Metals are naturally occurring chemicals that do not breakdown in the environment and can accumulate in soils, water and the sediments of lakes and rivers.
Some metals are essential for human health at very low levels but toxic at higher concentrations. Others such as lead, cadmium and mercury — loosely defined as ‘heavy metals’ — have no known benefits and can be harmful if ingested.
These metals are common air pollutants produced largely by industrial processes and fossil fuel combustion. They can persist in the environment, move from the air into soil and increase in concentration in the food-chain.
Heavy metals have been linked with a variety of health problems, such as kidney and bone disease, and developmental and behavioral disorders. Some metals may also contribute to other health problems including cardiovascular disease and cancers at higher doses.
People whose jobs expose them to heavy metals are at particularly high risk. For instances, overexposure to lead in the workplace is particularly common for people who work in construction, lead mines and smelters, radiator repair shops, and firing ranges.
Other sources of exposure to lead include paints (especially in old buildings) or in the exhaust fumes from cars that use leaded petrol. Children are more susceptible than adults to poisoning from such sources.
Poisoning can be chronic (building over a long time period) or acute (when exposure to a particularly high level of a toxin causes sudden health effects) as in 2010, when the BBC reported that at least 163 people – mostly children – died in northern Nigeria after villagers started digging for gold in areas with high concentrations of lead.
Mercury is another heavy metal that can cause various diseases in people who are exposed to it at high levels. The major source of exposure is through eating fish and other seafood which have accumulated mercury in their tissues because polluted water has enters rivers and the sea.
In Japan in the 1950s more than 600 people died and thousands more fell ill with a form of mercury poisoning that became known as Minimata disease after the worst-affected town. The disease arose after industrial effluent that contained mercury was discharged into local rivers.
Mercury is also a significant airborne pollutant that can travel thousands of kilometers to pose threats to the environment and health far from its source. It poses additional threats to small-scale miners who use the metal to extract gold. The United Nations Industrial Development Organization estimates that this use of mercury threatens the health of 15 million people.
ALTERNATIVES / SOLUTIONS
The best means of reducing threats from heavy metals are to limit people’s exposure to them, through legislation, the use of alternatives, and removal of existing sources.
For instance, various alternatives to adding lead to pesticides, paint and gasoline are now available but are not universally used. Other ways to limit lead exposure include efforts to remove household items such as pipes or paintwork that contain the metal.
In some countries, some heavy metals are severely controlled or banned. Many countries have imposed a total ban on lead in petrol or have strict limits on how much led is in soil or water.
Cadmium, another heavy metal, is one of six substances banned by the European Union’s Restriction on Hazardous Substances (RoHS) directive, which bans certain hazardous substances in electronics.
One positive side effect of the technologies being used in some power plants to control nitrous oxide and sulphur dioxide emissions (which contribute to acid rain) is that they also reduce mercury emissions by as much as 90 percent.
The Blacksmith Institute is also rich source of information on heavy-metal pollution and efforts to address it around the world.
One major story that is developing now is that of a global effort to control the use and emissions of mercury with a new multilateral environmental agreement that could be in place by 2013.
In June 2010 the Intergovernmental Negotiating Committee to Prepare a Global Legally Binding Instrument on Mercury (INC 1) had its first meeting. Over the coming years, governments will continue to negotiate the shape of the new agreement and journalists can follow these negotiations in the IISD Earth Negotiations Bulletin.
CASE STUDY – Mercury pollution in Wanshan, China
Many deaths have been linked to mercury poisoning in the Wanshan Special Administrative Region of China’s Guizhou Province.
Local health official say at least 200 of the region’s 60,000 people have some form of mercury poisoning – excluding those who have died already or have yet to show any symptoms.
The likely cause is the nearby mercury mine and smelting plant. It has now closed but its legacy lingers in the form of polluted rice fields and rivers, and high levels of cancer and other diseases.
Illegal mercury mining and smelting continues in the wider area, which once produced 70 percent of the world’s mercury.
Local experts estimate that at least 350 tonnes — or nearly 10 percent of the world’s annual mercury emissions — were released into the Wanshan environment. At one time, mercury levels in drinking water exceeded standards by more than 36 times.
Today the water remains a risk, and most fruit and vegetables much be imported from other areas because the farmland is contaminated.
To read how Chinese nongovernmental organizations are tackling heavy-metal pollution then by asking multinational brands to clean up their supply chains, see this ChinaDialogue article.