Clean air - Danish efforts
Lead and other metals
Many metals are poisonous, and WHO has proposed limit values for a series of them. The new EU directives for air quality will - beside lead - apply to cadmium, arsenic, nickel, and possibly mercury.
Lead
For many years lead was added to motor vehicle petrol in order to increase the octane number for motors with higher compression, and, thus, improve efficiency. Apart from the surroundings of certain industrial installations, these lead additives were the absolutely dominating source of lead in the air in Danish cities.
Denmark has, like the other EU countries, introduced limits for the content of lead in petrol. Measures were first taken in 1978, the rules were tightened during the 1980's, and since 1984 there has been no lead in the petrol - and not in the EU since 2000. The result has been almost complete disappearance of lead from the urban air, the present level in Copenhagen is approx. 15 µg/m3 or only 3% of the EU's planned limit value for 2010 (0.5 µg per m3).
This does not mean, however, that the human lead load has fallen correspondingly, because lead, like other heavy metals, can also be taken up with food. In this connection it is important to note that the concentration of lead in Danish rural areas has always been significantly lower than in the cities and to a large extent is influenced by longrange transport. Therefore, in relative terms, the lead load is not equally reduced. Since 1990 lead concentrations have fallen to about one third (from 25 to 8 µg/m3), and the deposition of lead has fallen correspondingly. The concentrations in the soil will, however, remain fairly constant, since the lead does not disappear, but remains in the soil.
Lead in petrol and lead emissions
Lead additives in motor vehicle petrol used to be the dominating source of air
pollution with lead in Danish urban areas and along busy roads. Starting in 1978 the
permitted lead content has gradually been reduced to zero. The result has been a
corresponding decrease of total lead emissions in Denmark.
Lead in urban air and in rural areas
In the same period the lead concentration in urban air has fallen to about 1/100. The
concentration in rural areas (approx. 1/10 of that in urban areas) - and thus of the lead
deposition - has not been equally reduced measured in relative terms. The reason is a
significant contribution from longrange transport.
(Source: NERI and City of Copenhagen)
Elevated levels of lead in the blood can reduce intelligence. Some scientists have even dared the hypothesis that extensive lead poisoning contributed to the fall of the Roman Empire. Air pollution with lead has largely disappeared in Denmark, but it is not the only source of lead in humans.
Other metals in the air
Emission inventories for other heavy metals than lead - for example cadmium, mercury, nickel and zinc - show less distinct, but in most cases significant reductions in recent years, due to purification of emissions from power plants, incineration plants and industrial plants. Also concentrations of a series of heavy metals in urban air have fallen, but as there appears to be many different sources it is difficult to point to one single reason.
Heavy metals in soil
In 1996 it was concluded that the present deposition of heavy metals is generally very small compared to the natural content in the soil. It is therefore not expected to be an acute problem. As deposition can take place directly on the eatable parts if the plants, there is still reason to follow closely the development for especially lead, cadmium and mercury.
Lead deposition in Danish rural areas
During the last decade lead deposition in rural areas (average of measurements at
Tange and Keldsnor) has been more than halved. Similar, but smaller reductions have been
observed for i.a. zink and copper.
(Source: NERI)