Analysis Of The Impact Of Occupational Aluminum Exposure On Workers’ Cognition And Their Brain Function Connections

Objective:To explore the cognitive changes caused by aluminum exposure and the changes in the brain function connection state of the corresponding regions by investigating aluminum workers in a large domestic aluminum factory.Methods:In this study,370 of all on-duty aluminum workers in a workshop in northern China were selected as the research’s participants.About participants,the basic features were gathered,and the plasma aluminum concentration（P-Al）was measured as an indicator of internal exposure.Three kinds of cognitive test questionnaires including the Montreal Cognitive Assessment（MoCA）were opted to pass judgement the perception of workers.We used multivariate model to probe influencing factors of cognition.We used generalized linear model to probe the association between P-Al and cognitive score.We used restricted cubic spline（RCS）to fit dose dependence.We used logistic regression to probe hazard of cognitive impairment,which caused by aluminum exposure.For cross-sectional survey of 370 workers,extraction 20 workers in the exposed workers with age 40 and older,aluminum working experience more than one year,MoCA score lower than 24 points with cognitive impairment（hereafter called cases）,and 20 workers in the same area in the same factory of non-exposed workers according to age,culture level and so on matching corresponding contrast.They all had an MRI.The functional connection of different brain areas was used as the research index.And we use Person’s correlation to probe the correlation of functional connection with cognition and P-Al.Results:1.Changes in cognition of occupational aluminum workers1.1 General information and cognitive function of the subjects:A total of 370 aluminum factory workers were included in this study.All of them were male,aged 23-57 years,and P-Al of M(P₂₅,P₇₅)was 27.6（13.1,48.5）g/L.They were divide into T1（<17.7 g/L）,T2（17.7～41.0 g/L）,T3（≥41.0 g/L）.Compared with T1 group,more workers in T3 group had junior high school education or below（62.6%）,more smokers（71.5%）,and less hypertension（6.5%）;T2 and T3 groups slept longer each day（8.0±1.3 and 7.9±1.2 hours,respectively）.The results of the three groups of cognitive tests showed that compared to T1group,the MoCA scores of the T2 and T3 groups were lower,and the T3 group took longer to complete the online test A（P<0.05）.1.2 Factors affecting cognition:We conducted single element and multi element analysis.And we got the result using a multivariate model.The results showed that P-Al,drinking,sleep duration,reading,age,and education level could affect cognition（all P<0.05）.Among them,P-Al,age,and sleep time can damage cognition.Education level and drinking can protect cognition.The effect of reading on cognition is unclear,and it is positively correlated with MoCA total score,naming,and abstract score,which can reduce the risk of damage in these areas,but is negatively correlated with orientation score,increasing the risk of impairment of orientation ability.1.3.Plasma aluminum concentration and cognitive function1.3.1 Relationship with cognitive scores:After adjusting for covariates such as age,generalized linear model analysis results showed that when plasma aluminum concentration was a continuous variable,it negatively affected MoCA scores and positively affected the time to complete online test A（P<0.05）.When plasma aluminum concentration was the tripartite variable,correlations with total MoCA score,naming,speech score,and time to completion of online test A appeared in T3 groups,and meaningful correlations with visuospatial and executive ability appeared in T2 and T3 groups（P<0.05）.Further analysis using RCS curves showed that as P-Al increased,MoCA score decreased and the time to finish online test A increased.1.3.2 The relationship with cognitive impairment:We used P-Al as the independent variable,and P-Al was divided into three quartiles and assigned as（<17.7 g/L=1,17.7～41.0 g/L=2,≥41.0 g/L=3）.Cognitive impairment was the dependent variable.Covariates such as age were adjusted in the analysis.Model analysis showed that the risk of impairment in visuospatial,naming,speech,and abstract domains increased with the increasement of P-Al.For each tertiles of P-Al increased,the risk of damage to visuospatial ability increased by 1.3%（OR=1.013,95%CI:1.002,1.023）,naming increased by 1.6%（OR=1.016,95%CI:1.005,1.028）,speech increased by 1.7% （OR=1.017,95%CI:1.006,1.028）,abstraction increased by 1.3%（OR=1.013,95%CI:1.002,1.024）respectively.2.Cognitive impairment of occupational aluminum workers and changes in brain function connection state2.1 Two groups of basic conditions:The P-Al of case group was 122%higher than control group（38.3μg/L vs 17.2μg/L）.Except that P-Al in case group was higher （P<0.05）,there was no statistically significant difference in other aspects（P>0.05）.2.2 Two groups of cognitive test results:The average MoCA score of the case group was 9.7 points lower than control group（18.20±2.50 vs 27.90±0.97）.In AVLT,two memory scores in case group were significantly lower were 5.4 points and 2.3 points lower than control group,respectively（17.0±4.5 vs 22.4±5.1,6.2±2.5 vs 8.5±2.9）,and the time to complete part A and part B in TMT was significantly longer（55.4±26.8 vs 37.0±12.4,156.7±89.2 vs 94.6±54.8）（all P<0.05）.2.3 Functional magnetic resonance results between the two groups:Based on voxels,we analyzed 30 independent components and identified network DMN1 and DMN2.We observed that functional connectivity of DMN1 and DMN2 were decreased in case group（P<0.05）.The cortex of left middle cingulate gyrus was also observed to drop（P=0.047）,and no significant differences were found in functional connections in other specific regions（P>0.05）.Bivariate correlation analysis showed that the average functional connection of DMN1 and DMN2 had a positive effect on the MoCA score.Aluminum working experience had a negative impact on the functional connection of DMN1 and DMN2（all P<0.05）.There was no correlation between the average functional connection of DMN1 and DMN2 and P-Al（P>0.05）.Conclusion:1.Occupational aluminum exposure can damage a variety of cognitive domains such as visual space ability,naming,speech,abstraction,etc.,and there was dose dependence.As the plasma aluminum concentration increased,age increased,and sleep time prolonged,cognitive impairment worsened.2.Decreases in the brain’s resting-state functional connections were found in cognitively impaired workers,and functional connection may become the imaging evidence for early detection of cognitive impairment in aluminum workers.