<p>Artisanal and small-scale gold mining (ASGM) is a major global source of mercury (Hg) contamination; however, the exposure pathways and associated health risks in legacy mining regions remain insufficiently constrained. Here, we conducted an integrated multimedia assessment of environmental Hg contamination, human exposure pathways, and health risks in a legacy ASGM area of central Fujian Province, southeastern China, where mining activities ceased decades ago but residual Hg persists in local agroecosystems. Total mercury (THg) and methylmercury (MeHg) were measured in rice grains, surface water, soils, ambient air, and human hair to link environmental levels with internal body burdens. Elevated Hg concentrations were observed across multiple media, with rice grains exhibiting THg and MeHg levels several-fold higher than national averages and exceptionally high MeHg/THg ratios (mean: 56.0 ± 27.1%), indicating that paddy field conditions favor MeHg production and its subsequent uptake into rice grains. Partial Least Squares Path Modeling (PLS-PM) indicated that rice consumption was the dominant exposure pathway influencing human Hg body burden (path coefficient = 0.827), whereas inhalation and soil-related pathways played comparatively minor roles. Dietary MeHg intake from locally produced rice frequently approached or exceeded internationally recommended tolerable limits, particularly among children. These results suggest that Hg exposure in post-ASGM systems is primarily controlled by coupled soil–water–plant processes and mediated through rice consumption. The persistence of elevated exposure levels highlights the long-term impact of legacy contamination and underscores the need for targeted mitigation strategies to reduce MeHg exposure in vulnerable populations.</p>