Several workplace exposures may increase risk of developing Parkinson’s disease

Head trauma, pesticides, manganese on the list

Several workplace exposures may increase risk of developing Parkinson’s disease


Muhammad Ali was arguably the greatest boxer of all time. He won the title of lineal heavyweight champion three times. He received countless accolades including being named the Sports Illustrated Sportsman of the 20th Century and Sports Personality of the Century by the BBC. Ali, who died last year, will always be remembered for his footwork in the ring, his outspoken views and humanitarian efforts, but he will also be remembered for his battle with Parkinson’s disease. 

Parkinson’s disease is the second most common neurodegenerative disorder after Alzheimer’s. It is estimated more than 100,000 Canadians have Parkinson’s disease and more than 25 people are diagnosed daily, according to Parkinson Canada.

It is a chronic disorder with a high survival rate that is characterized by muscle tremors, stiffness, balance problems and slow movements. More than 60 per cent of those with the disease experience memory limitation, anxiety and depression, according to Parkinson Canada.

And the disease is more prevalent now than ever. According to the Mayo Clinic in the United States, the incidence of Parkinson’s disease and parkinsonism (neurological signs and symptoms similar to Parkinson’s) increased significantly in 30 years from 1976 to 2005. By 2031, Parkinson Canada says the number of Canadians diagnosed with the disease is expected to be more than 163,700.

“As the population ages, demographically, we can expect the burden of Parkinson’s disease to be larger,” says Anne Harris, assistant professor in the School of Occupational and Public Health at Ryerson University in Toronto, speaking at a seminar at the Institute for Work and Health in Toronto earlier this year.

Parkinson’s takes years to develop, perhaps as much as 20 to 30 years after exposure, says Jonathan Squires, a neurologist at the Pacific Parkinson’s Research Centre in Vancouver.

Parkinson’s is a “major burden” for the working age population because it can affect people quite young, says Squires. While most people develop the disease around age 60, 20 per cent are diagnosed under age 50. Ali was diagnosed at 42. Young onset Parkinson’s (before age 40) occurs in five to 10 per cent of those diagnosed, says Parkinson Canada.

Because manual dexterity is affected early in the course of the disease, many office workers have trouble typing and their occupational performance can take a hit. Some of Squires’ patients have lost their jobs because they were not keeping up as well as they used to.

Professionals in very cognitively demanding jobs have noticed issued with multi-tasking and cognitive processing, such as business executives.

Other workers with Parkinson’s have found balance to be problematic.

“One individual worked for a telephone utility as a technician and he was up and down ladders as part of his job, but when he developed balance issues, he was having to change jobs as a result of that,” says Squires.

It is estimated that 25 to 35 per cent of people diagnosed with Parkinson’s are still in the workforce, says Parkinson Canada. Employers have a legal duty to accommodate workers with Parkinson’s disease.

One difficulty with the disease is that the causes remain largely unknown. While some cases may be inherited (about five to 10 per cent), it is likely that the large majority of cases have an environmental basis, says Kay Teschke, a professor in the School of Population and Public Health at the University of British Columbia in Vancouver.

Various studies show there are several workplace exposures that can increase the risk for Parkinson’s disease. Employers need to be well-versed in these risks and do their part to prevent their workers from developing this debilitating and chronic disease.



One such exposure is head trauma, which doctors blamed for Ali’s case. Head trauma is really well-known to be associated with Parkinson’s disease, says Harris, who was a part of a team of researchers who presented a report on Parkinson’s workplace risk factors to WorkSafeBC in 2011. Their study found the strongest risk relationships were for concussion injuries and head injuries that resulted in unconsciousness.

“If we prevent head injuries at work, we will prevent Parkinson’s disease,” Harris says. “I believe that’s true and I believe the results (of our study) bear that out. Fortunately, that’s a great target because that’s something we want to do anyway. Preventing head injuries is already a goal and you can get double bang for your buck because you also can prevent some future cases of neurological disease.”

Teschke, who was the lead author of the report to WorkSafeBC, says workers’ compensation boards should be particularly interested in the correlation between head injuries and Parkinson’s.

“Workers’ compensation boards in Canada would be wise to do a review of that literature on head injury and think about potentially compensating people who had documented head injuries at work, if they develop Parkinson’s disease later in life,” she says. “I think it’s worth at least examining that potential.”

The relationship between Parkinson’s and head injury is also making headlines in the class-action lawsuit against the NFL, which accused the league of hiding the dangers of concussions. The lawsuit provides compensation for former players who suffered serious medical conditions associated with repeated head trauma. Retired players diagnosed with Parkinson’s could receive up to US$3.5 million each. 

Workers in Canada can apply for workers’ compensation and provide evidence of a link between their workplace exposure — such as head trauma — and the disease. Many people think the disease needs to be on a board’s schedule of occupational diseases, but that’s not the case, says Teschke.



In 2008, an Ontario worker was granted compensation for his Parkinson’s disease after “significant exposure” to hydrocarbons in his work. He worked for a manufacturer of office furniture components and had been using paints that contained organic solvents, including hexane, xylene and toluene.

In 1983, the worker began his employment at the company. After seven years, he began to complain of weakness in his left arm. Ten years after that, in 2000, he was officially diagnosed with Parkinson’s disease.

Ontario’s Workplace Safety and Insurance Board, as well as the appeals resolution officer, originally denied the claim, but the Workplace Safety and Insurance Appeals Tribunal panel ruled in the worker’s favour. The panel said the evidence for and against the claim that exposure to hydrocarbons led to his Parkinson’s disease was approximately equal in weight, therefore, the claim must be granted.

Various studies have made links between Parkinson’s and toluene, xylene, n-hexane, carbon tetrachloride, trichloroethylene (TCE) and tetrachloroethylene (also known as perchloroethylene or PERC). A 2012 study examined these six chemicals and found ever exposure to TCE was associated with significantly increased risk of Parkinson’s, and exposure to PERC and carbon tetrachloride tended toward significance.

The researchers, who were from all over the world, including Toronto, studied 99 twin pairs, where one twin had Parkinson’s and the other did not. Results were similar regardless of the exposure duration and cumulative lifetime exposure, found Solvent Exposures and Parkinson’s Disease Risk in Twins.

TCE had been used extensively worldwide for decades — in coffee decaffeination and as an anesthetic — but today it is primarily used as a degreasing agent in metal parts fabrication. Carbon tetrachloride was formerly used as a dry cleaning solvent but has been almost entirely replaced by PERC.



One of the best-known potential risk factors for Parkinson’s is pesticides. The chemicals have been found to wreak havoc by disrupting enzymes, proteins and neurons within the  brain.

The pesticides paraquat and rotenone are fairly well-established to cause an increased risk for Parkinson’s, and they should not be used in the workplace, says Squires. The problem of course, he adds, is there may be other offending agents, but we just don’t know what they are yet.

A study published in May in the Scandinavian Journal of Work, Environment and Health conducted a systematic literature review and meta-analyses on Parkinson’s disease and occupational exposures. It concluded “there is now strong evidence that exposure to any pesticide involves at least a 50 per cent increased risk for developing Parkinson’s disease.”

But Harris is not convinced. In her research with Teschke and colleagues, they found recall bias to be a concern — individuals with Parkinson’s were more likely to report a history of pesticide exposure because they were aware of the suspected association between the two. Recall bias is a concern in any study where participants are asked to self-report.

While many individuals said they were exposed to pesticides, once an industrial hygienist reviewed the data, only about one-half showed a true exposure.

“This is a long suspected relationship and probably the best studied. Unfortunately, it doesn’t mean that that information is totally clear. We don’t necessarily have the answer as to whether or not pesticides are a cause of Parkinson’s,” says Harris.

Pesticides can be worked with safely if proper precautions are followed. All Canadian jurisdictions have either set their own occupational exposure limits for some pesticides or follow the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit values (TLV). However, a number of commonly used pesticides do not have such limits, so exposure must be kept as low as reasonably achievable. Workers are most commonly exposed when the chemicals are in storage and during application. Pesticides can enter the body by ingestion, inhalation or skin absorption.

When using pesticide products, check the label and the safety data sheet for the required personal protective equipment (PPE). This may include chemical resistant unlined gloves and footwear, a long-sleeved shirt and long pants, socks, a respirator and eye protection. Studies have shown that wearing chemical resistant gloves and footwear can significantly reduce exposure, says the Canadian government.



Teschke and Harris’ study found agricultural workers had “consistent, significant increased odds” for developing Parkinson’s, but pesticide exposure did not come out as the definitive cause. This led Teschke and her team to take look at other possible causes and they came up with whole body vibration, which occurs as the body rests on a vibrating surface, such as vehicles and heavy equipment.

“A good example is farmers. You get a subtle amount of vibration just driving on the road and you can get more dramatic vibration as you go off road and drive different kinds of equipment that has less suspension and then you can get these very dramatic shocks when you hit a pothole or, in the case of farming, probably every few feet,” says Teschke.

The researchers were interested in this as a potential occupational exposure because the mechanical stress of vibration and associated shocks could be similar to the stress precipitating a head injury. They asked study participants to report their occupational use of vehicles and then they identified the level of vibration intensity for each piece of equipment. They found an interesting U-shaped effect where the risk increased with no exposure but also with increasing intensity of exposure.

While the results are a bit tricky to interpret, they certainly warrant further study.

“These higher intensity vehicles are the ones that are associated with physical shocks — lots of bumps and high amplitude of exposure — and potentially repeated shocks could engage some neuroinflammation mechanisms,” says Harris. “This is the big area of interest in Parkinson’s disease etiology now, so it would be great to test that directly.”



Manganese exposure is another potential occupational risk factor for Parkinson’s-type symptoms that has been hotly debated. Some studies show an increased risk, while others show a decreased risk or no association. Manganese is a common compound in welding fume.

“We are aware of various studies that have been done in this area but we are not 100 per cent sure how conclusive those studies are,” says Dan Tadic, executive director of the Canadian Welding Association in Milton, Ont. “Even some of the studies that I have seen, there are some question marks.”

In 2013, the ACGIH lowered its TLV for manganese from 0.2 milligrams per cubic metre (mg/m3) to 0.02 mg/m3.  A review of studies over the previous 15 years indicated effects to the central nervous system occur at exposure levels below 0.2 mg/m3.

When the change was made, the Canadian Welding Association communicated this to its members and conducted events to raise awareness. While ACGIH limits are often adopted by Canadian jurisdictions and made law, the vast majority haven’t quite gotten there yet. Only Nova Scotia, Newfoundland and Labrador, P.E.I., Manitoba and the Labour Program (for federally regulated workplaces) have accepted the new TLV because their OHS regulations say to refer to the latest version of ACGIH limits. The majority of the provinces and territories are still using the old 0.2 mg/m3 TLV.

This is of concern because a recent study found signs of Parkinson’s disease showed up in welders with an estimated exposure of only 0.14 mg/m3. The study, released in December from the Washington University School of Medicine in St. Louis, Mo., found the more workers are exposed to manganese-containing welding fumes, the more quickly their symptoms of parkinsonism progress.

Exposure was most strongly associated with upper limb bradykinesia (slowness of movement) upper and lower limb rigidity and impairment of speech and facial expressions. Welders who worked in confined spaces appeared to have particularly marked worsening of parkinsonism.

Overall, the study found the prevalence of parkinsonism was 15.6 per cent in welding-exposed workers, demonstrating a “high prevalence of parkinsonism” compared to non-welding-exposed workers.

According to Tadic, there are a variety of controls employers can put in place to reduce welders’ exposure to manganese fumes:

• use welding consumables (such as wires) with lower manganese levels

• use lower welding voltages

• use ventilation equipment to exhaust fumes

• use newer welding technology, such as pulse welding, which generates less fumes than any other semi-automatic welding process

• use appropriate respiratory protection.

Manufacturers have made many improvements over the years when it comes to reducing the amount of manganese used in steel, but the industry has certainly been grappling with this issue, says Tadic. 

“Imagine how much steel is used in today’s bridges and pipelines and all the machinery that is being made, buildings and automotive industry and a variety of applications. If you were to eliminate (manganese) completely, you would drive the cost of these alloys through the roof and cause all kinds of serious damage to the economy,” he says.

Teschke’s study found welders had an elevated risk for Parkinson’s as did heavy equipment operators, farmers, carpenters, gas station workers, and perhaps a bit surprisingly, science, law and library jobs. The latter may be due to the fact that influenza is associated with an increased risk of Parkinson’s, says Teschke.

“It’s interesting because they show up as having an elevated risk but management and administration doesn’t. If you think of one of the biggest differences between those groups, it’s their interaction with people. Social sciences, and a lot of those folks, a lot of them are people who interact with a wide swath of the public in their regular work life, so they have more potential to be exposed to the flu.”

To this end, employers would be wise to promote good health and handwashing in the workplace, especially during flu season.

While the theories vary and sometimes contradict each other, the one thing researchers can all agree on when it comes to Parkinson’s is how difficult it is to figure out if there is a relationship. That’s why the best bet is to apply the precautionary principle, says Teschke.

“The biggest surprise to me when I started in this field was how little we know about so much,” she says. “To the extent that you can offer your employees a very clean, low exposure to either injury risk or chemical exposure risk, if you can give them that, that’s a positive in ways you may not know that you’d hate to find out in the future.”

This article originally appeared in the August/September 2017 issue of COS.