A ‘toxin’ can be defined as ‘a poisonous substance that causes disease’.Cambridge English Dictionary. (2017). ‘Toxin’. [online] Available at: [accessed 27 Nov. 2017].

There are two types of toxins: exogenous and endogenous:Galitzer, M. (2011). ‘Toxicity’. [online] American Health Institute. Available at: [accessed 4 Sept. 2017].

  • Exogenous toxins are all around us, and we absorb them by breathing, eating, drinking, using personal care products and pharmaceuticals etc.
  • Endogenous toxins are created in our bodies, usually by compromised digestion, inefficient metabolism, or poor detoxification

We are exposed to exogenous toxins every day, in a variety of ways, including:

  • The air we breathe
  • The food we eat and the beverages we drink
  • The personal hygiene and household products we use

And the levels of these toxins are getting higher. Between 1965 and 2006, the number of chemicals added to our environment rose from around 200,000 to over 88 million.Binetti, R., Costamagna, F.M., Marcello, I. (2008). ‘Exponential growth of new chemicals and evolution of information relevant to risk control’. Annali dell’Istituto Superiore di Sanita, [online] 44(1), pp.13–15. Available at: [accessed 4 Sept. 2017].

Toxins, both exogenous and endogenous, are already well-known for their physical health effects. But they can have significant effects on our mental health as well. For instance, they can affect our hormonal balance, inflammation levels, gut health etc., and it’s the disruption of these systems that contributes to mental health symptoms.

How toxicity happens

Our levels of toxicity are affected not only by our exposure to toxins, but by how well we eliminate them as they build up in our bodies.

Our detoxification systems include our:

  • Liver
  • Kidneys
  • Colon
  • Blood
  • Lymphatic system
  • Skin

If we’re chronically exposed to toxins, our detoxification systems may become unable to cope. Our bodies will hold onto these toxins, rather than eliminating them, which will affect our physical and mental health.

Poor detoxification can be caused by a range of factors:

  • Inefficient or reduced function in the organs of detoxification (as listed above)
  • Reduced enzyme function in the body, caused by damage to (for instance) the liver or the kidneys
  • Poor nutrition (diets low in fibre, food without nutrients)

Some common toxins, their sources, and their effects

Exogenous toxins are found in many of the things we encounter every day, from cleaning products to tap-water. Endogenous toxins, meanwhile, are produced by the body itself.

Below are some common sources of toxins.

Alcohol abuse can damage our brains both during their early development, and later on in our adult lives.

Alcohol and brain development

Alcohol is a neuro-developmental toxin. This means that it can affect children’s brain development during both the pregnancy and breastfeeding stages.

If an expectant mother consumes alcohol, for instance, research suggests that it may lead to a number of problems in the unborn child, such as:Falgreen, H.-L., Mortensen, E.L., Kilburn, T., Underbjerg, M., Bertrand, J., Støvring, H., Wimberley, T., Grove, J., Kesmodel, U.S. (2012). ‘The effects of low to moderate prenatal alcohol exposure in early pregnancy on IQ in 5-year-old children’. BJOG, [online] 119(10), pp.1191–1200. Available at: [accessed 27 Nov. 2017].

  • Reduced IQ
  • Impaired executive functions, including:
    • Attention
    • Memory
    • Reasoning
    • Problem-solving
    • Planning
  • Delinquent behaviour
  • Seizures
  • Problems with the sensory system

Alcohol and brain function

In adults, dementia and alcohol abuse are closely connected. There’s a high prevalence of alcohol abuse in patients with dementia, at 9–22%, while rates of dementia in alcohol abusers are also high, at 10–24%.Alzheimer’s Society. (2015). ‘Alcohol-related brain damage (including Korsakoff’s syndrome)’. [online] Available at: [accessed 27 Nov. 2017].

Two types of dementia are particularly associated with alcohol abuse:Edwards, T.J., Sherr, E.H., Barkovich, A.J., Richards, L.J. (2014). ‘Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes’. Brain, [online] 137(6), pp.1579–1613. Available at: [accessed 1 Sept. 2017].Ghosh, A. (2010). ‘Endocrine, metabolic, nutritional, and toxic disorders leading to dementia’. Annals of Indian Academy of Neurology, [online] 13(6), pp.63–68. Available at:;year=2010;volume=13;issue=6;spage=63;epage=68;aulast=Ghosh [accessed 1 Sept. 2017].Ridley, N.J., Draper, B., Withall, A. (2013). ‘Alcohol-related dementia: an update of the evidence’. [online] Alzheimer’s Research and Therapy, 5(3), p.3. Available at: [accessed 1 Sept. 2017].

  • Marchiafava-Bignami disease
    • This mainly affects male chronic alcoholics
    • Its presentation is variable, but it can progress rapidly
    • The cognitive problems resemble diseases that affect the frontal lobe of the brain
    • It results in disinhibited and socially inappropriate behaviour, with emotional outbursts
  • Alcoholic dementia, including Wernicke-Korsakoff syndrome
    • This is a vague category, which consists of various combinations of neurological disorders
    • They result in both poor memory and one of the following cognitive issues:
      • Aphasia (problems with speech)
      • Ataxia (problems with motor function)
      • Agnosia (problems identifying people or objects)
      • Difficulties with executive function (making plans, organising, and so on)

Research has suggested that for urban dwellers, air pollution may be a factor in any toxicity issues they have.

For instance, levels of black carbon in the air have been connected to decreased cognitive function, and there’s evidence for a connection between NO2 exposure and decreases in memory-span.van Kempen, E., Fischer, P., Janssen, N., Houthuijs, D., van Kamp, I., Stansfeld, S., Cassee, F. (2012). ‘Neurobehavioral effects of exposure to traffic-related air pollution and transportation noise in primary schoolchildren’. Environmental Research, [online] 115, pp.18–25. Available at: [accessed 1 Sept. 2017].

Bacteria, viruses, and parasites can all act as endocrine disruptors, and so disturb our hormonal balance. They can also create an inflammatory-immune response. In both cases, these effects can lead to mental health issues.


A number of bacterial species have been known to produce toxins, as part of their infectious effects.Los, F.C., Randis, T.M., Aroian, R.V., Ratner, A.J. (2013). ‘Role of pore-forming toxins in bacterial infectious diseases’. Microbiology and Molecular Biology Reviews, [online] 77(2), pp.173–207. Available at: [accessed 1 Sept. 2017].


Some viruses act like toxins, by causing cell damage and death. Others damage our bodies’ ability to fight toxins, by damaging our white blood cells.NIH – National Cancer Institute. (2017). ‘Leukocytes (white blood cells)’. [online] Available at: [accessed 27 Nov. 2017].


Parasites are organisms that live inside our bodies. They not only take for themselves the nutrients we’ve consumed, but they use them to produce toxins which are actively damaging to us.Wellcome Genome Campus. (2015). ‘What are infectious diseases?’ [online] Available at: [accessed 27 Nov. 2017].

The range of substances known as ‘drugs’ is very wide, but whether they’re pharmaceutical or recreational, they share a common set of toxic effects.

Recreational drugs

Plant-based recreational drugs include:

  • Heroin
  • Cocaine
  • Cannabis/marijuana

Synthetic drugs include:

  • Amphetamines, including speed
  • Methylenedioxymethamphetamine (MDMA), also known as ‘ecstasy’

One growing category of synthetic drug is ’Chemsex’ (‘chemical’ and ‘sex’) drugs. These include:McCall, H., Adams, N., Mason, D., Willis, J. (2015). ‘What is chemsex and why does it matter?’ British Medical Journal, [online] 351(h5790). Available at: [accessed 1 Sept. 2017].

  • Mephedrone
  • Gamma-hydroxybutyrate (GBH or just ‘G’)
  • Gamma-butyrolactone (GBL)
  • Crystallised methamphetamine (‘crystal meth’)

Pharmaceutical drugs

Many different kinds of prescription and over-the-counter medication can affect our detoxification systems. They can overload the liver and kidneys, damage the gut, and disturb our hormonal balance, all of which can contribute to mental health issues.

These pharmaceutical drugs include:

  • Antibiotics
  • Non-steroidal anti-inflammatory drugs (NSAIDs)
  • Contraceptive pills and synthetic hormone replacement therapies (HRTs)
  • Psychotropic medication

Pharmaceutical and personal-care products are also a major source of ocean pollution, which can in turn damage our environment and lead to further health issues. One study, for instance, found a large number of toxic substances connected to these products around the Antarctic coast.Emnet, P., Gaw, S., Northcott, G., Storey, B., Graham, L. (2015). ‘Personal care products and steroid hormones in the Antarctic coastal environment associated with two Antarctic research stations, McMurdo Station and Scott Base’. Environmental Research, [online] 136, pp.331–342. Available at: [accessed 1 Sept. 2017].

Both recreational and pharmaceutical drugs can contribute to:Degenhardt, L., Hall, W. (2012). ‘Extent of illicit drug use and dependence, and their contribution to the global burden of disease’. The Lancet, [online] 379(9810), pp.55–70. Available at: [accessed 1 Sept. 2017].

  • Intoxication, which can lead to violence/damage to ourselves or others
  • Psychological dependence, which involves a state of reduced pleasure, unease, or anxiety when we stop taking the drug
  • Other longer-term mental health symptoms, such as:

Contaminated food poses a risk to us all. Everyone eats regularly, and many of us don’t grow our own food or know exactly how it was produced.

There are a range of ways in which toxins can get into food. Different types of food are produced by different methods around the world, but there are some notable common issues:Greger, M., Stone, G. (2015). How Not to Die. London: Macmillan, pp.232–4.Gluck, M., Edgson, V. (2010). It Must Be My Hormones. Camberwell: Penguin, p.144.Chilkov, N. (2017.) ‘Grilled foods contain cancer-causing chemicals’. [online] Available at: [accessed 28 Nov. 2017].

  • Non-organic foods can be contamined by pesticides and herbicides (see below)
  • Dairy and fish products have been found to have high levels of hexachlorobenzene (a fungicide)
  • Seafood can accumulate toxins from industrial pollution in the ocean
  • Dairy, eggs, and processed meat products have been found to have unhealthy quantities of dioxins
  • A few growth hormones commonly added to meat and dairy can (even in tiny quantities) alter the balance of estrogen and progesterone in some women
  • Grilling and barbecuing meat may increase the risk of carcinogenic (cancer-causing) toxins being released

Fragrance, or perfume, is a key ingredient in many personal-care products.

It’s important to note that lots of different substances can be referred to as ‘fragrance’. It’s increasingly become a general, positive-sounding term for obscure chemicals.Ryan, J. (2017). ‘Dangers of fragrance’. The Hearty Soul. Available at: [accessed 28 Nov. 2017].

Many of these chemicals are endocrine disruptors. If we absorb them through our skin, they can get into our bloodstream and affect our hormonal balance.

They can affect our levels of:

And they’ve been linked to some cases of:Ryan, J. (2017). ‘Dangers of fragrance’. The Hearty Soul. Available at: [accessed 28 Nov. 2017].

  • Breast cancer
  • Prostate cancer
  • Obesity
  • Diabetes
  • Thyroid issues (hypothyroidism, autoimmune thyroid diseases)

Heavy metal poisoning can contribute to hormonal and neurotransmitter imbalances. They tend to be found in tap water, pesticides, and certain foods such as fish.

Some common heavy metals are listed below.


Mercury is found in large edible fish, such as tuna, swordfish, and shark. It’s also a key component of some dental fillings.

Mercury toxicity has been linked to several mental health issues, including:Wojcik, D.P., Godfrey, M.E., Christie, D., Haley, B.E. (2006). ‘Mercury toxicity presenting as chronic fatigue, memory impairment and depression: diagnosis, treatment, susceptibility, and outcomes in a New Zealand general practice setting (1994–2006)’. Neuro Endocrinology Letters, [online] 27(4), pp.415–423. Available at: [accessed 4 Sept. 2017].Ghosh, A. (2010). ‘Endocrine, metabolic, nutritional, and toxic disorders leading to dementia’. Annals of Indian Academy of Neurology, [online] 13(6), pp.63–68. Available at:;year=2010;volume=13;issue=6;spage=63;epage=68;aulast=Ghosh [accessed 1 Sept. 2017].Ridley, N.J., Draper, B., Withall, A. (2013). ‘Alcohol-related dementia: an update of the evidence’. Alzheimer’s Research and Therapy, [online] 5(3), p.3. Available at: [accessed 1 Sept. 2017].

  • Chronic fatigue disorder
  • Alzheimer’s disease
  • Depression

Mercury is an endocrine disruptor, and so it can cause severe hormonal imbalances too.Gersh, F. (2017). ‘Estrogen and mental health: exploring estrogen’s vital role linking the brain, the gut microbiome, and the immune system’. Paper given at the Eighth Annual Integrative Medicine for Mental Health Conference, September 2017.


Methylmercury has been shown to affect our neuro-development, by damaging stem cells in the brain.

One study showed that children who were exposed to methylmercury showed developmental deficits by the age of 7, and hadn’t overcome that deficit by their mid-teens.Debes, F., Weihe, P., Grandjean, P. (2016). ‘Cognitive deficits at age 22 years associated with prenatal exposure to methylmercury’. Cortex, [online] 74, pp.358–369. Available at: [accessed 1 Sept. 2017].


Lead is commonly found in old pipes and household paint, as well as some contaminated foods.Greger, M., Stone, G. (2015). How Not to Die. London: Macmillan, p.237.

It can have very severe effects on our mental health:Ghosh, A. (2010). ‘Endocrine, metabolic, nutritional, and toxic disorders leading to dementia’. Annals of Indian Academy of Neurology, [online] 13(6), pp.63–68. Available at:;year=2010;volume=13;issue=6;spage=63;epage=68;aulast=Ghosh [accessed 1 Sept. 2017].Reyes, J.W. (2015). ‘Lead exposure and behavior: Effects on antisocial and risky behavior among children and adolescents’. Economic Inquiry, [online] 53(3), pp.1580–1605. Available at: [accessed 1 Sept. 2017].

  • Patients exposed to lead often have lowered brain volumes
  • Exposure in early childhood is associated with reduced school performance and delinquent behaviour in later life
  • There is no safe level of lead exposure: very low levels of lead can still be highly damaging to the brain
  • Cognitive problems caused by lead exposure can occur a long time after exposure has stopped
  • The effects of lead neurotoxicity are almost always permanent

Lead is an endocrine disruptor, and so it can cause severe hormonal imbalances too.Gersh, F. (2017). ‘Estrogen and mental health: exploring estrogen’s vital role linking the brain, the gut microbiome, and the immune system’. Paper given at the Eighth Annual Integrative Medicine for Mental Health Conference, September 2017.


Arsenic is often found in poultry and rice. Because it’s used in pesticides, it’s also often present in non-organic produce.

It can have a range of different effects on our mental health:Ghosh, A. (2010). ‘Endocrine, metabolic, nutritional, and toxic disorders leading to dementia’. Annals of Indian Academy of Neurology, [online] 13(6), pp. 63–68. Available at:;year=2010;volume=13;issue=6;spage=63;epage=68;aulast=Ghosh [accessed 1 Sept. 2017].Ridley, N.J., Draper, B., Withall, A. (2013). ‘Alcohol-related dementia: an update of the evidence’. Alzheimer’s Research and Therapy, [online] 5(3), p.3. Available at: [accessed 1 Sept. 2017].Tolins, M., Ruchirawat, M., Landrigan, P. (2014). ‘The developmental neurotoxicity of arsenic: cognitive and behavioral consequences of early life exposure’. Annals of Global Health,  [online] 80(4), pp.303–314. Available at: [accessed 1 Sept. 2017].

  • Chronic arsenic exposure can lead to issues with cognitive functions such as memory and behaviour
  • It can also precipitate psychotic symptoms, such as delusions and hallucinations
  • Prenatal and early postnatal exposure have been linked with cognitive deficits in children, which become apparent by the time they start at school

This is by no means an exhaustive list. Other common heavy metals include cadmium, radium, copper, and barium, all of which can have similar health effects.

Toxic substances are present in a number of chemicals we use around our homes, or in the workplace.

Below are some of the most common.


Toluene is found in glue, paint, and petrol. Chronic toluene exposure can lead to cognitive and behavioural problems, because it crosses the blood-brain barrier easily, and can cause brain cell death.Ghosh, A. (2010). ‘Endocrine, metabolic, nutritional, and toxic disorders leading to dementia’. Annals of Indian Academy of Neurology, [online] 13(6), pp. 63–68. Available at:;year=2010;volume=13;issue=6;spage=63;epage=68;aulast=Ghosh [accessed 1 Sept. 2017].Ridley, N.J., Draper, B., Withall, A. (2013). ‘Alcohol-related dementia: an update of the evidence’. Alzheimer’s Research and Therapy, [online] 5(3), p.3. Available at: [accessed 1 Sept. 2017].


Solvents are often found in contaminated drinking water (see below), but many jobs also involve the heavy use of solvents.

Research shows that children with mothers using solvents at work (nurses, hospital workers, cleaners, hairdressers, beauticians) may be vulnerable to behavioural and psychiatric problems, from as young as the age of two.Pelé, F., Muckle, G., Costet, N., Garlantézec, R., Monfort, C., Multigner, L., Rouget, F., Cordier, S. (2013). ‘Occupational solvent exposure during pregnancy and child behaviour at age 2’. Occupational and Environmental Medicine, [online] 70(2), pp.114–119. Available at: [accessed 1 Sept. 2017].

Fire retardants

Fire retardants, also known as ‘flame retardants’, are found in foam, furniture, mattresses, and some clothing.Green Science Policy Institute. (2013). ‘Flame retardants’. [online] Available at: [accessed 28 Nov. 2017].

They’ve been shown to damage brains in the early stages of development.Costa, L.G., Giordano, G. (2011). ‘Is decabromodiphenyl ether (BDE-209) a developmental neurotoxicant?’ NeuroToxicology, [online] 32(1), pp.9–24. Available at: [accessed 28 Nov. 2017].


Formaldehyde is a chemical found in foam, fire retardants, wallpaper, mirrors, dyes, and other common household objects.Agency for Toxic Substances and Disease Registry. (2014). ‘Medical Management Guidelines for Formaldehyde’. [online] Available at: [accessed 28 Nov. 2017].

It can contribute to a range of serious physical symptoms. Some of these, including breathing problems and gut issues, may in turn contribute to mental health symptoms.

Water-damaged buildings often have bacteria growing in them, with fungal elements. These are collectively known as ‘mould’.

The toxic substances produced by mould are known as mycotoxins. If you ingest them, your gut and/or sinuses can become damaged, and there may be a range of mental health effects:Scott, T., Carnahan, J. (2015). ‘Is toxic mould the hidden cause of your anxiety?’ [online] The Anxiety Summit, Season 3. Available at: [accessed 28 Nov. 2017].Brewer, J.H., Thrasher, J.D, Hooper, D. (2014). ‘Chronic illness associated with mold and mycotoxins: is naso-sinus fungal biofilm the culprit?’ Toxins, [online] 6(1), pp.66–80. Available at: [accessed 28 Nov. 2017].

  • Mycotoxins affect our capillaries’ health and permeability, meaning that we may not get enough oxygen to our tissues; this can result in:
  • Mycotoxins increase the production of inflammatory cytokines, which have been linked to anxiety and depression
  • They can cause a deficit in the process of DNA methylation, which means that our bodies become less able to repair their cells
  • DNA methylation is also essential for the production of neurochemicals such as serotonin, GABA, dopamine, epinephrine, and norepinephrine, which regulate our moods

The overuse of pesticides, herbicides, and fungicides is a global problem.

Some of them are now banned in high-income countries, including the most toxic ones and the ones which accumulate slowest. Many, however, are still widely used in low- and middle-income countries.

These substances are used in residential, industrial, and agricultural environments, and tend to be found in:

  • Non-organic fruits, vegetables, meat, poultry, dairy, grains (and so on)
  • Tap water
  • Substances brought indoors on our shoes

The symptoms of pesticide poisoning (to which herbicide and fungicide poisoning are similar) include:Cornell University. (2012). ‘Symptoms of pesticide poisoning’. [online] Pesticide Safety Education Program. Available at: [accessed 26 Oct. 2017].

  • Headaches
  • Fatigue
  • Weakness
  • Dizziness
  • Restlessness
  • Nervousness
  • Moodiness

If the poisoning is acute, it can lead to lasting neurobehavioural deficits. These substances are able to disrupt our brain function, by altering the balance of our neurotransmitters.

For instance, atrazine (the most common agricultural pesticide) can decrease our levels of acetylcholinesterase, an enzyme involved in the production of acetylcholine. Low levels of acetylcholine have been linked with poor memory, anxiety, and depression; research has shown high levels of anxiety and depression levels in farmers who use these pesticides.Schmidel, A.J., Assmann, K.L., Werlang, C.C., Bertoncello, K.T., Francescon, F., Rambo, C.L., Beltrame, G.M., Calegari, D., Batista, C.B., Blaser, R.E., Roman Júnior, W.A., Conterato, G.M., Piato, A.L., Zanatta, L., Magro, J.D., Rosemberg, D.B. (2014). ‘Subchronic atrazine exposure changes defensive behaviour profile and disrupts brain acetylcholinesterase activity of zebrafish’. Neurotoxicology and Teratology, [online] 44, pp.62–69. Available at: [accessed 1 Sept. 2017].Higley, M.J., Picciotto, M.R. (2014). ‘Neuromodulation by acetylcholine: examples from schizophrenia and depression’. Current Opinion in Neurobiology, [online] 29, pp.88–95. Available at: [accessed 1 Sept. 2017].Nnama, H. (2017). ‘The benefits of acetylcholine’. [online] Available at: [accessed 15 Nov. 2017].

Pesticides can also deplete the nutrient levels in plants, depriving us of their nutritional benefits and contributing to nutritional imbalances. These, in turn, may lead to mental health issues.Scott, T., Rucklidge, J. (2015). ‘What if… nutrition could treat anxiety and depression?’ [online] The Anxiety Summit, Season 3. Available at: [accessed 28 Nov. 2017].

Petrochemicals are commonly found in petrol, and the vapour surrounding it at petrol stations or busy roads.

But this isn’t the only way we can be exposed to them. Other types of petrochemical, including parabens and DDT, can be found in household appliances and objects.

Many petrochemicals are xenoestrogens. This means that in women’s bodies, they can mimic the sex hormone estrogen. This may contribute to hormonal imbalances, which can lead to a number of mental health issues.

There are many different types of plastic chemical, all of which are toxic.

The three main kinds are:

  • BPA (bisphenol A), found in water bottles, CDs/DVDs, and sports equipment
  • Phthalates, found in cosmetics, detergents, and items made from PVC (polyvinyl chloride plastic)
  • PCBs (polychlorinated biphenyls), found in coolants, industrial fluids, and carbon-copy paper

Studies have connected exposure to plastic toxins with developmental problems in children. These toxins can affect our levels of male and female sex hormones, affecting children in the womb and in infancy.Scott, T. (2016). ‘Anxiety Summit Opening: benzos, electroshock, blueberries, sauerkraut and the vagus nerve’. [online] The Anxiety Summit, Season 4. Available at: [accessed 28 Nov 2017].Jurewicz, J., Polańska, K., Hanke, W. (2013). ‘Chemical exposure early in life and the neurodevelopment of children: an overview of current epidemiological evidence’. Annals of Agricultural and Environmental Medicine, [online] 20(3), pp.465–486. Available at: [accessed 1 Sept. 2017].

They’ve been connected to the onset of mental health symptoms including:

Research has shown a strong correlation between smoking and mental health symptoms.

Smoking can introduce huge numbers of oxidants into the body, including the brain. This may lead to healthy brain fats becoming damaged. Cigarette smoke also contains large amounts of cadmium, which can lower our zinc levels.Holford, P. (2004). Patrick Holford’s New Optimum Nutrition Bible. London: Piatkus, p.80.

Conversely, nicotine withdrawal has been shown to interfere with our serotonin levels, which can affect our moods, and also with the development of our brains in early adulthood.Smith, P.H., Homish, G.G., Giovino, G.A., Kozlowski, L.T. (2014). ‘Cigarette smoking and mental illness: a study of nicotine withdrawal’. American Journal of Public Health, [online] 104(2), e127–e133. Available at: [accessed 1 Sept. 2017].

Tap water varies considerably according to region, but in Western counties it’s usually safe to drink.

But it does contain varying degrees of chemicals, which can become toxic in high quantities, and are better filtered out if possible.

The two principal substances are:Herron, J.G. (2015). ‘The science behind enemas’. [online] The Gut Health Protocol. Available at: [accessed 28 Nov. 2017].Maserejian, N.N., Shrader, P., Trachtenberg, F.L., Hauser, R., Bellinger, D.C., Tavares, M. (2014). ‘Dental sealants and flowable composite restorations and psychosocial, neuropsychological, and physical development in children’. Pediatric Dentistry, [online] 36(1), pp.68–75. Available at: [accessed 1 Sept. 2017].

  • Chlorine
    • This is found not only in tap water, but in swimming pools and cleaning products
    • Excessive levels can be harmful for the bacteria in our gut, causing gut dysbiosis 
  • Fluorine, and related compounds
    • This is commonly added to public water supplies
    • Excessive levels have been shown to cause an average IQ decrease of 7 points in children

Contamination or poor preparation can cause many other chemicals to enter our water supply. These can include:Freshly Squeezed Water. (2017). ‘What’s in your drinking water?’ [online] Available at: [accessed 26 Oct. 2017].

  • Trihalomethanes (THMs)
  • Heavy metals, including:
    • Arsenic
    • Radium
    • Aluminum
    • Copper
    • Lead
    • Mercury
    • Cadmium
    • Barium
  • Hormones
  • Pharmaceuticals
  • Nitrates
  • Pesticides, herbicides, and fungicides

(For more on the potential effects of heavy metals and pesticides, see above.)

Proving the effects of toxins on our mental health

The relationship between toxins and mental health is still poorly understood.

We know that toxins affect our mental health indirectly, in the ways suggested above. For instance, they can affect our hormonal balance, inflammation levels, gut health and so on, and it’s the disruption of these systems that contributes to mental health symptoms.

The difficulty up to now has been showing how much of the disruption is caused by toxicity, and exactly how its various effects work. But research is beginning to prove the links between toxins and mental health.Hyman, M. (2009). The UltraMind Solution. New York, NY: Scribner, pp.216–242.

Some examples of recent evidence are described below.

During the foetal stage and early infancy, the blood-brain barrier only gives children a partial protection against the chemicals taken in from the womb or the surrounding world. This is because our growing brains need a lot of nutrients, so the barrier needs to be ‘leaky’ to allow them to cross.Zheng, W., Aschner, M., Ghersi-Egea, J.-F. (2003). ‘Brain barrier systems: a new frontier in metal neurotoxicological research’. Toxicology and Applied Pharmacology, [online] 192(1), pp.1–11. Available at: [accessed 4 Sept. 2017].

At these stages, children are particularly vulnerable to toxins. The developing nervous system, in particular, is at high risk of damage. Several neurodevelopmental disorders have recently been linked to toxic exposure, including:

  • Autism
  • Dyslexia
  • Attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD)

Studies show that these disorders affect around 10–15% of births, and are believed to be increasing in frequency. Since genetic factors account for only 30–40% of all neurodevelopmental disorders, we’re now learning that enviromental factors, such as toxins, must be playing a key role.Hagel, M. (2017). ‘Autism: the role of the microbiome’. [online] Naturopathic Currents. Available at: [accessed 28 Nov. 2017].

Some neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, have been linked to toxic pollutants. The potential contributors include:Greger, M., Stone, G. (2015). How Not to Die. London: Macmillan, pp.232–234.

  • Heavy metals
  • Solvents
  • Chemicals from plastics such as polychlorinated biphenyls (PCBs)
  • Pesticides such as DDT

Alzheimer’s disease is the most common neurodegenerative disease, and Parkinson’s disease is the second most common. They both, at different stages, affect our motor skills, cognitive function, and powers of speech.

Research is starting to show that environmental toxins may be linked to the development and progress of both of these diseases.Goldman, S.M. (2014). ‘Environmental toxins and Parkinson’s disease’. Annual Review of Pharmacological Toxicology, [online] 54, pp.141164. Available at: [accessed 28 Nov. 2017].Calderón-Garcidueñas, L., Reed, W., Maronpot, R.R., Henriquez-Roldán, C., Delgado-Chavez, R., Calderón-Garcidueñas, A., Dragustinovis, I., Franco-Lira, M., Aragón-Flores, M., Solt, A.C., Altenburg, M., Torres-Jardón, R., Swenberg, J.A. (2004). ‘Brain inflammation and Alzheimer’s-like pathology in individuals exposed to severe air pollution. Toxicologic Pathology, [online] 32(6), pp.850–858. Available at: [accessed 28 Nov. 2017].