Hidden Dangers: Uncovering The Carcinogenic Chemicals in Garden Products

Gardening is often seen as a tranquil retreat, a way to connect with nature and nurture life. However, some commonly used synthetic gardening chemicals may pose significant risks to gardeners and their families. While pesticides, herbicides and fungicides are widely used to combat pests and diseases, many gardeners may not realise that some of these chemicals are carcinogenic, posing cancer risks.

This article explores the risks associated with carcinogenic chemicals in gardening, revealing how substances intended to protect plants could potentially harm human health. From widely used herbicides to lesser-known fungicides, we explore the regulatory history, scientific findings, and health implications of garden chemicals classified as carcinogens.

What Are Carcinogens and How Are They Rated

The International Agency for Research on Cancer (IARC), part of the World Health Organization (WHO), classifies substances based on their potential carcinogenicity to humans. Here are the categories used by IARC for classifying these substances:

1. Group 1: Carcinogenic to humans
   • This category is used when there is sufficient evidence from epidemiological studies to support a causal association between exposure to the agent and human cancer. Examples include asbestos, tobacco smoke, and formaldehyde.
2. Group 2A: Probably carcinogenic to humans
   • Agents in this group have limited evidence of carcinogenicity in humans and sufficient evidence in experimental animals. This group suggests a probable risk to humans based on animal studies, supported by mechanistic data or limited data in humans. An example is glyphosate.
3. Group 2B: Possibly carcinogenic to humans
   • This classification is used when there is limited evidence of carcinogenicity in humans and less than sufficient evidence in experimental animals. The evidence suggests a possible risk but is not conclusive. Examples include cell phone radiation.
4. Group 3: Not classifiable as to its carcinogenicity to humans
   • Substances in this category do not fall into any of the other groups due to inadequate evidence of carcinogenicity in humans and animals. This classification does not mean that the agent is not carcinogenic, rather that the current evidence is insufficient to make an assessment. Examples include simazine.
5. Group 4: Probably not carcinogenic to humans
   • This is a rare classification and is used when there is evidence suggesting lack of carcinogenicity in humans and in experimental animals. An example is caprolactam, a chemical used in plastic and paint production.

Each IARC classification reflects a different level of scientific certainty about the carcinogenic risks associated with exposure to a substance. These classifications help guide regulatory decisions and inform public health policies.

It’s important to note that the International Agency for Research on Cancer (IARC) classifies substances as “probably carcinogenic to humans” (Group 2A) and “possibly carcinogenic to humans” (Group 2B) primarily based on animal studies and other indirect evidence, since direct testing of potentially harmful chemicals on humans for carcinogenicity is unethical.

• Group 2A is used when there is limited evidence of carcinogenicity in humans but sufficient evidence in animals, suggesting a probable risk to humans.
• Group 2B is applied when there is limited evidence in humans and less than sufficient evidence in animals, indicating a possible but not conclusively established risk.

These classifications allow for the assessment of potential human risks based on extrapolations from animal data and other scientific findings.

Why Animal Studies Are Used to Test Human Medicines and Poisons

For the sake of scientific precision, it’s important to note that humans are taxonomically categorized as animals within the Kingdom Animalia and, more specifically, as mammals in the Class Mammalia. Consequently, the distinction between the effects of carcinogenic chemicals on animals versus humans is, at best, a weak and tenuous one.

In pharmacological and toxicological research, animal studies are conducted because animals serve as a proxy for humans due to our shared physiological and biochemical functions, as we all belong to the mammalian class. This similarity allows researchers to study the effects of drugs and toxic substances in a controlled environment, providing insights into how these substances might interact with human systems.

Animal models help identify potential therapeutic benefits, side effects, and toxicological risks before proceeding to human trials. Ethical considerations mandate minimising harm and using alternatives when possible, but the biological parallels between humans and animals make these studies indispensable in early-stage research. By understanding how substances affect animals, scientists can make informed predictions about their safety and efficacy in humans, ultimately aiming to develop treatments that are both safe and effective.

Logically, if human trials of commercial drugs and medicines can commence based on their effects on animals, with the inference that the effects on humans will be similar and financially beneficial, then it follows that we can apply the same logic to harmful agricultural products. We can infer that their effects on humans are likely to be equally detrimental, regardless of the financial impact on the corporations that produce and market them.

Understanding Chemical Health Risks and Toxicological Terms Used to Describe Them

Many of these cancer-causing chemicals also have other harmful effects on living organisms, and these properties have been listed using the terms – reproductive toxins, teratogens, mutagens, endocrine disruptors and neurotoxins.

Here’s an explanation of each term related to toxicology and health effects:

1. Carcinogens
   • A carcinogen is any substance or agent that promotes the formation of cancer. Carcinogens can cause cancer by altering cellular metabolism or damaging DNA directly in cells, which interferes with biological processes and induces the uncontrolled, malignant growth. Carcinogens can be chemicals, radiation, or viral agents.
2. Reproductive toxins
   • These refer to the impact of a substance on the reproductive capacity of an organism. This includes effects on sexual function and fertility in adult males and females, as well as developmental effects in offspring. Reproductive effects can include alterations in sexual behavior, decreases in fertility, and menstrual cycle disorders.
3. Teratogens
   • Teratogens are agents that cause malformations of an embryo or fetus. In simpler terms, a teratogen can cause birth defects. The type and severity of the defect depend on when during the pregnancy the exposure occurs, the level and duration of exposure, and the specific type of teratogen.
4. Mutagens
   • Mutagens are substances or physical agents that induce genetic mutations by altering the DNA sequence of an organism. Mutations can lead to cancer and other health problems. A mutagen’s effect might not be directly carcinogenic, but by changing the DNA, it could contribute to the cancer development process indirectly.
5. Endocrine Disruptors
   • Endocrine disruptors are chemicals that can interfere with endocrine (hormonal) systems. These disruptions can cause cancerous tumors, birth defects, and other developmental disorders. Specifically, these agents may mimic a natural hormone, fooling the body into over-responding to the stimulus, or they may inhibit the effects of a hormone from being expressed.
6. Neurotoxins
   • These refer to the impact of substances on the nervous system, including the brain. Effects can include behavioral changes, cognitive impairment, neurodegeneration, and acute symptoms like headaches or dizziness.

Understanding these terms helps in assessing the risk and potential health impacts of exposure to various chemicals and environmental agents.

The List of Carcinogenic Garden and Agricultural Chemicals

Several garden chemicals have been evaluated for their carcinogenic potential by agencies such as the International Agency for Research on Cancer (IARC), the U.S. Environmental Protection Agency (EPA), and other regulatory bodies.

Here are some garden chemicals that are often rated as potentially carcinogenic, organised alphabetically, detailing their use, chemical class, carcinogenic ratings, and any other additional health effects:

1. Atrazine

• Use: Herbicide
• Class: Triazine
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: EPA considers atrazine a potential endocrine disruptor. Concerns about its effects on amphibians and possible links to hormonal disruption in humans. Banned in the EU since 2004 due to concerns over groundwater contamination
• Other Effects: Endocrine disruptor

2. Bifenthrin

• Use: Insecticide
• Class: Pyrethroid
• IARC Rating: Not specifically rated
• Additional Notes: EPA classifies as a possible human carcinogen based on animal studies showing liver tumors. Not explicitly banned but has not been approved for use in the EU due to environmental concerns, particularly its harmful effects on aquatic life
• Other Effects: Potential neurological effects

3. Carbaryl

• Use: Insecticide
• Class: Carbamate
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: EPA classifies it as likely to be carcinogenic to humans based on animal studies. Banned in the EU in 2011.
• Other Effects: Mutagenic and neurotoxic effects reported

4. Cypermethrin

• Use: Insecticide
• Class: Pyrethroid
• IARC Rating: Not specifically rated
• Additional Notes: EPA considers it a possible human carcinogen due to evidence of liver tumors in animal studies.
• Other Effects: Neurological effects

5. Glyphosate

• Use: Herbicide
• Class: Organophosphorus compound
• IARC Rating: Probably carcinogenic to humans (Group 2A)
• Additional Notes: Controversial and widely debated in regulatory and scientific circles. Glyphosate was added to the Proposition 65 list of chemicals known to the state to cause cancer in July 2017. This decision was based on IARC’s classification of glyphosate as “probably carcinogenic to humans.” Therefore, in California, glyphosate is subject to warning requirements under Proposition 65 for products containing it if exposures exceed specified levels. There have been allegations and concerns raised regarding the influence of the glyphosate industry on research and regulatory decisions. Some critics argue that the industry has attempted to downplay or discredit studies showing negative findings regarding glyphosate’s safety, particularly those linking it to cancer or other health risks.

6. Malathion

• Use: Insecticide
• Class: Organophosphate
• IARC Rating: Probably carcinogenic to humans (Group 2A)
• Additional Notes: EPA review suggests low potential for causing cancer in humans under typical exposure scenarios. Banned from use in the EU in 2006.
• Other Effects: Cholinesterase inhibitor, causing neurotoxic effects

7. Mancozeb

• Use: Fungicide
• Class: Dithiocarbamate
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: In February 2021, the European Commission prohibited the use of Mancozeb, the bestselling ethylene-dithiocarbamate (EBDC) fungicide, due to its potential carcinogenic effects on humans. Regulatory bodies in both Europe and the United States have previously assessed EBDCs and their primary metabolite, ethylene thiourea (ETU), arriving at differing conclusions despite reviewing the same data. The IARC reclassified ETU from Group 2B to Group 3 in 2001, signifying that it is not classifiable as to its carcinogenicity to humans. Systematic reviews have found inadequate evidence of carcinogenicity in human studies but sufficient evidence in animal studies concerning EBDC fungicides. Mancozeb is a combination of Zineb and Maneb. Zineb was never approved in the EU (2001), Maneb was banned in 2017.
• Other Effects: Teratogenic and possibly endocrine disruptor effects

8. Paraquat

• Use: Herbicide
• Class: Bipyridyl
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: Banned in many countries due to its high acute toxicity and potential for causing pulmonary fibrosis. Some animal studies show carcinogenic activity.
• Other Effects: Causes severe oxidative stress leading to acute lung injury and other organ damage.

9. Prochloraz

• Use: Fungicide
• Class: Imidazole
• IARC Rating: Not specifically rated
• Additional Notes: Used primarily in agriculture to control fungal diseases in crops such as fruits, vegetables, and cereals. It is also used in wood preservatives and antifungal treatments for textiles. While not specifically rated by the International Agency for Research on Cancer (IARC), regulatory agencies have raised concerns about its potential carcinogenicity and reproductive toxicity. In the European Union, it is classified as a suspected endocrine disruptor and is subject to restrictions.
• Other Effects: Potential endocrine disruptor, reproductive effects.

10. Propiconazole

• Use: Fungicide
• Class: Triazole
• IARC Rating: Not specifically rated
• Additional Notes: EPA classifies as a possible human carcinogen due to evidence of liver tumors in animal studies.
• Other Effects: Possible endocrine disruptor

11. Propoxur

• Use: Insecticide
• Class: Carbamate
• IARC Rating: Not specifically rated
• Additional Notes: EPA classifies propoxur to be a probable human carcinogen, based on bladder tumors in male rats. 
• Other Effects: Neurotoxic effects

12. Rhodamine B

• Use: Synthetic dye used as red marker dye for herbicide application to help visibly identify areas that have been treated.
• Class: Xanthene dye
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3).
• Additional Notes: Restricted in the use of foods and cosmetics in many countries due to potential health risks as a neurotoxic and carcinogenic chemical. Not approved for any foods or products that contact food in the United States.
• Other Effects: Possible carcinogen, concerns about environmental persistence and toxicity as it is considered non-degradable.

13. Simazine

• Use: Herbicide
• Class: Triazine
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: Evidence of endocrine disruption and carcinogenic effects in animal studies. Banned in the EU due to environmental risks, particularly its potential to contaminate groundwater
• Other Effects: Endocrine disruptor

14. Tebuconazole

• Use: Fungicide
• Class: Triazole
• IARC Rating: Not specifically rated
• Additional Notes: EPA classifies as a possible human carcinogen based on animal data showing liver tumors.
• Other Effects: Possible endocrine disruptor

15. Thiram

• Use: Fungicide
• Class: Dithiocarbamate
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: Animal studies show tumor-initiating and promoting effects. Thiram was banned in the European Union (EU) in 2018, and is part of a group of chemicals called Dithiocarbamates (DTCs) that also includes the EU banned Mancozeb and unapproved Zineb fungicides.
• Other Effects: Teratogenic and neurotoxic effects

16. Trifluralin

• Use: Herbicide
• Class: Dinitroaniline
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: EPA classifies as a possible human carcinogen based on thyroid tumors in rats.
• Other Effects: Possible endocrine disruptor

17. Zineb

• Use: Fungicide
• Class: Dithiocarbamate
• IARC Rating: Not classifiable as to its carcinogenicity to humans (Group 3)
• Additional Notes: Not approved in the EU; considered part of the group of chemicals called dithiocarbamates, with several of them being banned or not approved
• Other Effects: Teratogenic and possibly mutagenic effects

Banned Carcinogenic Agricultural and Garden Chemicals

The essence of science is in researching, learning, and revising our understanding of facts. As evidence accumulates over time, it becomes evident that certain chemicals pose significant risks, leading to their prohibition.

Europe, known for its stringent safety regulations, often leads the way in banning or restricting hazardous substances before other countries follow suit. As shown in the previous list, many chemicals have been banned or restricted in Europe due to these strict regulations.

Numerous agricultural and garden chemicals have been banned or restricted due to concerns about their carcinogenic, reproductive, teratogenic, mutagenic, and endocrine-disrupting effects. Here are some notable examples:

1. DDT (Dichloro-Diphenyl-Trichloroethane)

• Use: Pesticide, primarily for mosquito control
• Class: Organochlorine

• Reason for Ban: Banned due to its persistence in the environment, ability to bioaccumulate, and adverse effects on wildlife, particularly birds. It is also a suspected human carcinogen.
• Effects: Carcinogenic, endocrine disruptor.
• Year/Decade Banned: Widely banned starting in the 1970s; U.S. ban took effect in 1972.

2. Aldrin and Dieldrin

• Use: Insecticides for soil and crop protection
• Class: Organochlorine

• Reason for Ban: Both were banned due to their high toxicity, persistence in the environment, and potential to bioaccumulate. They are also linked to health risks including cancer.
• Effects: Carcinogenic, neurotoxic.
• Year/Decade Banned: Banned in the U.S. and many other countries during the 1970s and 1980s.

3. Chlordane

• Use: Insecticide for termite control and crop protection
• Class: Organochlorine

• Reason for Ban: Banned because of its environmental persistence and potential to harm human health.
• Effects: Carcinogenic, potential endocrine disruptor.
• Year/Decade Banned: U.S. ban took effect in 1988.

4. Heptachlor

• Use: Insecticide for termite control and soil treatment
• Class: Organochlorine

• Reason for Ban: Banned due to its toxicity, persistence, and bioaccumulation potential.
• Effects: Carcinogenic, reproductive and developmental effects.
• Year/Decade Banned: Banned in the U.S. for agricultural uses in 1988.

5. Endrin

• Use: Insecticide and rodenticide
• Class: Organochlorine

• Reason for Ban: Banned because of its high acute toxicity, persistence in the environment, and potential for bioaccumulation.
• Effects: Carcinogenic, neurotoxic.
• Year/Decade Banned: Phased out in the U.S. by 1986.

6. Paraquat

• Use: Herbicide for weed and grass control
• Class: Bipyridyl (or Dipyridyl)

• Reason for Ban: Restricted in many countries due to high acute toxicity and potential link to Parkinson’s disease.
• Effects: Potentially carcinogenic, oxidative stress leading to acute lung damage and other organ damage.
• Year/Decade Banned: Severely restricted in the EU and banned in over 50 countries; still used under strict regulations in the U.S. as of 2020.

7. Vinclozolin

• Use: Fungicide for fruit and vegetable crops
• Class: Dicarboximide

• Reason for Ban: Banned or restricted due to its anti-androgenic activity and endocrine-disrupting potential.
• Effects: Endocrine disruptor, reproductive effects.
• Year/Decade Banned: Banned in the European Union in 2002.

8. Methyl Parathion

• Use: Insecticide for pest control in agriculture
• Class: Organophosphate

• Reason for Ban: Severely restricted in many countries due to its high toxicity to humans, especially children.
• Effects: Neurotoxic, mutagenic.
• Year/Decade Banned: Severe restrictions implemented in the early 2000s.

9. Endosulfan

• Use: Insecticide and acaricide (control of mites) for crop protection
• Class: Organochlorine

• Reason for Ban: Banned or severely restricted in many countries due to its high toxicity to humans and wildlife, as well as its persistence in the environment.
• Effects: Classified as a possible human carcinogen by some regulatory agencies and research bodies. Known to have neurotoxic effects and can also impact reproductive health and fertility.
• Year/Decade Banned: Phased out in the United States by 2016 due to concerns about its extreme toxicity and environmental impact. Banned or restricted in several other countries in the early 2000s due to similar concerns.

These dates and the nature of restrictions or bans reflect the gradual recognition and regulatory response to the health and environmental risks posed by these chemicals.

Over time, as more evidence is collected, it is anticipated that numerous carcinogenic chemicals now available to the general public will be banned and included in the expanding list of prohibited agricultural and garden chemicals.

In conclusion, understanding the risks associated with garden chemicals transcends mere familiarity with their chemical names and safety data sheets; it’s about making informed decisions that affect our health and environmental legacy. Whether you’re a home gardener, a professional landscaper, or simply someone concerned about environmental health, this article about carcinogenic garden chemicals is both a caution and a call to action. Stay informed, safeguard your health, and consider natural and environmentally-friendly alternatives to help keep your garden beautiful and your body healthy.