Impairments of Memory and Learning in Older Adults Exposed to Polychlorinated Biphenyls via Consumption of Great Lakes Fish

Because serum lead and mercury concentrations were slightly elevated in fish eaters, we also evaluated the effects of these two contaminants on the various cognitive outcomes. As with PCB and DDE, lead and mercury were entered on the log scale and nondetectable values were replaced with one-half the detection limit. However, unlike the primary exposure variables, lead and mercury were retained in the final model only if they significantly (p [is less than] 0.10) added to its predictive power.

Results

Neuropsychological evaluations and blood samples were available from 180 subjects. However, one male non-fish eater who reported recent carotid artery surgery and had severely impaired cognitive performance was excluded a priori from all statistical analyses, leaving a final sample size of 179 (101 fish eaters and 78 non-fish eaters). All participants were white, lived independently, and were in good general health. The median age was 64.3 years (range 49-86 years), 42.5% were male, and 48% had a high school education or less. Approximately 57% of the sample had an annual income of [is less than] $40,000.

In the final sample of 179 people, total serum PCBs ranged from below the detection limit to 75 ng/g, with a median of 7.9 ng/g. DDE values ranged from nondetectable to 145 ng/g, with a median of 8.1 ng/g.

Measures of Memory and Learning

After controlling for potential confounders, higher PCB exposure was associated with lower scores on the verbal delayed recall (logical memory) portion of the WMS (Table 4). PCB was significant in the initial bivariate analysis (p = 0.009) and remained significant in the final multivariate regression model (p = 0.001). The negative beta coefficient for PCB (on the log scale) indicates an inverse relationship between PCB exposure and verbal delayed recall. DDE was not significant in the initial bivariate analysis (p = 0.312), but became significant in the presence of PCB, age, and the Wechsler Adult Intelligence Scale vocabulary score (p = 0.016). The beta coefficient for DDE was positive, indicating that higher DDE exposure was associated with higher scores on verbal delayed recall. Lead and mercury exposure did not significantly impact verbal delayed recall and were not retained in the final model.