Pesticide exposure link to ME/CFS

Pesticides are chemicals that control pests. Pesticides include insecticides (which control insects) and herbicides (which control weeds). The main classes of insecticides are: organophosphates, carbamates, pyrethroids, neonicotinoids and organochlorines. Common organophosphate pesticides include malathion, parathion and chlorpyrifos.

Organophosphates
In one study, Scottish sheep farmers using organophosphate-based sheep dip to protect their sheep against parasites were found to suffer much higher rates of myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS): the prevalence of ME/CFS in these farmers was 4 times the national UK average, implicating organophosphates as a probable causal factor in ME/CFS. Farmers who used organophosphate-based sheep dip were also found to be 10,000 times more likely to suffer from mental health disorders.

Across the UK, at least 500 farmers were left with debilitating health problems after using organophosphate sheep dip, and the Countess of Mar, a life peer in the House of Lords who developed ME/CFS after coming into contact with sheep dip on her farm, has spent the past decades campaigning on the organophosphate issue.

ME/CFS researcher Professor Peter Behan studied the organophosphate link to ME/CFS, and talks about it in this 1997 newspaper article.

In Gulf War Illness (some types of which resemble ME/CFS), most of the toxic exposures and vaccinations that soldiers were exposed to have been ruled out as playing a causal role in GWI. Except for organophosphates, which the studies found strong evidence of playing a role.

Organochlorines
Another class of pesticides called organochlorines (which includes DDT and dieldrin) have also been linked to ME/CFS. However most organochlorines were banned in the 1980s, with some exceptions such as dicofol which is banned in Europe but still used on cotton and fruit crops in the US, and DDT which is still used for malaria control in Africa and parts of Asia.

Pyrethroids
Pyrethroids are synthetic compounds similar to the pyrethrins produced by Chrysanthemum flowers. Pyrethroids are considered less toxic to human than organophosphates, but nevertheless are also linked to ME/CFS.

Broad range of diseases linked to pesticides
An article in The Herald summarizes the wide range of diseases that are associated with pesticide exposure:
 * Asthma — 41 studies linking pesticides to asthma. Studies show that pesticides not only trigger asthma attacks, but are also a root cause of asthma.
 * Birth defects — 19 studies linking pesticides to fetal and birth defects.
 * Cancer — 260 studies linking pesticides to various forms of cancer: 30 studies linking pesticides to brain cancer, 11 studies linking pesticides to breast cancer, 40 studies linking pesticides to leukemia, 46 studies linking pesticides to lymphoma, 23 studies linking pesticides to prostate cancer, 7 studies linking pesticides to soft tissue sarcoma.
 * Learning and developmental disorders — 26 studies linking pesticides to these disorders: 8 studies linking pesticides to ADHD, 5 studies linking pesticides to autism.
 * Diabetes — 6 studies linking pesticides to diabetes.
 * Parkinson’s disease — 65 studies linking pesticides to Parkinson’s.
 * Reproductive health effects — 22 studies linking pesticides to reproductive health issues. These include decreased fertility in both males and females, an androgenic (demasculinizing) effects, increased rates of miscarriage, altered sex ratios and altered maturity.

Pesticides are associated with autoimmune disease: a study of nearly 77,000 women found that those who personally mixed or applied insecticides for 20 years had double the rate of the autoimmune conditions rheumatoid arthritis and systemic lupus erythematosus.

Organophosphate pesticide exposure is linked to psychiatric changes that result in suicidal thoughts and suicidal ideation (suicidality), and may lead to suicide.

Organophosphate exposure during pregnancy causes a 7-point IQ drop in children
A large study in an agricultural community in California found that children who were exposed to organophosphate pesticides during pregnancy had poorer scores for working memory, processing speed, verbal comprehension, perceptual reasoning and intelligence quotient (IQ). Children with the highest prenatal exposures to organophosphates had an IQ which was 7 points lower on average compared to children with the lowest prenatal organophosphate exposures. Organophosphate exposure was determined by measuring organophosphate metabolites in the urine. In this study postnatal exposure to organophosphates was not correlated to poorer intellectual development, only prenatal exposure.

Another large study in New York City found that inner-city children whose mothers had the highest organophosphate exposures during pregnancy (as measured by organophosphate metabolites in the mother's urine) had an IQ which was on average 6.7 points lower compared to children whose mother's had the lowest exposure.

In a study in a farming valley in Mexico employing pesticides agriculturally, the researchers asked children in the valley to draw a person using pencil and paper. The children from the valley were unable to do draw a person: their drawings looked unintelligible, nothing like the human subjects they were asked to draw. But when the researchers asked children of similar age in an adjacent foothills region which did not use pesticides to draw a person, the children from the foothills were quite capable of producing intelligible drawings of a person. The image shows a representative example of the children's drawings from the study.

Pesticides cause structural changes in the basal ganglia of the brain
Studies on asymptomatic agricultural workers exposed to pesticides found micro-structural changes in their substantia nigra, a region in the basal ganglia of the brain. Basal ganglia injury was also found in Gulf War illness patients.

Organophosphates cause immunosuppression
A study in sheep found that the organophosphate pesticide parathion suppressed both the IgM and IgG immune antibody responses, which is thought to be due to the  cholinergic stimulation caused by organophosphates. This may in part explain why organophosphate exposure is a risk factor for ME/CFS, as this disease is usually precipitated by a viral infection, and immunosuppression during the acute phase of infection may allow the virus to breach into tissues compartments such as the brain which it would normally not reach. Exposure to immunosuppressive corticosteroids during acute viral infection is also a risk factor for developing ME/CFS from the infection (see corticosteroids given during acute viral infection may trigger myalgic encephalomyelitis).

Routes of human exposure to pesticides
Pesticides can enter the body through the mouth, skin, eyes or lungs. Sources of pesticide exposure include garden pesticide sprays used by you or your neighbor, which can be tracked into the house on shoes. Agricultural exposure may occur in rural areas through crop spraying. Pesticide exposure can also occur through treating wood with preservatives, and treating livestock with anti-parastitic preparations, such as sheep dip.

The pesticide malathion multiplies its toxicity 1000-fold indoors
The household organophosphate pesticide malathion is particularly dangerous if a significant quantity is spilt in an indoor environment (in a house, workplace, garage or barn): although malathion itself is rated as "class III slightly toxic" in its pesticide toxicity class, the breakdown product of malathion called malaoxon is 33 times more toxic than malathion, and 1,000 times more toxic than malathion in terms of its acetylcholinesterase activity. Thus when malathion is spilt indoors, because it is not dispersed by the wind or rain, it will remain indoors, and as it breaks down into malaoxon, the toxicty is increased by 1000 times, thereby becoming highly toxic to the inhabitants. Absorption or ingestion of malathion into the human body also results in its metabolism to malaoxon.

The oxon breakdown products of malathion, parathion and chlorpyrifos (malaoxon, paraoxon and chloroxon) have also been shown to be 10 to 100 times more toxic than their parent compound to amphibians.

Detoxification of pesticides
Organophosphate pesticides are detoxified from the body by an enzyme called paraoxonase, whose gene is PON1. Mutations in the PON1 gene greatly reduce the ability of paraoxonase to detoxify organophosphates. The person-to-person variation in the ability of paraoxonase to detoxify organophosphate is in the range of 10- to 40-fold, and is determined in part by four SNP mutations in the PON1 gene. Individuals who have PON1 mutations which make paraoxonase less active are much more susceptible to the damage caused by organophosphates. The hormone leptin markedly decreases plasma PON1 activity. High leptin is found in obesity.

Organophosphate and carbamates pesticides do not bioaccumulate to a great degree, and so are removed from the body quickly (the metabolic half-live of organophosphates in the body is in the range of hours to days). They also have low environmental persistence. Organochlorines pesticides on the other hand are environmentally persistent and bioaccumulate in the body fat tissues, so can remain in the body for years or decades (this is the reason organochlorines were banned and largely replaced by organophosphates and carbamates).

One study found organochlorines are expelled during sweating in a sauna. Some ME/CFS patients with high blood levels of organochlorines achieved remission from their symptoms after a detoxification regimen comprising choline and ascorbic acid.

Call to ban all organophosphate pesticides
A systematic review in PLOS Medicine is calling for a blanket ban of all organophosphate pesticides. The paper says that widespread use of organophosphate pesticides to control insects has resulted in ubiquitous human exposures, and that compelling evidence indicates that prenatal organophosphate exposure at low levels is putting children at risk for cognitive and behavioral deficits and for neurodevelopmental disorders. The authors point out that there is no safe level of exposure to any organophosphate pesticide for pregnant women, whose babies suffer disorders ranging from impaired mental and motor skills and memory loss to autism and attention-deficit hyperactivity disorder.

The paper also describes how high exposures to organophosphate pesticides are responsible for poisonings and deaths, particularly in developing countries. The United Nations estimates that 200,000 people die each year from pesticide poisonings, about 99% of them in the developing world.

Learn more

 * Pesticide Action Network (PAN) International
 * Pesticide Action Network USA
 * Pesticide Action Network UK
 * Beyond Pesticides
 * Website of UK pesticide campaigner and journalist Georgina Downs