Pondering on Pesticides Long-Term Low Levels Impair Thinking 

Commentary / Tina Adler / Environmental Health Perspectives v.109, n.8 Aug01

As Homer wrote, "Wine can of their wits the wise beguile," but what of the grapes that make the wine--or rather, the pesticides with which they are treated? Isabelle Baldi of the Institut de Santé Publique d'Epidémiologie et de Développement in Bordeaux, France and colleagues went to their local vineyards to measure workers' cognitive well-being and see how it related to the amount of pesticides they had encountered over the years [EHP 109:839-844]. Previous studies had shown that high-dose pesticide poisoning can cause acute human health effects such as motor skill damage, impaired intellectual functioning, and memory loss. In this study, the first to assess long-term neuropsychologic effects of chronic, low-level pesticide exposures in a large sample of workers, Baldi and colleagues found many examples of impaired cognitive functioning among exposed workers.

The team interviewed 917 men and women, aged 43-58, between February 1997 and August 1998. Of the study participants, 528 had been directly exposed to pesticides through mixing or spraying over a mean of 22 years, another 173 had been indirectly exposed by contact with treated plants, and 216 had never been exposed. The pesticides used were primarily fungicides.

The team administered nine neuropsychologic tests to the workers, including the Mini-Mental Status Examination (which measures different cognitive components), the Wechsler Paired Associates Test of memory, the Benton Visual Retention Test, the Isaacs Set Test (which measures the ability to quickly generate lists of words in different semantic categories), and the Finger Tapping Test (which assesses motor speed). The team controlled for factors that could alter test scores, including educational level, age, sex, alcohol consumption, smoking, environmental exposures, and depressive symptoms.

Workers who were either directly or indirectly exposed performed worse on tests of memory, selective attention, verbal fluency, and abstraction compared with nonexposed workers. On a test of both selective attention and working memory, directly exposed workers were 3.5 times more likely to score low compared with nonexposed subjects. On a similar test of selective attention and mental flexibility, the exposed individuals were 3.1 times more likely to score low. The exposed men and women processed information less quickly than nonexposed colleagues, although performances of exposed workers were similar to those of the nonexposed if the tasks were slowed.

The study participants' symptoms were subclinical and didn't appear to interfere with their work, the team writes, and the participants didn't complain about their cognitive deficits. But they might run into cognitive problems as they age, Baldi notes. "This is why we planned a four-year follow-up of the population [starting in 2001] to assess evolution of performances," she says.

One surprising finding: although large amounts of alcohol are neurotoxic, the workers who drank moderately had better test scores than nondrinkers. Other studies have shown a protective effect of moderate wine consumption on cognitive performance. Baldi can't explain the finding, but notes that among these workers alcohol is considered "a noble product."