Sociodemographic Disparities in Exposure to Environmental Heavy Metals: Temporal Trends in Blood Lead, Mercury, and Cadmium Among Korean Adults (KNHANES 2005–2017)

Heavy metals, such as lead (Pb), mercury (Hg), and cadmium (Cd), pose significant public health risks even at low levels of exposure. This study examined temporal trends in blood heavy metal concentrations among Korean adults over a 12-year period using nationally representative data. We analyzed data from 17,192 adults aged ≥ 20 years who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) Cycles 3–7 (2005, 2008–2009, 2010–2012, 2013, and 2016–2017). Blood Pb, Hg, and Cd concentrations, along with relevant covariates, were measured using standardized methods. Temporal trends and sociodemographic disparities were assessed according to sex, age, body mass index, education, income, occupation, residential area, smoking status, and alcohol consumption. All three metals exhibited statistically significant declining trends over the 12-year study period (all p for trend < 0.001). Males consistently had higher Pb and Hg concentrations than females; however, the decline in Cd was steeper in men compared to women, resulting in a reversal of the sex difference, with females having higher Cd levels than males by Cycle 7. Older adults, current smokers, blue-collar workers, and individuals with lower educational attainment had persistently elevated Pb concentrations. For Hg, individuals aged 40–59 years and alcohol consumers had the highest concentrations, whereas education, income, and residential area were not significantly associated with Hg levels. For Cd, older age, smoking, and lower educational attainment were associated with higher concentrations, with the sex difference reversing over time. These findings demonstrate the need for targeted public health strategies, including occupational Pb control, dietary guidance to reduce Hg exposure, and smoking cessation programs.