Background Occupational aluminum exposure can cause significant cognitive impairment in workers, which involves memory, learning, language, execution, and visual space. The results from different studies cannot be directly compared due to different cognitive evaluation scales used and correlated scale indicators. Therefore, the main cognitive areas damaged by occupational aluminum exposure have not been identified.

Objective This study deploys a factor analysis to explore the main cognitive areas of workers affected by occupational aluminum exposure.

Methods In 2014, a total of 1 304 aluminum electrolysis workers and maintenance workers were selected from a large aluminum plant in Shanxi Province by cluster sampling method. Fasting elbow venous blood (10 mL) of the study subjects was collected, of which 2 mL was extracted for the determination of plasma aluminum by inductively coupled plasma mass spectrometry (ICP-MS). According to tertiles of blood aluminum concentration, the subjects were divided into low, medium, and high exposure groups (Q1, Q2, and Q3 groups, respectively). A self-designed epidemiological questionnaire was used to collect general information of the subjects, including age, gender, marital status, education level, occupational history, disease history, and living habits. A combined questionnaire set was used for cognitive function tests, including Mini-mental State Examination, Clock-drawing Test, Digitspan Test, Fuld Object Memory Evaluation, Verbal Fluency Test, and Simple Reaction Time. Factor analysis was conducted to extract common factors from 16 original indicators to represent the original indicators, variance analysis was used to compare differences in common factor scores, and multiple linear regression was used to analyze the relationship between blood aluminum concentration and cognitive function.

Results All the study subjects were male, aged 20-56 years, and their median (P₂₅, P₇₅) blood aluminum concentration was 26.3 (11.8, 50.7)μg/L. The blood aluminum concentration ranges in the Q1, Q2, and Q3 groups were < 16.21, 16.21-40.83, and ≥ 40.83μg/L, respectively. There was no statistical difference in age, education, marital status, smoking, and drinking among the three groups (P>0.05). Common factors 1-6 were extracted from the original cognitive function indicators, and represented attention, long delay memory, reaction ability, execution function, short delay memory, and immediate memory, respectively. The variance analysis results showed that only the score of common factor 4 was significantly different among the three groups (P < 0.05). The multiple linear regression results showed that when blood aluminum concentration was used as a categorical variable, there were negative correlations between blood aluminum concentration and the scores of common factors 1 and 4 in the Q3 group (b=-0.136 and -0.180, respectively, P < 0.05), and compared with the Q1 group, the scores of common factors 1 and 4 decreased by 12.7% and 16.5%, respectively; when blood aluminum concentration was used as a continuous variable, the trend test results showed that there were dose-effect relationships between blood aluminum concentration and the scores of common factors 1 and 4 (t=-2.15 and -2.67, P < 0.05).

Conclusion Occupational exposure to aluminum can impair the cognitive function of workers, mainly affecting attention and executive function.