Heavy metals (Pb, Cd, Hg)

Lead, cadmium and inorganic mercury are the heavy metals most consistently associated with chronic low-level human exposure and adverse health outcomes in epidemiological research. Lead enters via ageing drinking-water infrastructure and legacy paint; cadmium accumulates through cigarette smoke, contaminated soil and certain foods; methylmercury is concentrated in large predatory fish through bioaccumulation. Mechanistically, these metals displace essential ions, inhibit enzymatic activity, generate reactive oxygen species and alter DNA methylation patterns — epigenetic effects linked to accelerated biological ageing. NHANES blood-lead studies have reported a continuous dose-response relationship between blood lead levels and all-cause and cardiovascular mortality even at concentrations previously considered safe, contributing to successive downward revisions of reference values.