Arsenic, cadmium, chromium, copper, nickel, lead and mercury are the most common heavy metal pollutants, and mercury and cadmium are of the greatest concern. Living organisms, including marine species, concentrate heavy metals in their tissues, becoming highly toxic in the process. Hot spots for heavy metals are operational and former mining sites, industrial production - particular foundries and smelters - untreated sewage sludge and diffuse sources such as metal piping, traffic and combustion by-products from coal-burning power stations. In 1996, the OECD agreed to phase out many uses of lead, and in June 1998, the UNECE added a protocol on heavy metals to the Convention on Long-range Transboundary Air Pollution.
Mercury accumulates at the top of aquatic and marine food chains and fish is the major source of dietary exposure. The principal health risks associated with mercury are damage to the nervous system, with such symptoms as uncontrollable shaking, muscle wasting, partial blindness, and deformities in children exposed in the womb. At levels well below WHO limits, it can damage the foetal and embryonic nervous systems with consequent learning difficulties, poor memory and shortened attention spans. Low-level exposures can also adversely affect male fertility.
Like POPs (Persistent Organic Pollutants), mercury is a global problem. Most of the mercury found in high concentrations in the Everglades in Florida comes from thousands of miles away, travelling on trade winds from Europe and Africa. Although it appears that less mercury than previously thought is polluting Greenland, global transfers of mercury to the poles are still substantial, with base-levels three times what they were two centuries ago. Every spring, a toxic rain of mercury falls on the arctic, at the time when ecosystems are most active. As a consequence, one in six Greenlanders have potentially harmful blood-levels of mercury, from eating contaminated fish and whales.