"Our findings are particularly important because exposure to solvents is very common, even in industrialized countries like the United States," said study author Erika L Sabbath, of Harvard School of Public Health in Boston. (Agencies)
The study involved 2,143 retirees from Electricite de France, a French utility company. Researchers assessed the workers' lifetime exposure to chlorinated solvents, petroleum solvents, and benzene.
Benzene is used to make plastics, rubber, dye, detergents and other synthetic materials. Chlorinated solvents can be found in dry cleaning solutions, engine cleaners, paint removers and degreasers. Petroleum solvents are used in carpet glue, furniture polishes, paint, paint thinner and varnish.
Of the participants, 26 per cent were exposed to benzene, 33 per cent to chlorinated solvents and 25 per cent to petroleum solvents.
Participants took eight tests of their memory and thinking skills an average of 10 years after they had retired, when they were an average age of 66.
A total of 59 per cent of the participants had impairment on one to three of the eight tests; 23 per cent had impairment on four or more tests; 18 per cent had no impaired scores.
The average lifetime solvent exposure was determined based on historical company records, and the participants were categorized as having no exposure, moderate exposure if they had less than the average and high exposure if they had higher than the average.
They were also divided by when the last exposure occurred, with those last exposed from 12 to 30 years prior to the testing considered as recent exposure and those last exposed 31 to 50 years prior considered as more distant exposure.
The research found that people with high, recent exposure to solvents were at greatest risk for memory and thinking deficits.
For example, those with high, recent exposure to chlorinated solvents were 65 per cent more likely to have impaired scores on tests of memory and visual attention and task switching than those who were not exposed to solvents.
"The people with high exposure within the last 12 to 30 years showed impairment in almost all areas of memory and thinking, including those not usually associated with solvent exposure," Sabbath said.
"But what was really striking was that we also saw some cognitive problems in those who had been highly exposed much longer ago, up to 50 years before testing. This suggests that time may not fully lessen the effect of solvent exposure on some memory and cognitive skills when lifetime exposure is high," Sabbath said.
The study was published in Neurology, the medical journal of the American Academy of Neurology.
"Our findings are particularly important because exposure to solvents is very common, even in industrialized countries like the United States," said study author Erika L Sabbath, of Harvard School of Public Health in Boston.