HEAVY METAL IN THE AIR
123 September 1997
UN/ECE negotiations in full swing
"Heavy metals, like lead, cadmium and mercury, are increasingly present in the
atmosphere," notes Kaj Bärlund, Director of the Environment and Human
Settlements Division of the United Nations Economic Commission for Europe
(UN/ECE). "They cause damage to the environment, but above all they may
have harmful effects on our health -- effects that we cannot yet fully assess."
What are heavy metals?
The most harmful heavy metals in our atmosphere are cadmium, lead and
mercury. Humans are responsible for some of these emissions. The largest
sources of emissions into the air are the combustion of fossil fuels, industrial
processes and road transport, which are all the result of human activity.
Anthropogenic emissions of heavy metals in Europe and North America have
greatly increased the concentrations of cadmium, mercury and lead -- even in
remote areas. As metals are stable environmental contaminants, they tend to
accumulate in the biosphere and are stored in soils and sediments.
Heavy metals are also natural components of the Earth's crust. They cannot be
degraded or destroyed. To a small extent they enter our bodies via food, drinking
water and air. As trace elements, some heavy metals (e.g. copper, selenium,
zinc) are essential to maintain the metabolism of the human body. However, at
higher concentrations they can lead to poisoning. Heavy metal poisoning could
result, for instance, from drinking-water contamination (e.g. lead pipes), high
ambient air concentrations near emission sources, or intake via the food chain.
How do heavy metals affect our health?
Several metals such as lead, cadmium, cobalt, nickel and alkyl mercury
compounds have an effect on haematopoiesis and can lead to blood disorders.
The liver, the kidneys, the circulatory system and the nervous system may also be
affected. Beside their toxic effects, some heavy metals (arsenic, hexavalent
chromium and nickel) also have potential carcinogenic effects. High concentrations
of mercury in fish in some regions poses a potential risk to human health and
foetal development. In several countries people are advised to avoid eating fish
from lakes in regions with high mercury levels.
Is the environment also at risk?
Forest soils and other natural soils with a surface layer rich in organic matter are
especially sensitive to atmospheric deposition of heavy metals. The organic matter
in the topsoil layer absorbs heavy metals effectively and can be regarded as a filter
between the supply from atmospheric deposition and deeper soil layers. There are
strong indications that high concentrations of lead, cadmium, copper, zinc and
mercury affect the decomposition of organic matter and have an adverse effect on
the recycling of important nutrients. These effects are reinforced by the
acidification of soils, especially for elements like cadmium and zinc. So the
ongoing accumulation of heavy metals is probably a considerable stress factor for
the forest ecosystem and for tree vitality.
Sub-lethal neurobehavioural effects (impaired vision, coordination and body
movement) induced, for instance, by methyl mercury or lead could severely
compromise the ability of a predatory species to obtain food in the wild, resulting
in emaciation and an increased susceptibility to disease or other environmental
stresses. In addition, piscivore birds and mammals risk increased exposure to
dietary methyl mercury, especially in acidified habitats, and mercury
concentrations in prey may reach levels known to cause reproductive impairment
in birds and mammals.
How can UN/ECE help rid the region of these harmful substances?
Concentrations of lead in the air can of course be cut by removing lead from
petrol. This is relatively straightforward. But much more needs to be done
if we are to curb the emissions of heavy metals. More stringent emission standards
could be introduced; best available techniques (BAT) for industrial processes,
such as mercury-free processes in the chlor-alkali industry, could be applied.
Pollution with heavy metals is a region-wide problem, there is no point in
countries acting on their own. Unless everyone agrees that something ought
to be done, the problem will not be solved. The member States of the United
Nations Economic Commission for Europe (UN/ECE) have just met in Geneva to
negotiate a protocol on heavy metals to the Convention
on Long-range Transboundary Air Pollution. This new protocol will deal
primarily with lead, mercury and cadmium. It aims to reduce emissions from
industrial sources (iron and steel industry, non-ferrous metal industry),
combustion processes (power generation, road transport) and waste incineration.
Also, primary measures to reduce the heavy metal content in products, such
as mercury and cadmium in batteries, mercury-free measuring instruments and
electrical components, limiting the mercury content in fluorescent light tubes,
cadmium and lead used as stabilizers and pigments in paints and plastics,
etc., are under negotiation. All these measures are to reduce the emissions
of heavy metals finding their way into the environment.
Like the new protocol on persistent organic pollutants (POPs), the negotiations on
the heavy metals protocol are now entering their final stages. The aim is to
finalize both protocols in the run-up to the Aarhus Ministerial Conference
"Environment for Europe" in June 1998. So far UN/ECE has mainly tackled
acidification, but with these two protocols, it is moving to a different type of
substances altogether -- a sure sign that UN/ECE is swinging... and not only
because of the abbreviations of its protocols.