The aim of this study was to identify links between potential long-term environmental exposure to mixed contamination and the neuropsychological performance of a group of adults (> 55 years old) living near an industrial facility. Fifty-eight permanent residents were evaluated with the Mini-Mental State Examination and Clinical Dementia Rating scale (CDR) tests. Human biomonitoring involved the measurement of trace elements in fingernails to determine exposure. Only fingernail Hg contents of the Estarreja group are above the mean content found for non-exposed and healthy centenaries populations, although several outlier values were observed for the majority of the elements. From the total of individuals recruited for the study, 29% obtained a 0 score on CDR indicating a normal status, 34% scored 0.5 which is suggestive of mild cognitive impairment (MCI), 22% had a cognitive performance indicative of mild dementia, and 14% fall under the categories of moderate and severe dementia. Principal component analysis and multiple discriminant analysis (MDA) were combined to identify groups of correlated variables discriminating well the cognitive functions examined by the different neuropsychological tests. The results obtained show that fingernails’ data discriminate well between CDR scores for normal and altered cognitive statuses, and further suggest that elevated levels of Mn and Zn in fingernails of the elderly residents of Estarreja are associated to a condition of severe dementia. The poor discriminating ability of the MDA model for intermediate categories of the cognitive tests (MCI, mild dementia) may be attributed either to a lack of sensitivity of the cognitive tests for the screening of these intermediate conditions or to the similar Zn and Mn contents in fingernail observed in participants falling under such categories.