Heavy Metal

Heavy metals are dense metallic elements that are toxic at low concentrations and do not degrade, persisting indefinitely once released. The marine priority metals are mercury, cadmium, and lead, joined by arsenic, chromium, copper, nickel, and zinc. Sources include antifouling paint, sewage, mining runoff, and atmospheric deposition. Toxicity depends on speciation and bioavailability: methylmercury biomagnifies through food webs while inorganic mercury does not, and dissolved copper is far more toxic than particle-bound copper. Mercury is regulated globally under the Minamata Convention; OSPAR and HELCOM set background and environmental assessment concentrations for sediment and biota.