Vike, E. 2002. Air pollution from aluminium smelters; dispersal patterns, deposition and uptake in plants, and effects on urban vegetation. Doctor Scientiarum Theses 2002: 46. Agricultural University of Norway. ISSN 0802-3220. ISBN 82-575-0531-5.
Variation in fluoride content and leaf injury in common indigenous and cultivated plant species was investigated near three aluminium smelters in Norway; Mosjøen, Husnes and Øvre Årdal. Fluoride content in leaves was low in spring and increased during the growing season in all deciduous species. It also varied between species, locations, genotypes, young and old leaves, and lee and windward side of trees/bushes.
The dispersal patterns for fluoride and the distribution of damages, investigated for three years in the urban areas at the three smelters, were mainly determined by the dominant wind direction and topography. Damage, recorded as leaf injury and reduced plant vitality, was restricted to the areas closest to the smelters, within 2 km in the prevailing wind direction. Despite low emissions, the most severe damage was observed in Mosjøen, where the pollutants were spread in a narrow belt through the urban areas. Common plant species were evaluated for fluoride tolerance. Pollution affected both species composition in natural areas and plant use in gardens.
Leaf injury and fluoride content in leaves of Betula pubescens Ehrh., Salix caprea L. and Sorbus aucuparia L. was positively correlated. The relationship varied with location. Clear leaf injury symptoms occurred at an average fluoride content of 100 mg kg-1 at Mosjøen, about 150 mg kg-1 at Husnes and as much as about 300 mg kg-1 at Øvre Årdal. The results indicate that climatic conditions affect the dose-response relationship.
The effect of precipitation on deposition and uptake of fluoride and aluminium on/in plants near the Al smelter in Øvre Årdal was studied during two growing seasons, by growing plants under cover and in the open, and by washing the leaves. With an average ambient air concentration of 2.2 µg F- m3, the fluoride content varied between species from 138 to 665 mg F- kg-1 when cultivated under cover. Precipitation washed off on average 51% the first year and 33% of the fluoride the second year, and the wash off percentages were highest among deciduous species with glabrous leaves and conifers. The results also indicate that rain causes a moderate leaching of fluoride from the leaves.
Particle fluoride also constituted a considerable part of the total fluoride content in plants exposed to precipitation, an average of 39% and 51% could be washed off the two years. Aluminium contents in plants varied from 150 to 1025 mg Al kg-1 when cultivated under cover, and it did not seem to be washed off by precipitation. Washed leaves of plants exposed to precipitation had higher Al content than leaves from washed, covered plants, on average 84% and 52% the two years. The results indicate uptake of aluminium dissolved in rainwater through the leaf cuticle.
Lysimeter experiments with four plant species cultivated in polluted soil collected near an Al smelter and in unpolluted soil, showed that contents of fluoride and aluminium in plants were highly correlated to the contents of water-soluble and CaCl2 –soluble fluoride and aluminium in the soil. Uptake of fluoride from polluted soil varied strongly between plant species. Highest fluoride content was found in Trifolium repens L., 190 mg kg-1. The aluminium contents in leaves and roots were about twice as high when cultivated in polluted soil compared to unpolluted soil. Leaching of F- and Al was about 30 times higher from polluted soil compared to unpolluted soil. Liming reduced uptake and leaching of both fluoride and aluminium. Increasing fertilizer rates increased the uptake and leaching of fluoride. It also led to an increase in leaching of Al, but no significant increase in plant uptake.
Soil pollution seems to be important for some plant species near the smelters. A reduction in dry weight in T. repens and in the number of nitrogen-fixing root nodules in T. repens and Caragana arborescens Lam. was observed when cultivated in polluted soil. For Lolium perenne L., Caragana arborescens and Salix ‘Brekkavier’, cultivation in polluted soil had no clear effect on dry weight.
