Pesticides and Parkinson’s

The causes of Parkinson’s are complex and still not fully understood. For the vast majority of people with the condition, there is no way to tell what has caused them to develop Parkinson’s. Multiple factors are likely to have contributed.

Age is the greatest risk factor associated with the condition, but a range of genetic, environmental and lifestyle factors have also been identified that can increase risk.

When we talk about environmental factors this can include someone’s exposure to chemicals or substances that may cause changes within the body. We all are exposed to different things and in differing amounts in our environment depending on our jobs, where we live and many other factors.

Pesticides are one group of chemicals that we get asked about a lot at Parkinson’s UK.

What are pesticides?

Pesticides are a broad group of chemicals that are used to kill pests, from insects to weeds. They can be used on a small scale in people’s gardens to on a more industrial scale for instance in farming.

Pesticides work by targeting a specific function of the insect’s or plant’s biology to kill the unwanted pest. Different pesticides will come with different warnings to human health and instructions should be followed. Pesticides are carefully regulated in the UK, and beyond, to help protect from harmful effects.

What’s the evidence that pesticides increase the risk of Parkinson’s?

Over 50 studies have been carried out in the last 40 years.

The results have been varied, but overall the current evidence suggests that exposure to certain pesticides may increase risk of Parkinson’s. However the evidence isn’t strong enough to say that pesticides cause Parkinson’s directly.

In other words, it may be a factor in the development of the condition for some people. But it is not as clear-cut as, for instance, the link between smoking and lung cancer.

Which pesticides have been linked to Parkinson’s?

Let’s take a look at some of the pesticides that have been linked to Parkinson’s:

Trifluralin

Most commonly used in the cotton agricultural industry has been banned in the UK, among other places, since 2008. A study looking at various pesticides and how they impacted brain cells grown in the lab, showed that pesticides containing trifluralin were the most damaging. More research is needed to understand more about the toxic effects of trifluralin.

Read our news story from 2023 that summarises the research looking at specific pesticides on brain cells grown in the lab.

Paraquat (PQ)

Probably the most high profile pesticide that has been linked to Parkinson’s. In 2011, a US study showed a link between paraquat use and an increased risk of Parkinson’s in farm workers. Read more about this US-based study on the National Institutes of Health website.

A recent study from 2020 in mice showed that inhaling low levels of paraquat led to changes in the mice’s brains that led to a loss of smell, something that can be an early sign of Parkinson’s. Read more about the 2020 study of paraquat in mice.

Aside from its possible connections to Parkinson’s, paraquat is extremely dangerous and ingesting it can be fatal. Paraquat has been banned in the UK since 2007.

Rotenone

In 2000, researchers discovered that rotenone injections, in higher doses than humans are exposed to, caused the development of symptoms similar to Parkinson’s in rats. Research from 2023 builds on this, showing that a shorter exposure to rotenone showed a delayed but progressive effect in the brain cells of rats. This might help explain why symptoms may occur years after someone has been exposed to the chemical. Read the full scientific paper investigating rotenone in rats.

In 2011, a US study showed a link between rotenone use and Parkinson’s in farm workers. Read more about the US based study of rotenone in farm workers.

Sales of rotenone have been banned in the UK since 2009.

Glyphosate

Research into the potential links between glyphosate and Parkinson’s has been limited so far. A few isolated cases have reported Parkinson's in people after they ingested glyphosate. One large study carried out in the US suggests that people with Parkinson’s who live in agricultural areas where glyphosate is used are more likely to die earlier compared to those who live in areas without agricultural glyphosate use.

Glyphosate is the world’s most widely used weedkiller and is currently used in the UK. The charity Pesticides Action Network is calling for the UK to tighten regulations on the use of glyphosate based on its potential effects on human health and the environment. You can find out more about their campaign here.

Organochlorines

These include chemicals like DDT and β-HCH which were widely used up until the 1960s and 1970s when their dangers to both the environment and humans became apparent. Most are now banned in the UK and in many countries. A US-based study in 2017 estimates that those who were using organochlorines or pesticides more generally within their job for over 10 years doubled their risk of developing Parkinson’s. Read the full scientific paper detailing the US study into occupational use of pesticides.

Agent Orange

Agent Orange is a cocktail of 2 main herbicides, 2,4-D and 2,4,5-T. The cocktail was used in high concentrations as a chemical weapon to destroy crops, most famously in the Vietnam War. The chemical had devastating health effects on millions of Vietnamese people. Studies of US veterans who were exposed show an increased risk of various health conditions including many cancers and potentially Parkinson’s. The 2 herbicides that made up Agent Orange are now either widely banned or strictly regulated.

Should pesticides be banned to prevent Parkinson’s?

Many of the pesticides that have been linked with Parkinson’s so far are already either banned or strictly regulated in the UK and Europe. These decisions are based on the impacts these chemicals have on both the environment and on the health and safety of those exposed to them which often goes far beyond their potential relationship with Parkinson’s.

There is an urgent need for better quality, independent studies to be conducted into the possible links between pesticide exposure and Parkinson’s as well as on their wider health and environmental impacts. These will give regulatory authorities the evidence they need to make decisions that safeguard people and the environment.

Should I worry about pesticides in the food I eat or use in my garden?

There is no evidence to suggest that very low-level exposure to pesticides increases risk of Parkinson’s. So there’s no need to worry about using weed killer occasionally in your garden or about eating non-organic food. Although it’s probably a good idea to wear gloves when handling garden chemicals and washing fruit and veg before you eat it!