Environmental pollution caused by foreign substances and the question of their harmfulness is currently being widely discussed.
This also applies to roof and wall elements made of zinc or steel sheet with zinc coating or a metallic coating of 55%AlZn (Aluzinc), without additional organic coating.
One aspect here is the replacement of the corrosion products of zinc by weathering and their washing away by precipitation.
The washed away corrosion products reach sewage treatment plants, receiving waters or infiltration systems.
In recent years, this amount has continuously decreased due to significantly reduced sulphur dioxide (SO²) concentration in the air as a result of pollutant reduction in exhaust gases from heating systems and vehicles, and will continue to decrease.
Whereas the SO² content of the air was about 90µg/m³ in 1978, in 1992 it was only about 9µg/m³, or 10%.
The wash-off rate, measure of the detachment of the outer protective corrosion layer of zinc by precipitation, is measured in g/m² and year or in µm/year.
During measurements in Hanover, the zinc run-off rate had halved from approx. 6g/m² and year in 1991 to only approx. 3g/m² and year in 1998.
For galvanized surfaces one can therefore today assume an average wash-off rate of max. 3g/m² and year, corresponding to 0.4µm/year.
In the building stock of the Federal Republic of Germany approx. 260 million m² are exposed to the weather as weathered surface of roofs and roof drainage systems made of zinc.
From this, the total amount of zinc washed away is calculated to be about 780,000 kg/year.
However, the washing away of roof and wall surfaces is only about 6% of the other zinc pollution from the atmosphere through dust.
Zinc is naturally present everywhere in our environment.
Zinc is an essential trace element for humans and many other organisms.
Over 300 metabolic processes depend on an adequate supply of zinc.
Cell growth, wound healing, the immune system, convalescence, but also memory and concentration, even skin changes and the condition of the hair - all this depends in one way or another on the zinc concentration in our body.
If one considers that zinc is an essential trace element, then in accordance with the previous toxicological findings on zinc, it is possible to dispense with limit values for the protection of humans from excessive stress.
(Including extracts from the status report
"Use of copper and zinc for roofs, gutters and down pipes"
from Prof. Dr.-Ing. habil. Heinz Hullmann and Dipl. Ing. Udo Kraft)
Netphen, May 03