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 structurally and functionally diverse. They are used to kill pests, from insects to weeds. They can be used on a small scale in people’s gardens, or on a more industrial scale in farming for example.

Pesticides work by targeting a specific function of the insect’s or plant’s biology to ultimately get rid of 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 us from harmful effects. 

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

Many studies across the world have investigated whether exposure to pesticides may increase the risk of developing Parkinson’s. The results have been varied and inconsistent, but overall the evidence suggests that exposure to certain pesticides may increase the risk of Parkinson’s. But the evidence isn’t good enough to say if a pesticide has definitely caused someone's Parkinson’s.

Over 50 studies in the last 40 years have been conducted. A lot of these studies have been done in different ways, and look at pesticides in general rather than specific types. Often, the studies don't take into account other factors that might have contributed to a person's risk of developing Parkinson's. This is something that makes this particular form of research very tricky, and may explain some of the inconsistencies and limitations of results so far.

Within the more general research, there are some specific pesticides that have evidence to suggest they have a link to Parkinson’s.

What specific pesticides have been linked to Parkinson’s?

This is not an exhaustive list but here are a few specific chemicals found in pesticides that have been linked to Parkinson’s.

Trifluralin 

Most commonly used in the cotton agricultural industry, trifluralin 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. The use of paraquat was banned in 2007 in the UK. 

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.

In the UK, the sale of rotenone insecticides was banned in 2009.

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.

Currently, the research evidence suggests that exposure to pesticides may increase the risk of Parkinson’s, but is not strong enough to demonstrate a causal link. 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.

Should pesticides be banned to prevent Parkinson’s?

Parkinson’s was first recognised and described by James Parkinson in 1817, around 100 years before many of these pesticides were developed.

Although pesticides were widely used initially, their use rapidly declined, with some being banned, and there is no clear correlation between this period of high usage and a rise in the incidence of 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.

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 the risk of Parkinson’s. So there’s no need to worry about using weed killer occasionally in your back 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!

The problem with research into pesticides and Parkinson’s

Research studies looking at environmental risk factors are notoriously tricky. For instance, people who have Parkinson’s and people without may be asked about their exposure to various chemicals earlier in their lives. Our memories are unreliable and easily biased. People with health problems may be more likely to recall and report factors that they believe may have played a part in the development of their condition.

Another problem in studies of this type is how you define exposure. Many studies approach this differently, which makes it difficult to compare between studies. Is it how much contact with the chemical counts? If so, does living in a rural area near fields where pesticides were used count as exposure? Or does exposure mean that you need to have been working directly with the pesticides? And how long does this contact need to continue for it to be a risk?

What’s next for research into pesticides and Parkinson’s

There are always going to be limitations to this type of research due to the points we have already covered and the complexity of Parkinson’s as a condition.

However, the more research there is in this area, the more comprehensive the evidence will be. With more research evidence, we’ll be able to build a clearer picture of the risks of pesticides and Parkinson’s.