Heavy metal pollution has emerged as a global environmental and public health challenge driven by rapid industrialization and urbanization. Characterized by persistence, bioaccumulation, and high toxicity, heavy metals such as lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As) infiltrate human systems through atmospheric, aquatic, and terrestrial pathways, posing severe health threats (1, 2). Cumulative evidence indicates that occupational populations chronically exposed to these metals may face elevated risks of neurological impairment, renal dysfunction, cardiovascular disorders, and even carcinogenesis (3). For instance, an increase in blood Pb levels is closely related to cognitive decline and anemia (4). Exposure to Cd can cause renal damage and bone diseases (5). Higher blood Hg levels are associated with neurotoxicity and an elevated risk of cardiovascular diseases (6). Blood As exposure is linked to various diseases like skin lesions and cancers (7). Notably, occupational cohorts always exhibit higher blood metal burdens due to prolonged workplace exposure, correlating with increased morbidity and mortality rates in epidemiological studies (8).

Despite advancements in assessing occupational heavy metal exposure and its influencing factors, existing research remains fragmented by its focus on single industries or localized regions. Comprehensive evaluations integrating multi-metal co-exposure analyses and influencing factors are limited. This gap is particularly relevant in Hunan Province, a pivotal industrial hub in China with a substantial workforce engaged in mining, manufacturing, and construction. Inadequate environmental safeguards and insufficient occupational protection awareness have exacerbated heavy metal exposure risks among these populations (9, 10). Although efforts for occupational disease prevention have intensified in recent years, systematic investigations into whole blood heavy metal levels across diverse occupational groups remain sparse, particularly regarding multi-metal assessments and mechanistic exploration of influencing factors.

This study aims to investigate the distribution patterns of whole blood heavy metals (Pb, Cd, Hg, As) among occupationally exposed populations in Hunan Province and elucidate determinants spanning demographic traits, occupational exposure characteristics, and lifestyle behaviors. By integrating multi-metal biomonitoring with multivariate analysis, our findings will clarify regional exposure profiles and inform evidence-based occupational health strategies. These efforts align with national objectives to mitigate workplace hazards and advance the implementation of occupational disease prevention and control frameworks.

To intuitively present the core logic of “heavy metal exposure among occupational populations” that this study focuses on, we constructed a conceptual framework diagram of heavy metal exposure (Figure 1), which clearly sorts out the association chain of “key determining factors → whole - blood heavy metal levels → potential health outcomes.” Among them, demographic characteristics such as gender and age, occupational attributes such as employment duration and occupation type, and lifestyle habits such as smoking and alcohol consumption constitute the key determining factors of exposure; these factors affect the levels of heavy metals such as Pb, Cd, Hg, and As in whole blood through pathways like occupational contact and environmental exposure; and the long - term accumulation of heavy metals may induce health hazards such as neurotoxicity, nephrotoxicity, cardiovascular damage, and carcinogenicity.

Heavy metals, commonly including Pb, Cd, Hg, and As, represent a class of elements with significant toxicological potential and widely present in natural environments and industrial processes. These metals enter the human body through inhalation, ingestion, and dermal contact, bioaccumulating in tissues and organs. Prolonged exposure can cause damage to the nervous system, kidneys, cardiovascular system, and immune system, and may even induce carcinogenesis (13). Occupational populations, particularly those engaged in mining, manufacturing, and construction, face disproportionate exposure risks due to inhalation of metal-laden particulates, dermal contact with contaminated surfaces, and ingestion of tainted water or food (14). Industrial processes such as smelting, metal refining, battery production, and chemical production exacerbate workplace contamination, resulting in elevated blood metal concentrations among workers compared to the general population. Studies have demonstrated that occupational exposure not only correlates with elevated heavy metal burden but also exacerbates risks of hypertension, renal dysfunction, neurological disorders, and malignancies (15, 16). In Hunan Province, a pivotal industrial hub in central-south China, diverse industries and complex occupational environments amplify heavy metal exposure risks, necessitating systematic investigations on the current status and influencing factors of heavy metal exposure among occupational populations in this region to inform targeted interventions.

This study found that whole blood heavy metal levels among the occupational populations in Hunan Province exhibited significant differences, with higher levels observed in males, individuals aged > 50 years, and those with employment duration > 20 years, particularly pronounced in the mining and manufacturing industries. These findings are generally consistent with global epidemiological trends. For example, a study on smelter workers reported that longer employment duration and male sex were associated with significantly higher blood Pb levels (17), which may be attributable to the cumulative effect of prolonged occupational exposure and sex-related differences in metal metabolism (18). Similarly, an epidemiological investigation on battery factories in low- and middle-income countries identified employment duration and sex as important determinants of blood Pb and Cd levels (19), suggesting broad applicability of these risk factors. However, some studies did not find a significant sex difference, which might be explained by differences in sample composition, a higher proportion of females in high-risk positions, or variations in detection methods (20). The results of our study facilitate the identification and targeted intervention of susceptible populations at the regional level.

In our study, mining workers exhibited significantly elevated blood Pb, Cd, and As levels, consistent with their occupational exposure characteristics. Processes including ore extraction, crushing, and transportation generate dust and wastewater containing Pb, Cd, and As, which enter the body via inhalation and dermal contact and bioaccumulate over time. This exposure pathway is well documented in prior occupational studies (21). Conversely, agricultural workers showed higher blood Hg levels, potentially reflecting residual mercury-based pesticides and contaminated irrigation water and crops in some areas (22). Additionally, elevated blood Hg among drinkers may originate from homemade alcohol production using mercury-contaminated containers in rural regions (23), indicating the role of lifestyle factors in exposure modulation.

Significant regional differences were also observed: higher blood Pb in Chang-Zhu-Tan, elevated Hg in Xiangnan, increased Cd in Dongting Lake, and higher As in Xiangxi. These patterns correspond to localized industrial activities and pollution sources. Chang-Zhu-Tan, as an industrial hub, faces heavy metal pollution mainly from industrial and vehicular emissions (24). Xiangnan’s non-ferrous metal smelting releases large amounts of Hg vapor (25). Dongting Lake shows Cd contamination from long-term fertilization and wastewater discharge (26, 27). Small-scale mining in Xiangxi contributes to As accumulation in soil and water, posing health risks to workers (28). These results confirm regional characteristics and emphasize the need for targeted, location-specific exposure interventions.

Behavioral cofactors further demonstrated synergistic interactions with smoking, drinking, and heavy metal exposure in collectively impacting human health (29, 30). In this study, smokers exhibited elevated blood Pb and Cd levels, while drinkers showed higher blood Hg concentrations. These findings suggest that smoking may contribute to Pb and Cd bioaccumulation either through both direct inhalation of metal-containing tobacco smoke and enhanced respiratory mucosal permeability (31). The elevated Hg observed among drinkers may relate to artisanal alcohol contamination or storage in Hg-tainted vessels, further exacerbated by alcohol-induced hepatic impairment that diminishes Hg clearance capacity (32). These findings emphasize the critical need to integrate lifestyle modification strategies into occupational health programs.

Multivariate linear regression analysis confirmed that gender, age, employment duration, occupation type, smoking, and drinking were significant determinants of whole blood heavy metal levels. These findings underscore that heavy metal exposure among occupational populations in Hunan Province is not only linked to workplace hazards but also influenced by individual characteristics and lifestyle habits. K-means clustering analysis further identified a high-exposure subgroup with markedly elevated blood Pb, Cd, Hg, and As concentrations, with some samples reaching or even exceeding OELs. This subgroup warrants urgent intervention through comprehensive mitigation strategies: (1) regular whole blood heavy metal screening and long-term health surveillance for high-risk occupations (e.g., mining, manufacturing) to enable early detection and intervention; (2) enhanced health education to raise awareness of heavy metal hazards and promote self-protection practices; (3) implementation of advanced pollution control technologies (e.g., waste gas scrubbers, wastewater treatment systems, dust suppression equipment) to minimize workplace contamination, coupled with systematic environmental monitoring of soil, water, and air quality; (4) provision and enforcement of certified personal protective equipment, including dust-proof masks, gloves, and protective clothing; (5) lifestyle interventions to reduce smoking and alcohol consumption; and (6) dietary interventions incorporating antioxidants (vitamins C/E, selenium) to counteract heavy metal-induced toxicity (33).

This study characterized heavy metal exposure patterns among occupational populations in Hunan Province, China. Through large-scale sample analysis, key factors influencing whole blood heavy metal levels were identified, providing important evidence to support the development of targeted occupational health protection measures. However, this study has several limitations. First, due to its cross-sectional design, causal relationships cannot be established. Second, despite the large sample size, the coverage of occupation types and geographic regions was limited, which may affect the representativeness of our findings. Third, the detection limits for some heavy metals were relatively low, potentially introducing measurement errors in low-concentration samples. Finally, potential confounding factors such as residential environmental exposure and genetic susceptibility were not adequately considered. Future studies should incorporate these factors to achieve a more comprehensive understanding of the determinants of heavy metal exposure. Furthermore, this study did not explore potential interaction effects between variables. Previous research has suggested that significant interactions may exist between factors such as sex and age or occupational environment, which can influence heavy metal exposure levels. A comprehensive review indicates that males and females exhibit different accumulation and toxicological responses to long-term exposure to Pb, Hg, Cd, and As, likely attributable to divergent metabolic pathways and hormonal regulation (34). Consequently, future studies should consider incorporating interaction terms (e.g., age × gender, occupation × region) into regression models to unravel the complexity of exposure pathways.

This study delineates high-risk industries, geographic hotspots, and vulnerable subpopulations for heavy metal exposure among Hunan’s occupational cohorts, informing region- and industry-specific regulatory strategies. Evidence-based measures include: implementing stricter emission standards and OELs for high-exposure industries (e.g., mining, manufacturing); enhancing environmental remediation and occupational hygiene supervision in high-burden regions (e.g., Chang-Zhu-Tan, Xiangnan); and establishing regular health surveillance with preventive mechanisms for high-risk groups. Such targeted approaches would reduce occupational metal exposure, mitigate disease burden, and improve workforce health outcomes.

Occupational populations in Hunan Province exhibit heterogeneous heavy metal exposure profiles shaped by industrial activities, geographic factors, and individual behaviors. Sustained biomonitoring, enhanced workplace protections, and longitudinal studies are urgently needed to elucidate exposure-disease relationships and safeguard worker health. Future research should expand geographic coverage and incorporate molecular biomarkers to assess subclinical toxicity pathways. These findings provide an empirical foundation for developing region- and industry-specific occupational health policies, strengthening environmental remediation, and optimizing personal protective interventions.