Exposure to workplace solvents, particularly at high levels, may contribute to problems with thinking and memory even decades later.

An unusual study led by Erika Sabbath of Harvard University, published Monday in Neurology, analyzed more than 2,100 retirees from a French utility company. The company kept records of solvent exposure using air tests from a variety of work areas. Previous studies involving solvent exposure have relied on self-reporting.

The sample included everyone from linemen to executives. Levels of exposure varied company-wide and by position. Some retirees had shuffled between several positions in the company over the course of many years. Employees of the utility worked there for a lifetime and could not choose to retire early.

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Employees completed eight tests measuring memory and thinking, known as cognitive skills, an average of 10 years after retirement. Some had not been exposed to solvents for 50 years. The researchers accounted for other factors that could influence the tests, such as age, education level, and tobacco and alcohol use. The average age at test time was 66.

The study analyzed workers’ lifetime exposure to solvents made of chlorine, petroleum, and benzene. One-third of the workers had been exposed to chlorinated solvents, and about one fourth had been exposed to benzene or petroleum solvents.

Those recently exposed to high doses were 65 percent more likely to do poorly on the memory and thinking tests than those who were not exposed. But even those who had been highly exposed half a century ago exhibited cognitive problems.

“It has been known for many years, through many studies, that exposure to solvents in occupational settings can have negative effects on cognitive functions,” Sabbath told Healthline. “It was often thought that with increasing time since the last exposure, the effects sort of faded away.”

Sabbath said a major limitation of the study was that the participants were only evaluated once, so the researchers didn't have a baseline for each person's cognitive ability. 

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Why Solvents May Be Harmful

The work of Sabbath and her colleagues comes at a time when the number of Americans with dementia, a term for a collection of symptoms related to poor cognition, is exploding. As Americans live longer, the symptoms have more time to develop.

Dr. Claudine Berr, a biomedical expert in France and co-author of the paper, told Healthline that recent research shows that occupational solvent exposure is associated with reduced activation in certain areas of the brain, such as the prefrontal cortex. “Because this is the last human brain region to develop, it may be most vulnerable to insults from chemical or physical agents, which may explain its sensitivity to solvent exposure,” she said.

Solvents impact working memory, attention, and processing speeds because they are easily absorbed by fatty tissue and cellular membranes, Berr said. “Several hundred million tons of organic solvents are still used worldwide per year, although regulatory pressure and concerns for the environment are leading to a reduction in use," she said. "Occupational exposures are clearly modifiable factors.”

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Which Workers Are Most at Risk?

Solvents made of chlorine include those used at the dry cleaners as well as solutions made for cleaning engines and removing paint. Furniture polish, paint, and glue also have a petroleum base. Benzene is used to make plastics, rubber, dye, and detergents.

Millions of workers are exposed each year to solvents, according to the U.S. Centers for Disease Control and Prevention (CDC). Everyone from carpet layers who work around glue to factory works who paint parts are at risk. The Occupational Safety and Health Administration (OSHA) has a section of its website devoted to the safety and regulation of solvents in the workplace. The CDC has a page dedicated specifically to hazards in the dry cleaning industry.

Sabbath stressed that people working around solvent vapors should use a respirator. “It’s important to know that it’s your right to do that,” she said. For detailed OSHA requirements regarding the use of respirators, click here.

Sabbath noted that protecting workers from solvent exposure could result in reduced healthcare costs after retirement. It also may allow people to stay on the job longer.

In a news release, Sabbath said that retirees who have experienced prolonged solvent exposure should be screened regularly for cognitive problems. She added that learning new things helps keep the mind sharp.