. And the truth is, the air we breathe, the water we drink, and the surfaces we touch carry an invisible chemical burden that most of us never even consider.
The World Health Organization estimates that roughly 20% of cancers worldwide are attributable to environmental risks, predominantly from air pollution, management of chemicals, radiation, and occupational exposures (WHO, 2018). Twenty percent. That number should stop us in our tracks. Because unlike genetic predisposition, environmental exposure is something we can actually influence… at least in part.
Since 1971, the International Agency for Research on Cancer (IARC) has evaluated more than 1,000 agents, and over 500 have been identified as carcinogenic, probably carcinogenic, or possibly carcinogenic to humans (IARC Monographs Program). The EPA’s Integrated Risk Information System has identified over 150 chemicals as carcinogenic or likely to be carcinogenic (US EPA IRIS). These aren’t fringe claims. This is the accumulated weight of decades of research. And yet… most patients I see have never had a conversation with a physician about environmental toxin exposure and cancer prevention. That’s a gap I want to help close.
So let’s walk through the five environmental toxins that carry the highest burden of cancer risk based on current evidence. These are the ones I think every person should know about.
1. Arsenic in Drinking Water
This one hits close to home for those of us who rely on well water. Arsenic is a naturally occurring element that shows up in groundwater all across the United States, and it’s classified by IARC as a Group 1 carcinogen… meaning there is sufficient evidence that it causes cancer in humans. The cancers most strongly associated with chronic arsenic exposure include bladder, lung, skin, kidney, and liver cancers.
What’s particularly alarming is that even low-level exposure appears to carry risk. A 2024 study from Texas A&M University published in Environmental Pollution examined 28,896 cancer cases across 240 Texas counties and found that arsenic exposure between just 1 and 5 parts per billion (ppb) raised kidney cancer risk by 6%, and exposure above 5 ppb raised it by 22% (Hasan et al., 2024). To put that in perspective, the current EPA regulatory threshold is 10 ppb. We’re seeing elevated cancer risk at concentrations below the legal limit.
A separate 2024 systematic review in Toxicology and Applied Pharmacology analyzed 51 studies spanning 35 years and confirmed a dose-response relationship between arsenic in drinking water and lung cancer, with elevated risk even at concentrations below 150 µg/L (Issanov et al., 2024). Approximately 40 million Americans rely on private wells that are completely unregulated, and roughly 2.1 million people across 25 states are estimated to be exposed to elevated arsenic concentrations (Hasan et al., 2024). If you’re on well water, get it tested. It’s one of the simplest and most impactful things you can do.
2. PFAS (“Forever Chemicals”)
Per- and polyfluoroalkyl substances… better known as PFAS or “forever chemicals”… are some of the most persistent compounds in existence. They don’t break down in the environment. They bioaccumulate in our bodies. They’re detectable in the blood of more than 98% of the U.S. population. And they’ve been found in roughly 45% of U.S. drinking water supplies. That is staggering.
In 2023, IARC classified PFOA (one of the most common PFAS compounds) as a known human carcinogen (Group 1), and PFOS as a possible human carcinogen (Group 2B). The cancer associations are broad and deeply concerning… kidney, testicular, thyroid, breast, and liver cancers have all been linked to PFAS exposure in epidemiological studies.
A landmark 2025 study from the Keck School of Medicine at USC, published in the Journal of Exposure Science and Environmental Epidemiology, compared cancer incidence data from 2016–2021 with PFAS contamination data from the EPA’s drinking water monitoring program. The findings were sobering: counties with PFAS-contaminated water experienced up to a 33% higher incidence of certain cancers, and the researchers estimated that PFAS in drinking water contributes to approximately 6,864 cancer cases per year in the United States (Li et al., 2025).
The mechanisms are multifactorial. PFAS promote oxidative stress, disrupt endocrine signaling, suppress immune function, and interfere with DNA repair. They’ve even been detected in breast milk and umbilical cord blood. The NCI’s Occupational and Environmental Epidemiology Branch has identified PFAS research as a top priority, with particular emphasis on kidney cancer, breast cancer, and hormone receptor-positive tumors (NCI DCEG, 2023).
In April 2024, the EPA finally set legally enforceable limits for six PFAS chemicals in drinking water, setting the maximum contaminant level for PFOA and PFOS at 4 parts per trillion. Use a quality water filter. Reduce your exposure to nonstick cookware, stain-resistant fabrics, and waterproof coatings where possible. These chemicals are everywhere, but awareness is the first step toward reducing your burden.
3. Benzene
Benzene is one of those chemicals that’s been hiding in plain sight for over a century. It’s a colorless, sweet-smelling compound found in crude oil, gasoline, cigarette smoke, and industrial emissions. IARC classifies it as a Group 1 carcinogen, and the evidence linking benzene to acute myeloid leukemia (AML) is about as strong as it gets in environmental toxicology.
A major cohort study of 74,497 benzene-exposed workers in China found significant increases in AML, malignant lymphoma, myelodysplastic syndrome, and aplastic anemia compared to 35,805 controls (Yin et al., as reviewed in Snyder, 2012). The mechanism is well-characterized… benzene metabolites damage bone marrow, cause chromosomal aberrations, and disrupt hematopoietic stem cell function. Researchers at UC Berkeley have demonstrated dose-dependent effects on lymphocyte counts and leukemia-relevant gene expression even at low occupational exposures below 1 ppm (Smith, 2010; Lan et al., 2004).
Beyond occupational settings, benzene exposure comes from gasoline vapors at the pump, automobile exhaust, secondhand smoke, and even certain consumer products. On average, smokers inhale about 10 times more benzene daily than nonsmokers. Studies in children have also shown associations between environmental benzene exposure and elevated risk of acute lymphoblastic leukemia (ALL), particularly from traffic-related air pollution during the postnatal period (reviewed in Carroquino et al., 2024).
This is one of those toxins where simple behavioral changes can make a meaningful difference. Don’t smoke. Avoid prolonged exposure to gasoline fumes. Keep your indoor air clean. If you live near a busy highway, consider a quality air purifier. And if you work in an industry where benzene is present, make sure your protective equipment is up to standard.
4. Formaldehyde
Most people think of formaldehyde as something found in a lab or a funeral home. And while those are certainly high-exposure settings, the reality is that formaldehyde is one of the most ubiquitous indoor air pollutants we encounter on a daily basis. It off-gases from pressed-wood products (think particleboard furniture, plywood, laminate flooring), certain insulation materials, paints, coatings, cigarette smoke, and even some cosmetic and hair-smoothing treatments.
IARC classified formaldehyde as a Group 1 carcinogen in 2004, and that classification has been reaffirmed multiple times since. The primary cancer association is with nasopharyngeal cancer, and there is also sufficient evidence linking it to myeloid leukemia (IARC, 2006; NTP 12th Report on Carcinogens, 2011). The NCI has conducted extensive studies of workers in formaldehyde-exposed occupations… anatomists, embalmers, and industrial workers… and found elevated risks of leukemia and brain cancer in some cohorts (NCI Formaldehyde Fact Sheet, 2023).
The genotoxic mechanism is well understood. Formaldehyde binds covalently to DNA, causing DNA-protein crosslinks, strand breaks, chromosomal aberrations, and micronucleus formation. In rat studies, cytotoxicity-induced cell proliferation in the nasal epithelium is a key driver of cancer development, with a clear dose-response relationship (Nielsen and Wolkoff, 2010; WHO IAQG, 2010). The WHO’s indoor air quality guideline sets a threshold of 0.08 ppm (0.1 mg/m³) for long-term exposure, which is considered protective against carcinogenic effects.
Practical steps? Ventilate your home. Choose solid wood or low-emission furniture when possible. Avoid unvented fuel-burning appliances. If you’re renovating, be mindful of the products you bring into your living space… especially if you have children. Many formaldehyde-emitting materials off-gas most aggressively when they’re new.
5. Glyphosate (Roundup)
This one is controversial, and I want to be transparent about that. Glyphosate is the most widely used herbicide in the world, and in 2015, IARC classified it as a “probably carcinogenic to humans” (Group 2A), based primarily on evidence linking it to non-Hodgkin lymphoma (NHL) in occupationally exposed workers. However, several other regulatory bodies, including the US EPA and the European Food Safety Authority, have maintained that glyphosate does not pose a carcinogenic risk at current exposure levels.
So who do we believe? I think the honest answer is that we should look at the whole body of evidence and remain cautious. A comprehensive long-term carcinogenicity study published in 2025 by the Global Glyphosate Study group (led by the Ramazzini Institute and involving researchers from Boston College, George Mason University, King’s College London, and Mount Sinai) found that rats administered glyphosate and commercial glyphosate-based formulations at doses currently considered safe by regulatory agencies developed increased incidences of benign and malignant tumors at multiple anatomic sites (Global Glyphosate Study, 2025). This is the most comprehensive toxicological study ever conducted on glyphosate.
A 2023 study from the NCI, published in the Journal of the National Cancer Institute, found exposure-response relationships between urine glyphosate concentrations and biomarkers of oxidative stress (8-hydroxy-2’-deoxyguanosine and malondialdehyde) among farmers in the Agricultural Health Study (Chang et al., 2023). Oxidative stress is a recognized mechanism by which chemicals can induce DNA damage and promote carcinogenesis.
A 2025 review in Clinical Lymphoma, Myeloma and Leukemia by Weisenburger concluded that the epidemiologic, animal, and mechanistic studies over the past five years provide a consistent and compelling pattern of evidence that glyphosate and glyphosate-based formulations are a cause of NHL in exposed humans (Weisenburger, 2025).
My clinical perspective? I err on the side of caution with my patients. Choose organic produce when possible, especially for items on the EWG’s Dirty Dozen list. Wash your fruits and vegetables thoroughly. If you’re a farmer or gardener, consider alternatives to glyphosate-based products. We don’t need to wait for every regulatory agency to agree before we take reasonable precautions.
The Bigger Picture
I want to close with something I think about often. Rachel Carson wrote Silent Spring in 1962, and her work ultimately led to the founding of the EPA. Over sixty years later, the growing use of environmental chemicals, the changing climate, and the waxing and waning of political will for environmental protections all remind us that this is an ongoing battle. We’ve made progress, but tens of thousands of chemicals remain in commercial use without adequate cancer risk assessment.
As a naturopathic physician, I’ve always believed that the body has a remarkable capacity for healing… Vis Medicatrix Naturae, the healing power of nature. But that healing power works best when we aren’t overwhelming the system with a constant burden of environmental insult. Reducing your toxic load is one of the most foundational things you can do for cancer prevention and for your overall longevity.
Test your water. Filter your air. Choose organic when you can. Read labels. And most importantly, don’t let the scale of the problem paralyze you into doing nothing. Small, consistent choices compound over time. So it is with toxins, and so it is with healing.
If you’re concerned about your environmental toxin exposure and would like a personalized assessment, we’re here for you at Denver Naturopathic. Let’s walk this path together.
References
Carson, R. (1962). Silent Spring. Houghton Mifflin.
Chang, V.C., Hofmann, J.N., et al. (2023). Glyphosate exposure and urinary oxidative stress biomarkers in the Agricultural Health Study. Journal of the National Cancer Institute, 115(4), 394–404. doi: 10.1093/jnci/djac242
Carroquino, M.J., et al. (2024). Benzene exposure and pediatric leukemia: From molecular clues to epidemiological insights. Toxicology Letters, 398, 107–118.
Global Glyphosate Study (2025). Carcinogenicity study of glyphosate and glyphosate-based herbicides. Cesare Maltoni Cancer Research Center, Ramazzini Institute, in collaboration with Boston College, George Mason University, King’s College London, and Mount Sinai.
Hasan, N.T., Han, D., Xu, X., Sansom, G., & Roh, T. (2024). Relationship between low-level arsenic exposure in drinking water and kidney cancer risk in Texas. Environmental Pollution, 363, 125097. doi: 10.1016/j.envpol.2024.125097
IARC (2006). Formaldehyde, 2-butoxyethanol and 1-tert-butoxypropanol-2-ol. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 88. World Health Organization, Lyon.
IARC (2015). Glyphosate. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 112. World Health Organization, Lyon.
IARC (2023). PFOA classified as carcinogenic to humans (Group 1); PFOS classified as possibly carcinogenic to humans (Group 2B). IARC Monographs, Volume 135.
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Lan, Q., et al. (2004). Hematotoxicity in workers exposed to low levels of benzene. Science, 306(5702), 1774–1776.
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NCI Division of Cancer Epidemiology and Genetics (2023). OEEB Research on “Forever Chemicals.” National Cancer Institute.
NCI (2023). Formaldehyde and Cancer Risk. National Cancer Institute Fact Sheet.
Nielsen, G.D. & Wolkoff, P. (2010). Cancer effects of formaldehyde: a proposal for an indoor air guideline value. Archives of Toxicology, 84(6), 423–446. doi: 10.1007/s00204-010-0549-1
National Toxicology Program (2011). Formaldehyde. Report on Carcinogens, 12th Edition. U.S. Department of Health and Human Services.
Smith, M.T. (2010). Advances in understanding benzene health effects and susceptibility. Annual Review of Public Health, 31, 133–148.
Snyder, R. (2012). Leukemia and Benzene. International Journal of Environmental Research and Public Health, 9(8), 2875–2893. doi: 10.3390/ijerph9082875
US EPA (2024). Final PFAS National Primary Drinking Water Regulation. 89 FR 32532.
US EPA Integrated Risk Information System (IRIS). Available at: https://www.epa.gov/iris
Weisenburger, D.D. (2025). An Update of Evidence that the Herbicide Glyphosate (Roundup) is a Cause of Non-Hodgkin Lymphoma. Clinical Lymphoma, Myeloma and Leukemia. doi: 10.1016/j.clml.2025.10.006
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