Objective To explore the correlation and dose-response relationship between blood cell manganese (Mn) and hemoglobin (Hb) levels among workers occupationally exposed to manganese, providing the scientific basis for preventing health damage caused by occupational manganese exposure.

Methods A total of 826 manganese-exposed workers from a ferromanganese alloy smelting plant in Guangxi were studied. Data from the epidemiologic questionnaires survey and on-site occupational health investigation were conducted during follow-up in 2017. The mass concentration of manganese in blood cells was measured using inductively coupled plasma mass spectrometry (ICP-MS), and hemoglobin levels were measured using an automatic blood cell analyzer. Generalized linear models (GLMs) and restricted cubic spline analyses were used to investigate the correlation and dose-response relationship between blood cell manganese and hemoglobin levels.

Results Finally, this study included 823 study subjects due to data missed. The manganese concentration in the air ranged from 0.004 to 0.061 mg/m³ for the workers in the control group (n = 141), while 0.004 to 1.557 mg/m³ for the workers in the low-exposure group (n = 141), and 0.060 to 2.461 mg/m³ for workers in the high-exposure group (n = 141). The median manganese mass concentrations in blood cells of the three study groups were 25.68 μg/L, 30.87 μg/L, and 32.11 μg/L, respectively, with significant differences (P < 0.001); the mean hemoglobin levels were (150.1 ±17.4) μg/L, (143.9 ±17.5) μg/L, and (149.2 ±15.8) μg/L, respectively, also showing significant differences (P < 0.001). Higher blood cell manganese concentrations were observed in the females, non-smokers, non-drinkers, and individuals with a BMI ≥ 28.0 kg/m² (all P < 0.05). GLM analysis showed that compared to the Q1 group (blood cell manganese mass concentration < 24.17 μg/L), hemoglobin levels increased by 4.771 μg/L, 7.747 μg/L, and 2.995 μg/L in the Q2 (24.17-30.62 μg/L), Q3 (> 30.62-39.11 μg/L), and Q4 (> 39.11 μg/L) groups, respectively (all P < 0.05). Compared to the males, the females had 20.824 μg/L lower hemoglobin levels (P < 0.05). Restricted cubic spline analysis indicated an inverted U-shaped dose-response relationship between blood cell manganese concentration and hemoglobin levels (F = 53.9, P < 0.05).

Conclusions The level of manganese in blood cells of manganese-exposed workers was higher than that of the general population. Lower levels of blood cell manganese may promote hemoglobin synthesis, while higher concentrations may inhibit hemoglobin synthesis.