In the workplace, fumes from solvents such as paints, glues, degreasers and adhesives have been implicated in cognitive damage - in other words, impaired thinking and memory abilities. Now, researchers report in the journal Neurology that the detriments linked to these chemicals might last many years.
"What it shows is that these chemicals might have more long-term effects than have previously been thought, and continue to affect people long after they are retired," said Erika Sabbath, research fellow at the Harvard Center for Population and Development Studies and lead author of the study.
A solvent is a substance used to dissolve another chemical. For instance, water dissolves salt. The solvents targeted in this study included benzene (found in detergents and plastics), chlorinated solvents (found in paint strippers and dry cleaning solutions) and petroleum solvents (found in varnish).
But note that researchers did not directly measure whether these chemicals cause brain damage. They simply found a statistical association between impairment on tests and exposure to chemicals. More research would be needed to prove that one directly results in the other.
Researchers obtained information from 2,143 male retirees in France who had worked for a French utility company. They had retired, on average, around age 55. Most had started working around their late teens or early 20s and worked at the same company for their whole careers.
About 33% of these retirees had been exposed to chlorinated solvents, 26% to benzene and 25% to petroleum solvents. There were 12% of participants with high exposure to one kind of solvent, while 11% had high exposure to two or three.
Those exposed to industrial solvents 12 to 30 years before cognitive testing were deemed to have been "recently" exposed. Others had been exposed 31 to 50 years earlier.
Researchers estimated how much people had been exposed each year from 1960 to 1998. The study did not directly measure how long individuals had been exposed to certain chemicals, however.
"During that time, the practices around using chemicals and personal protective equipment and the extent to which we know about harmful effects have certainly changed," Sabbath said. "It's possible that these people were exposed to higher levels than what people are exposed to today. That being said, these are some of the most common chemicals in U.S. workplaces."
Study authors gave participants cognitive tests to measure such abilities as working memory, attention and thinking skills. The men were on average 66 at the time of this testing.
Participants whose exposure to solvents was greater and most recent had the highest risk of memory and thinking problems.
High exposure to chlorinated solvents, petroleum solvents and benzene during one's lifetime was linked to impairment on a test measuring general cognitive function. For those with moderate exposure, only chlorinated solvents was related to higher risk.
A different cognitive test found similar results, with high exposure to chlorinated solvents and petroleum solvents related to elevated risk. Other assessments found similar patterns.
Timing mattered, too. Poorer scores on tests that measured visual attention and memory, as well as task switching, were more likely to be seen in men whose exposure to chlorinated solvents was both high and recent. Researchers looked at other factors such as smoking, age, education and alcohol consumption, but none of these explanations could account for the strong association.
High exposures 31 to 50 years before testing were also associated with some types of cognitive impairment.
"We expecting to see this relationship between total lifetime dose and cognitive outcomes, but we weren’t expecting that the effects would have lasted this long," Sabbath said.
Researchers did not test the cognitive functioning of participants before their exposure to solvents.
"This could potentially induce bias if individuals with poorer baseline cognition were more likely to stay in higher-exposure jobs, incurring additional damage from solvents," researchers wrote.
The participants also took a variety of different tests, and some results may be explained by random chance.
Researchers additionally did not take into account factors such as physical activity, diet and cardiovascular disease. But they did adjust for hypertension and body mass index, which are related.
This study did not look at what happens to the brain directly as a result of solvent exposure in the workplace. But a previous study that used functional magnetic resonance imaging found implications to the anterior cingulate cortex, dorsolateral prefrontal cortex and prefrontal cortex while participants took attention and working memory tests. Researchers noted that deterioration of the prefrontal cortex is also associated with aging.
Solvents are used in nearly all manual tasks in the French working population, with 12% to 13% being exposed, the study said.
Policy changes may be necessary to reduce the level of chemical exposure that is permissible, but historically such reforms have been difficult to achieve, Sabbath said.
In the meantime, people who work with paints or dry cleaning fluid all day may benefit from wearing a respirator and having good ventilation, Sabbath said.
"There’s absolutely nothing to be lost by prevention," Sabbath said.
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