Occupational neurotoxicant exposures, cognitive reserve, and brain aging: a scoping review

BACKGROUND: Occupational neurotoxicant exposure may contribute to cognitive decline, neurological dysfunction, and brain aging. However, the role of cognitive reserve in explaining differences in cognitive and neurological outcomes among exposed workers remains insufficiently characterized. OBJECTIVE: This scoping review aimed to map evidence linking occupational neurotoxicant exposure with cognitive reserve or brain aging outcomes in adults, characterize exposure categories, cognitive reserve operationalizations, and neuroimaging methodologies, and identify evidence gaps. METHODS: Searches were conducted in PubMed/MEDLINE, Scopus, Embase, and APA PsycInfo for English-language studies published from January 2011 onward. The review followed Joanna Briggs Institute guidance for scoping reviews and PRISMA-ScR reporting standards. Eligible studies examined adult populations with occupational neurotoxicant exposure and cognitive reserve or brain aging outcomes. RESULTS: Sixteen studies met the inclusion criteria. Exposure categories included aluminum, lead, combustion-related exposures, organic solvents, and mixed-metal exposures. Cross-sectional and case-control designs predominated, and biological monitoring was the most frequently used exposure assessment approach. Cognitive decline or impairment was the most common brain aging outcome, while neuroimaging studies identified functional connectivity, white matter, cortical thickness, and brain volume alterations. Six studies did not explicitly operationalize cognitive reserve; among the remaining studies, approaches included educational attainment, biological susceptibility factors, and neuroimaging-based measures of brain structure or function. China was the most represented country, while evidence from other low- and middle-income regions remained limited. CONCLUSION: Diverse occupational neurotoxicant exposures were associated with adverse cognitive and neurological findings relevant to brain aging, although causality cannot be established. Cognitive reserve remains inconsistently examined, and neuroimaging measures should not be interpreted as direct measures of cognitive reserve. Future research should prioritize longitudinal studies integrating repeated exposure assessment, cognitive evaluation, multidimensional cognitive reserve measures, and multimodal neuroimaging.