*2.1. Survey Data*

The Korean National Environmental Health Survey (KoNEHS) is a nationwide cross-sectional biomonitoring survey that aims to monitor the trends of environmental chemicals, including blood Hg, and to identify major exposure sources. Approximately 2000 subjects (≥19 years) were annually recruited via stratified multistage sampling units to represent the residential distributions of geographical area, sex, and age. A total of 6454 participants provided blood and urine samples and questionnaire responses, including demographic information and lifestyle. The KoNEHS was approved by the Research Ethics Committee of the National Institute of Environmental Research (NIER #2014-01-01-074, date of approval: 20 March 2014), Korea. Written informed consents were obtained from all participants. Detailed study information is provided in a prior publication [17]. The present study used data from the second cycle of the KoNEHS, conducted between 2012 and 2014.
