Objectives: To extend our knowledge of how exposure to neurotoxic substances during working life affects cognitive functioning in the long term. Does long term occupational exposure to organic solvents lead to aggravated cognitive impairment later in life? Methods: A follow up was conducted of floor layers exposed to solvents and their unexposed referents (carpenters) 18 years after the baseline assessment. The pattern of cognitive changes in the two groups was compared, with the same 10 neuropsychological tests from the test battery for investigating functional disorders (TUFF) that were used at baseline. The study included 41 floor layers and 40 carpenters. A medical examination focused on health at the present and during the past 18 years. An extensive exposure assessment made in the initial study included questionnaires, interviews, and measurements. Additional exposure during the follow up period was minor, as explored in interviews at follow up. Results: The entire group of floor layers did not deteriorate significantly more over time than did the carpenters. However, among the oldest subjects (>60 years), only floor layers showed decline in visual memory. Moreover, the most highly exposed floor layers deteriorated significantly more than their referents in visual memory and perceptual speed, and they tended to display larger decrements in motor speed. Significant dose effect relations were found; higher cumulative exposure was associated with decrements in visual episodic memory, perceptual speed and attention, and visuospatial skill. Conclusions: The hypothesis that floor layers would deteriorate more in cognitive performance than their unexposed referents over a period of 18 years was partly supported by the results of this study. The results are consistent with the view that the negative effects of exposure to solvents may interact with the normal aging process, primarily at heavy exposure.

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The authors used tests of attention and memory, which are sensitive to the influence of aging, to explore possible adverse effects on cognitive functioning following past heavy exposure to solvent-based glues, with special reference to dose-effect relationships and interactions with the aging process. The study included 41 floor layers and 40 carpenters (referents) who participated in a longitudinal follow-up assessment. The authors assessed cognitive functioning with the following tests: trail-making, color words, and word recall. Higher cumulative exposure was associated with poorer test performance that was related to concept shifting, episodic memory, and speed of congruent and incongruent color naming. The magnitude of the decrements in memory tasks was equivalent to about 20 yr of age-related decline. Dose-effect relationships were seen mainly for contact adhesives, and there was partial evidence for an interaction between exposure and aging.

Whether long-term occupational exposure to organic solvents may affect mental and cognitive functioning later in life, remains unclear. In this study, twelve rotogravure printers formerly exposed to toluene and 19 referents, all initially examined in the mid-1980s, were reexamined after twenty years, applying neuropsychological tests, symptoms and social interaction questionnaires, medical examination, and exposure assessment of each individual's cumulative exposure. By far the most extensive exposure, mainly toluene, had occurred before 1985. The printers were found to have deteriorated more than their referents in cognitive functioning affecting reasoning and associative learning. No relevant additional exposure during the lengthy time period between assessments could explain this discrepancy. In addition, printers performed significantly worse than the referents in verbal memory and sustained attention at follow-up, where also a dose-effect relationship was noted for reasoning. While the printers did not report more subjective cognitive complaints than the referents, a slightly higher depression score was noted for the printers. The findings of significantly worse deteriorations in cognitive functioning in previously toluene-exposed printers are in line with our hypothesis that sub-clinical deficits during the working life may become manifest later in life, indicating that exposure may in fact interact with ageing. However, considering the small study groups the results must be interpreted with caution.