Fluoride in birch leaves, ground vegetation, litter and humus in the surroundings of a fertilizer plant and apatite mine in Siilinjärvi, eastern Finland

Fluoride is one of the main emission components of the fertilizer plant and strip mine located at Siilinjärvi, in eastern Finland. The fluoride concentration of birch (Betula pendula Roth.) leaves, ground vegetation, litter layer and humus layer were determined in the surroundings of the plant and the mine to evaluate their validity as bioindicators of fluoride pollution. The highest fluoride concentrations were observed near the fertilizer plant, the strip mine or tailings impoundments in all studied materials. Highest total fluoride concentration was observed in the litter and humus layers where the fluoride has been accumulating over three decades. The fluoride concentration of both vegetation (birch leaves and ground vegetation) and soil organic horizon (litter and humus layers) can be regarded as good indicators of fluoride load but their role is quite different. Especially birch leaves, but also ground vegetation, can be used as indicators of annual or short time fluoride load and are available in repeated monitoring, whereas litter or humus layer reveal the long time accumulation of fluoride-containing fallout.